src/base/process_mutex.h

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#ifndef MOZC_BASE_PROCESS_MUTEX_H_
#define MOZC_BASE_PROCESS_MUTEX_H_

#include <string>

#ifdef OS_WIN
#include "base/scoped_handle.h"
#endif  // OS_WIN

#include "base/port.h"

// Process-wide named mutex class:
// Make a simple process-wide named mutex using file locking.
// Useful to prevent a process from being instantiated twice or more.
//
// Example:
// ProcessMutex foo("foo");
// if (!foo.Lock()) {
//   process foo is already running
//   exit(-1);
// }
//
// foo.Lock();
// /* process named "foo" is never instatiated inside this block */
// foo.Unlock();

namespace mozc {

class ProcessMutex {
 public:
  explicit ProcessMutex(const char *name);
  ~ProcessMutex();

  // return false if the process is already locked
  bool Lock();

  // Lock the mutex file and write some message to this file
  bool LockAndWrite(const string &message);

  // always return true at this moment.
  bool UnLock();

  // return lock filename
  // filename: <user_profile>/.lock.<name>
  const string &lock_filename() const {
    return filename_;
  }

  void set_lock_filename(const string &filename) {
    filename_ = filename;
  }

  bool locked() const {
    return locked_;
  }

 private:
#ifdef OS_WIN
  ScopedHandle handle_;
#endif

  // TODO(yukawa): Remove this flag as it can always be determined by other
  //     internal state.
  bool locked_;
  string filename_;

  DISALLOW_COPY_AND_ASSIGN(ProcessMutex);
};

}  // namespace mozc

#endif  // MOZC_BASE_PROCESS_MUTEX_H_