Switch base::Semaphore to use dispatch_semaphore_t on Mac.

The dispatch_semaphore_t is a higher-level, more-efficient semaphore
primitive if the cross-process capabilities of semaphore_t are not
needed.

Bug: chromium:1012386
Change-Id: I9cc6f025f00159f9424c054a3395542b9db00b89
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1848211Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64254}

src/base/platform/platform-posix.cc

@@ -48,6 +48,7 @@
 
 #if V8_OS_MACOSX
 #include <dlfcn.h>
+#include <mach/mach.h>
 #endif
 
 #if V8_OS_LINUX

src/base/platform/semaphore.cc

@@ -5,8 +5,7 @@
 #include "src/base/platform/semaphore.h"
 
 #if V8_OS_MACOSX
-#include <mach/mach_init.h>
-#include <mach/task.h>
+#include <dispatch/dispatch.h>
 #endif
 
 #include <errno.h>
@@ -21,53 +20,23 @@ namespace base {
 #if V8_OS_MACOSX
 
 Semaphore::Semaphore(int count) {
-  kern_return_t result = semaphore_create(
-      mach_task_self(), &native_handle_, SYNC_POLICY_FIFO, count);
-  DCHECK_EQ(KERN_SUCCESS, result);
-  USE(result);
+  native_handle_ = dispatch_semaphore_create(count);
+  DCHECK(native_handle_);
 }
 
+Semaphore::~Semaphore() { dispatch_release(native_handle_); }
 
-Semaphore::~Semaphore() {
-  kern_return_t result = semaphore_destroy(mach_task_self(), native_handle_);
-  DCHECK_EQ(KERN_SUCCESS, result);
-  USE(result);
-}
-
-void Semaphore::Signal() {
-  kern_return_t result = semaphore_signal(native_handle_);
-  DCHECK_EQ(KERN_SUCCESS, result);
-  USE(result);
-}
-
+void Semaphore::Signal() { dispatch_semaphore_signal(native_handle_); }
 
 void Semaphore::Wait() {
-  while (true) {
-    kern_return_t result = semaphore_wait(native_handle_);
-    if (result == KERN_SUCCESS) return;  // Semaphore was signalled.
-    DCHECK_EQ(KERN_ABORTED, result);
-  }
+  dispatch_semaphore_wait(native_handle_, DISPATCH_TIME_FOREVER);
 }
 
 
 bool Semaphore::WaitFor(const TimeDelta& rel_time) {
-  TimeTicks now = TimeTicks::Now();
-  TimeTicks end = now + rel_time;
-  while (true) {
-    mach_timespec_t ts;
-    if (now >= end) {
-      // Return immediately if semaphore was not signalled.
-      ts.tv_sec = 0;
-      ts.tv_nsec = 0;
-    } else {
-      ts = (end - now).ToMachTimespec();
-    }
-    kern_return_t result = semaphore_timedwait(native_handle_, ts);
-    if (result == KERN_SUCCESS) return true;  // Semaphore was signalled.
-    if (result == KERN_OPERATION_TIMED_OUT) return false;  // Timeout.
-    DCHECK_EQ(KERN_ABORTED, result);
-    now = TimeTicks::Now();
-  }
+  dispatch_time_t timeout =
+      dispatch_time(DISPATCH_TIME_NOW, rel_time.InNanoseconds());
+  return dispatch_semaphore_wait(native_handle_, timeout) == 0;
 }
 
 #elif V8_OS_POSIX

src/base/platform/semaphore.h

@@ -12,7 +12,7 @@
 #endif
 
 #if V8_OS_MACOSX
-#include <mach/semaphore.h>  // NOLINT
+#include <dispatch/dispatch.h>  // NOLINT
 #elif V8_OS_POSIX
 #include <semaphore.h>  // NOLINT
 #endif
@@ -50,7 +50,7 @@ class V8_BASE_EXPORT Semaphore final {
   bool WaitFor(const TimeDelta& rel_time) V8_WARN_UNUSED_RESULT;
 
 #if V8_OS_MACOSX
-  using NativeHandle = semaphore_t;
+  using NativeHandle = dispatch_semaphore_t;
 #elif V8_OS_POSIX
   using NativeHandle = sem_t;
 #elif V8_OS_WIN