zircon/system/ulib/fbl/include/fbl/mutex.h

// Copyright 2016 The Fuchsia 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 FBL_MUTEX_H_
#define FBL_MUTEX_H_

#ifdef __cplusplus

#include <zircon/compiler.h>
#include <fbl/macros.h>

// Notes about class Mutex
//
// Mutex is a C++ helper class intended to wrap a mutex-style synchronization
// primitive and provide a common interface for library code which is intended
// to be shared between user-mode and kernel code.  It is also responsible for
// automatically initializing and destroying the internal mutex object.
#if _KERNEL
#include <kernel/mutex.h>

namespace fbl {
using Mutex = ::Mutex;
}  // namespace fbl

#else  // if _KERNEL

#include <threads.h>

namespace fbl {

class __TA_CAPABILITY("mutex") Mutex {
 public:
#ifdef MTX_INIT
  constexpr Mutex() : mutex_(MTX_INIT) {}
#else
  Mutex() { mtx_init(&mutex_, mtx_plain); }
#endif
  ~Mutex() { mtx_destroy(&mutex_); }
  void Acquire() __TA_ACQUIRE() { mtx_lock(&mutex_); }
  void Release() __TA_RELEASE() { mtx_unlock(&mutex_); }

  /* IsHeld is not supported by the Mutex wrapper in user-mode as C11 mtx_t
   * instances do not support a direct IsHeld style check.  A possible
   * implementation could be built out of mtx_trylock, but would require
   * either relaxing away the const constraint on the method signature, or
   * flagging the mutex_ member as mutable */

  mtx_t* GetInternal() __TA_RETURN_CAPABILITY(mutex_) { return &mutex_; }

  // suppress default constructors
  DISALLOW_COPY_ASSIGN_AND_MOVE(Mutex);

 private:
  mtx_t mutex_;
};

}  // namespace fbl

#endif  // if _KERNEL
#endif  // ifdef __cplusplus

#endif  // FBL_MUTEX_H_