myvtm/libtoolkit/spinlock.c

#include "precompile.h"
#include "spinlock.h"

// please refer http://book.opensourceproject.org.cn/kernel/kernel3rd/opensource/0596005652/understandlk-chp-5-sect-2.html

static __inline void backoff(unsigned int nloop)
{
	__asm {
		and ecx, nloop  ;
		cmovz ecx, nloop ;
		rep nop         ;
	}
}


TOOLKIT_API void spinlock_enter(volatile spinlock_t *sl, int spin_count)
{
	DWORD tid = GetCurrentThreadId();
	if (sl->_value == tid) {
		sl->_reentrance++;
	} else {
		int i = 0;
		if (spin_count <= 0)
			spin_count = DEFAULT_SPIN_COUNT;
		while (InterlockedCompareExchange((LONG*)&sl->_value, (LONG)tid, 0) != 0) {
			for (; i < spin_count; ++i)
				if (sl->_value == 0)
					break;
			if (i >= spin_count)
				Sleep(1); /* yield cpu */
		}
		sl->_reentrance++;
	}
}
TOOLKIT_API void spinlock_leave(volatile spinlock_t *sl)
{
	_ReadWriteBarrier();
	if (--sl->_reentrance == 0)
		InterlockedExchange((LONG*)&sl->_value, 0);	
}

TOOLKIT_API void rw_spinlock_read_lock(rw_spinlock_t *rwlock)
{
	union rw_spinlock_barrier bnew, b;
	for (;;) {
		bnew.nAtomic = b.nAtomic = rwlock->barrier.nAtomic    ;
		bnew.readerCount++      ;   
		bnew.writerActive = b.writerActive = 0  ;
		bnew.writerCount = b.writerCount = 0    ;
		if (InterlockedCompareExchange(&rwlock->barrier.nAtomic, bnew.nAtomic, b.nAtomic) == b.nAtomic)
			break;
		backoff(DEFAULT_SPIN_COUNT) ;
	}
}

TOOLKIT_API void rw_spinlock_read_unlock(rw_spinlock_t *rwlock)
{
	union rw_spinlock_barrier bnew, b ;
	_ReadWriteBarrier();
	for (;;) {
		bnew.nAtomic = b.nAtomic = rwlock->barrier.nAtomic    ;
		bnew.readerCount--      ;
		assert( b.writerActive == 0 ) ;
		if (InterlockedCompareExchange(&rwlock->barrier.nAtomic, bnew.nAtomic, b.nAtomic) == b.nAtomic)
			break;
		backoff(DEFAULT_SPIN_COUNT) ;
	}
}

TOOLKIT_API void rw_spinlock_write_lock(rw_spinlock_t *rwlock)
{
	union rw_spinlock_barrier bnew, b ;

	for (;;) {
		bnew.nAtomic = b.nAtomic = rwlock->barrier.nAtomic    ;
		bnew.writerCount++      ;
		if (InterlockedCompareExchange(&rwlock->barrier.nAtomic, bnew.nAtomic, b.nAtomic) == b.nAtomic)
			break;
		backoff(DEFAULT_SPIN_COUNT)	;
	}

	for (;;) {
		bnew.nAtomic = b.nAtomic = rwlock->barrier.nAtomic    ;
		bnew.readerCount = 
			b.readerCount = 0   ;
		b.writerActive = 0      ;					
		bnew.writerActive = 1   ;
		if (InterlockedCompareExchange(&rwlock->barrier.nAtomic, bnew.nAtomic, b.nAtomic) == b.nAtomic)
			break;
		backoff(DEFAULT_SPIN_COUNT)	;
	}
}

TOOLKIT_API void rw_spinlock_write_unlock(rw_spinlock_t *rwlock)
{
	union rw_spinlock_barrier bnew, b ;

	_ReadWriteBarrier();

	for (;;) {
		bnew.nAtomic = b.nAtomic = rwlock->barrier.nAtomic    ;
		assert( b.writerActive == 1 ) ;
		assert( b.readerCount == 0 )  ;
		bnew.writerActive = 0   ;
		--bnew.writerCount      ;
		if (InterlockedCompareExchange(&rwlock->barrier.nAtomic, bnew.nAtomic, b.nAtomic) == b.nAtomic)
			break;
		backoff(DEFAULT_SPIN_COUNT)	;
	}
}

#define BACKOFF_LIMIT 1000

TOOLKIT_API void fastlock_enter( lock_t l )
{
	int i = 0;
	int spin_count = 0;
	int backoffs = 0;
	while (InterlockedCompareExchange(l, 1, 0) == 1) {
		for (spin_count = i + 10000; i < spin_count; ++i) {
			if (*l == 0)
				break;
#if _MSC_VER < 1400
			__asm { rep nop }
#else
			YieldProcessor();		//关闭sphost时，调试在这里停止，且无法通过taskkill关闭sphost
#endif
		}
		backoffs++;
		if (backoffs % BACKOFF_LIMIT == 0) {
			Sleep(500);
		}
		SwitchToThread();
	}
}