google base之LockImpl

为了兼容不同的平台，这个类采用了impl模式，win平台通过CRITICAL_SECTION, 这样的话还是相对比较简单，具体就不详解了，不过不得不说boost的实现方式就要复杂到哪里去了，当然，好处就是功能强大，坏处就是学习成本高，会用的人少。

#if defined(OS_WIN)
#include <windows.h>
#elif defined(OS_POSIX)
#include <pthread.h>
#endif

#include "base/base_export.h"
#include "base/basictypes.h"

namespace base {
namespace internal {

// This class implements the underlying platform-specific spin-lock mechanism
// used for the Lock class.  Most users should not use LockImpl directly, but
// should instead use Lock.
class BASE_EXPORT LockImpl {
 public:
#if defined(OS_WIN)
  typedef CRITICAL_SECTION NativeHandle;
#elif defined(OS_POSIX)
  typedef pthread_mutex_t NativeHandle;
#endif

  LockImpl();
  ~LockImpl();

  // If the lock is not held, take it and return true.  If the lock is already
  // held by something else, immediately return false.
  bool Try();

  // Take the lock, blocking until it is available if necessary.
  void Lock();

  // Release the lock.  This must only be called by the lock's holder: after
  // a successful call to Try, or a call to Lock.
  void Unlock();

  // Return the native underlying lock.
  // TODO(awalker): refactor lock and condition variables so that this is
  // unnecessary.
  NativeHandle* native_handle() { return &native_handle_; }

 private:
  NativeHandle native_handle_;

  DISALLOW_COPY_AND_ASSIGN(LockImpl);
};

}  // namespace internal
}  // namespace base

#endif  // BASE_SYNCHRONIZATION_LOCK_IMPL_H_