test/linuxrwlocksyield.c

   1 #include <stdio.h>
   2 #include <threads.h>
   3 #include <stdatomic.h>
   4
   5 #include "librace.h"
   6
   7 #define RW_LOCK_BIAS            0x00100000
   8 #define WRITE_LOCK_CMP          RW_LOCK_BIAS
   9
  10 /** Example implementation of linux rw lock along with 2 thread test
  11  *  driver... */
  12
  13 typedef union {
  14         atomic_int lock;
  15 } rwlock_t;
  16
  17 static inline int read_can_lock(rwlock_t *lock)
  18 {
  19         return atomic_load_explicit(&lock->lock, memory_order_relaxed) > 0;
  20 }
  21
  22 static inline int write_can_lock(rwlock_t *lock)
  23 {
  24         return atomic_load_explicit(&lock->lock, memory_order_relaxed) == RW_LOCK_BIAS;
  25 }
  26
  27 static inline void read_lock(rwlock_t *rw)
  28 {
  29         int priorvalue = atomic_fetch_sub_explicit(&rw->lock, 1, memory_order_acquire);
  30         while (priorvalue <= 0) {
  31                 atomic_fetch_add_explicit(&rw->lock, 1, memory_order_relaxed);
  32                 do {
  33                         priorvalue = atomic_load_explicit(&rw->lock, memory_order_relaxed);
  34                         if (priorvalue > 0)
  35                                 break;
  36                         thrd_yield();
  37                 } while (true);
  38                 priorvalue = atomic_fetch_sub_explicit(&rw->lock, 1, memory_order_acquire);
  39         }
  40 }
  41
  42 static inline void write_lock(rwlock_t *rw)
  43 {
  44         int priorvalue = atomic_fetch_sub_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_acquire);
  45         while (priorvalue != RW_LOCK_BIAS) {
  46                 atomic_fetch_add_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_relaxed);
  47                 do {
  48                         priorvalue = atomic_load_explicit(&rw->lock, memory_order_relaxed);
  49                         if (priorvalue == RW_LOCK_BIAS)
  50                                 break;
  51                         thrd_yield();
  52                 } while (true);
  53                 priorvalue = atomic_fetch_sub_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_acquire);
  54         }
  55 }
  56
  57 static inline int read_trylock(rwlock_t *rw)
  58 {
  59         int priorvalue = atomic_fetch_sub_explicit(&rw->lock, 1, memory_order_acquire);
  60         if (priorvalue > 0)
  61                 return 1;
  62
  63         atomic_fetch_add_explicit(&rw->lock, 1, memory_order_relaxed);
  64         return 0;
  65 }
  66
  67 static inline int write_trylock(rwlock_t *rw)
  68 {
  69         int priorvalue = atomic_fetch_sub_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_acquire);
  70         if (priorvalue == RW_LOCK_BIAS)
  71                 return 1;
  72
  73         atomic_fetch_add_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_relaxed);
  74         return 0;
  75 }
  76
  77 static inline void read_unlock(rwlock_t *rw)
  78 {
  79         atomic_fetch_add_explicit(&rw->lock, 1, memory_order_release);
  80 }
  81
  82 static inline void write_unlock(rwlock_t *rw)
  83 {
  84         atomic_fetch_add_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_release);
  85 }
  86
  87 rwlock_t mylock;
  88 int shareddata;
  89
  90 static void a(void *obj)
  91 {
  92         int i;
  93         for(i = 0; i < 2; i++) {
  94                 if ((i % 2) == 0) {
  95                         read_lock(&mylock);
  96                         load_32(&shareddata);
  97                         read_unlock(&mylock);
  98                 } else {
  99                         write_lock(&mylock);
 100                         store_32(&shareddata,(unsigned int)i);
 101                         write_unlock(&mylock);
 102                 }
 103         }
 104 }
 105
 106 int user_main(int argc, char **argv)
 107 {
 108         thrd_t t1, t2;
 109         atomic_init(&mylock.lock, RW_LOCK_BIAS);
 110
 111         thrd_create(&t1, (thrd_start_t)&a, NULL);
 112         thrd_create(&t2, (thrd_start_t)&a, NULL);
 113
 114         thrd_join(t1);
 115         thrd_join(t2);
 116
 117         return 0;
 118 }