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117 lines
2.8 KiB
C++
117 lines
2.8 KiB
C++
// Copyright (C) 2001
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// William E. Kempf
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//
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// Permission to use, copy, modify, distribute and sell this software
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// and its documentation for any purpose is hereby granted without fee,
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// provided that the above copyright notice appear in all copies and
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// that both that copyright notice and this permission notice appear
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// in supporting documentation. William E. Kempf makes no representations
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// about the suitability of this software for any purpose.
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// It is provided "as is" without express or implied warranty.
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#include <boost/thread/once.hpp>
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#include <cstdio>
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#include <cassert>
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#if defined(BOOST_HAS_WINTHREADS)
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# include <windows.h>
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# if defined(BOOST_NO_STRINGSTREAM)
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# include <strstream>
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class unfreezer
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{
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public:
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unfreezer(std::ostrstream& s) : m_stream(s) {}
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~unfreezer() { m_stream.freeze(false); }
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private:
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std::ostrstream& m_stream;
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};
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# else
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# include <sstream>
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# endif
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#endif
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#ifdef BOOST_NO_STDC_NAMESPACE
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namespace std { using ::sprintf; }
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#endif
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#if defined(BOOST_HAS_PTHREADS)
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namespace {
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pthread_key_t key;
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pthread_once_t once = PTHREAD_ONCE_INIT;
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typedef void (*once_callback)();
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}
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extern "C" {
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static void key_init()
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{
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pthread_key_create(&key, 0);
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}
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static void do_once()
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{
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once_callback* cb = reinterpret_cast<once_callback*>(pthread_getspecific(key));
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(**cb)();
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}
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}
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#endif
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namespace boost {
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void call_once(void (*func)(), once_flag& flag)
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{
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#if defined(BOOST_HAS_WINTHREADS)
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once_flag tmp = flag;
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// Memory barrier would be needed here to prevent race conditions on some platforms with
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// partial ordering.
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if (!tmp)
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{
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#if defined(BOOST_NO_STRINGSTREAM)
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std::ostrstream strm;
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strm << "2AC1A572DB6944B0A65C38C4140AF2F4" << std::hex << GetCurrentProcessId() << &flag << std::ends;
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unfreezer unfreeze(strm);
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HANDLE mutex = CreateMutex(NULL, FALSE, strm.str());
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#else
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std::ostringstream strm;
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strm << "2AC1A572DB6944B0A65C38C4140AF2F4" << std::hex << GetCurrentProcessId() << &flag << std::ends;
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HANDLE mutex = CreateMutex(NULL, FALSE, strm.str().c_str());
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#endif
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assert(mutex != NULL);
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int res = 0;
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res = WaitForSingleObject(mutex, INFINITE);
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assert(res == WAIT_OBJECT_0);
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tmp = flag;
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if (!tmp)
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{
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func();
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tmp = true;
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// Memory barrier would be needed here to prevent race conditions on some platforms
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// with partial ordering.
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flag = tmp;
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}
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res = ReleaseMutex(mutex);
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assert(res);
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res = CloseHandle(mutex);
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assert(res);
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}
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#elif defined(BOOST_HAS_PTHREADS)
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pthread_once(&once, &key_init);
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pthread_setspecific(key, &func);
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pthread_once(&flag, do_once);
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#endif
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}
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}
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// Change Log:
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// 1 Aug 01 WEKEMPF Initial version.
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