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103 lines
2.5 KiB
C++
103 lines
2.5 KiB
C++
// VFSAtomic.cpp - atomic operations and thread locking
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// For conditions of distribution and use, see copyright notice in VFS.h
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/** --- Atomic operations and thread safety ---
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* You may want to add your own implementation if thread safety is needed.
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* If not, just leave everything like it is.
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* If you are on windows, Interlocked[In/De]crement is faster than
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explicit mutex locking for integer operations.
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* TODO: The actual locking that is done in the tree when VFS_THREADSAFE is defined
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is rather crude for the time beeing; a somewhat more efficient ReadWriteLock
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implementation would be nice to have, someday.
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* If you can, leave VFS_THREADSAFE undefined and do the locking externally,
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it will probably have much better performance than if each and every operation
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does a lock and unlock call.
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(For a rather I/O based library this should not really make a difference, anyway.
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But don't say you haven't been warned :) )
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*/
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#include "VFSInternal.h"
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#include "VFSAtomic.h"
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// for Interlocked[In/De]crement, if required
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#if defined(_WIN32) && defined(VFS_THREADSAFE)
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# define WIN32_LEAN_AND_MEAN
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# include <windows.h>
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#endif
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VFS_NAMESPACE_START
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#ifdef VFS_THREADSAFE
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static Mutex mtx;
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#endif
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int Atomic_Incr(volatile int &i)
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{
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#ifdef VFS_THREADSAFE
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# ifdef _WIN32
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volatile LONG* dp = (volatile LONG*) &i;
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return InterlockedIncrement( dp );
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# else
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Guard g(mtx);
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# endif
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#endif
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return ++i;
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}
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int Atomic_Decr(volatile int &i)
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{
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#ifdef VFS_THREADSAFE
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# ifdef _WIN32
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volatile LONG* dp = (volatile LONG*) &i;
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return InterlockedDecrement( dp );
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# else
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Guard g(mtx);
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# endif
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#endif
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return --i;
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}
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/* Implement your Mutex class here.
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Important: The mutex must be re-entrant/recursive,
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means it must be possible to lock it from the same thread multiple times.
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*/
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Mutex::Mutex()
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{
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// implement your own if needed. Remove the trap below when you are done.
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// This is to prevent people from defining VFS_THREADSAFE and expecting everything to work just like that :)
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#ifdef VFS_THREADSAFE
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#error VFSAtomic: Hey, you forgot to implement the mutex class, cant guarantee thread safety! Either undef VFS_THREADSAFE or read the docs and get your hands dirty.
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#endif
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}
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Mutex::~Mutex()
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{
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// implement your own if needed
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}
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void Mutex::Lock(void)
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{
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// implement your own if needed
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}
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void Mutex::Unlock(void)
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{
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// implement your own if needed
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}
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Guard::Guard(Mutex& m)
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: _m(m)
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{
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_m.Lock();
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}
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Guard::~Guard()
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{
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_m.Unlock();
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}
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VFS_NAMESPACE_END
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