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.;
12           // EMC Corporation; Symantec Corporation; The Open Group.
13           //
14           // Permission is hereby granted, free of charge, to any person obtaining a copy
15           // of this software and associated documentation files (the "Software"), to
16           // deal in the Software without restriction, including without limitation the
17           // rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
18           // sell copies of the Software, and to permit persons to whom the Software is
19           // furnished to do so, subject to the following conditions:
20           // 
21           // THE ABOVE COPYRIGHT NOTICE AND THIS PERMISSION NOTICE SHALL BE INCLUDED IN
22 mike  1.2 // ALL COPIES OR SUBSTANTIAL PORTIONS OF THE SOFTWARE. THE SOFTWARE IS PROVIDED
23           // "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
24           // LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
25           // PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
26           // HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
27           // ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
28           // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
29           //
30           //==============================================================================
31           //
32           // Author: Mike Brasher (m.brasher@inovadevelopment.com)
33           //
34           //%/////////////////////////////////////////////////////////////////////////////
35           
36           #ifndef Pegasus_Once_h
37           #define Pegasus_Once_h
38           
39           #include <Pegasus/Common/Config.h>
40           #include <Pegasus/Common/Linkage.h>
41           #include <Pegasus/Common/Mutex.h>
42           
43 mike  1.2 #define PEGASUS_ONCE_INITIALIZER { PEGASUS_MUTEX_INITIALIZER, 0 }
44           
45           PEGASUS_NAMESPACE_BEGIN
46           
47           /** Once implements the "once" concept as introduced by POSIX threads.
48               That is, it arranges for a function to be called just once in a thread
49               safe manner. The following example shows how to constuct an object of
50               type X the first time any thread reaches the line that calls once().
51           
52                   static Once _once = PEGASUS_ONCE_INITIALIZER;
53                   static static X* _ptr;
54           
55                   static void _create_X()
56                   {
57                       ptr = new X;
58                   }
59           
60                   ...
61           
62                   once(&_once, _create_X());
63           
64 mike  1.2     The _create_X() function is called exactly once no matter how many times
65               once() is called on it. Also, once() may be called safely from multiple
66               threads.
67           
68               CAUTION: Once instances must always be defined statically.
69           */
70           struct Once
71           {
72               MutexType mutex;
73               int initialized;
74           };
75           
76           void PEGASUS_COMMON_LINKAGE __once(Once* once, void (*function)());
77           
78           inline void once(Once* once, void (*function)())
79           {
80               if (once->initialized == 0)
81                   __once(once, function);
82           }
83           
84           PEGASUS_NAMESPACE_END
85 mike  1.2 
86           #endif /* Pegasus_Once_h */