60 lines
1.6 KiB
C
60 lines
1.6 KiB
C
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#include "config.h"
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#include "rwlock.h"
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#include "bool.h"
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#include "atomic.h"
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#include "threads.h"
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/* A simple spinlock. Yield the thread while the given integer is set by
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* another. Could probably be improved... */
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#define LOCK(l) do { \
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while(ATOMIC_FLAG_TEST_AND_SET(&(l), almemory_order_acq_rel) == true) \
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althrd_yield(); \
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} while(0)
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#define UNLOCK(l) ATOMIC_FLAG_CLEAR(&(l), almemory_order_release)
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void RWLockInit(RWLock *lock)
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{
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InitRef(&lock->read_count, 0);
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InitRef(&lock->write_count, 0);
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ATOMIC_FLAG_CLEAR(&lock->read_lock, almemory_order_relaxed);
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ATOMIC_FLAG_CLEAR(&lock->read_entry_lock, almemory_order_relaxed);
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ATOMIC_FLAG_CLEAR(&lock->write_lock, almemory_order_relaxed);
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}
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void ReadLock(RWLock *lock)
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{
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LOCK(lock->read_entry_lock);
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LOCK(lock->read_lock);
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/* NOTE: ATOMIC_ADD returns the *old* value! */
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if(ATOMIC_ADD(&lock->read_count, 1, almemory_order_acq_rel) == 0)
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LOCK(lock->write_lock);
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UNLOCK(lock->read_lock);
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UNLOCK(lock->read_entry_lock);
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}
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void ReadUnlock(RWLock *lock)
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{
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/* NOTE: ATOMIC_SUB returns the *old* value! */
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if(ATOMIC_SUB(&lock->read_count, 1, almemory_order_acq_rel) == 1)
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UNLOCK(lock->write_lock);
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}
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void WriteLock(RWLock *lock)
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{
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if(ATOMIC_ADD(&lock->write_count, 1, almemory_order_acq_rel) == 0)
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LOCK(lock->read_lock);
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LOCK(lock->write_lock);
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}
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void WriteUnlock(RWLock *lock)
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{
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UNLOCK(lock->write_lock);
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if(ATOMIC_SUB(&lock->write_count, 1, almemory_order_acq_rel) == 1)
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UNLOCK(lock->read_lock);
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}
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