system_wrappers/source/rw_lock_generic.cc

/*
 *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include "webrtc/system_wrappers/source/rw_lock_generic.h"

#include "webrtc/system_wrappers/interface/condition_variable_wrapper.h"
#include "webrtc/system_wrappers/interface/critical_section_wrapper.h"

namespace webrtc {

RWLockGeneric::RWLockGeneric()
    : readers_active_(0),
      writer_active_(false),
      readers_waiting_(0),
      writers_waiting_(0) {
  critical_section_ = CriticalSectionWrapper::CreateCriticalSection();
  read_condition_ = ConditionVariableWrapper::CreateConditionVariable();
  write_condition_ = ConditionVariableWrapper::CreateConditionVariable();
}

RWLockGeneric::~RWLockGeneric() {
  delete write_condition_;
  delete read_condition_;
  delete critical_section_;
}

void RWLockGeneric::AcquireLockExclusive() {
  CriticalSectionScoped cs(critical_section_);
  if (writer_active_ || readers_active_ > 0) {
    ++writers_waiting_;
    while (writer_active_ || readers_active_ > 0) {
      write_condition_->SleepCS(*critical_section_);
    }
    --writers_waiting_;
  }
  writer_active_ = true;
}

void RWLockGeneric::ReleaseLockExclusive() {
  CriticalSectionScoped cs(critical_section_);
  writer_active_ = false;
  if (writers_waiting_ > 0) {
    write_condition_->Wake();
  } else if (readers_waiting_ > 0) {
    read_condition_->WakeAll();
  }
}

void RWLockGeneric::AcquireLockShared() {
  CriticalSectionScoped cs(critical_section_);
  if (writer_active_ || writers_waiting_ > 0) {
    ++readers_waiting_;

    while (writer_active_ || writers_waiting_ > 0) {
      read_condition_->SleepCS(*critical_section_);
    }
    --readers_waiting_;
  }
  ++readers_active_;
}

void RWLockGeneric::ReleaseLockShared() {
  CriticalSectionScoped cs(critical_section_);
  --readers_active_;
  if (readers_active_ == 0 && writers_waiting_ > 0) {
    write_condition_->Wake();
  }
}

}  // namespace webrtc