Improve Windows sleep accuracy from 15ms to 15µs

libc/calls/clock_nanosleep-nt.c

@@ -16,6 +16,7 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/atomic.h"
 #include "libc/calls/internal.h"
 #include "libc/calls/struct/sigset.internal.h"
 #include "libc/calls/struct/timespec.h"
@@ -23,26 +24,37 @@
 #include "libc/calls/syscall-sysv.internal.h"
 #include "libc/errno.h"
 #include "libc/intrin/atomic.h"
+#include "libc/nt/enum/status.h"
+#include "libc/nt/ntdll.h"
 #include "libc/stdio/sysparam.h"
+#include "libc/sysv/consts/clock.h"
 #include "libc/sysv/consts/timer.h"
 #include "libc/thread/tls.h"
 #ifdef __x86_64__
 
+static atomic_int usingRes;
+static atomic_bool changedRes;
+
 static textwindows int sys_clock_nanosleep_nt_impl(int clock,
                                                    struct timespec abs,
                                                    sigset_t waitmask) {
-  uint32_t msdelay;
-  struct timespec now;
-  for (;;) {
-    if (sys_clock_gettime_nt(clock, &now))
-      return -1;
-    if (timespec_cmp(now, abs) >= 0)
-      return 0;
-    msdelay = timespec_tomillis(timespec_sub(abs, now));
-    msdelay = MIN(msdelay, -1u);
-    if (_park_norestart(msdelay, waitmask) == -1)
-      return -1;
-  }
+  struct timespec now, wall;
+  uint32_t minRes, maxRes, oldRes;
+  sys_clock_gettime_nt(0, &wall);
+  if (sys_clock_gettime_nt(clock, &now))
+    return -1;
+  bool wantRes = clock == CLOCK_REALTIME ||   //
+                 clock == CLOCK_MONOTONIC ||  //
+                 clock == CLOCK_BOOTTIME;
+  if (wantRes && !atomic_fetch_add(&usingRes, 1))
+    changedRes = NtSuccess(NtQueryTimerResolution(&minRes, &maxRes, &oldRes)) &&
+                 NtSuccess(NtSetTimerResolution(maxRes, true, &oldRes));
+  if (timespec_cmp(abs, now) > 0)
+    wall = timespec_add(wall, timespec_sub(abs, now));
+  int rc = _park_norestart(wall, waitmask);
+  if (wantRes && atomic_fetch_sub(&usingRes, 1) == 1 && changedRes)
+    NtSetTimerResolution(0, false, &minRes);
+  return rc;
 }
 
 textwindows int sys_clock_nanosleep_nt(int clock, int flags,

libc/calls/clock_nanosleep.c

@@ -57,6 +57,7 @@
  *
  * @param clock may be
  *     - `CLOCK_REALTIME`
+ *     - `CLOCK_BOOTTIME`
  *     - `CLOCK_MONOTONIC`
  *     - `CLOCK_REALTIME_COARSE` but is likely to sleep negative time
  *     - `CLOCK_MONTONIC_COARSE` but is likely to sleep negative time

libc/calls/internal.h

@@ -3,6 +3,7 @@
 #include "libc/atomic.h"
 #include "libc/calls/struct/sigset.h"
 #include "libc/calls/struct/sigval.h"
+#include "libc/calls/struct/timespec.h"
 #include "libc/dce.h"
 #include "libc/intrin/fds.h"
 #include "libc/macros.h"
@@ -46,8 +47,8 @@ int _check_signal(bool);
 int _check_cancel(void);
 bool _is_canceled(void);
 int sys_close_nt(int, int);
-int _park_norestart(uint32_t, uint64_t);
-int _park_restartable(uint32_t, uint64_t);
+int _park_norestart(struct timespec, uint64_t);
+int _park_restartable(struct timespec, uint64_t);
 int sys_openat_metal(int, const char *, int, unsigned);
 
 #ifdef __x86_64__

libc/calls/park.c

@@ -19,65 +19,96 @@
 #include "libc/calls/internal.h"
 #include "libc/calls/sig.internal.h"
 #include "libc/calls/struct/sigset.h"
+#include "libc/calls/struct/timespec.h"
 #include "libc/calls/syscall_support-nt.internal.h"
+#include "libc/fmt/wintime.internal.h"
 #include "libc/intrin/atomic.h"
 #include "libc/intrin/weaken.h"
-#include "libc/nt/enum/wait.h"
 #include "libc/nt/events.h"
 #include "libc/nt/runtime.h"
 #include "libc/nt/synchronization.h"
+#include "libc/str/str.h"
 #include "libc/sysv/consts/sicode.h"
 #include "libc/sysv/errfuns.h"
 #include "libc/thread/posixthread.internal.h"
+
 #ifdef __x86_64__
 
-// returns 0 on timeout or spurious wakeup
+// returns 0 if deadline is reached
 // raises EINTR if a signal delivery interrupted wait operation
 // raises ECANCELED if this POSIX thread was canceled in masked mode
-textwindows static int _park_thread(uint32_t msdelay, sigset_t waitmask,
+textwindows static int _park_thread(struct timespec deadline, sigset_t waitmask,
                                     bool restartable) {
-  struct PosixThread *pt = _pthread_self();
+  for (;;) {
+    uint32_t handl = 0;
+    intptr_t hands[2];
 
-  // perform the wait operation
-  intptr_t sigev;
-  if (!(sigev = CreateEvent(0, 0, 0, 0)))
-    return __winerr();
-  pt->pt_event = sigev;
-  pt->pt_blkmask = waitmask;
-  atomic_store_explicit(&pt->pt_blocker, PT_BLOCKER_EVENT,
-                        memory_order_release);
-  //!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!//
-  int sig = 0;
-  uint32_t ws = 0;
-  if (!_is_canceled() &&
-      !(_weaken(__sig_get) && (sig = _weaken(__sig_get)(waitmask))))
-    ws = WaitForSingleObject(sigev, msdelay);
-  //!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!//
-  atomic_store_explicit(&pt->pt_blocker, 0, memory_order_release);
-  CloseHandle(sigev);
+    // create event object
+    intptr_t sigev;
+    if (!(sigev = CreateEvent(0, 0, 0, 0)))
+      return __winerr();
+    hands[handl++] = sigev;
 
-  // recursion is now safe
-  if (ws == -1u)
-    return __winerr();
-  int handler_was_called = 0;
-  if (sig)
-    handler_was_called = _weaken(__sig_relay)(sig, SI_KERNEL, waitmask);
-  if (_check_cancel())
-    return -1;
-  if (handler_was_called & SIG_HANDLED_NO_RESTART)
-    return eintr();
-  if (handler_was_called & SIG_HANDLED_SA_RESTART)
-    if (!restartable)
+    // create high precision timer if needed
+    if (memcmp(&deadline, &timespec_max, sizeof(struct timespec))) {
+      intptr_t hTimer;
+      if ((hTimer = CreateWaitableTimer(NULL, true, NULL))) {
+        int64_t due = TimeSpecToWindowsTime(deadline);
+        if (SetWaitableTimer(hTimer, &due, 0, NULL, NULL, false)) {
+          hands[handl++] = hTimer;
+        } else {
+          CloseHandle(hTimer);
+        }
+      }
+    }
+
+    // perform wait operation
+    struct PosixThread *pt = _pthread_self();
+    pt->pt_event = sigev;
+    pt->pt_blkmask = waitmask;
+    atomic_store_explicit(&pt->pt_blocker, PT_BLOCKER_EVENT,
+                          memory_order_release);
+    //!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!//
+    int sig = 0;
+    uint32_t wi = 0;
+    if (!_is_canceled() &&
+        !(_weaken(__sig_get) && (sig = _weaken(__sig_get)(waitmask))))
+      wi = WaitForMultipleObjects(handl, hands, false, -1u);
+    //!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!/!//
+    atomic_store_explicit(&pt->pt_blocker, 0, memory_order_release);
+    for (int i = 0; i < handl; ++i)
+      CloseHandle(hands[i]);
+
+    // recursion is now safe
+    if (wi == 1)
+      return 0;
+    if (wi == -1u)
+      return __winerr();
+    int handler_was_called = 0;
+    if (!sig) {
+      if (_check_cancel())
+        return -1;
+      if (_weaken(__sig_get))
+        sig = _weaken(__sig_get)(waitmask);
+    }
+    if (sig)
+      handler_was_called = _weaken(__sig_relay)(sig, SI_KERNEL, waitmask);
+    if (_check_cancel())
+      return -1;
+    if (handler_was_called & SIG_HANDLED_NO_RESTART)
       return eintr();
-  return 0;
+    if (handler_was_called & SIG_HANDLED_SA_RESTART)
+      if (!restartable)
+        return eintr();
+  }
 }
 
-textwindows int _park_norestart(uint32_t msdelay, sigset_t waitmask) {
-  return _park_thread(msdelay, waitmask, false);
+textwindows int _park_norestart(struct timespec deadline, sigset_t waitmask) {
+  return _park_thread(deadline, waitmask, false);
 }
 
-textwindows int _park_restartable(uint32_t msdelay, sigset_t waitmask) {
-  return _park_thread(msdelay, waitmask, true);
+textwindows int _park_restartable(struct timespec deadline, sigset_t waitmask) {
+  return _park_thread(deadline, waitmask, true);
 }
 
 #endif /* __x86_64__ */

libc/calls/pause-nt.c

@@ -18,21 +18,20 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/internal.h"
 #include "libc/calls/struct/sigset.internal.h"
+#include "libc/calls/struct/timespec.h"
 #include "libc/calls/syscall_support-nt.internal.h"
 #ifdef __x86_64__
 
 textwindows int sys_pause_nt(void) {
-  int rc;
   // we don't strictly need to block signals, but it reduces signal
   // delivery latency, by preventing other threads from delivering a
   // signal asynchronously. it takes about ~5us to deliver a signal
   // using SetEvent() whereas it takes ~30us to use SuspendThread(),
   // GetThreadContext(), SetThreadContext(), and ResumeThread().
   BLOCK_SIGNALS;
-  while (!(rc = _park_norestart(-1u, 0)))
-    donothing;
+  _park_norestart(timespec_max, 0);
   ALLOW_SIGNALS;
-  return rc;
+  return -1;
 }
 
 #endif /* __x86_64__ */

libc/calls/poll-nt.c

@@ -318,8 +318,8 @@ textwindows static int sys_poll_nt_actual(struct pollfd *fds, uint64_t nfds,
 textwindows static int sys_poll_nt_impl(struct pollfd *fds, uint64_t nfds,
                                         struct timespec deadline,
                                         const sigset_t waitmask) {
-  uint32_t waitms;
   int i, n, rc, got = 0;
+  struct timespec now, next, target;
 
   // we normally don't check for signals until we decide to wait, since
   // it's nice to have functions like write() be unlikely to EINTR, but
@@ -344,9 +344,16 @@ textwindows static int sys_poll_nt_impl(struct pollfd *fds, uint64_t nfds,
     }
     if (got)
       return got;
-    if (!(waitms = sys_poll_nt_waitms(deadline)))
+    now = sys_clock_gettime_monotonic_nt();
+    if (timespec_cmp(now, deadline) >= 0)
       return 0;
-    if (_park_norestart(waitms, waitmask) == -1)
+    next = timespec_add(now, timespec_frommillis(POLL_INTERVAL_MS));
+    if (timespec_cmp(next, deadline) >= 0) {
+      target = deadline;
+    } else {
+      target = next;
+    }
+    if (_park_norestart(target, waitmask) == -1)
       return -1;
   }
 }

libc/calls/sigsuspend.c

@@ -21,6 +21,7 @@
 #include "libc/calls/sig.internal.h"
 #include "libc/calls/struct/sigset.h"
 #include "libc/calls/struct/sigset.internal.h"
+#include "libc/calls/struct/timespec.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/intrin/atomic.h"
@@ -59,8 +60,7 @@ int sigsuspend(const sigset_t *ignore) {
       // using SetEvent() whereas it takes ~30us to use SuspendThread(),
       // GetThreadContext(), SetThreadContext(), and ResumeThread().
       BLOCK_SIGNALS;
-      while (!(rc = _park_norestart(-1u, waitmask)))
-        donothing;
+      rc = _park_norestart(timespec_max, waitmask);
       ALLOW_SIGNALS;
     } else {
       rc = sys_sigsuspend((uint64_t[2]){waitmask}, 8);