src/pagespeed/kernel/thread/pthread_rw_lock.cc

/*
 * Copyright 2011 Google Inc.
 *
 * 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.
 */

// Author: pulkitg@google.com (Pulkit Goyal)

#include "pagespeed/kernel/thread/pthread_rw_lock.h"

#include <pthread.h>

namespace net_instaweb {

PthreadRWLock::PthreadRWLock() {
  pthread_rwlockattr_init(&attr_);
  // POSIX does not provide any sort of guarantee that prevents writer
  // starvation for reader-writer locks. On, Linux one can avoid
  // writer starvation as long as readers are non-recursive via the
  // call below. (PTHREAD_RWLOCK_PREFER_WRITER_NP does not work).
  //
  // Other OS's (FreeBSD, Darwin, OpenSolaris) documentation suggests
  // that they prefer writers by default.
#ifdef linux
  pthread_rwlockattr_setkind_np(&attr_,
                                PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP);
#endif
  pthread_rwlock_init(&rwlock_, &attr_);
}

PthreadRWLock::~PthreadRWLock() {
  pthread_rwlockattr_destroy(&attr_);
  pthread_rwlock_destroy(&rwlock_);
}

bool PthreadRWLock::TryLock() {
  return (pthread_rwlock_trywrlock(&rwlock_) == 0);
}

void PthreadRWLock::Lock() {
  pthread_rwlock_wrlock(&rwlock_);
}

void PthreadRWLock::Unlock() {
  pthread_rwlock_unlock(&rwlock_);
}

bool PthreadRWLock::ReaderTryLock() {
  return (pthread_rwlock_tryrdlock(&rwlock_) == 0);
}

void PthreadRWLock::ReaderLock() {
  pthread_rwlock_rdlock(&rwlock_);
}

void PthreadRWLock::ReaderUnlock() {
  pthread_rwlock_unlock(&rwlock_);
}

}  // namespace net_instaweb