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 static void Lock(volatile int *l)
  14 {
  15     while(ExchangeInt(l, true) == true)
  16         althrd_yield();
  17 }
  18
  19 static void Unlock(volatile int *l)
  20 {
  21     ExchangeInt(l, false);
  22 }
  23
  24
  25 void RWLockInit(RWLock *lock)
  26 {
  27     InitRef(&lock->read_count, 0);
  28     InitRef(&lock->write_count, 0);
  29     lock->read_lock = false;
  30     lock->read_entry_lock = false;
  31     lock->write_lock = false;
  32 }
  33
  34 void ReadLock(RWLock *lock)
  35 {
  36     Lock(&lock->read_entry_lock);
  37     Lock(&lock->read_lock);
  38     if(IncrementRef(&lock->read_count) == 1)
  39         Lock(&lock->write_lock);
  40     Unlock(&lock->read_lock);
  41     Unlock(&lock->read_entry_lock);
  42 }
  43
  44 void ReadUnlock(RWLock *lock)
  45 {
  46     if(DecrementRef(&lock->read_count) == 0)
  47         Unlock(&lock->write_lock);
  48 }
  49
  50 void WriteLock(RWLock *lock)
  51 {
  52     if(IncrementRef(&lock->write_count) == 1)
  53         Lock(&lock->read_lock);
  54     Lock(&lock->write_lock);
  55 }
  56
  57 void WriteUnlock(RWLock *lock)
  58 {
  59     Unlock(&lock->write_lock);
  60     if(DecrementRef(&lock->write_count) == 0)
  61         Unlock(&lock->read_lock);
  62 }