1 mike  1.2 //%2006////////////////////////////////////////////////////////////////////////
 2           //
 3           // Copyright (c) 2000, 2001, 2002 BMC Software; Hewlett-Packard Development
 4           // Company, L.P.; IBM Corp.; The Open Group; Tivoli Systems.
 5           // Copyright (c) 2003 BMC Software; Hewlett-Packard Development Company, L.P.;
 6           // IBM Corp.; EMC Corporation, The Open Group.
 7           // Copyright (c) 2004 BMC Software; Hewlett-Packard Development Company, L.P.;
 8           // IBM Corp.; EMC Corporation; VERITAS Software Corporation; The Open Group.
 9           // Copyright (c) 2005 Hewlett-Packard Development Company, L.P.; IBM Corp.;
10           // EMC Corporation; VERITAS Software Corporation; The Open Group.
11           // Copyright (c) 2006 Hewlett-Packard Development Company, L.P.; IBM Corp.;
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23           // "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
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30           //==============================================================================
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32           //%/////////////////////////////////////////////////////////////////////////////
33           
34           #ifndef Pegasus_Once_h
35           #define Pegasus_Once_h
36           
37           #include <Pegasus/Common/Config.h>
38           #include <Pegasus/Common/Linkage.h>
39           #include <Pegasus/Common/Mutex.h>
40           
41           #define PEGASUS_ONCE_INITIALIZER { PEGASUS_MUTEX_INITIALIZER, 0 }
42           
43 mike  1.2 PEGASUS_NAMESPACE_BEGIN
44           
45           /** Once implements the "once" concept as introduced by POSIX threads.
46               That is, it arranges for a function to be called just once in a thread
47               safe manner. The following example shows how to constuct an object of
48               type X the first time any thread reaches the line that calls once().
49           
50                   static Once _once = PEGASUS_ONCE_INITIALIZER;
51                   static static X* _ptr;
52           
53                   static void _create_X()
54                   {
55                       ptr = new X;
56                   }
57           
58                   ...
59           
60                   once(&_once, _create_X());
61           
62               The _create_X() function is called exactly once no matter how many times
63               once() is called on it. Also, once() may be called safely from multiple
64 mike  1.2     threads.
65           
66               CAUTION: Once instances must always be defined statically.
67           */
68           struct Once
69           {
70               MutexType mutex;
71               int initialized;
72           };
73           
74           void PEGASUS_COMMON_LINKAGE __once(Once* once, void (*function)());
75           
76           inline void once(Once* once, void (*function)())
77           {
78               if (once->initialized == 0)
79                   __once(once, function);
80           }
81           
82           PEGASUS_NAMESPACE_END
83           
84           #endif /* Pegasus_Once_h */