diff --git a/build/bootstrap/cocmd.com b/build/bootstrap/cocmd.com
index ddbaac8b6..ff1769d7b 100755
Binary files a/build/bootstrap/cocmd.com and b/build/bootstrap/cocmd.com differ
diff --git a/examples/clock_getres.c b/examples/clock_getres.c
index e45e97f44..a6fcb996d 100644
--- a/examples/clock_getres.c
+++ b/examples/clock_getres.c
@@ -38,10 +38,12 @@ int main(int argc, char *argv[]) {
   show(CLOCK_REALTIME);
   show(CLOCK_REALTIME_FAST);
   show(CLOCK_REALTIME_PRECISE);
+  show(CLOCK_REALTIME_COARSE);
   show(CLOCK_MONOTONIC);
   show(CLOCK_MONOTONIC_RAW);
   show(CLOCK_MONOTONIC_FAST);
   show(CLOCK_MONOTONIC_PRECISE);
+  show(CLOCK_MONOTONIC_COARSE);
   show(CLOCK_PROCESS_CPUTIME_ID);
   show(CLOCK_THREAD_CPUTIME_ID);
   show(CLOCK_PROF);
diff --git a/examples/sleep.c b/examples/nanosleep.c
similarity index 100%
rename from examples/sleep.c
rename to examples/nanosleep.c
diff --git a/examples/nanosleep_test.c b/examples/nanosleep_test.c
new file mode 100644
index 000000000..dbeea1c20
--- /dev/null
+++ b/examples/nanosleep_test.c
@@ -0,0 +1,43 @@
+#if 0
+/*─────────────────────────────────────────────────────────────────╗
+│ To the extent possible under law, Justine Tunney has waived      │
+│ all copyright and related or neighboring rights to this file,    │
+│ as it is written in the following disclaimers:                   │
+│   • http://unlicense.org/                                        │
+│   • http://creativecommons.org/publicdomain/zero/1.0/            │
+╚─────────────────────────────────────────────────────────────────*/
+#endif
+#include "libc/assert.h"
+#include "libc/calls/struct/timespec.h"
+#include "libc/stdio/stdio.h"
+#include "libc/sysv/consts/clock.h"
+
+/**
+ * @fileoverview shows how accurate clock_nanosleep() is
+ */
+
+int main(int argc, char *argv[]) {
+  long i, ns;
+  struct timespec x, y, w;
+  timespec_sleep(timespec_fromnanos(0));  // warmup
+
+  printf("\nrelative sleep\n");
+  for (i = 0; i < 28; ++i) {
+    ns = 1l << i;
+    x = timespec_real();
+    timespec_sleep(timespec_fromnanos(ns));
+    y = timespec_real();
+    printf("%,11ld ns sleep took %,ld ns\n", ns,
+           timespec_tonanos(timespec_sub(y, x)));
+  }
+
+  printf("\nabsolute sleep\n");
+  for (i = 0; i < 28; ++i) {
+    ns = 1l << i;
+    x = timespec_real();
+    timespec_sleep_until(timespec_add(x, timespec_fromnanos(ns)));
+    y = timespec_real();
+    printf("%,11ld ns sleep took %,ld ns\n", ns,
+           timespec_tonanos(timespec_sub(y, x)));
+  }
+}
diff --git a/libc/calls/clock_gettime.c b/libc/calls/clock_gettime.c
index 64134ad11..6c19dd221 100644
--- a/libc/calls/clock_gettime.c
+++ b/libc/calls/clock_gettime.c
@@ -50,20 +50,23 @@
  *     sys_clock_gettime   l:       220𝑐        71𝑛𝑠
  *
  * @param clock can be one of:
- *     - `CLOCK_REALTIME`: universally supported
- *     - `CLOCK_REALTIME_FAST`: ditto but faster on freebsd
- *     - `CLOCK_MONOTONIC`: universally supported
- *     - `CLOCK_MONOTONIC_FAST`: ditto but faster on freebsd
- *     - `CLOCK_MONOTONIC_RAW`: nearly universally supported
- *     - `CLOCK_PROCESS_CPUTIME_ID`: linux and bsd
- *     - `CLOCK_THREAD_CPUTIME_ID`: linux and bsd
- *     - `CLOCK_REALTIME_COARSE`: : linux and openbsd
- *     - `CLOCK_MONOTONIC_COARSE`: linux
- *     - `CLOCK_PROF`: linux and netbsd
- *     - `CLOCK_BOOTTIME`: linux and openbsd
- *     - `CLOCK_REALTIME_ALARM`: linux-only
- *     - `CLOCK_BOOTTIME_ALARM`: linux-only
- *     - `CLOCK_TAI`: linux-only
+ *    - `CLOCK_REALTIME`: universally supported
+ *    - `CLOCK_REALTIME_FAST`: ditto but faster on freebsd
+ *    - `CLOCK_REALTIME_PRECISE`: ditto but better on freebsd
+ *    - `CLOCK_REALTIME_COARSE`: : like `CLOCK_REALTIME_FAST` w/ Linux 2.6.32+
+ *    - `CLOCK_MONOTONIC`: universally supported
+ *    - `CLOCK_MONOTONIC_FAST`: ditto but faster on freebsd
+ *    - `CLOCK_MONOTONIC_PRECISE`: ditto but better on freebsd
+ *    - `CLOCK_MONOTONIC_COARSE`: : like `CLOCK_MONOTONIC_FAST` w/ Linux 2.6.32+
+ *    - `CLOCK_MONOTONIC_RAW`: is actually monotonic but needs Linux 2.6.28+
+ *    - `CLOCK_PROCESS_CPUTIME_ID`: linux and bsd
+ *    - `CLOCK_THREAD_CPUTIME_ID`: linux and bsd
+ *    - `CLOCK_MONOTONIC_COARSE`: linux, freebsd
+ *    - `CLOCK_PROF`: linux and netbsd
+ *    - `CLOCK_BOOTTIME`: linux and openbsd
+ *    - `CLOCK_REALTIME_ALARM`: linux-only
+ *    - `CLOCK_BOOTTIME_ALARM`: linux-only
+ *    - `CLOCK_TAI`: linux-only
  * @param ts is where the result is stored
  * @return 0 on success, or -1 w/ errno
  * @error EPERM if pledge() is in play without stdio promise
diff --git a/libc/calls/clock_nanosleep.c b/libc/calls/clock_nanosleep.c
index 892db647f..29d9d6218 100644
--- a/libc/calls/clock_nanosleep.c
+++ b/libc/calls/clock_nanosleep.c
@@ -16,7 +16,11 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
 #include "libc/calls/asan.internal.h"
+#include "libc/calls/blockcancel.internal.h"
+#include "libc/calls/calls.h"
+#include "libc/calls/clock_gettime.internal.h"
 #include "libc/calls/cp.internal.h"
 #include "libc/calls/state.internal.h"
 #include "libc/calls/struct/timespec.h"
@@ -27,11 +31,161 @@
 #include "libc/errno.h"
 #include "libc/intrin/describeflags.internal.h"
 #include "libc/intrin/strace.internal.h"
+#include "libc/intrin/weaken.h"
+#include "libc/macros.internal.h"
+#include "libc/nt/ntdll.h"
+#include "libc/str/str.h"
 #include "libc/sysv/consts/clock.h"
 #include "libc/sysv/consts/timer.h"
 #include "libc/sysv/errfuns.h"
+#include "libc/thread/thread.h"
 #include "libc/thread/tls.h"
 
+static int64_t g_nanosleep_latency;
+
+static errno_t sys_clock_nanosleep(int clock, int flags,
+                                   const struct timespec *req,
+                                   struct timespec *rem) {
+  int e, rc;
+  BEGIN_CANCELLATION_POINT;
+  e = errno;
+  STRACE("clock_nanosleep(%s, %s, %s, %s) → ...", DescribeClockName(clock),
+         DescribeSleepFlags(flags), DescribeTimespec(0, req),
+         DescribeTimespec(0, rem));
+  if (IsLinux() || IsFreebsd() || IsNetbsd()) {
+    rc = __sys_clock_nanosleep(clock, flags, req, rem);
+  } else if (IsXnu()) {
+    rc = sys_clock_nanosleep_xnu(clock, flags, req, rem);
+  } else if (IsOpenbsd()) {
+    rc = sys_clock_nanosleep_openbsd(clock, flags, req, rem);
+  } else {
+    rc = sys_clock_nanosleep_nt(clock, flags, req, rem);
+  }
+  if (rc == -1) {
+    rc = errno;
+    errno = e;
+  }
+  END_CANCELLATION_POINT;
+  return rc;
+}
+
+// determine sched_yield() vs. clock_nanosleep() threshold
+// 1ns sys_clock_nanosleep() on Windows takes milliseconds :'(
+// 1ns sys_clock_nanosleep() on Linux/FreeBSD takes tens of microseconds
+// 1ns sys_clock_nanosleep() on OpenBSD/NetBSD takes tens of milliseconds D:
+static struct timespec GetNanosleepLatency(void) {
+  errno_t rc;
+  int64_t nanos;
+  clock_gettime_f *cgt;
+  struct timespec x, y, w = {0, 1};
+  if (!(nanos = g_nanosleep_latency)) {
+    BLOCK_CANCELLATIONS;
+    for (cgt = __clock_gettime_get(0);;) {
+      _npassert(!cgt(CLOCK_REALTIME_PRECISE, &x));
+      rc = sys_clock_nanosleep(CLOCK_REALTIME, 0, &w, 0);
+      _npassert(!rc || rc == EINTR);
+      if (!rc) {
+        _npassert(!cgt(CLOCK_REALTIME_PRECISE, &y));
+        nanos = timespec_tonanos(timespec_sub(y, x));
+        g_nanosleep_latency = nanos;
+        break;
+      }
+    }
+    ALLOW_CANCELLATIONS;
+  }
+  return timespec_fromnanos(nanos);
+}
+
+static errno_t CheckCancel(void) {
+  if (_weaken(pthread_testcancel_np)) {
+    return _weaken(pthread_testcancel_np)();
+  } else {
+    return 0;
+  }
+}
+
+static errno_t SpinNanosleep(int clock, int flags, const struct timespec *req,
+                             struct timespec *rem) {
+  errno_t rc;
+  clock_gettime_f *cgt;
+  struct timespec now, start, elapsed;
+  if ((rc = CheckCancel())) {
+    if (rc == EINTR && !flags && rem) {
+      *rem = *req;
+    }
+    return rc;
+  }
+  cgt = __clock_gettime_get(0);
+  _npassert(!cgt(CLOCK_REALTIME, &start));
+  for (;;) {
+    sched_yield();
+    _npassert(!cgt(CLOCK_REALTIME, &now));
+    if (flags & TIMER_ABSTIME) {
+      if (timespec_cmp(now, *req) >= 0) {
+        return 0;
+      }
+      if ((rc = CheckCancel())) {
+        return rc;
+      }
+    } else {
+      if (timespec_cmp(now, start) < 0) continue;
+      elapsed = timespec_sub(now, start);
+      if ((rc = CheckCancel())) {
+        if (rc == EINTR && rem) {
+          if (timespec_cmp(elapsed, *req) >= 0) {
+            bzero(rem, sizeof(*rem));
+          } else {
+            *rem = elapsed;
+          }
+        }
+        return rc;
+      }
+      if (timespec_cmp(elapsed, *req) >= 0) {
+        return 0;
+      }
+    }
+  }
+}
+
+static bool ShouldUseSpinNanosleep(int clock, int flags,
+                                   const struct timespec *req) {
+  errno_t e;
+  struct timespec now;
+  if (IsWindows()) {
+    // Our spin technique here is intended to take advantage of the fact
+    // that sched_yield() takes about a hundred nanoseconds. But Windows
+    // SleepEx(0, 0) a.k.a. NtYieldExecution() takes a whole millisecond
+    // and it matters not whether our intent is to yielding or sleeping,
+    // since we use the SleepEx() function to implement both. Therefore,
+    // there's no reason to use SpinNanosleep() on Windows.
+    return false;
+  }
+  if (clock != CLOCK_REALTIME &&          //
+      clock != CLOCK_REALTIME_PRECISE &&  //
+      clock != CLOCK_MONOTONIC &&         //
+      clock != CLOCK_MONOTONIC_RAW &&     //
+      clock != CLOCK_MONOTONIC_PRECISE) {
+    return false;
+  }
+  if (!flags) {
+    return timespec_cmp(*req, GetNanosleepLatency()) < 0;
+  }
+  // We need a clock_gettime() system call to perform this check if the
+  // sleep request is an absolute timestamp. So we avoid doing that on
+  // systems where sleep latency isn't too outrageous.
+  if (timespec_cmp(GetNanosleepLatency(), timespec_fromnanos(50 * 1000)) < 0) {
+    return false;
+  }
+  e = errno;
+  if (__clock_gettime_get(0)(clock, &now)) {
+    // punt to the nanosleep system call
+    errno = e;
+    return false;
+  }
+  return timespec_cmp(*req, now) < 0 ||
+         timespec_cmp(timespec_sub(*req, now), GetNanosleepLatency()) < 0;
+}
+
 /**
  * Sleeps for particular amount of time.
  *
@@ -88,36 +242,22 @@
  */
 errno_t clock_nanosleep(int clock, int flags, const struct timespec *req,
                         struct timespec *rem) {
-  int rc, e = errno;
-  BEGIN_CANCELLATION_POINT;
-
-  if (!req || (IsAsan() && (!__asan_is_valid_timespec(req) ||
-                            (rem && !__asan_is_valid_timespec(rem))))) {
-    rc = efault();
+  int rc;
+  if (IsMetal()) {
+    rc = ENOSYS;
+  } else if (!req || (IsAsan() && (!__asan_is_valid_timespec(req) ||
+                                   (rem && !__asan_is_valid_timespec(rem))))) {
+    rc = EFAULT;
   } else if (clock == 127 ||              //
              (flags & ~TIMER_ABSTIME) ||  //
              req->tv_sec < 0 ||           //
              !(0 <= req->tv_nsec && req->tv_nsec <= 999999999)) {
-    rc = einval();
-  } else if (IsLinux() || IsFreebsd() || IsNetbsd()) {
-    rc = sys_clock_nanosleep(clock, flags, req, rem);
-  } else if (IsXnu()) {
-    rc = sys_clock_nanosleep_xnu(clock, flags, req, rem);
-  } else if (IsOpenbsd()) {
-    rc = sys_clock_nanosleep_openbsd(clock, flags, req, rem);
-  } else if (IsMetal()) {
-    rc = enosys();
+    rc = EINVAL;
+  } else if (ShouldUseSpinNanosleep(clock, flags, req)) {
+    rc = SpinNanosleep(clock, flags, req, rem);
   } else {
-    rc = sys_clock_nanosleep_nt(clock, flags, req, rem);
+    rc = sys_clock_nanosleep(clock, flags, req, rem);
   }
-
-  if (rc == -1) {
-    rc = errno;
-    errno = e;
-  }
-
-  END_CANCELLATION_POINT;
-
 #if SYSDEBUG
   if (__tls_enabled && !(__get_tls()->tib_flags & TIB_FLAG_TIME_CRITICAL)) {
     STRACE("clock_nanosleep(%s, %s, %s, [%s]) → %s", DescribeClockName(clock),
@@ -125,6 +265,5 @@ errno_t clock_nanosleep(int clock, int flags, const struct timespec *req,
            DescribeTimespec(rc, rem), DescribeErrnoResult(rc));
   }
 #endif
-
   return rc;
 }
diff --git a/libc/calls/clock_nanosleep_latency.c b/libc/calls/clock_nanosleep_latency.c
new file mode 100644
index 000000000..be5766bf1
--- /dev/null
+++ b/libc/calls/clock_nanosleep_latency.c
@@ -0,0 +1,25 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
+#include "libc/calls/blockcancel.internal.h"
+#include "libc/calls/calls.h"
+#include "libc/calls/clock_gettime.internal.h"
+#include "libc/errno.h"
+#include "libc/macros.internal.h"
+#include "libc/sysv/consts/clock.h"
diff --git a/libc/calls/now.c b/libc/calls/now.c
index 815e152f1..4a6d6da20 100644
--- a/libc/calls/now.c
+++ b/libc/calls/now.c
@@ -45,10 +45,10 @@ static long double GetTimeSample(void) {
   uint64_t tick1, tick2;
   long double time1, time2;
   sched_yield();
-  time1 = dtime(CLOCK_REALTIME_FAST);
+  time1 = dtime(CLOCK_REALTIME_PRECISE);
   tick1 = rdtsc();
   nanosleep(&(struct timespec){0, 1000000}, NULL);
-  time2 = dtime(CLOCK_REALTIME_FAST);
+  time2 = dtime(CLOCK_REALTIME_PRECISE);
   tick2 = rdtsc();
   return (time2 - time1) * 1e9 / MAX(1, tick2 - tick1);
 }
@@ -74,13 +74,13 @@ static long double MeasureNanosPerCycle(void) {
 void RefreshTime(void) {
   struct Now now;
   now.cpn = MeasureNanosPerCycle();
-  now.r0 = dtime(CLOCK_REALTIME_FAST);
+  now.r0 = dtime(CLOCK_REALTIME_PRECISE);
   now.k0 = rdtsc();
   memcpy(&g_now, &now, sizeof(now));
 }
 
 static long double nowl_sys(void) {
-  return dtime(CLOCK_REALTIME_FAST);
+  return dtime(CLOCK_REALTIME_PRECISE);
 }
 
 static long double nowl_art(void) {
@@ -92,7 +92,7 @@ static long double nowl_vdso(void) {
   long double secs;
   struct timespec tv;
   _unassert(__gettime);
-  __gettime(CLOCK_REALTIME_FAST, &tv);
+  __gettime(CLOCK_REALTIME_PRECISE, &tv);
   secs = tv.tv_nsec;
   secs *= 1 / 1e9L;
   secs += tv.tv_sec;
diff --git a/libc/calls/struct/timespec.internal.h b/libc/calls/struct/timespec.internal.h
index 768549b7b..88c6b2577 100644
--- a/libc/calls/struct/timespec.internal.h
+++ b/libc/calls/struct/timespec.internal.h
@@ -6,13 +6,13 @@
 COSMOPOLITAN_C_START_
 /* clang-format off */
 
+int __sys_clock_nanosleep(int, int, const struct timespec *, struct timespec *) hidden;
 int __sys_utimensat(int, const char *, const struct timespec[2], int) hidden;
 int __utimens(int, const char *, const struct timespec[2], int) hidden;
 int sys_clock_getres(int, struct timespec *) hidden;
 int sys_clock_gettime(int, struct timespec *) hidden;
 int sys_clock_gettime_nt(int, struct timespec *) hidden;
 int sys_clock_gettime_xnu(int, struct timespec *) hidden;
-int sys_clock_nanosleep(int, int, const struct timespec *, struct timespec *) hidden;
 int sys_clock_nanosleep_nt(int, int, const struct timespec *, struct timespec *) hidden;
 int sys_clock_nanosleep_openbsd(int, int, const struct timespec *, struct timespec *) hidden;
 int sys_clock_nanosleep_xnu(int, int, const struct timespec *, struct timespec *) hidden;
diff --git a/libc/calls/timespec_mono.c b/libc/calls/timespec_mono.c
index 514db06a6..a37e7b2ae 100644
--- a/libc/calls/timespec_mono.c
+++ b/libc/calls/timespec_mono.c
@@ -29,6 +29,6 @@
  */
 struct timespec timespec_mono(void) {
   struct timespec ts;
-  _npassert(!clock_gettime(CLOCK_MONOTONIC_FAST, &ts));
+  _npassert(!clock_gettime(CLOCK_MONOTONIC, &ts));
   return ts;
 }
diff --git a/libc/calls/timespec_real.c b/libc/calls/timespec_real.c
index 6b97142d2..dbebd20c5 100644
--- a/libc/calls/timespec_real.c
+++ b/libc/calls/timespec_real.c
@@ -31,6 +31,6 @@
  */
 struct timespec timespec_real(void) {
   struct timespec ts;
-  _npassert(!clock_gettime(CLOCK_REALTIME_FAST, &ts));
+  _npassert(!clock_gettime(CLOCK_REALTIME, &ts));
   return ts;
 }
diff --git a/libc/intrin/createthread.c b/libc/intrin/createthread.c
index 3e5cfad76..5cd8774f2 100644
--- a/libc/intrin/createthread.c
+++ b/libc/intrin/createthread.c
@@ -16,9 +16,9 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/intrin/strace.internal.h"
 #include "libc/calls/syscall_support-nt.internal.h"
 #include "libc/intrin/describeflags.internal.h"
+#include "libc/intrin/strace.internal.h"
 #include "libc/nt/struct/securityattributes.h"
 #include "libc/nt/thread.h"
 
@@ -29,7 +29,7 @@ __msabi extern typeof(CreateThread) *const __imp_CreateThread;
  *
  * @param dwStackSize may be 0 for default per executable
  * @return thread handle, or 0 on failure
- * @note this wrapper takes care of ABI, STRACE(), and __winerr()
+ * @note this wrapper takes care of ABI, STRACE()
  */
 textwindows int64_t CreateThread(
     struct NtSecurityAttributes *lpThreadAttributes, size_t dwStackSize,
@@ -38,7 +38,6 @@ textwindows int64_t CreateThread(
   int64_t hHandle;
   hHandle = __imp_CreateThread(lpThreadAttributes, dwStackSize, lpStartAddress,
                                lpParameter, dwCreationFlags, opt_lpThreadId);
-  if (hHandle == -1) __winerr();
   NTTRACE("CreateThread(%s, %'zu, %p, %p, %s, %p) → %ld% m",
           DescribeNtSecurityAttributes(lpThreadAttributes), dwStackSize,
           lpStartAddress, lpParameter, dwCreationFlags, opt_lpThreadId,
diff --git a/libc/intrin/kclocknames.S b/libc/intrin/kclocknames.S
index 02c6e9f14..2f2f85bb1 100644
--- a/libc/intrin/kclocknames.S
+++ b/libc/intrin/kclocknames.S
@@ -32,14 +32,14 @@
 	.underrun
 kClockNames:
 	.e	CLOCK_REALTIME,"REALTIME"
-	.e	CLOCK_REALTIME_FAST,"REALTIME_FAST"
-	.e	CLOCK_REALTIME_PRECISE,"REALTIME_PRECISE"
+	.e	CLOCK_REALTIME_FAST,"REALTIME_FAST"		# order matters
+	.e	CLOCK_REALTIME_PRECISE,"REALTIME_PRECISE"	# order matters
+	.e	CLOCK_REALTIME_COARSE,"REALTIME_COARSE"		# order matters
 	.e	CLOCK_MONOTONIC,"MONOTONIC"
-	.e	CLOCK_MONOTONIC_FAST,"MONOTONIC_FAST"
-	.e	CLOCK_MONOTONIC_RAW,"MONOTONIC_RAW"
-	.e	CLOCK_MONOTONIC_PRECISE,"MONOTONIC_PRECISE"
-	.e	CLOCK_REALTIME_COARSE,"REALTIME_COARSE"
-	.e	CLOCK_MONOTONIC_COARSE,"MONOTONIC_COARSE"
+	.e	CLOCK_MONOTONIC_FAST,"MONOTONIC_FAST"		# order matters
+	.e	CLOCK_MONOTONIC_RAW,"MONOTONIC_RAW"		# order matters
+	.e	CLOCK_MONOTONIC_PRECISE,"MONOTONIC_PRECISE"	# order matters
+	.e	CLOCK_MONOTONIC_COARSE,"MONOTONIC_COARSE"	# order matters
 	.e	CLOCK_PROCESS_CPUTIME_ID,"PROCESS_CPUTIME_ID"
 	.e	CLOCK_THREAD_CPUTIME_ID,"THREAD_CPUTIME_ID"
 	.e	CLOCK_TAI,"TAI"
diff --git a/libc/runtime/clone-linux.S b/libc/runtime/clone-linux.S
index bdc5fd028..be1bc422f 100644
--- a/libc/runtime/clone-linux.S
+++ b/libc/runtime/clone-linux.S
@@ -28,7 +28,7 @@
 //	@param	r8 is tls
 //	@param	r9 is func(void*,int)→int
 //	@param	8(rsp) is arg
-//	@return	tid of child on success, or -1 w/ errno
+//	@return	tid of child on success, or -errno on error
 sys_clone_linux:
 	push	%rbp
 	mov	%rsp,%rbp
@@ -39,13 +39,9 @@ sys_clone_linux:
 	syscall
 	test	%rax,%rax
 	jz	2f
-	cmp	$-4095,%rax
-	jae	1f
 0:	pop	%rbx
 	pop	%rbp
 	ret
-1:	call	systemfive_error
-	jmp	0b
 2:	xor	%ebp,%ebp		# child thread
 	mov	%rbx,%rdi		# arg
 	mov	(%r10),%esi		# tid
diff --git a/libc/runtime/clone-xnu.S b/libc/runtime/clone-xnu.S
new file mode 100644
index 000000000..ec5841ac7
--- /dev/null
+++ b/libc/runtime/clone-xnu.S
@@ -0,0 +1,26 @@
+/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-│
+│vi: set et ft=asm ts=8 tw=8 fenc=utf-8                                     :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/macros.internal.h"
+
+sys_clone_xnu:
+	mov	$0x02000168,%eax		# bsdthread_create
+	mov	%rcx,%r10
+	syscall
+	ret
+	.endfn	sys_clone_xnu,globl,hidden
diff --git a/libc/runtime/clone.c b/libc/runtime/clone.c
index 6dc681bc0..f1a06269f 100644
--- a/libc/runtime/clone.c
+++ b/libc/runtime/clone.c
@@ -16,12 +16,14 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
 #include "libc/calls/calls.h"
 #include "libc/calls/struct/ucontext-netbsd.internal.h"
 #include "libc/calls/syscall-sysv.internal.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/intrin/asan.internal.h"
+#include "libc/intrin/describeflags.internal.h"
 #include "libc/intrin/strace.internal.h"
 #include "libc/limits.h"
 #include "libc/macros.internal.h"
@@ -32,6 +34,7 @@
 #include "libc/runtime/clone.internal.h"
 #include "libc/runtime/internal.h"
 #include "libc/runtime/runtime.h"
+#include "libc/sock/internal.h"
 #include "libc/stdalign.internal.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/clone.h"
@@ -66,7 +69,6 @@ struct CloneArgs {
     uint32_t utid;
     int64_t tid64;
   };
-  pthread_spinlock_t lock;
   int *ptid;
   int *ctid;
   int *ztid;
@@ -99,7 +101,6 @@ WinThreadEntry(int rdi,                                 // rcx
                struct CloneArgs *wt) {                  // r9
   int rc;
   if (wt->tls) __set_tls_win32(wt->tls);
-  *wt->ptid = wt->tid;
   *wt->ctid = wt->tid;
   rc = WinThreadLaunch(wt->arg, wt->tid, wt->func, (intptr_t)wt & -16);
   // we can now clear ctid directly since we're no longer using our own
@@ -112,15 +113,14 @@ WinThreadEntry(int rdi,                                 // rcx
   notpossible;
 }
 
-static textwindows int CloneWindows(int (*func)(void *, int), char *stk,
-                                    size_t stksz, int flags, void *arg,
-                                    void *tls, int *ptid, int *ctid) {
+static textwindows errno_t CloneWindows(int (*func)(void *, int), char *stk,
+                                        size_t stksz, int flags, void *arg,
+                                        void *tls, int *ptid, int *ctid) {
   int64_t h;
   struct CloneArgs *wt;
   wt = (struct CloneArgs *)(((intptr_t)(stk + stksz) -
                              sizeof(struct CloneArgs)) &
                             -alignof(struct CloneArgs));
-  wt->ptid = flags & CLONE_PARENT_SETTID ? ptid : &wt->tid;
   wt->ctid = flags & CLONE_CHILD_SETTID ? ctid : &wt->tid;
   wt->ztid = flags & CLONE_CHILD_CLEARTID ? ctid : &wt->tid;
   wt->func = func;
@@ -128,9 +128,12 @@ static textwindows int CloneWindows(int (*func)(void *, int), char *stk,
   wt->tls = flags & CLONE_SETTLS ? tls : 0;
   if ((h = CreateThread(0, 4096, (void *)WinThreadEntry, wt, 0, &wt->utid))) {
     CloseHandle(h);
-    return wt->tid;
+    if (flags & CLONE_PARENT_SETTID) {
+      *ptid = wt->tid;
+    }
+    return 0;
   } else {
-    return -1;
+    return __dos2errno(GetLastError());
   }
 }
 
@@ -161,9 +164,8 @@ XnuThreadMain(void *pthread,                    // rdi
               unsigned xnuflags) {              // r9
   int ax;
   wt->tid = tid;
-  *wt->ptid = tid;
   *wt->ctid = tid;
-  pthread_spin_unlock(&wt->lock);
+  *wt->ptid = tid;
 
   if (wt->tls) {
     // XNU uses the same 0x30 offset as the WIN32 TIB x64. They told the
@@ -192,23 +194,16 @@ XnuThreadMain(void *pthread,                    // rdi
   notpossible;
 }
 
-static int CloneXnu(int (*fn)(void *), char *stk, size_t stksz, int flags,
-                    void *arg, void *tls, int *ptid, int *ctid) {
+static errno_t CloneXnu(int (*fn)(void *), char *stk, size_t stksz, int flags,
+                        void *arg, void *tls, int *ptid, int *ctid) {
   int rc;
   bool failed;
   static bool once;
-  static int broken;
   struct CloneArgs *wt;
   if (!once) {
-    if (sys_bsdthread_register(XnuThreadThunk, 0, 0, 0, 0, 0, 0) == -1) {
-      broken = errno;
-    }
+    _npassert(sys_bsdthread_register(XnuThreadThunk, 0, 0, 0, 0, 0, 0) != -1);
     once = true;
   }
-  if (broken) {
-    errno = broken;
-    return -1;
-  }
   wt = (struct CloneArgs *)(((intptr_t)(stk + stksz) -
                              sizeof(struct CloneArgs)) &
                             -alignof(struct CloneArgs));
@@ -216,14 +211,7 @@ static int CloneXnu(int (*fn)(void *), char *stk, size_t stksz, int flags,
   wt->ctid = flags & CLONE_CHILD_SETTID ? ctid : &wt->tid;
   wt->ztid = flags & CLONE_CHILD_CLEARTID ? ctid : &wt->tid;
   wt->tls = flags & CLONE_SETTLS ? tls : 0;
-  wt->lock._lock = 1;
-  if ((rc = sys_bsdthread_create(fn, arg, wt, 0, PTHREAD_START_CUSTOM_XNU)) !=
-      -1) {
-    pthread_spin_lock(&wt->lock);
-    rc = wt->tid;
-    pthread_spin_unlock(&wt->lock);
-  }
-  return rc;
+  return sys_clone_xnu(fn, arg, wt, 0, PTHREAD_START_CUSTOM_XNU);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -231,7 +219,6 @@ static int CloneXnu(int (*fn)(void *), char *stk, size_t stksz, int flags,
 
 static wontreturn void FreebsdThreadMain(void *p) {
   struct CloneArgs *wt = p;
-  *wt->ptid = wt->tid;
   *wt->ctid = wt->tid;
   wt->func(wt->arg, wt->tid);
   // we no longer use the stack after this point
@@ -249,8 +236,9 @@ static wontreturn void FreebsdThreadMain(void *p) {
   notpossible;
 }
 
-static int CloneFreebsd(int (*func)(void *, int), char *stk, size_t stksz,
-                        int flags, void *arg, void *tls, int *ptid, int *ctid) {
+static errno_t CloneFreebsd(int (*func)(void *, int), char *stk, size_t stksz,
+                            int flags, void *arg, void *tls, int *ptid,
+                            int *ctid) {
   int ax;
   bool failed;
   int64_t tid;
@@ -258,7 +246,6 @@ static int CloneFreebsd(int (*func)(void *, int), char *stk, size_t stksz,
   wt = (struct CloneArgs *)(((intptr_t)(stk + stksz) -
                              sizeof(struct CloneArgs)) &
                             -alignof(struct CloneArgs));
-  wt->ptid = flags & CLONE_PARENT_SETTID ? ptid : &wt->tid;
   wt->ctid = flags & CLONE_CHILD_SETTID ? ctid : &wt->tid;
   wt->ztid = flags & CLONE_CHILD_CLEARTID ? ctid : &wt->tid;
   wt->tls = tls;
@@ -278,11 +265,9 @@ static int CloneFreebsd(int (*func)(void *, int), char *stk, size_t stksz,
                : CFLAG_CONSTRAINT(failed), "=a"(ax)
                : "1"(__NR_thr_new), "D"(&params), "S"(sizeof(params))
                : "rcx", "rdx", "r8", "r9", "r10", "r11", "memory");
-  if (failed) {
-    errno = ax;
-    tid = -1;
-  }
-  return tid;
+  if (failed) return ax;
+  if (flags & CLONE_PARENT_SETTID) *ptid = tid;
+  return 0;
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -292,7 +277,6 @@ static int CloneFreebsd(int (*func)(void *, int), char *stk, size_t stksz,
 //   1. __asan_handle_no_return wipes stack [todo?]
 noasan static wontreturn void OpenbsdThreadMain(void *p) {
   struct CloneArgs *wt = p;
-  *wt->ptid = wt->tid;
   *wt->ctid = wt->tid;
   wt->func(wt->arg, wt->tid);
   asm volatile("mov\t%2,%%rsp\n\t"     // so syscall can validate stack exists
@@ -308,9 +292,10 @@ noasan static wontreturn void OpenbsdThreadMain(void *p) {
   notpossible;
 }
 
-static int CloneOpenbsd(int (*func)(void *, int), char *stk, size_t stksz,
-                        int flags, void *arg, void *tls, int *ptid, int *ctid) {
-  int tid;
+static errno_t CloneOpenbsd(int (*func)(void *, int), char *stk, size_t stksz,
+                            int flags, void *arg, void *tls, int *ptid,
+                            int *ctid) {
+  int rc;
   intptr_t sp;
   struct __tfork *tf;
   struct CloneArgs *wt;
@@ -321,7 +306,6 @@ static int CloneOpenbsd(int (*func)(void *, int), char *stk, size_t stksz,
   sp -= sizeof(struct CloneArgs);
   sp &= -MAX(16, alignof(struct CloneArgs));
   wt = (struct CloneArgs *)sp;
-  wt->ptid = flags & CLONE_PARENT_SETTID ? ptid : &wt->tid;
   wt->ctid = flags & CLONE_CHILD_SETTID ? ctid : &wt->tid;
   wt->ztid = flags & CLONE_CHILD_CLEARTID ? ctid : &wt->tid;
   wt->arg = arg;
@@ -329,11 +313,15 @@ static int CloneOpenbsd(int (*func)(void *, int), char *stk, size_t stksz,
   tf->tf_stack = (char *)wt - 8;
   tf->tf_tcb = flags & CLONE_SETTLS ? tls : 0;
   tf->tf_tid = &wt->tid;
-  if ((tid = __tfork_thread(tf, sizeof(*tf), OpenbsdThreadMain, wt)) < 0) {
-    errno = -tid;
-    tid = -1;
+  if ((rc = __tfork_thread(tf, sizeof(*tf), OpenbsdThreadMain, wt)) >= 0) {
+    _npassert(rc);
+    if (flags & CLONE_PARENT_SETTID) {
+      *ptid = rc;
+    }
+    return 0;
+  } else {
+    return -rc;
   }
-  return tid;
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -343,8 +331,7 @@ static wontreturn void NetbsdThreadMain(void *arg,                 // rdi
                                         int (*func)(void *, int),  // rsi
                                         int *tid,                  // rdx
                                         int *ctid,                 // rcx
-                                        int *ztid,                 // r8
-                                        int *ptid) {               // r9
+                                        int *ztid) {               // r9
   int ax, dx;
   // TODO(jart): Why are we seeing flakes where *tid is zero?
   // ax = *tid;
@@ -370,7 +357,6 @@ static int CloneNetbsd(int (*func)(void *, int), char *stk, size_t stksz,
   int ax, *tid;
   intptr_t dx, sp;
   static bool once;
-  static int broken;
   struct ucontext_netbsd *ctx;
   static struct ucontext_netbsd netbsd_clone_template;
 
@@ -380,15 +366,9 @@ static int CloneNetbsd(int (*func)(void *, int), char *stk, size_t stksz,
                  : CFLAG_CONSTRAINT(failed), "=a"(ax)
                  : "1"(__NR_getcontext_netbsd), "D"(&netbsd_clone_template)
                  : "rcx", "rdx", "r8", "r9", "r10", "r11", "memory");
-    if (failed) {
-      broken = ax;
-    }
+    _npassert(!failed);
     once = true;
   }
-  if (broken) {
-    errno = broken;
-    return -1;
-  }
   sp = (intptr_t)(stk + stksz);
 
   // allocate memory for tid
@@ -420,7 +400,6 @@ static int CloneNetbsd(int (*func)(void *, int), char *stk, size_t stksz,
   ctx->uc_mcontext.rdx = (intptr_t)tid;
   ctx->uc_mcontext.rcx = (intptr_t)(flags & CLONE_CHILD_SETTID ? ctid : tid);
   ctx->uc_mcontext.r8 = (intptr_t)(flags & CLONE_CHILD_CLEARTID ? ctid : tid);
-  ctx->uc_mcontext.r9 = (intptr_t)(flags & CLONE_PARENT_SETTID ? ptid : tid);
   ctx->uc_flags |= _UC_STACK;
   ctx->uc_stack.ss_sp = stk;
   ctx->uc_stack.ss_size = stksz;
@@ -436,10 +415,13 @@ static int CloneNetbsd(int (*func)(void *, int), char *stk, size_t stksz,
                : "1"(__NR__lwp_create), "D"(ctx), "S"(LWP_DETACHED), "2"(tid)
                : "rcx", "r8", "r9", "r10", "r11", "memory");
   if (!failed) {
-    return *tid;
+    _npassert(*tid);
+    if (flags & CLONE_PARENT_SETTID) {
+      *ptid = *tid;
+    }
+    return 0;
   } else {
-    errno = ax;
-    return -1;
+    return ax;
   }
 }
 
@@ -454,8 +436,9 @@ int sys_clone_linux(int flags,   // rdi
                     void *func,  // r9
                     void *arg);  // 8(rsp)
 
-static int CloneLinux(int (*func)(void *arg, int tid), char *stk, size_t stksz,
+static int CloneLinux(int (*func)(void *arg, int rc), char *stk, size_t stksz,
                       int flags, void *arg, void *tls, int *ptid, int *ctid) {
+  int rc;
   long sp;
   sp = (intptr_t)(stk + stksz);
   if (~flags & CLONE_CHILD_SETTID) {
@@ -465,7 +448,12 @@ static int CloneLinux(int (*func)(void *arg, int tid), char *stk, size_t stksz,
     ctid = (int *)sp;
   }
   sp = sp & -16;  // align the stack
-  return sys_clone_linux(flags, sp, ptid, ctid, tls, func, arg);
+  if ((rc = sys_clone_linux(flags, sp, ptid, ctid, tls, func, arg)) >= 0) {
+    // clone() is documented as setting ptid before return
+    return 0;
+  } else {
+    return -rc;
+  }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -478,14 +466,19 @@ static int CloneLinux(int (*func)(void *arg, int tid), char *stk, size_t stksz,
  *
  *     int worker(void *arg) { return 0; }
  *     struct CosmoTib tib = {.tib_self = &tib, .tib_tid = -1};
+ *     atomic_int tid;
  *     char *stk = _mapstack();
- *     tid = clone(worker, stk, GetStackSize() - 16,
- *                 CLONE_VM | CLONE_THREAD | CLONE_FS | CLONE_FILES |
- *                 CLONE_SIGHAND | CLONE_CHILD_SETTID |
- *                 CLONE_CHILD_CLEARTID | CLONE_SETTLS,
- *                 arg, 0, &tib, &tib.tib_tid);
- *     // ...
- *     while (atomic_load(&tib.tib_tid)) sched_yield();
+ *     clone(worker, stk, GetStackSize() - 16,
+ *           CLONE_VM | CLONE_THREAD | CLONE_FS | CLONE_FILES |
+ *           CLONE_SIGHAND | CLONE_PARENT_SETTID | CLONE_CHILD_SETTID |
+ *           CLONE_CHILD_CLEARTID | CLONE_SETTLS,
+ *           arg, &tid, &tib, &tib.tib_tid);
+ *     while (atomic_load(&tid) == 0) sched_yield();
+ *     // thread is known
+ *     while (atomic_load(&tib.tib_tid) < 0) sched_yield();
+ *     // thread is running
+ *     while (atomic_load(&tib.tib_tid) > 0) sched_yield();
+ *     // thread has terminated
  *     _freestack(stk);
  *
  * Threads are created in a detached manner. They currently can't be
@@ -543,14 +536,14 @@ static int CloneLinux(int (*func)(void *arg, int tid), char *stk, size_t stksz,
  *     Your `flags` may also optionally also additionally bitwise-OR any
  *     combination of the following additional flags:
  *
- *     - `CLONE_PARENT_SETTID` must be specified if you intend to set
- *       the `ptid` argument, which is guaranteed to be updated with the
- *       child tid BEFORE BOTH clone() returns and `func` is invoked
- *
  *     - `CLONE_CHILD_SETTID` must be specified if you intend to set the
- *       `ctid` argument, which is guaranteed to be updated with the
- *       child tid before `func` is called, however we CAN NOT guarantee
- *       this will happen BEFORE clone() returns
+ *       `ctid` argument, which will updated with the child tid once the
+ *       child has started.
+ *
+ *     - `CLONE_PARENT_SETTID` must be specified if you intend to set
+ *       the `ptid` argument, which is updated at the most opportune
+ *       moment. On all platforms except XNU, this happens before
+ *       clone() returns. On XNU, it happens once the thread starts.
  *
  *     - `CLONE_CHILD_CLEARTID` causes `*ctid = 0` upon child thread
  *       termination. This is used to implement join so that the parent
@@ -568,11 +561,11 @@ static int CloneLinux(int (*func)(void *arg, int tid), char *stk, size_t stksz,
  *     this parameter is ignored if `CLONE_SETTLS` is not set
  * @param ctid lets the child receive its thread id without having to
  *     call gettid() and is ignored if `CLONE_CHILD_SETTID` isn't set
- * @return tid of child on success, or -1 w/ errno
+ * @return 0 on success, or errno on errno
  * @threadsafe
  */
-int clone(void *func, void *stk, size_t stksz, int flags, void *arg, int *ptid,
-          void *tls, void *ctid) {
+errno_t clone(void *func, void *stk, size_t stksz, int flags, void *arg,
+              void *ptid, void *tls, void *ctid) {
   int rc;
 
   if (flags & CLONE_THREAD) {
@@ -580,17 +573,17 @@ int clone(void *func, void *stk, size_t stksz, int flags, void *arg, int *ptid,
   }
 
   if (!func) {
-    rc = einval();
+    rc = EINVAL;
   } else if (!IsTiny() &&
              ((flags & CLONE_VM) && (stksz < PAGESIZE || (stksz & 15)))) {
-    rc = einval();
+    rc = EINVAL;
   } else if (IsAsan() &&
              (((flags & CLONE_SETTLS) && !__asan_is_valid(tls, 64)) ||
               ((flags & CLONE_PARENT_SETTID) &&
-               !__asan_is_valid(ptid, sizeof(*ptid))) ||
+               !__asan_is_valid(ptid, sizeof(int))) ||
               ((flags & CLONE_CHILD_SETTID) &&
                !__asan_is_valid(ctid, sizeof(int))))) {
-    rc = efault();
+    rc = EFAULT;
   } else if (IsLinux()) {
     rc = CloneLinux(func, stk, stksz, flags, arg, tls, ptid, ctid);
   } else if (!IsTiny() &&
@@ -599,7 +592,7 @@ int clone(void *func, void *stk, size_t stksz, int flags, void *arg, int *ptid,
                  (CLONE_THREAD | CLONE_VM | CLONE_FS | CLONE_FILES |
                   CLONE_SIGHAND)) {
     STRACE("clone flag unsupported on this platform");
-    rc = einval();
+    rc = EINVAL;
   } else if (IsXnu()) {
     rc = CloneXnu(func, stk, stksz, flags, arg, tls, ptid, ctid);
   } else if (IsFreebsd()) {
@@ -611,16 +604,11 @@ int clone(void *func, void *stk, size_t stksz, int flags, void *arg, int *ptid,
   } else if (IsWindows()) {
     rc = CloneWindows(func, stk, stksz, flags, arg, tls, ptid, ctid);
   } else {
-    rc = enosys();
+    rc = ENOSYS;
   }
 
-  // TODO(jart): do we need it?
-  if (rc != -1 && (flags & CLONE_PARENT_SETTID)) {
-    *ptid = rc;
-  }
-
-  STRACE("clone(%t, %p, %'zu, %#x, %p, %p, %p, %p) → %d% m", func, stk, stksz,
-         flags, arg, ptid, tls, ctid, rc);
+  STRACE("clone(%t, %p, %'zu, %#x, %p, %p, %p, %p) → %s", func, stk, stksz,
+         flags, arg, ptid, tls, ctid, DescribeErrnoResult(rc));
 
   return rc;
 }
diff --git a/libc/runtime/clone.internal.h b/libc/runtime/clone.internal.h
index e1a9142c6..89f4b826a 100644
--- a/libc/runtime/clone.internal.h
+++ b/libc/runtime/clone.internal.h
@@ -4,7 +4,7 @@
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 COSMOPOLITAN_C_START_
 
-int clone(void *, void *, size_t, int, void *, int *, void *, void *);
+int clone(void *, void *, size_t, int, void *, void *, void *, void *);
 
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
diff --git a/libc/runtime/enable_tls.c b/libc/runtime/enable_tls.c
index 18c7f4cae..35f5fca48 100644
--- a/libc/runtime/enable_tls.c
+++ b/libc/runtime/enable_tls.c
@@ -117,8 +117,8 @@ void __enable_tls(void) {
     tid = sys_gettid();
   }
   atomic_store_explicit(&tib->tib_tid, tid, memory_order_relaxed);
+  _pthread_main.ptid = tid;
   _pthread_main.tib = tib;
-  _pthread_main.tid = tid;
   _pthread_main.flags = PT_MAINTHREAD;
   __repmovsb(tls, _tdata_start, _TLDZ);
 
diff --git a/libc/runtime/fork.c b/libc/runtime/fork.c
index 48da63f7a..10c060fa7 100644
--- a/libc/runtime/fork.c
+++ b/libc/runtime/fork.c
@@ -34,7 +34,9 @@
 #include "libc/thread/tls.h"
 
 int _fork(uint32_t dwCreationFlags) {
-  int ax, dx, parent;
+  struct CosmoTib *tib;
+  struct PosixThread *pt;
+  int ax, dx, tid, parent;
   BLOCK_SIGNALS;
   if (__threaded && _weaken(_pthread_onfork_prepare)) {
     _weaken(_pthread_onfork_prepare)();
@@ -53,9 +55,12 @@ int _fork(uint32_t dwCreationFlags) {
     parent = __pid;
     __pid = dx;
     if (__tls_enabled) {
-      atomic_store_explicit(&__get_tls()->tib_tid,
-                            IsLinux() ? dx : sys_gettid(),
-                            memory_order_relaxed);
+      tib = __get_tls();
+      tid = IsLinux() ? dx : sys_gettid();
+      atomic_store_explicit(&tib->tib_tid, tid, memory_order_relaxed);
+      if ((pt = (struct PosixThread *)tib->tib_pthread)) {
+        atomic_store_explicit(&pt->ptid, tid, memory_order_relaxed);
+      }
     }
     if (__threaded && _weaken(_pthread_onfork_child)) {
       _weaken(_pthread_onfork_child)();
diff --git a/libc/sysv/calls/__sys_clock_nanosleep.s b/libc/sysv/calls/__sys_clock_nanosleep.s
new file mode 100644
index 000000000..89ebfbc68
--- /dev/null
+++ b/libc/sysv/calls/__sys_clock_nanosleep.s
@@ -0,0 +1,2 @@
+.include "o/libc/sysv/macros.internal.inc"
+.scall __sys_clock_nanosleep,0x9ddfff8f4ffff8e6,globl,hidden
diff --git a/libc/sysv/calls/sys_bsdthread_create.s b/libc/sysv/calls/sys_bsdthread_create.s
deleted file mode 100644
index 03f328b4d..000000000
--- a/libc/sysv/calls/sys_bsdthread_create.s
+++ /dev/null
@@ -1,2 +0,0 @@
-.include "o/libc/sysv/macros.internal.inc"
-.scall sys_bsdthread_create,0xfffffffff2168fff,globl,hidden
diff --git a/libc/sysv/calls/sys_clock_nanosleep.s b/libc/sysv/calls/sys_clock_nanosleep.s
deleted file mode 100644
index 82c21586c..000000000
--- a/libc/sysv/calls/sys_clock_nanosleep.s
+++ /dev/null
@@ -1,2 +0,0 @@
-.include "o/libc/sysv/macros.internal.inc"
-.scall sys_clock_nanosleep,0x9ddfff8f4ffff8e6,globl,hidden
diff --git a/libc/sysv/syscalls.sh b/libc/sysv/syscalls.sh
index 631fb7aaf..44d6da896 100755
--- a/libc/sysv/syscalls.sh
+++ b/libc/sysv/syscalls.sh
@@ -71,7 +71,7 @@ scall	sys_dup			0x0290290292029020	globl hidden
 scall	sys_dup2		0x05a05a05a205a021	globl hidden
 scall	sys_pause		0xfffffffffffff022	globl hidden
 scall	sys_nanosleep		0x9ae85b8f0ffff823	globl hidden
-scall	sys_clock_nanosleep	0x9ddfff8f4ffff8e6	globl hidden
+scall	__sys_clock_nanosleep	0x9ddfff8f4ffff8e6	globl hidden
 scall	sys_getitimer		0x1aa0460562056024	globl hidden
 scall	sys_setitimer		0x1a90450532053026	globl hidden
 scall	sys_alarm		0xfffffffffffff025	globl hidden
@@ -492,7 +492,7 @@ scall	sys_closefrom		0xfff11f1fdfffffff	globl hidden
 #scall	audit_session_join	0xfffffffff21adfff	globl
 #scall	audit_session_port	0xfffffffff21b0fff	globl
 #scall	audit_session_self	0xfffffffff21acfff	globl
-scall	sys_bsdthread_create	0xfffffffff2168fff	globl hidden
+#scall	sys_bsdthread_create	0xfffffffff2168fff	globl
 #scall	bsdthread_ctl		0xfffffffff21defff	globl
 scall	sys_bsdthread_register	0xfffffffff216efff	globl hidden
 #scall	bsdthread_terminate	0xfffffffff2169fff	globl
diff --git a/libc/thread/posixthread.internal.h b/libc/thread/posixthread.internal.h
index 45629691d..72fd9dd3a 100644
--- a/libc/thread/posixthread.internal.h
+++ b/libc/thread/posixthread.internal.h
@@ -66,7 +66,7 @@ struct PosixThread {
   int flags;               // 0x00: see PT_* constants
   _Atomic(int) cancelled;  // 0x04: thread has bad beliefs
   _Atomic(enum PosixThreadStatus) status;
-  int tid;                 // clone parent tid
+  _Atomic(int) ptid;       // transitions 0 → tid
   void *(*start)(void *);  // creation callback
   void *arg;               // start's parameter
   void *rc;                // start's return value
diff --git a/libc/thread/pthread_atfork.c b/libc/thread/pthread_atfork.c
index 5bf8204fa..18a6bceaf 100644
--- a/libc/thread/pthread_atfork.c
+++ b/libc/thread/pthread_atfork.c
@@ -73,7 +73,6 @@ void _pthread_onfork_child(void) {
   tib = __get_tls();
   pt = (struct PosixThread *)tib->tib_pthread;
   atomic_store_explicit(&pt->cancelled, false, memory_order_relaxed);
-  pt->tid = atomic_load_explicit(&tib->tib_tid, memory_order_relaxed);
   pthread_mutexattr_init(&attr);
   pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
   pthread_mutex_init(&__mmi_lock_obj, &attr);
diff --git a/libc/thread/pthread_cancel.c b/libc/thread/pthread_cancel.c
index 3c6339245..b3a0b1e64 100644
--- a/libc/thread/pthread_cancel.c
+++ b/libc/thread/pthread_cancel.c
@@ -87,7 +87,7 @@ static void ListenForSigThr(void) {
  *
  * By default, pthread_cancel() can only take effect when a thread
  * reaches a cancellation point. Such functions are documented with
- * @cancellationpoint. They check the cancellation state before the
+ * `@cancellationpoint`. They check the cancellation state before the
  * underlying system call is issued. If the system call is issued and
  * blocks, then pthread_cancel() will interrupt the operation in which
  * case the syscall wrapper will check the cancelled state a second
@@ -277,18 +277,20 @@ errno_t pthread_cancel(pthread_t thread) {
     }
     return 0;
   }
-  if (IsWindows()) return 0;  // no true cancellations on Windows yet
-  tid = atomic_load_explicit(&pt->tib->tib_tid, memory_order_acquire);
-  if (tid <= 0) return 0;  // -1 means still starting, 0 means exited
-  e = errno;
-  if (!__tkill(tid, SIGTHR, pt->tib)) {
-    return 0;
-  } else {
-    rc = errno;
-    errno = e;
-    return rc;
+  if (!(rc = pthread_getunique_np(thread, &tid))) {
+    if (!IsWindows()) {
+      e = errno;
+      if (!__tkill(tid, SIGTHR, pt->tib)) {
+        rc = 0;
+      } else {
+        rc = errno;
+        errno = e;
+      }
+    } else {
+      rc = 0;
+    }
   }
-  return 0;
+  return rc;
 }
 
 /**
diff --git a/libc/thread/pthread_create.c b/libc/thread/pthread_create.c
index 339d32cb6..f41439aab 100644
--- a/libc/thread/pthread_create.c
+++ b/libc/thread/pthread_create.c
@@ -19,38 +19,27 @@
 #include "libc/assert.h"
 #include "libc/calls/blocksigs.internal.h"
 #include "libc/calls/calls.h"
-#include "libc/calls/sched-sysv.internal.h"
-#include "libc/calls/state.internal.h"
 #include "libc/calls/struct/sigaltstack.h"
-#include "libc/calls/struct/sigset.h"
 #include "libc/calls/syscall-sysv.internal.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/intrin/asan.internal.h"
 #include "libc/intrin/atomic.h"
 #include "libc/intrin/bits.h"
-#include "libc/intrin/kprintf.h"
-#include "libc/intrin/weaken.h"
 #include "libc/log/internal.h"
 #include "libc/macros.internal.h"
 #include "libc/mem/mem.h"
-#include "libc/nexgen32e/gc.internal.h"
 #include "libc/runtime/clone.internal.h"
 #include "libc/runtime/runtime.h"
 #include "libc/runtime/stack.h"
-#include "libc/stdio/stdio.h"
 #include "libc/sysv/consts/clone.h"
 #include "libc/sysv/consts/map.h"
 #include "libc/sysv/consts/prot.h"
-#include "libc/sysv/consts/sig.h"
 #include "libc/sysv/consts/ss.h"
-#include "libc/sysv/errfuns.h"
 #include "libc/thread/posixthread.internal.h"
 #include "libc/thread/spawn.h"
 #include "libc/thread/thread.h"
-#include "libc/thread/tls.h"
 #include "libc/thread/wait0.internal.h"
-#include "third_party/dlmalloc/dlmalloc.h"
 
 STATIC_YOINK("nsync_mu_lock");
 STATIC_YOINK("nsync_mu_unlock");
@@ -254,15 +243,13 @@ static errno_t pthread_create_impl(pthread_t *thread,
 
   // launch PosixThread(pt) in new thread
   pt->sigmask = oldsigs;
-  if (clone(PosixThread, pt->attr.__stackaddr,
-            pt->attr.__stacksize - (IsOpenbsd() ? 16 : 0),
-            CLONE_VM | CLONE_THREAD | CLONE_FS | CLONE_FILES | CLONE_SIGHAND |
-                CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_SETTID |
-                CLONE_CHILD_CLEARTID,
-            pt, &pt->tid, pt->tib, &pt->tib->tib_tid) == -1) {
-    rc = errno;
+  if ((rc = clone(PosixThread, pt->attr.__stackaddr,
+                  pt->attr.__stacksize - (IsOpenbsd() ? 16 : 0),
+                  CLONE_VM | CLONE_THREAD | CLONE_FS | CLONE_FILES |
+                      CLONE_SIGHAND | CLONE_SETTLS | CLONE_PARENT_SETTID |
+                      CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID,
+                  pt, &pt->ptid, pt->tib, &pt->tib->tib_tid))) {
     _pthread_free(pt);
-    errno = e;
     return rc;
   }
 
diff --git a/libc/thread/pthread_getaffinity_np.c b/libc/thread/pthread_getaffinity_np.c
index 91d8ed55b..20dcdeeed 100644
--- a/libc/thread/pthread_getaffinity_np.c
+++ b/libc/thread/pthread_getaffinity_np.c
@@ -20,6 +20,7 @@
 #include "libc/calls/struct/cpuset.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
+#include "libc/intrin/atomic.h"
 #include "libc/intrin/describeflags.internal.h"
 #include "libc/intrin/strace.internal.h"
 #include "libc/str/str.h"
@@ -33,37 +34,40 @@
  * @return 0 on success, or errno on error
  * @raise EINVAL if `size` or `bitset` is invalid
  * @raise ENOSYS if not Linux, FreeBSD, or NetBSD
+ * @raise ESRCH if thread isn't alive
  */
 errno_t pthread_getaffinity_np(pthread_t thread, size_t size,
                                cpu_set_t *bitset) {
-  int tid, rc, e = errno;
-  tid = ((struct PosixThread *)thread)->tid;
+  int e, rc, tid;
 
-  if (size != sizeof(cpu_set_t)) {
-    rc = einval();
-  } else if (IsWindows() || IsMetal() || IsOpenbsd()) {
-    rc = enosys();
-  } else if (IsFreebsd()) {
-    if (!sys_sched_getaffinity_freebsd(CPU_LEVEL_WHICH, CPU_WHICH_TID, tid, 32,
-                                       bitset)) {
-      rc = 32;
+  if (!(rc = pthread_getunique_np(thread, &tid))) {
+    e = errno;
+    if (size != sizeof(cpu_set_t)) {
+      rc = einval();
+    } else if (IsWindows() || IsMetal() || IsOpenbsd()) {
+      rc = enosys();
+    } else if (IsFreebsd()) {
+      if (!sys_sched_getaffinity_freebsd(CPU_LEVEL_WHICH, CPU_WHICH_TID, tid,
+                                         32, bitset)) {
+        rc = 32;
+      } else {
+        rc = -1;
+      }
+    } else if (IsNetbsd()) {
+      if (!sys_sched_getaffinity_netbsd(tid, 0, 32, bitset)) {
+        rc = 32;
+      } else {
+        rc = -1;
+      }
     } else {
-      rc = -1;
+      rc = sys_sched_getaffinity(tid, size, bitset);
     }
-  } else if (IsNetbsd()) {
-    if (!sys_sched_getaffinity_netbsd(tid, 0, 32, bitset)) {
-      rc = 32;
-    } else {
-      rc = -1;
+    if (rc > 0) {
+      if (rc < size) {
+        bzero((char *)bitset + rc, size - rc);
+      }
+      rc = 0;
     }
-  } else {
-    rc = sys_sched_getaffinity(tid, size, bitset);
-  }
-  if (rc > 0) {
-    if (rc < size) {
-      bzero((char *)bitset + rc, size - rc);
-    }
-    rc = 0;
   }
 
   STRACE("pthread_getaffinity_np(%d, %'zu, %p) → %s", tid, size, bitset,
diff --git a/libc/thread/pthread_getname_np.c b/libc/thread/pthread_getname_np.c
index 02eeb89f7..4170d7c3f 100644
--- a/libc/thread/pthread_getname_np.c
+++ b/libc/thread/pthread_getname_np.c
@@ -23,6 +23,7 @@
 #include "libc/errno.h"
 #include "libc/fmt/itoa.h"
 #include "libc/intrin/asmflag.h"
+#include "libc/intrin/atomic.h"
 #include "libc/macros.internal.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/o.h"
@@ -30,11 +31,12 @@
 #include "libc/thread/posixthread.internal.h"
 
 static errno_t pthread_getname_impl(pthread_t thread, char *name, size_t size) {
-  int fd, rc, tid, len, e = errno;
+  int e, fd, rc, tid, len;
 
+  if ((rc = pthread_getunique_np(thread, &tid))) return rc;
   if (!size) return 0;
   bzero(name, size);
-  tid = ((struct PosixThread *)thread)->tid;
+  e = errno;
 
   if (IsLinux()) {
     // TASK_COMM_LEN is 16 on Linux so we're just being paranoid.
diff --git a/libc/thread/pthread_getunique_np.c b/libc/thread/pthread_getunique_np.c
index d3bf75032..753d66eb7 100644
--- a/libc/thread/pthread_getunique_np.c
+++ b/libc/thread/pthread_getunique_np.c
@@ -16,12 +16,26 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/errno.h"
+#include "libc/intrin/atomic.h"
 #include "libc/thread/posixthread.internal.h"
+#include "libc/thread/thread.h"
 
 /**
- * Returns thread id of POSIX thread.
+ * Returns system thread id of POSIX thread.
+ *
+ * @return 0 on success, or errno on error
  */
-int64_t pthread_getunique_np(pthread_t thread) {
-  struct PosixThread *pt = (struct PosixThread *)thread;
-  return pt->tid;
+errno_t pthread_getunique_np(pthread_t thread, pthread_id_np_t *out_tid) {
+  int tid;
+  struct PosixThread *pt;
+  for (pt = (struct PosixThread *)thread;;) {
+    tid = atomic_load_explicit(&pt->ptid, memory_order_acquire);
+    if (!tid) {
+      pthread_yield();
+    } else {
+      *out_tid = tid;
+      return 0;
+    }
+  }
 }
diff --git a/libc/thread/pthread_kill.c b/libc/thread/pthread_kill.c
index 570302615..f4390cede 100644
--- a/libc/thread/pthread_kill.c
+++ b/libc/thread/pthread_kill.c
@@ -19,6 +19,7 @@
 #include "libc/calls/calls.h"
 #include "libc/calls/syscall_support-sysv.internal.h"
 #include "libc/errno.h"
+#include "libc/intrin/atomic.h"
 #include "libc/thread/posixthread.internal.h"
 #include "libc/thread/thread.h"
 
@@ -33,13 +34,17 @@
  * @asyncsignalsafe
  */
 errno_t pthread_kill(pthread_t thread, int sig) {
-  int rc, e = errno;
-  struct PosixThread *pt = (struct PosixThread *)thread;
-  if (!__tkill(pt->tid, sig, pt->tib)) {
-    rc = 0;
-  } else {
-    rc = errno;
-    errno = e;
+  int e, rc, tid;
+  struct PosixThread *p;
+  if (!(rc = pthread_getunique_np(thread, &tid))) {
+    e = errno;
+    p = (struct PosixThread *)thread;
+    if (!__tkill(tid, sig, p->tib)) {
+      rc = 0;
+    } else {
+      rc = errno;
+      errno = e;
+    }
   }
   return rc;
 }
diff --git a/libc/thread/pthread_reschedule.c b/libc/thread/pthread_reschedule.c
index 4aca1c16e..18461a53c 100644
--- a/libc/thread/pthread_reschedule.c
+++ b/libc/thread/pthread_reschedule.c
@@ -20,23 +20,29 @@
 #include "libc/calls/struct/sched_param.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
+#include "libc/intrin/atomic.h"
 #include "libc/sysv/errfuns.h"
 #include "libc/thread/posixthread.internal.h"
 
 errno_t _pthread_reschedule(struct PosixThread *pt) {
-  int rc, e = errno;
+  int e, rc, tid;
   int policy = pt->attr.__schedpolicy;
   struct sched_param param = {pt->attr.__schedparam};
-  if (IsNetbsd()) {
-    rc = sys_sched_setparam_netbsd(0, pt->tid, policy, &param);
-  } else if (IsLinux()) {
-    rc = sys_sched_setscheduler(pt->tid, policy, &param);
-  } else if (IsFreebsd()) {
-    rc = _pthread_setschedparam_freebsd(pt->tid, policy, &param);
-  } else {
-    rc = enosys();
+  if (!(rc = pthread_getunique_np((pthread_t)pt, &tid))) {
+    e = errno;
+    if (IsNetbsd()) {
+      rc = sys_sched_setparam_netbsd(0, tid, policy, &param);
+    } else if (IsLinux()) {
+      rc = sys_sched_setscheduler(tid, policy, &param);
+    } else if (IsFreebsd()) {
+      rc = _pthread_setschedparam_freebsd(tid, policy, &param);
+    } else {
+      rc = enosys();
+    }
+    if (rc == -1) {
+      rc = errno;
+      errno = e;
+    }
   }
-  rc = rc != -1 ? 0 : errno;
-  errno = e;
   return rc;
 }
diff --git a/libc/thread/pthread_setaffinity_np.c b/libc/thread/pthread_setaffinity_np.c
index 415e85ff4..a4ed86415 100644
--- a/libc/thread/pthread_setaffinity_np.c
+++ b/libc/thread/pthread_setaffinity_np.c
@@ -21,6 +21,7 @@
 #include "libc/calls/syscall_support-nt.internal.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
+#include "libc/intrin/atomic.h"
 #include "libc/intrin/describeflags.internal.h"
 #include "libc/intrin/strace.internal.h"
 #include "libc/nt/enum/threadaccess.h"
@@ -52,23 +53,25 @@ static dontinline textwindows int sys_pthread_setaffinity_nt(
  */
 errno_t pthread_setaffinity_np(pthread_t thread, size_t size,
                                const cpu_set_t *bitset) {
-  int tid, rc, e = errno;
-  tid = ((struct PosixThread *)thread)->tid;
-  if (size != sizeof(cpu_set_t)) {
-    rc = einval();
-  } else if (IsWindows()) {
-    rc = sys_pthread_setaffinity_nt(tid, size, bitset);
-  } else if (IsFreebsd()) {
-    rc = sys_sched_setaffinity_freebsd(CPU_LEVEL_WHICH, CPU_WHICH_TID, tid, 32,
-                                       bitset);
-  } else if (IsNetbsd()) {
-    rc = sys_sched_setaffinity_netbsd(tid, 0, 32, bitset);
-  } else {
-    rc = sys_sched_setaffinity(tid, size, bitset);
-  }
-  if (rc == -1) {
-    rc = errno;
-    errno = e;
+  int e, rc, tid;
+  if (!(rc = pthread_getunique_np(thread, &tid))) {
+    e = errno;
+    if (size != sizeof(cpu_set_t)) {
+      rc = einval();
+    } else if (IsWindows()) {
+      rc = sys_pthread_setaffinity_nt(tid, size, bitset);
+    } else if (IsFreebsd()) {
+      rc = sys_sched_setaffinity_freebsd(CPU_LEVEL_WHICH, CPU_WHICH_TID, tid,
+                                         32, bitset);
+    } else if (IsNetbsd()) {
+      rc = sys_sched_setaffinity_netbsd(tid, 0, 32, bitset);
+    } else {
+      rc = sys_sched_setaffinity(tid, size, bitset);
+    }
+    if (rc == -1) {
+      rc = errno;
+      errno = e;
+    }
   }
   STRACE("pthread_setaffinity_np(%d, %'zu, %p) → %s", tid, size, bitset,
          DescribeErrnoResult(rc));
diff --git a/libc/thread/pthread_setname_np.c b/libc/thread/pthread_setname_np.c
index 3123dce94..1effca9a7 100644
--- a/libc/thread/pthread_setname_np.c
+++ b/libc/thread/pthread_setname_np.c
@@ -24,6 +24,7 @@
 #include "libc/fmt/itoa.h"
 #include "libc/intrin/asan.internal.h"
 #include "libc/intrin/asmflag.h"
+#include "libc/intrin/atomic.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/o.h"
 #include "libc/sysv/consts/pr.h"
@@ -31,12 +32,13 @@
 
 static errno_t pthread_setname_impl(pthread_t thread, const char *name) {
   char path[128], *p;
-  int fd, rc, tid, len, e = errno;
+  int e, fd, rc, tid, len;
 
-  tid = ((struct PosixThread *)thread)->tid;
+  if ((rc = pthread_getunique_np(thread, &tid))) return rc;
   len = strlen(name);
 
   if (IsLinux()) {
+    e = errno;
     if (tid == gettid()) {
       if (prctl(PR_SET_NAME, name) == -1) {
         rc = errno;
diff --git a/libc/thread/spawn.c b/libc/thread/spawn.c
index 21a72aba1..20bedfb53 100644
--- a/libc/thread/spawn.c
+++ b/libc/thread/spawn.c
@@ -17,6 +17,7 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
+#include "libc/errno.h"
 #include "libc/macros.internal.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/clone.internal.h"
@@ -92,6 +93,7 @@ static int Spawner(void *arg, int tid) {
  * @return 0 on success, or -1 w/ errno
  */
 int _spawn(int fun(void *, int), void *arg, struct spawn *opt_out_thread) {
+  errno_t rc;
   struct spawn *th, ths;
   struct spawner *spawner;
   __require_tls();
@@ -122,11 +124,13 @@ int _spawn(int fun(void *, int), void *arg, struct spawn *opt_out_thread) {
   spawner = malloc(sizeof(struct spawner));
   spawner->fun = fun;
   spawner->arg = arg;
-  if (clone(Spawner, th->stk, GetStackSize() - 16 /* openbsd:stackbound */,
-            CLONE_VM | CLONE_THREAD | CLONE_FS | CLONE_FILES | CLONE_SIGHAND |
-                CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_SETTID |
-                CLONE_CHILD_CLEARTID,
-            spawner, &th->ptid, th->tib, &th->tib->tib_tid) == -1) {
+  rc = clone(Spawner, th->stk, GetStackSize() - 16 /* openbsd:stackbound */,
+             CLONE_VM | CLONE_THREAD | CLONE_FS | CLONE_FILES | CLONE_SIGHAND |
+                 CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_SETTID |
+                 CLONE_CHILD_CLEARTID,
+             spawner, &th->ptid, th->tib, &th->tib->tib_tid);
+  if (rc) {
+    errno = rc;
     _freestack(th->stk);
     free(th->tls);
     return -1;
diff --git a/libc/thread/thread.h b/libc/thread/thread.h
index b3f70496b..b6d7330aa 100644
--- a/libc/thread/thread.h
+++ b/libc/thread/thread.h
@@ -115,7 +115,7 @@ int pthread_testcancel_np(void);
 void pthread_exit(void *) wontreturn;
 pthread_t pthread_self(void) pureconst;
 pthread_id_np_t pthread_getthreadid_np(void);
-int64_t pthread_getunique_np(pthread_t);
+int pthread_getunique_np(pthread_t, pthread_id_np_t *);
 int pthread_setname_np(pthread_t, const char *);
 int pthread_getname_np(pthread_t, char *, size_t);
 int pthread_getattr_np(pthread_t, pthread_attr_t *);
diff --git a/libc/thread/tls.h b/libc/thread/tls.h
index d6b773169..a78a3c426 100644
--- a/libc/thread/tls.h
+++ b/libc/thread/tls.h
@@ -24,7 +24,7 @@ struct CosmoTib {
   intptr_t tib_locale;            /* 0x20 */
   intptr_t tib_pthread;           /* 0x28 */
   struct CosmoTib *tib_self2;     /* 0x30 */
-  _Atomic(int32_t) tib_tid;       /* 0x38 */
+  _Atomic(int32_t) tib_tid;       /* 0x38 transitions -1 → tid → 0 */
   int32_t tib_errno;              /* 0x3c */
   uint64_t tib_flags;             /* 0x40 */
   void *tib_nsync;
diff --git a/libc/thread/xnu.internal.h b/libc/thread/xnu.internal.h
index 6462f8cf4..71d5d5fba 100644
--- a/libc/thread/xnu.internal.h
+++ b/libc/thread/xnu.internal.h
@@ -8,8 +8,8 @@ COSMOPOLITAN_C_START_
  * See darwin-libpthread/kern/kern_support.c
  */
 
-int sys_bsdthread_create(void *func, void *func_arg, void *stack, void *pthread,
-                         uint32_t flags);
+errno_t sys_clone_xnu(void *func, void *func_arg, void *stack, void *pthread,
+                      uint32_t flags);
 int sys_bsdthread_register(
     void (*threadstart)(void *pthread, int machport, void *(*func)(void *),
                         void *arg, intptr_t *, unsigned),
diff --git a/libc/time/iso8601us.c b/libc/time/iso8601us.c
index e993be55b..77aff570c 100644
--- a/libc/time/iso8601us.c
+++ b/libc/time/iso8601us.c
@@ -65,7 +65,6 @@
  * @threadsafe
  */
 char *iso8601us(char p[hasatleast 27], struct tm *tm, long ns) {
-  int x;
   p = iso8601(p, tm);
   _unassert(0 <= ns && ns < 1000000000);
   *p++ = '.';
diff --git a/test/libc/calls/nanosleep_test.c b/test/libc/calls/nanosleep_test.c
index 8b8ca9603..5bd1ea2a6 100644
--- a/test/libc/calls/nanosleep_test.c
+++ b/test/libc/calls/nanosleep_test.c
@@ -22,6 +22,7 @@
 #include "libc/calls/struct/timespec.h"
 #include "libc/errno.h"
 #include "libc/intrin/describeflags.internal.h"
+#include "libc/intrin/strace.internal.h"
 #include "libc/sysv/consts/clock.h"
 #include "libc/sysv/consts/itimer.h"
 #include "libc/sysv/consts/sa.h"
@@ -31,6 +32,7 @@
 
 void OnAlrm(int sig) {
   // do nothing
+  STRACE("OnAlrm()");
 }
 
 TEST(nanosleep, testFault) {
@@ -54,7 +56,7 @@ TEST(nanosleep, testInterrupt_remIsUpdated) {
       .sa_flags = SA_RESETHAND,
   };
   ASSERT_SYS(0, 0, sigaction(SIGALRM, &sa, 0));
-  struct itimerval it = {{0, 0}, {0, 10000}};  // 10ms singleshot
+  struct itimerval it = {{0, 0}, {0, 100000}};  // 100ms singleshot
   ASSERT_SYS(0, 0, setitimer(ITIMER_REAL, &it, 0));
   struct timespec ts = {500, 0};
   ASSERT_SYS(EINTR, -1, nanosleep(&ts, &ts));
@@ -75,7 +77,7 @@ TEST(clock_nanosleep, testInterrupt_remIsUpdated) {
       .sa_flags = SA_RESETHAND,
   };
   ASSERT_SYS(0, 0, sigaction(SIGALRM, &sa, 0));
-  struct itimerval it = {{0, 0}, {0, 10000}};  // 10ms singleshot
+  struct itimerval it = {{0, 0}, {0, 100000}};  // 100ms singleshot
   ASSERT_SYS(0, 0, setitimer(ITIMER_REAL, &it, 0));
   struct timespec ts = {500, 0};
   ASSERT_EQ(EINTR, clock_nanosleep(CLOCK_REALTIME, 0, &ts, &ts));
diff --git a/test/libc/calls/tkill_test.c b/test/libc/calls/tkill_test.c
index defed8bef..b7f0be24d 100644
--- a/test/libc/calls/tkill_test.c
+++ b/test/libc/calls/tkill_test.c
@@ -39,8 +39,8 @@ void *Worker(void *arg) {
 
 TEST(tkill, test) {
   if (IsWindows()) return;  // TODO(jart): fix me
-  int i;
   void *res;
+  int i, tid;
   pthread_t t;
   sigset_t ss, oldss;
   sighandler_t oldsig;
@@ -49,7 +49,8 @@ TEST(tkill, test) {
   oldsig = signal(SIGUSR1, OnSig);
   ASSERT_SYS(0, 0, sigprocmask(SIG_BLOCK, &ss, &oldss));
   ASSERT_EQ(0, pthread_create(&t, 0, Worker, 0));
-  ASSERT_SYS(0, 0, tkill(pthread_getunique_np(t), SIGUSR1));
+  ASSERT_EQ(0, pthread_getunique_np(t, &tid));
+  ASSERT_SYS(0, 0, tkill(tid, SIGUSR1));
   ASSERT_EQ(0, pthread_join(t, &res));
   ASSERT_EQ(SIGUSR1, (intptr_t)res);
   ASSERT_SYS(0, 0, sigprocmask(SIG_SETMASK, &oldss, 0));
diff --git a/test/libc/stdio/getentropy_test.c b/test/libc/stdio/getentropy_test.c
index 4e324f0fc..3881cf850 100644
--- a/test/libc/stdio/getentropy_test.c
+++ b/test/libc/stdio/getentropy_test.c
@@ -22,6 +22,7 @@
 #include "libc/calls/struct/sigset.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
+#include "libc/macros.internal.h"
 #include "libc/mem/gc.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/runtime.h"
@@ -50,9 +51,9 @@ void *TortureWorker(void *arg) {
   ready = true;
   while (!done) {
     if (!IsWindows()) pthread_kill(parent, SIGUSR1);
-    usleep(3);
+    usleep(1);
     if (!IsWindows()) pthread_kill(parent, SIGUSR2);
-    usleep(3);
+    usleep(1);
   }
   return 0;
 }
@@ -61,7 +62,7 @@ TEST(getentropy, test) {
   pthread_t child;
   double e, w = 7.7;
   struct sigaction sa;
-  int i, j, k, n = 999;
+  int i, j, k, m, n = 999;
   char *buf = _gc(calloc(1, n));
   sa.sa_flags = 0;
   sa.sa_handler = OnSig;
@@ -71,11 +72,13 @@ TEST(getentropy, test) {
   parent = pthread_self();
   ASSERT_EQ(0, pthread_create(&child, 0, TortureWorker, 0));
   while (!ready) pthread_yield();
-  for (k = 0; k < 200; ++k) {
-    ASSERT_SYS(0, 0, getrandom(0, 0, 0));
-    ASSERT_SYS(0, n, getrandom(buf, n, 0));
-    ASSERT_SYS(EFAULT, -1, getrandom(0, n, 0));
-    ASSERT_SYS(EINVAL, -1, getrandom(buf, n, -1));
+  for (k = 0; k < 10; ++k) {
+    ASSERT_SYS(0, 0, getentropy(0, 0));
+    for (i = 0; i < n; i += m) {
+      m = MIN(n - i, 256);
+      ASSERT_SYS(0, 0, getentropy(buf + i, m));
+      ASSERT_SYS(EFAULT, -1, getentropy(0, m));
+    }
     if ((e = MeasureEntropy(buf, n)) < w) {
       fprintf(stderr, "error: entropy suspect! got %g but want >=%g\n", e, w);
       for (i = 0; i < n;) {
diff --git a/test/libc/stdio/getrandom_test.c b/test/libc/stdio/getrandom_test.c
index 430fa2dc0..04b13eea6 100644
--- a/test/libc/stdio/getrandom_test.c
+++ b/test/libc/stdio/getrandom_test.c
@@ -24,6 +24,7 @@
 #include "libc/errno.h"
 #include "libc/intrin/bits.h"
 #include "libc/log/check.h"
+#include "libc/macros.internal.h"
 #include "libc/math.h"
 #include "libc/mem/gc.h"
 #include "libc/mem/mem.h"
@@ -41,6 +42,29 @@
 #include "libc/testlib/testlib.h"
 #include "libc/thread/thread.h"
 
+atomic_int done;
+atomic_int ready;
+pthread_t parent;
+atomic_int gotsome;
+
+void OnSig(int sig) {
+  ++gotsome;
+}
+
+void *TortureWorker(void *arg) {
+  sigset_t ss;
+  sigfillset(&ss);
+  ASSERT_SYS(0, 0, sigprocmask(SIG_SETMASK, &ss, 0));
+  ready = true;
+  while (!done) {
+    if (!IsWindows()) pthread_kill(parent, SIGUSR1);
+    usleep(1);
+    if (!IsWindows()) pthread_kill(parent, SIGUSR2);
+    usleep(1);
+  }
+  return 0;
+}
+
 TEST(getrandom, test) {
   double e, w = 7.7;
   int i, j, n = 999;
@@ -61,6 +85,45 @@ TEST(getrandom, test) {
   }
 }
 
+TEST(getrandom, test2) {
+  pthread_t child;
+  double e, w = 7.7;
+  struct sigaction sa;
+  int i, j, k, m, n = 999;
+  char *buf = _gc(calloc(1, n));
+  sa.sa_flags = 0;
+  sa.sa_handler = OnSig;
+  sigemptyset(&sa.sa_mask);
+  ASSERT_SYS(0, 0, sigaction(SIGUSR1, &sa, 0));
+  ASSERT_SYS(0, 0, sigaction(SIGUSR2, &sa, 0));
+  parent = pthread_self();
+  ASSERT_EQ(0, pthread_create(&child, 0, TortureWorker, 0));
+  while (!ready) pthread_yield();
+  for (k = 0; k < 10; ++k) {
+    ASSERT_SYS(0, 0, getrandom(0, 0, 0));
+    for (i = 0; i < n; i += m) {
+      ASSERT_NE(-1, (m = getrandom(buf + i, n - i, 0)));
+    }
+    ASSERT_SYS(EFAULT, -1, getrandom(0, n, 0));
+    ASSERT_SYS(EINVAL, -1, getrandom(buf, n, -1));
+    if ((e = MeasureEntropy(buf, n)) < w) {
+      fprintf(stderr, "error: entropy suspect! got %g but want >=%g\n", e, w);
+      for (i = 0; i < n;) {
+        if (!(i % 16)) fprintf(stderr, "%6x ", i);
+        fprintf(stderr, "%lc", kCp437[buf[i] & 255]);
+        if (!(++i % 16)) fprintf(stderr, "\n");
+      }
+      fprintf(stderr, "\n");
+      done = true;
+      pthread_join(child, 0);
+      exit(1);
+    }
+  }
+  done = true;
+  ASSERT_EQ(0, pthread_join(child, 0));
+  if (!IsWindows()) ASSERT_GT(gotsome, 0);
+}
+
 /* JustReturnZero                   */
 /* entropy:            0            */
 /* chi-square:         2.55e+07     */
diff --git a/third_party/nsync/futex.c b/third_party/nsync/futex.c
index b432e8531..f630a3a35 100644
--- a/third_party/nsync/futex.c
+++ b/third_party/nsync/futex.c
@@ -16,6 +16,7 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
 #include "libc/atomic.h"
 #include "libc/calls/calls.h"
 #include "libc/calls/internal.h"
@@ -111,29 +112,36 @@ __attribute__((__constructor__)) static void nsync_futex_init_ (void) {
 	}
 }
 
-static int nsync_futex_polyfill_ (atomic_int *w, int expect, struct timespec *timeout) {
+static int nsync_futex_polyfill_ (atomic_int *w, int expect, struct timespec *abstime) {
 	int rc;
 	int64_t nanos, maxnanos;
-	struct timespec ts, deadline;
+	struct timespec now, wait, remain, deadline;
 
-	ts = timespec_real ();
-	if (!timeout) {
+	if (!abstime) {
 		deadline = timespec_max;
 	} else {
-		deadline = *timeout;
+		deadline = *abstime;
 	}
 
 	nanos = 100;
 	maxnanos = __SIG_POLLING_INTERVAL_MS * 1000L * 1000;
-	while (timespec_cmp (deadline, ts) > 0) {
-		ts = timespec_add (ts, timespec_fromnanos (nanos));
-		if (timespec_cmp (ts, deadline) > 0) {
-			ts = deadline;
-		}
+	for (;;) {
 		if (atomic_load_explicit (w, memory_order_acquire) != expect) {
 			return 0;
 		}
-		if ((rc = timespec_sleep_until (ts))) {
+		now = timespec_real ();
+		if (atomic_load_explicit (w, memory_order_acquire) != expect) {
+			return 0;
+		}
+		if (timespec_cmp (now, deadline) >= 0) {
+			break;
+		}
+		wait = timespec_fromnanos (nanos);
+		remain = timespec_sub (deadline, now);
+		if (timespec_cmp(wait, remain) > 0) {
+			wait = remain;
+		}
+		if ((rc = clock_nanosleep (CLOCK_REALTIME, 0, &wait, 0))) {
 			return -rc;
 		}
 		if (nanos < maxnanos) {
diff --git a/tool/emacs/cosmo-c-constants.el b/tool/emacs/cosmo-c-constants.el
index 824aab5ca..e9cd247e4 100644
--- a/tool/emacs/cosmo-c-constants.el
+++ b/tool/emacs/cosmo-c-constants.el
@@ -103,7 +103,8 @@
     "DBL_MIN"
     "DBL_MAX"
     "FLT_MIN"
-    "FLT_MAX"))
+    "FLT_MAX"
+    "PIPE_BUF"))
 
 (defconst cosmo-c-constants-math
   '("NAN"
diff --git a/tool/net/definitions.lua b/tool/net/definitions.lua
index c33411f41..0e6a2d24e 100644
--- a/tool/net/definitions.lua
+++ b/tool/net/definitions.lua
@@ -3322,6 +3322,8 @@ unix = {
     --- @type integer
     CLOCK_MONOTONIC_COARSE = nil,
     --- @type integer
+    CLOCK_MONOTONIC_PRECISE = nil,
+    --- @type integer
     CLOCK_MONOTONIC_FAST = nil,
     --- @type integer
     CLOCK_MONOTONIC_RAW = nil,
@@ -3332,6 +3334,8 @@ unix = {
     --- @type integer
     CLOCK_REALTIME = nil,
     --- @type integer
+    CLOCK_REALTIME_PRECISE = nil,
+    --- @type integer
     CLOCK_REALTIME_ALARM = nil,
     --- @type integer
     CLOCK_REALTIME_COARSE = nil,
@@ -5247,13 +5251,16 @@ function unix.syslog(priority, msg) end
 ---
 --- - `CLOCK_REALTIME`: universally supported
 --- - `CLOCK_REALTIME_FAST`: ditto but faster on freebsd
+--- - `CLOCK_REALTIME_PRECISE`: ditto but better on freebsd
+--- - `CLOCK_REALTIME_COARSE`: : like `CLOCK_REALTIME_FAST` but needs Linux 2.6.32+
 --- - `CLOCK_MONOTONIC`: universally supported
 --- - `CLOCK_MONOTONIC_FAST`: ditto but faster on freebsd
---- - `CLOCK_MONOTONIC_RAW`: nearly universally supported
+--- - `CLOCK_MONOTONIC_PRECISE`: ditto but better on freebsd
+--- - `CLOCK_MONOTONIC_COARSE`: : like `CLOCK_MONOTONIC_FAST` but needs Linux 2.6.32+
+--- - `CLOCK_MONOTONIC_RAW`: is actually monotonic but needs Linux 2.6.28+
 --- - `CLOCK_PROCESS_CPUTIME_ID`: linux and bsd
 --- - `CLOCK_THREAD_CPUTIME_ID`: linux and bsd
---- - `CLOCK_REALTIME_COARSE`: : linux and openbsd
---- - `CLOCK_MONOTONIC_COARSE`: linux
+--- - `CLOCK_MONOTONIC_COARSE`: linux, freebsd
 --- - `CLOCK_PROF`: linux and netbsd
 --- - `CLOCK_BOOTTIME`: linux and openbsd
 --- - `CLOCK_REALTIME_ALARM`: linux-only
diff --git a/tool/net/help.txt b/tool/net/help.txt
index 92230e863..defc8c38d 100644
--- a/tool/net/help.txt
+++ b/tool/net/help.txt
@@ -3597,13 +3597,16 @@ UNIX MODULE
 
     - `CLOCK_REALTIME`: universally supported
     - `CLOCK_REALTIME_FAST`: ditto but faster on freebsd
+    - `CLOCK_REALTIME_PRECISE`: ditto but better on freebsd
+    - `CLOCK_REALTIME_COARSE`: : like `CLOCK_REALTIME_FAST` but needs Linux 2.6.32+
     - `CLOCK_MONOTONIC`: universally supported
     - `CLOCK_MONOTONIC_FAST`: ditto but faster on freebsd
-    - `CLOCK_MONOTONIC_RAW`: nearly universally supported
+    - `CLOCK_MONOTONIC_PRECISE`: ditto but better on freebsd
+    - `CLOCK_MONOTONIC_COARSE`: : like `CLOCK_MONOTONIC_FAST` but needs Linux 2.6.32+
+    - `CLOCK_MONOTONIC_RAW`: is actually monotonic but needs Linux 2.6.28+
     - `CLOCK_PROCESS_CPUTIME_ID`: linux and bsd
     - `CLOCK_THREAD_CPUTIME_ID`: linux and bsd
-    - `CLOCK_REALTIME_COARSE`: : linux and openbsd
-    - `CLOCK_MONOTONIC_COARSE`: linux
+    - `CLOCK_MONOTONIC_COARSE`: linux, freebsd
     - `CLOCK_PROF`: linux and netbsd
     - `CLOCK_BOOTTIME`: linux and openbsd
     - `CLOCK_REALTIME_ALARM`: linux-only