Make fixes and improvements

- clock_nanosleep() is now much faster on OpenBSD and NetBSD
- Thread joining is now much faster on NetBSD
- FreeBSD timestamps are now more accurate
- Thread spawning now goes faster on XNU
- Clean up the clone() code

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)));
+  }
+}