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RW_Process_Mutex.h

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00001 /* -*- C++ -*- */
00002 
00003 //=============================================================================
00004 /**
00005  *  @file    RW_Process_Mutex.h
00006  *
00007  *  $Id: RW_Process_Mutex.h,v 1.1.1.1 2001/12/04 14:33:07 chad Exp $
00008  *
00009  *  @author Douglas C. Schmidt <schmidt@cs.wustl.edu>
00010  */
00011 //=============================================================================
00012 
00013 #ifndef ACE_RW_PROCESS_MUTEX_H
00014 #define ACE_RW_PROCESS_MUTEX_H
00015 #include "ace/pre.h"
00016 
00017 #include "ace/File_Lock.h"
00018 
00019 #if !defined (ACE_LACKS_PRAGMA_ONCE)
00020 # pragma once
00021 #endif /* ACE_LACKS_PRAGMA_ONCE */
00022 
00023 /**
00024  * @class ACE_RW_Process_Mutex
00025  *
00026  * @brief Wrapper for readers/writer locks that exist across processes.
00027  *
00028  * Note that because this class uses the
00029  * <ACE_File_Lock> as its implementation it only can be reliably
00030  * used between separate processes, rather than threads in the
00031  * same process.  This isn't a limitation of ACE, it's simply
00032  * the file lock semantics on UNIX and Win32.
00033  */
00034 class ACE_Export ACE_RW_Process_Mutex
00035 {
00036 public:
00037   /// Create a readers/writer <Process_Mutex>, passing in the optional
00038   /// <name>.  If not specified, a name is generated.
00039   ACE_RW_Process_Mutex (const ACE_TCHAR *name = 0,
00040                         int flags = O_CREAT|O_RDWR);
00041 
00042   ~ACE_RW_Process_Mutex (void);
00043 
00044   /**
00045    * Explicitly destroy the mutex.  Note that only one thread should
00046    * call this method since it doesn't protect against race
00047    * conditions.
00048    */
00049   int remove (void);
00050 
00051   /// Acquire lock ownership (wait on queue if necessary).
00052   int acquire (void);
00053 
00054   /**
00055    * Conditionally acquire lock (i.e., don't wait on queue).  Returns
00056    * -1 on failure.  If we "failed" because someone else already had
00057    * the lock, <errno> is set to <EBUSY>.
00058    */
00059   int tryacquire (void);
00060 
00061   /// Release lock and unblock a thread at head of queue.
00062   int release (void);
00063 
00064   /// Acquire lock ownership (wait on queue if necessary).
00065   int acquire_read (void);
00066 
00067   /// Acquire lock ownership (wait on queue if necessary).
00068   int acquire_write (void);
00069 
00070   /**
00071    * Conditionally acquire a lock (i.e., won't block).  Returns -1 on
00072    * failure.  If we "failed" because someone else already had the
00073    * lock, <errno> is set to <EBUSY>.
00074    */
00075   int tryacquire_read (void);
00076 
00077   /**
00078    * Conditionally acquire a lock (i.e., won't block).  Returns -1 on
00079    * failure.  If we "failed" because someone else already had the
00080    * lock, <errno> is set to <EBUSY>.
00081    */
00082   int tryacquire_write (void);
00083 
00084   /// Attempt to upgrade a read lock to a write lock. Returns 0 on
00085   /// success, -1 on failure.
00086   int tryacquire_write_upgrade (void);
00087 
00088   /// Return the underlying lock.
00089   const ACE_File_Lock &lock (void) const;
00090 
00091   /// Dump the state of an object.
00092   void dump (void) const;
00093 
00094   /// Declare the dynamic allocation hooks.
00095   ACE_ALLOC_HOOK_DECLARE;
00096 
00097 private:
00098   /// If the user does not provide a name we generate a unique name in
00099   /// this buffer.
00100   ACE_TCHAR name_[ACE_UNIQUE_NAME_LEN];
00101 
00102   /// Create and return the unique name.
00103   const ACE_TCHAR *unique_name (void);
00104 
00105   /// We need this to get the readers/writer semantics...
00106   ACE_File_Lock lock_;
00107 };
00108 
00109 #if defined (__ACE_INLINE__)
00110 #include "ace/RW_Process_Mutex.inl"
00111 #endif /* __ACE_INLINE__ */
00112 
00113 #include "ace/post.h"
00114 #endif /* ACE_RW_PROCESS_MUTEX_H */

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