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_EXCHANGE(int, &(l), true) == true)                            \
  15         althrd_yield();                                                       \
  16 } while(0)
  17 #define UNLOCK(l) ATOMIC_STORE(&(l), false)
  18
  19
  20 void RWLockInit(RWLock *lock)
  21 {
  22     InitRef(&lock->read_count, 0);
  23     InitRef(&lock->write_count, 0);
  24     ATOMIC_INIT(&lock->read_lock, false);
  25     ATOMIC_INIT(&lock->read_entry_lock, false);
  26     ATOMIC_INIT(&lock->write_lock, false);
  27 }
  28
  29 void ReadLock(RWLock *lock)
  30 {
  31     LOCK(lock->read_entry_lock);
  32     LOCK(lock->read_lock);
  33     if(IncrementRef(&lock->read_count) == 1)
  34         LOCK(lock->write_lock);
  35     UNLOCK(lock->read_lock);
  36     UNLOCK(lock->read_entry_lock);
  37 }
  38
  39 void ReadUnlock(RWLock *lock)
  40 {
  41     if(DecrementRef(&lock->read_count) == 0)
  42         UNLOCK(lock->write_lock);
  43 }
  44
  45 void WriteLock(RWLock *lock)
  46 {
  47     if(IncrementRef(&lock->write_count) == 1)
  48         LOCK(lock->read_lock);
  49     LOCK(lock->write_lock);
  50 }
  51
  52 void WriteUnlock(RWLock *lock)
  53 {
  54     UNLOCK(lock->write_lock);
  55     if(DecrementRef(&lock->write_count) == 0)
  56         UNLOCK(lock->read_lock);
  57 }