Add Semaphore and its test, and use it where semaphores are needed

util/synchronization/semaphore.h

Index: util/synchronization/semaphore.h
diff --git a/util/synchronization/semaphore.h b/util/synchronization/semaphore.h
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+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef CRASHPAD_UTIL_SYNCHRONIZATION_SEMAPHORE_H_
+#define CRASHPAD_UTIL_SYNCHRONIZATION_SEMAPHORE_H_
+
+#include "build/build_config.h"
+
+#if defined(OS_MACOSX)
+#include <dispatch/dispatch.h>
+#else
+#include <semaphore.h>
+#endif
+
+namespace crashpad {
+
+//! \brief An anonymous in-process counting sempahore.
+class Semaphore {
+ public:
+  //! \brief Initializes the semaphore.
+  //!
+  //! \param[in] value The initial value of the semaphore.
+  //!
+  //! If the semaphore cannot be created, execution is terminated.
+  explicit Semaphore(int value);
+
+  ~Semaphore();
+
+  //! \brief Performs the wait (or “procure”) operation on the semaphore.
+  //!
+  //! Atomically decrements the value of the semaphore by 1. If the new value is
+  //! negative, this function blocks and will not return until the semaphore’s
+  //! value is incremented to 0 by Signal().
+  void Wait();
+
+  //! \brief Performs the signal (or “post”) operation on the semaphore.
+  //!
+  //! Atomically increments the value of the semaphore by 1. If the new value is
+  //! 0, a caller blocked in Wait() will be awakened.
+  void Signal();
+
+ private:
+#if defined(OS_MACOSX)
+  dispatch_semaphore_t semaphore_;
+#else
+  sem_t semaphore_;
+#endif
+};
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_SYNCHRONIZATION_SEMAPHORE_H_