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/BdbCondRemote/BdbCondReadWriteLock.hh

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//-----------------------------------------------------------------------------
//
// File and Version Information:
//      $Id: BdbCondReadWriteLock.hh,v 1.2 2000/07/17 21:44:34 gapon Exp $
//
// Description:
//      This class represents a missing feature in the POSIX library -
//      "read/write lock" allowing to have either one WRITER or unlimited
//      number of READERs waiting for a resource to be released.
//
// Environment:
//      Software developed for the BaBar Detector at the SLAC B-Factory.
//
// Author List:
//      Igor A. Gaponenko       Original Author
//
// Copyright Information:
//      Copyright (C) 2000      Lawrence Berkeley Laboratory
//
//-----------------------------------------------------------------------------

#ifndef BDBCONDREADWRITELOCK_HH
#define BDBCONDREADWRITELOCK_HH

//-----------------
// C/C++ Headers --
//-----------------

extern "C" {
#include <pthread.h>
}

// -------------------
// -- BaBar Headers --
// -------------------

#include "BaBar/BaBar.hh"

//-------------------------------
// Collaborating Class Headers --
//-------------------------------

// ---------------------
// -- Class Interface --
// ---------------------
 
class BdbCondReadWriteLock {

public:

  // Constructor(s).

    BdbCondReadWriteLock( );

  // Destructor

    virtual ~BdbCondReadWriteLock( );

  // Operations

  /** The following operations may block the calling thread if the corresponding
   ** lock is not available:
   **
   **     beginRead()
   **     beginWrite()
   **
   ** The following operations do not block the calling thread but may unblock
   ** other threads waiting for the resource.
   **
   **     endRead()
   **     downgrade()
   **     endWrite()
   **
   ** The "false" return status of these operations means that something has failed
   ** during their execution. This means that the results of operation are unreliable.
   **/

    bool beginRead( );
    bool endRead( );

    bool downgrade( );

    bool beginWrite( );
    bool endWrite( );

protected:

  // The copy constructor and assignment operator are not available
  // to the end users because the semantics of these operations
  // is not defined yet.

    BdbCondReadWriteLock( const BdbCondReadWriteLock& theLock );

  // Operators

    BdbCondReadWriteLock& operator=( const BdbCondReadWriteLock& theLock );

private:

  // A mutex and a conditions variable regulating the synchronized behavior
  // of code accessing/modifying the counters.

    pthread_mutex_t _myMutex;
    pthread_cond_t  _myCondVar;

  // The counters for the clients.

    int _numReaders;        // The current number of READERs.
    int _numWriters;        // The current number of WRITERs.
    int _numPendings;       // The current number of READERS and WRITERs waiting for
                            // the lock to be released.
};

#endif /* BDBCONDREADWRITELOCK_HH */

 

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