1 martin 1.5 //%LICENSE////////////////////////////////////////////////////////////////

 2 martin 1.6 //

 3 martin 1.5 // Licensed to The Open Group (TOG) under one or more contributor license
 4            // agreements.  Refer to the OpenPegasusNOTICE.txt file distributed with
 5            // this work for additional information regarding copyright ownership.
 6            // Each contributor licenses this file to you under the OpenPegasus Open
 7            // Source License; you may not use this file except in compliance with the
 8            // License.

 9 martin 1.6 //

10 martin 1.5 // Permission is hereby granted, free of charge, to any person obtaining a
11            // copy of this software and associated documentation files (the "Software"),
12            // to deal in the Software without restriction, including without limitation
13            // the rights to use, copy, modify, merge, publish, distribute, sublicense,
14            // and/or sell copies of the Software, and to permit persons to whom the
15            // Software is furnished to do so, subject to the following conditions:

16 martin 1.6 //

17 martin 1.5 // The above copyright notice and this permission notice shall be included
18            // in all copies or substantial portions of the Software.

19 martin 1.6 //

20 martin 1.5 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS

21 martin 1.6 // OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF

22 martin 1.5 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
23            // IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
24            // CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
25            // TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
26            // SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

27 martin 1.6 //

28 martin 1.5 //////////////////////////////////////////////////////////////////////////

29 mike   1.2 //
30            //%/////////////////////////////////////////////////////////////////////////////
31            
32            #ifndef Pegasus_Once_h
33            #define Pegasus_Once_h
34            
35            #include <Pegasus/Common/Config.h>
36            #include <Pegasus/Common/Linkage.h>
37            #include <Pegasus/Common/Mutex.h>
38            
39            #define PEGASUS_ONCE_INITIALIZER { PEGASUS_MUTEX_INITIALIZER, 0 }
40            
41            PEGASUS_NAMESPACE_BEGIN
42            
43            /** Once implements the "once" concept as introduced by POSIX threads.
44                That is, it arranges for a function to be called just once in a thread
45                safe manner. The following example shows how to constuct an object of
46                type X the first time any thread reaches the line that calls once().
47            
48                    static Once _once = PEGASUS_ONCE_INITIALIZER;
49                    static static X* _ptr;
50 mike   1.2 
51                    static void _create_X()
52                    {
53                        ptr = new X;
54                    }
55            
56                    ...
57            

58 mike   1.4         once(&_once, _create_X);

59 mike   1.2 
60                The _create_X() function is called exactly once no matter how many times
61                once() is called on it. Also, once() may be called safely from multiple
62                threads.
63            
64                CAUTION: Once instances must always be defined statically.
65            */
66            struct Once
67            {
68                MutexType mutex;
69                int initialized;
70            };
71            
72            void PEGASUS_COMMON_LINKAGE __once(Once* once, void (*function)());
73            
74            inline void once(Once* once, void (*function)())
75            {
76                if (once->initialized == 0)
77                    __once(once, function);
78            }
79            
80 mike   1.2 PEGASUS_NAMESPACE_END
81            
82            #endif /* Pegasus_Once_h */