RW_Process_Mutex.h

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// -*- C++ -*-
//
//=============================================================================
/**
 *  @file    RW_Process_Mutex.h
 *
 *  $Id: RW_Process_Mutex.h 81509 2008-04-28 22:00:49Z shuston $
 *
 *  @author Douglas C. Schmidt <schmidt@cs.wustl.edu>
 */
//=============================================================================

#ifndef ACE_RW_PROCESS_MUTEX_H
#define ACE_RW_PROCESS_MUTEX_H

#include /**/ "ace/pre.h"

#include "ace/File_Lock.h"

#if !defined (ACE_LACKS_PRAGMA_ONCE)
# pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */

#include "ace/Default_Constants.h"
#include "ace/OS_NS_fcntl.h"

ACE_BEGIN_VERSIONED_NAMESPACE_DECL

/**
 * @class ACE_RW_Process_Mutex
 *
 * @brief Wrapper for readers/writer locks that exist across processes.
 *
 * @note This class uses an ACE_File_Lock as its implementation. Thus, it
 * can only be reliably used between separate processes, rather than
 * threads in the same process.  This isn't a limitation of ACE, it's simply
 * the file lock semantics on UNIX and Win32.
 *
 * @todo For systems with pthread_rwlockattr_setpshared one
 * may consider using them to make the mutex faster.
 */
class ACE_Export ACE_RW_Process_Mutex
{
public:
  /// Create a cross-process readers/writer mutex, passing in the optional
  /// @a name, @a flags and @a mode \sa ACE_File_Lock.
  ///  If not specified, a name is generated and flags and mode are set
  ///  to default platform values.
#if defined (ACE_WIN32)
  ACE_RW_Process_Mutex (const ACE_TCHAR *name = 0,
                        int flags = O_CREAT|O_RDWR,
                        mode_t mode =  ACE_DEFAULT_OPEN_PERMS);
#else
  ACE_RW_Process_Mutex (const ACE_TCHAR *name = 0,
                        int flags = O_CREAT|O_RDWR,
                        mode_t mode = S_IRUSR | S_IWUSR );
#endif /* ACE_WIN32 */

  ~ACE_RW_Process_Mutex (void);

  /**
   * Explicitly destroy the mutex.  Note that only one thread should
   * call this method since it doesn't protect against race
   * conditions.
   */
  int remove (void);

  /// Same as acquire_write().
  /// Acquire lock ownership; blocks until the lock is acquired or the
  /// operation fails.
  int acquire (void);

  /**
   * Same as tryacquire_write().
   * Try to acquire the lock, but do not block if the lock is not immediately
   * acquired.
   *
   * @retval -1 on failure. If the lock is already held, @c errno is set
   *         to @c EBUSY.
   */
  int tryacquire (void);

  /// Release lock.
  int release (void);

  /// Acquire read lock; blocks until the lock is acquired or the
  /// operation fails.
  int acquire_read (void);

  /// Acquire write lock; blocks until the lock is acquired or the
  /// operation fails.
  int acquire_write (void);

  /**
   * Try to acquire the read lock, but do not block if the lock is not
   * immediately acquired.
   *
   * @retval -1 on failure. If the lock is already held, @c errno is set
   *         to @c EBUSY.
   */
  int tryacquire_read (void);

  /**
   * Try to acquire the write lock, but do not block if the lock is not
   * immediately acquired.
   *
   * @retval -1 on failure. If the lock is already held, @c errno is set
   *         to @c EBUSY.
   */
  int tryacquire_write (void);

  /// Attempt to upgrade a read lock to a write lock. Returns 0 on
  /// success, -1 on failure.
  int tryacquire_write_upgrade (void);

  /// Return the underlying lock.
  const ACE_File_Lock &lock (void) const;

  /// Dump the state of an object.
  void dump (void) const;

  /// Declare the dynamic allocation hooks.
  ACE_ALLOC_HOOK_DECLARE;

private:
  /// If the user does not provide a name we generate a unique name in
  /// this buffer.
  ACE_TCHAR name_[ACE_UNIQUE_NAME_LEN];

  /// Create and return the unique name.
  const ACE_TCHAR *unique_name (void);

  /// We need this to get the readers/writer semantics...
  ACE_File_Lock lock_;
};

ACE_END_VERSIONED_NAMESPACE_DECL

#if defined (__ACE_INLINE__)
#include "ace/RW_Process_Mutex.inl"
#endif /* __ACE_INLINE__ */

#include /**/ "ace/post.h"
#endif /* ACE_RW_PROCESS_MUTEX_H */

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