src/base/mutex.cc

// Copyright 2010-2018, Google Inc.
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#include "base/mutex.h"

#ifdef OS_WIN
#include <Windows.h>
#else
#include <pthread.h>
#endif

#include <atomic>

#include "base/port.h"

#if defined(OS_WIN)
// We do not use pthread on Windows
#elif defined(OS_NACL)
// TODO(team): Consider to use glibc rwlock.
#else
#define MOZC_PTHREAD_HAS_READER_WRITER_LOCK
#endif

namespace mozc {
namespace {

// State for once_t.
enum CallOnceState {
  ONCE_INIT = 0,
  ONCE_RUNNING = 1,
  ONCE_DONE = 2,
};

}  // namespace

#ifdef OS_WIN  // Hereafter, we have Win32 implementations
namespace {

template <typename T>
CRITICAL_SECTION *AsCriticalSection(T* opaque_buffer) {
  static_assert(sizeof(T) >= sizeof(CRITICAL_SECTION),
                "The opaque buffer must have sufficient space to store a "
                "CRITICAL_SECTION structure");
  return reinterpret_cast<CRITICAL_SECTION *>(opaque_buffer);
}

template <typename T>
SRWLOCK *AsSRWLock(T* opaque_buffer) {
  static_assert(sizeof(T) >= sizeof(SRWLOCK),
                "The opaque buffer must have sufficient space to store a "
                "SRWLOCK structure");
  return reinterpret_cast<SRWLOCK *>(opaque_buffer);
}

}  // namespace

Mutex::Mutex() {
  ::InitializeCriticalSection(AsCriticalSection(&opaque_buffer_));
}

Mutex::~Mutex() {
  ::DeleteCriticalSection(AsCriticalSection(&opaque_buffer_));
}

void Mutex::Lock() {
  ::EnterCriticalSection(AsCriticalSection(&opaque_buffer_));
}

bool Mutex::TryLock() {
  return ::TryEnterCriticalSection(AsCriticalSection(&opaque_buffer_)) != FALSE;
}

void Mutex::Unlock() {
  ::LeaveCriticalSection(AsCriticalSection(&opaque_buffer_));
}

ReaderWriterMutex::ReaderWriterMutex() {
  ::InitializeSRWLock(AsSRWLock(&opaque_buffer_));
}

ReaderWriterMutex::~ReaderWriterMutex() {
}

void ReaderWriterMutex::ReaderLock() {
  ::AcquireSRWLockShared(AsSRWLock(&opaque_buffer_));
}

void ReaderWriterMutex::WriterLock() {
  ::AcquireSRWLockExclusive(AsSRWLock(&opaque_buffer_));
}

void ReaderWriterMutex::ReaderUnlock() {
  ::ReleaseSRWLockShared(AsSRWLock(&opaque_buffer_));
}

void ReaderWriterMutex::WriterUnlock() {
  ::ReleaseSRWLockExclusive(AsSRWLock(&opaque_buffer_));
}

bool ReaderWriterMutex::MultipleReadersThreadsSupported() {
  return true;
}

#else  // Hereafter, we have pthread-based implementation

namespace {

template <typename T>
pthread_mutex_t *AsPthreadMutexT(T* opaque_buffer) {
  static_assert(sizeof(T) >= sizeof(pthread_mutex_t),
                "The opaque buffer must have sufficient space to store a "
                "pthread_mutex_t structure");
  return reinterpret_cast<pthread_mutex_t *>(opaque_buffer);
}

}  // namespace

Mutex::Mutex() {
  // make RECURSIVE lock:
  // The default is no-recursive lock.
  // When mutex.Lock() is called while the mutex is already locked,
  // mutex will be blocked. This behavior is not compatible with windows.
  // We set PTHREAD_MUTEX_RECURSIVE_NP to make the mutex recursive-lock

  // PTHREAD_MUTEX_RECURSIVE_NP and PTHREAD_MUTEX_RECURSIVE seem to be
  // variants.  For example, Mac OS X 10.4 had
  // PTHREAD_MUTEX_RECURSIVE_NP but Mac OS X 10.5 does not
  pthread_mutexattr_t attr;
  pthread_mutexattr_init(&attr);
#if defined(OS_MACOSX) || defined(OS_DRAGONFLY)
  pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
#elif defined(OS_LINUX) || defined(OS_ANDROID) || defined(OS_NACL)
  pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE_NP);
#else
#error "This platform is not supported."
#endif
  pthread_mutex_init(AsPthreadMutexT(&opaque_buffer_), &attr);
}

Mutex::~Mutex() {
  pthread_mutex_destroy(AsPthreadMutexT(&opaque_buffer_));
}

void Mutex::Lock() {
  pthread_mutex_lock(AsPthreadMutexT(&opaque_buffer_));
}

bool Mutex::TryLock() {
  return pthread_mutex_trylock(AsPthreadMutexT(&opaque_buffer_)) == 0;
}

void Mutex::Unlock() {
  pthread_mutex_unlock(AsPthreadMutexT(&opaque_buffer_));
}

#ifdef MOZC_USE_PEPPER_FILE_IO
pthread_mutex_t *Mutex::raw_mutex() {
  return AsPthreadMutexT(&opaque_buffer_);
}
#endif  // MOZC_USE_PEPPER_FILE_IO

#ifdef MOZC_PTHREAD_HAS_READER_WRITER_LOCK
// Use pthread native reader writer lock.
namespace {

template <typename T>
pthread_rwlock_t *AsPthreadRWLockT(T* opaque_buffer) {
  static_assert(sizeof(T) >= sizeof(pthread_rwlock_t),
                "The opaque buffer must have sufficient space to store a "
                "pthread_rwlock_t structure");
  return reinterpret_cast<pthread_rwlock_t *>(opaque_buffer);
}

}  // namespace

ReaderWriterMutex::ReaderWriterMutex() {
  pthread_rwlock_init(AsPthreadRWLockT(&opaque_buffer_), NULL);
}

ReaderWriterMutex::~ReaderWriterMutex() {
  pthread_rwlock_destroy(AsPthreadRWLockT(&opaque_buffer_));
}

void ReaderWriterMutex::ReaderLock() {
  pthread_rwlock_rdlock(AsPthreadRWLockT(&opaque_buffer_));
}

void ReaderWriterMutex::ReaderUnlock() {
  pthread_rwlock_unlock(AsPthreadRWLockT(&opaque_buffer_));
}

void ReaderWriterMutex::WriterLock() {
  pthread_rwlock_wrlock(AsPthreadRWLockT(&opaque_buffer_));
}

void ReaderWriterMutex::WriterUnlock() {
  pthread_rwlock_unlock(AsPthreadRWLockT(&opaque_buffer_));
}

bool ReaderWriterMutex::MultipleReadersThreadsSupported() {
  return true;
}

#else

// Fallback implementations as ReaderWriterLock is not available.
ReaderWriterMutex::ReaderWriterMutex() {
  // Non-recursive lock is OK.
  pthread_mutex_init(AsPthreadMutexT(&opaque_buffer_), NULL);
}

ReaderWriterMutex::~ReaderWriterMutex() {
  pthread_mutex_destroy(AsPthreadMutexT(&opaque_buffer_));
}

void ReaderWriterMutex::ReaderLock() {
  pthread_mutex_lock(AsPthreadMutexT(&opaque_buffer_));
}

void ReaderWriterMutex::WriterLock() {
  pthread_mutex_lock(AsPthreadMutexT(&opaque_buffer_));
}

void ReaderWriterMutex::ReaderUnlock() {
  pthread_mutex_unlock(AsPthreadMutexT(&opaque_buffer_));
}

void ReaderWriterMutex::WriterUnlock() {
  pthread_mutex_unlock(AsPthreadMutexT(&opaque_buffer_));
}

bool ReaderWriterMutex::MultipleReadersThreadsSupported() {
  return false;
}

#endif  // MOZC_PTHREAD_HAS_READER_WRITER_LOCK

#endif  // OS_WIN or pthread

void CallOnce(once_t *once, void (*func)()) {
  if (once == nullptr || func == nullptr) {
    return;
  }
  int expected_state = ONCE_INIT;
  if (once->compare_exchange_strong(expected_state, ONCE_RUNNING)) {
    (*func)();
    *once = ONCE_DONE;
    return;
  }
  // If the above compare_exchange_strong() returns false, it stores the value
  // of once to expected_state, which is ONCE_RUNNING or ONCE_DONE.
  if (expected_state == ONCE_DONE) {
    return;
  }
  // Here's the case where expected_state == ONCE_RUNNING, indicating that
  // another thread is calling func.  Wait for it to complete.
  while (*once == ONCE_RUNNING) {
#ifdef OS_WIN
    ::YieldProcessor();
#endif  // OS_WIN
  }  // Busy loop
}

void ResetOnce(once_t *once) {
  if (once) {
    *once = ONCE_INIT;
  }
}

}  // namespace mozc