//%2006////////////////////////////////////////////////////////////////////////
//
// Copyright (c) 2000, 2001, 2002 BMC Software; Hewlett-Packard Development
// Company, L.P.; IBM Corp.; The Open Group; Tivoli Systems.
// Copyright (c) 2003 BMC Software; Hewlett-Packard Development Company, L.P.;
// IBM Corp.; EMC Corporation, The Open Group.
// Copyright (c) 2004 BMC Software; Hewlett-Packard Development Company, L.P.;
// IBM Corp.; EMC Corporation; VERITAS Software Corporation; The Open Group.
// Copyright (c) 2005 Hewlett-Packard Development Company, L.P.; IBM Corp.;
// EMC Corporation; VERITAS Software Corporation; The Open Group.
// Copyright (c) 2006 Hewlett-Packard Development Company, L.P.; IBM Corp.;
// EMC Corporation; Symantec Corporation; The Open Group.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to
// deal in the Software without restriction, including without limitation the
// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
// sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// 
// THE ABOVE COPYRIGHT NOTICE AND THIS PERMISSION NOTICE SHALL BE INCLUDED IN
// ALL COPIES OR SUBSTANTIAL PORTIONS OF THE SOFTWARE. THE SOFTWARE IS PROVIDED
// "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
// LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
// ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
//==============================================================================
//
// Author: Mike Brasher (m.brasher@inovadevelopment.com)
//
//%/////////////////////////////////////////////////////////////////////////////

#ifndef Pegasus_Once_h
#define Pegasus_Once_h

#include <Pegasus/Common/Config.h>
#include <Pegasus/Common/Linkage.h>
#include <Pegasus/Common/Mutex.h>

#define PEGASUS_ONCE_INITIALIZER { PEGASUS_MUTEX_INITIALIZER, 0 }

PEGASUS_NAMESPACE_BEGIN

/** Once implements the "once" concept as introduced by POSIX threads.
    That is, it arranges for a function to be called just once in a thread
    safe manner. The following example shows how to constuct an object of
    type X the first time any thread reaches the line that calls once().

        static Once _once = PEGASUS_ONCE_INITIALIZER;
        static static X* _ptr;

        static void _create_X()
        {
            ptr = new X;
        }

        ...

        once(&_once, _create_X());

    The _create_X() function is called exactly once no matter how many times
    once() is called on it. Also, once() may be called safely from multiple
    threads.

    CAUTION: Once instances must always be defined statically.
*/
struct Once
{
    MutexType mutex;
    int initialized;
};

void PEGASUS_COMMON_LINKAGE __once(Once* once, void (*function)());

inline void once(Once* once, void (*function)())
{
    if (once->initialized == 0)
        __once(once, function);
}

PEGASUS_NAMESPACE_END

#endif /* Pegasus_Once_h */