Improve time/sleep accuracy on Windows

It's now almost as good as Linux thanks to a Windows 8+ API.

libc/calls/clktck.c

@@ -40,7 +40,11 @@ static dontinline int __clk_tck_init(void) {
   size_t len;
   struct clockinfo_netbsd clock;
   if (IsWindows()) {
-    x = 1000;
+    // MSVC defines CLK_TCK as 1000 but 1ms is obviously not the
+    // scheduling quantum Windows actually uses. If we define it
+    // as 30 rather than 1000, then clock_nanosleep is much more
+    // accurately able to predict the duration of its busy waits
+    x = 30;
   } else if (IsXnu() || IsOpenbsd()) {
     x = 100;
   } else if (IsFreebsd()) {

libc/calls/clock_getres.c

@@ -25,14 +25,20 @@
 #include "libc/sysv/errfuns.h"
 #include "libc/time/time.h"
 
-static int sys_clock_getres_poly(int clock, struct timespec *ts, int64_t real) {
+static int sys_clock_getres_poly(int clock, struct timespec *ts, int64_t real,
+                                 int64_t real_coarse, int64_t boot) {
+  ts->tv_sec = 0;
   if (clock == CLOCK_REALTIME) {
-    ts->tv_sec = 0;
     ts->tv_nsec = real;
     return 0;
+  } else if (clock == CLOCK_REALTIME_COARSE) {
+    ts->tv_nsec = real_coarse;
+    return 0;
   } else if (clock == CLOCK_MONOTONIC) {
-    ts->tv_sec = 0;
-    ts->tv_nsec = 1;
+    ts->tv_nsec = 10;
+    return 0;
+  } else if (clock == CLOCK_BOOTTIME) {
+    ts->tv_nsec = boot;
     return 0;
   } else {
     return einval();
@@ -40,11 +46,11 @@ static int sys_clock_getres_poly(int clock, struct timespec *ts, int64_t real) {
 }
 
 static int sys_clock_getres_nt(int clock, struct timespec *ts) {
-  return sys_clock_getres_poly(clock, ts, 100);
+  return sys_clock_getres_poly(clock, ts, 100, 1000000, 1000000);
 }
 
 static int sys_clock_getres_xnu(int clock, struct timespec *ts) {
-  return sys_clock_getres_poly(clock, ts, 1000);
+  return sys_clock_getres_poly(clock, ts, 1000, 1000, 1000);
 }
 
 /**

libc/calls/clock_gettime-nt.c

@@ -18,26 +18,61 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/struct/timespec.h"
 #include "libc/calls/struct/timespec.internal.h"
+#include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/fmt/wintime.internal.h"
-#include "libc/nt/struct/filetime.h"
 #include "libc/nt/synchronization.h"
-#include "libc/sysv/consts/clock.h"
+
+#define _CLOCK_REALTIME        0
+#define _CLOCK_MONOTONIC       1
+#define _CLOCK_REALTIME_COARSE 2
+#define _CLOCK_BOOTTIME        3
+
+static struct {
+  uint64_t base;
+  uint64_t freq;
+} g_winclock;
 
 textwindows int sys_clock_gettime_nt(int clock, struct timespec *ts) {
+  uint64_t t;
   struct NtFileTime ft;
-  if (clock == CLOCK_REALTIME) {
-    if (!ts) return 0;
-    GetSystemTimeAsFileTime(&ft);
-    *ts = FileTimeToTimeSpec(ft);
-    return 0;
-  } else if (clock == CLOCK_MONOTONIC) {
-    if (!ts) return 0;
-    return sys_clock_gettime_mono(ts);
-  } else if (clock == CLOCK_BOOTTIME) {
-    if (ts) *ts = timespec_frommillis(GetTickCount64());
-    return 0;
-  } else {
-    return -EINVAL;
+  switch (clock) {
+    case _CLOCK_REALTIME:
+      if (ts) {
+        GetSystemTimePreciseAsFileTime(&ft);
+        *ts = FileTimeToTimeSpec(ft);
+      }
+      return 0;
+    case _CLOCK_REALTIME_COARSE:
+      if (ts) {
+        GetSystemTimeAsFileTime(&ft);
+        *ts = FileTimeToTimeSpec(ft);
+      }
+      return 0;
+    case _CLOCK_MONOTONIC:
+      if (ts) {
+        QueryPerformanceCounter(&t);
+        t = ((t - g_winclock.base) * 1000000000) / g_winclock.freq;
+        *ts = timespec_fromnanos(t);
+      }
+      return 0;
+    case _CLOCK_BOOTTIME:
+      if (ts) {
+        *ts = timespec_frommillis(GetTickCount64());
+      }
+      return 0;
+    default:
+      return -EINVAL;
   }
 }
+
+static textstartup void winclock_init() {
+  if (IsWindows()) {
+    QueryPerformanceCounter(&g_winclock.base);
+    QueryPerformanceFrequency(&g_winclock.freq);
+  }
+}
+
+const void *const winclock_ctor[] initarray = {
+    winclock_init,
+};

libc/calls/utimensat-nt.c

@@ -65,7 +65,7 @@ static textwindows int sys_utimensat_nt_impl(int dirfd, const char *path,
   }
 
   if (!ts || ts[0].tv_nsec == UTIME_NOW || ts[1].tv_nsec == UTIME_NOW) {
-    GetSystemTimeAsFileTime(ft);
+    GetSystemTimePreciseAsFileTime(ft);
   }
   if (ts) {
     for (i = 0; i < 2; ++i) {