CrowdMonitor.h

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/*
   For more information, please see: http://software.sci.utah.edu

   The MIT License

   Copyright (c) 2009 Scientific Computing and Imaging Institute,
   University of Utah.

   
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///
///@file   CrowdMonitor.h
///@brief  Multiple reader/single writer locks
///
///@author Steve Parker
///        Department of Computer Science
///        University of Utah
///@date   June 1997
///

#ifndef Core_Thread_CrowdMonitor_h
#define Core_Thread_CrowdMonitor_h

#include <Core/Thread/Legacy/share.h>

namespace SCIRun {
  struct CrowdMonitor_private;
/**************************************
 
@class
   CrowdMonitor
   
KEYWORDS
   Thread
   
@details
   Multiple reader, single writer synchronization primitive.  Some
   applications do not need the strict level of synchronization
   provided by the <b>Mutex</b>.  The <b>CrowdMonitor</b> relaxes
   the synchronization by allowing multiple threads access to a
   resource (usually a data area), on the condition that the thread
   will only read the data.  When a thread needs to write the data,
   it can access the monitor in write mode (using <i>writeLock</i>).
   At any given time, one writer thread can be active, or multiple
   reader threads can be active.  <b>CrowdMonitor</b> guards against
   multiple writers accessing a data, and against a thread writing
   to the data while other threads are reading it.

WARNING
   <p> Calling <i>readLock</i> within a <i>writeLock/write_unlock</i>
   section may result in a deadlock.  Likewise, calling <i>writeLock</i>
   within a <i>readLock/readUnlock</i> section may result in a deadlock.
   Calling <i>readUnlock</i> or <i>writeUnlock</i> when the lock is
   not held is not legal and may result in undefined behavior.
   
****************************************/

    class SCISHARE CrowdMonitor {
    public:
        //////////
        /// Create and initialize the CrowdMonitor. <i>name</i> should
        /// be a static which describes the primitive for debugging
        /// purposes.
        CrowdMonitor(const char* name);
    
        //////////
        /// Destroy the CrowdMonitor.
        ~CrowdMonitor();
    
        //////////
        /// Acquire the read-only lock associated with this
        /// <b>CrowdMonitor</b>. Multiple threads may hold the
        /// read-only lock simultaneously.
        void readLock();
    
        //////////
        /// Release the read-only lock obtained from <i>readLock</i>.
        /// Undefined behavior may result when <i>readUnlock</i> is
        /// called and a <i>readLock</i> is not held by the calling
        /// Thread.
        void readUnlock();
    
        //////////
        /// Acquire the write lock associated with this
        /// <b>CrowdMonitor</b>. Only one thread may hold the write
        /// lock, and during the time that this lock is not held, no
        /// threads may hold the read-only lock.
        void writeLock();

        //////////
        /// Release the write-only lock obtained from <i>writeLock</i>.
        /// Undefined behavior may result when <i>writeUnlock</i> is
        /// called and a <i>writeLock</i> is not held by the calling
        /// Thread.
        void writeUnlock();

    private:
        const char* name_;
        CrowdMonitor_private* priv_;

        // Cannot copy them
        CrowdMonitor(const CrowdMonitor&);
        CrowdMonitor& operator=(const CrowdMonitor&);
    };
} // End namespace SCIRun

#endif