From 4eeaa07477d84698785545b4429c79ca10e16036 Mon Sep 17 00:00:00 2001
From: Chinmay Garde <chinmaygarde@gmail.com>
Date: Wed, 17 Aug 2016 14:28:23 -0700
Subject: [PATCH] flow::Semaphore for simple platform specific unnamed
 semaphores. (#2937)

---
 flow/BUILD.gn                |   1 +
 synchronization/BUILD.gn     |  14 ++++
 synchronization/semaphore.cc | 121 +++++++++++++++++++++++++++++++++++
 synchronization/semaphore.h  |  39 +++++++++++
 4 files changed, 175 insertions(+)
 create mode 100644 synchronization/BUILD.gn
 create mode 100644 synchronization/semaphore.cc
 create mode 100644 synchronization/semaphore.h

diff --git a/flow/BUILD.gn b/flow/BUILD.gn
index 1100c403a6058..3bcb43e2f8bda 100644
--- a/flow/BUILD.gn
+++ b/flow/BUILD.gn
@@ -46,6 +46,7 @@ source_set("flow") {
   deps = [
     "//flutter/glue",
     "//flutter/skia",
+    "//flutter/synchronization",
     "//lib/ftl",
     "//mojo/services/gfx/composition/interfaces",
   ]
diff --git a/synchronization/BUILD.gn b/synchronization/BUILD.gn
new file mode 100644
index 0000000000000..fa027d887c239
--- /dev/null
+++ b/synchronization/BUILD.gn
@@ -0,0 +1,14 @@
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+source_set("synchronization") {
+  sources = [
+    "semaphore.cc",
+    "semaphore.h",
+  ]
+
+  deps = [
+    "//lib/ftl",
+  ]
+}
diff --git a/synchronization/semaphore.cc b/synchronization/semaphore.cc
new file mode 100644
index 0000000000000..a863a07285bd0
--- /dev/null
+++ b/synchronization/semaphore.cc
@@ -0,0 +1,121 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/synchronization/semaphore.h"
+#include "lib/ftl/build_config.h"
+#include "lib/ftl/logging.h"
+
+#if OS_MACOSX
+
+#include <dispatch/dispatch.h>
+
+namespace flutter {
+
+class PlatformSemaphore {
+ public:
+  explicit PlatformSemaphore(uint32_t count)
+      : _sem(dispatch_semaphore_create(count)) {}
+
+  ~PlatformSemaphore() {
+    if (_sem != nullptr) {
+      dispatch_release(reinterpret_cast<dispatch_object_t>(_sem));
+      _sem = nullptr;
+    }
+  }
+
+  bool IsValid() const { return _sem != nullptr; }
+
+  bool TryWait() {
+    if (_sem == nullptr) {
+      return false;
+    }
+
+    return dispatch_semaphore_wait(_sem, DISPATCH_TIME_NOW) == 0;
+  }
+
+  void Signal() {
+    if (_sem != nullptr) {
+      dispatch_semaphore_signal(_sem);
+    }
+  }
+
+ private:
+  dispatch_semaphore_t _sem;
+
+  FTL_DISALLOW_COPY_AND_ASSIGN(PlatformSemaphore);
+};
+
+}  // namespace flutter
+
+#else  // OS_MACOSX
+
+#include <semaphore.h>
+#include "lib/ftl/files/eintr_wrapper.h"
+
+namespace flutter {
+
+class PlatformSemaphore {
+ public:
+  explicit PlatformSemaphore(uint32_t count)
+      : valid_(::sem_init(&sem_, 0 /* not shared */, count) == 0) {}
+
+  ~PlatformSemaphore() {
+    if (valid_) {
+      int result = ::sem_destroy(&sem_);
+      // Can only be EINVAL which should not be possible since we checked for
+      // validity.
+      FTL_DCHECK(result == 0);
+    }
+  }
+
+  bool IsValid() const { return valid_; }
+
+  bool TryWait() {
+    if (!valid_) {
+      return false;
+    }
+
+    return HANDLE_EINTR(::sem_trywait(&sem_)) == 0;
+  }
+
+  void Signal() {
+    if (!valid_) {
+      return;
+    }
+
+    ::sem_post(&sem_);
+
+    return;
+  }
+
+ private:
+  bool valid_;
+  sem_t sem_;
+
+  FTL_DISALLOW_COPY_AND_ASSIGN(PlatformSemaphore);
+};
+
+}  // namespace flutter
+
+#endif
+
+namespace flutter {
+
+Semaphore::Semaphore(uint32_t count) : _impl(new PlatformSemaphore(count)) {}
+
+Semaphore::~Semaphore() = default;
+
+bool Semaphore::IsValid() const {
+  return _impl->IsValid();
+}
+
+bool Semaphore::TryWait() {
+  return _impl->TryWait();
+}
+
+void Semaphore::Signal() {
+  return _impl->Signal();
+}
+
+}  // namespace flutter
diff --git a/synchronization/semaphore.h b/synchronization/semaphore.h
new file mode 100644
index 0000000000000..41e7355da9e0d
--- /dev/null
+++ b/synchronization/semaphore.h
@@ -0,0 +1,39 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SYNCHRONIZATION_SEMAPHORE_H_
+#define SYNCHRONIZATION_SEMAPHORE_H_
+
+#include <memory>
+
+#include "lib/ftl/macros.h"
+#include "lib/ftl/time/time_delta.h"
+#include "lib/ftl/compiler_specific.h"
+
+namespace flutter {
+
+class PlatformSemaphore;
+
+class Semaphore {
+ public:
+  explicit Semaphore(uint32_t count);
+
+  ~Semaphore();
+
+  bool IsValid() const;
+
+  FTL_WARN_UNUSED_RESULT
+  bool TryWait();
+
+  void Signal();
+
+ private:
+  std::unique_ptr<PlatformSemaphore> _impl;
+
+  FTL_DISALLOW_COPY_AND_ASSIGN(Semaphore);
+};
+
+}  // namespace flutter
+
+#endif  // SYNCHRONIZATION_SEMAPHORE_H_