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//
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// in the documentation and/or other materials provided with the
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//
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#ifdef OS_WINDOWS
#include <windows.h>
#else
#include <pthread.h>
#endif

#ifdef OS_MACOSX
#include <libkern/OSAtomic.h>
#endif

#include "base/base.h"
#include "base/mutex.h"

namespace mozc {

// Wrapper for Windows InterlockedCompareExchange
namespace {
#ifdef OS_LINUX
// Linux doesn't provide InterlockedCompareExchange-like function.
inline int InterlockedCompareExchange(volatile int *target,
                                      int new_value,
                                      int old_value) {
  // TODO(yusukes): For now, we use the architecture-neutral implementation,
  // but I believe it's definitely better to port Chromium's singleton to Mozc.
  // The implementation should be much faster and supports ARM Linux.
  // http://src.chromium.org/viewvc/chrome/trunk/src/base/singleton.h

  static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
  pthread_mutex_lock(&lock);
  int result = *target;
  if (result == old_value) {
    *target = new_value;
  }
  pthread_mutex_unlock(&lock);
  return result;
}
#endif  // OS_LINUX

// Use OSAtomicCompareAndSwapInt on Mac OSX
// http://developer.apple.com/iphone/library/documentation/
// system/conceptual/manpages_iphoneos/man3/OSAtomicCompareAndSwapInt.3.html
// TODO(taku): should we use OSAtomicCompareAndSwapIntBarrier?
#ifdef OS_MACOSX
inline int InterlockedCompareExchange(volatile int *target,
                                      int new_value,
                                      int old_value) {
  return OSAtomicCompareAndSwapInt(old_value, new_value, target)
      ? old_value : *target;
}
#endif  // OX_MACOSX
}  // namespace

void CallOnce(once_t *once, void (*func)()) {
  if (once == NULL || func == NULL) {
    return;
  }

  if (once->state != ONCE_INIT) {
    return;
  }

  // change the counter in atomic
  if (0 == InterlockedCompareExchange(&(once->counter), 1, 0)) {
    // call func
    (*func)();
    // change the status to be ONCE_DONE in atomic
    // Maybe we won't use it, but in order to make memory barrier,
    // we use InterlockedCompareExchange just in case.
    InterlockedCompareExchange(&(once->state), ONCE_DONE, ONCE_INIT);
  } else {
    while (once->state == ONCE_INIT) {
#ifdef OS_WINDOWS
      YieldProcessor();
#endif
    }  // busy loop
  }
}

void ResetOnce(once_t *once) {
  InterlockedCompareExchange(&(once->state), ONCE_INIT, ONCE_DONE);
  InterlockedCompareExchange(&(once->counter), 0, 1);
}
}  // namespace mozc