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/*
* Copyright (c) 2005, Eric Crahen
*
* 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.
*
*/
#ifndef __ZTFASTLOCK_H__
#define __ZTFASTLOCK_H__
#include "zthread/NonCopyable.h"
#include <windows.h>
#include <assert.h>
namespace ZThread {
/**
* @class FastLock
*
* @author Eric Crahen <http://www.code-foo.com>
* @date <2003-07-16T23:31:51-0400>
* @version 2.2.0
*
* This uses a custom spin lock based on the older swap & compare approach
* using the XCHG instruction. You should only use this is you *absolutely* need
* to use an older system, like Windows 95. If you can, use the Win32 version.
*
* Because Windows 95 and earlier can run on processors prior to the 486, they
* don't all support the CMPXCHG function, and so Windows 95 an earlier dont support
* InterlockedCompareExchange.
*
* This is asm inlined for microsoft visual c, it needs to be changed in order to
* compile with gcc, or another win32 compiler - but more likely than not you'll
* be using the Win32 version on those compilers and this won't be a problem.
*/
class FastLock : private NonCopyable {
// Add def for mingw32 or other non-ms compiler to align on 32-bit boundary
#pragma pack(push, 4)
unsigned char volatile _lock;
#pragma pack(pop)
public:
/**
* Create a new FastLock
*/
inline FastLock() : _lock(0) { }
inline ~FastLock() {
assert(_lock == 0);
}
inline void acquire() {
DWORD dw = (DWORD)&_lock;
_asm { // swap & compare
spin_lock:
mov al, 1
mov esi, dw
xchg [esi], al
and al,al
jz spin_locked
}
::Sleep(0);
_asm {
jmp spin_lock
spin_locked:
}
}
inline void release() {
DWORD dw = (DWORD)&_lock;
_asm {
mov al, 0
mov esi, dw
xchg [esi], al
}
}
inline bool tryAcquire(unsigned long timeout=0) {
volatile DWORD dw = (DWORD)&_lock;
volatile DWORD result;
_asm {
mov al, 1
mov esi, dw
xchg [esi], al
and al,al
mov esi, result
xchg [esi], al
}
return result == 0;
}
}; /* Fast Lock */
} // namespace ZThread
#endif
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