linuxrwlocks/linuxrwlocks.h

   1 #include <stdio.h>
   2 #include <stdatomic.h>
   3
   4 #include "librace.h"
   5
   6 #define RW_LOCK_BIAS            0x00100000
   7 #define WRITE_LOCK_CMP          RW_LOCK_BIAS
   8
   9 /** Example implementation of linux rw lock along with 2 thread test
  10  *  driver... */
  11
  12 typedef union {
  13         atomic_int lock;
  14 } rwlock_t;
  15
  16 static inline int read_can_lock(rwlock_t *lock)
  17 {
  18         return atomic_load_explicit(&lock->lock, memory_order_relaxed) > 0;
  19 }
  20
  21 static inline int write_can_lock(rwlock_t *lock)
  22 {
  23         return atomic_load_explicit(&lock->lock, memory_order_relaxed) == RW_LOCK_BIAS;
  24 }
  25
  26 static inline void read_lock(rwlock_t *rw)
  27 {
  28         int priorvalue = atomic_fetch_sub_explicit(&rw->lock, 1, memory_order_acquire);
  29         while (priorvalue <= 0) {
  30                 atomic_fetch_add_explicit(&rw->lock, 1, memory_order_relaxed);
  31                 while (atomic_load_explicit(&rw->lock, memory_order_relaxed) <= 0) {
  32                         thrd_yield();
  33                 }
  34                 priorvalue = atomic_fetch_sub_explicit(&rw->lock, 1, memory_order_acquire);
  35         }
  36 }
  37
  38 static inline void write_lock(rwlock_t *rw)
  39 {
  40         int priorvalue = atomic_fetch_sub_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_acquire);
  41         while (priorvalue != RW_LOCK_BIAS) {
  42                 atomic_fetch_add_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_relaxed);
  43                 while (atomic_load_explicit(&rw->lock, memory_order_relaxed) != RW_LOCK_BIAS) {
  44                         thrd_yield();
  45                 }
  46                 priorvalue = atomic_fetch_sub_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_acquire);
  47         }
  48 }
  49
  50 static inline int read_trylock(rwlock_t *rw)
  51 {
  52         int priorvalue = atomic_fetch_sub_explicit(&rw->lock, 1, memory_order_acquire);
  53         if (priorvalue > 0)
  54                 return 1;
  55
  56         atomic_fetch_add_explicit(&rw->lock, 1, memory_order_relaxed);
  57         return 0;
  58 }
  59
  60 static inline int write_trylock(rwlock_t *rw)
  61 {
  62         int priorvalue = atomic_fetch_sub_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_acquire);
  63         if (priorvalue == RW_LOCK_BIAS)
  64                 return 1;
  65
  66         atomic_fetch_add_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_relaxed);
  67         return 0;
  68 }
  69
  70 static inline void read_unlock(rwlock_t *rw)
  71 {
  72         atomic_fetch_add_explicit(&rw->lock, 1, memory_order_release);
  73 }
  74
  75 static inline void write_unlock(rwlock_t *rw)
  76 {
  77         atomic_fetch_add_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_release);
  78 }