test/linuxrwlocks.c

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