common/rwlock.c

   1
   2 #include "config.h"
   3
   4 #include "rwlock.h"
   5
   6 #include "bool.h"
   7 #include "atomic.h"
   8 #include "threads.h"
   9
  10
  11 /* A simple spinlock. Yield the thread while the given integer is set by
  12  * another. Could probably be improved... */
  13 #define LOCK(l) do {                                                          \
  14     while(ATOMIC_FLAG_TEST_AND_SET(&(l), almemory_order_acq_rel) == true)     \
  15         althrd_yield();                                                       \
  16 } while(0)
  17 #define UNLOCK(l) ATOMIC_FLAG_CLEAR(&(l), almemory_order_release)
  18
  19
  20 void RWLockInit(RWLock *lock)
  21 {
  22     InitRef(&lock->read_count, 0);
  23     InitRef(&lock->write_count, 0);
  24     ATOMIC_FLAG_CLEAR(&lock->read_lock, almemory_order_relaxed);
  25     ATOMIC_FLAG_CLEAR(&lock->read_entry_lock, almemory_order_relaxed);
  26     ATOMIC_FLAG_CLEAR(&lock->write_lock, almemory_order_relaxed);
  27 }
  28
  29 void ReadLock(RWLock *lock)
  30 {
  31     LOCK(lock->read_entry_lock);
  32     LOCK(lock->read_lock);
  33     /* NOTE: ATOMIC_ADD returns the *old* value! */
  34     if(ATOMIC_ADD(&lock->read_count, 1, almemory_order_acq_rel) == 0)
  35         LOCK(lock->write_lock);
  36     UNLOCK(lock->read_lock);
  37     UNLOCK(lock->read_entry_lock);
  38 }
  39
  40 void ReadUnlock(RWLock *lock)
  41 {
  42     /* NOTE: ATOMIC_SUB returns the *old* value! */
  43     if(ATOMIC_SUB(&lock->read_count, 1, almemory_order_acq_rel) == 1)
  44         UNLOCK(lock->write_lock);
  45 }
  46
  47 void WriteLock(RWLock *lock)
  48 {
  49     if(ATOMIC_ADD(&lock->write_count, 1, almemory_order_acq_rel) == 0)
  50         LOCK(lock->read_lock);
  51     LOCK(lock->write_lock);
  52 }
  53
  54 void WriteUnlock(RWLock *lock)
  55 {
  56     UNLOCK(lock->write_lock);
  57     if(ATOMIC_SUB(&lock->write_count, 1, almemory_order_acq_rel) == 1)
  58         UNLOCK(lock->read_lock);
  59 }