读写锁

读共享，写独占

pthread_rwlock_t
pthread_rwlock_init
pthread_rwlock_destroy
pthread_rwlock_rdlock
pthread_rwlock_wrlock
pthread_rwlock_tryrdlock
pthread_rwlock_trywrlock
pthread_rwlock_unlock

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

int counter;
pthread_rwlock_t rwlock;
//3个线程不定时写同一全局资源，5个线程不定时读同一全局资源
void *th_write(void *arg)
{
  int t;
  while (1)
  {
    pthread_rwlock_wrlock(&rwlock);
    t = counter;
    usleep(100);
    printf("write %x : counter=%d ++counter=%d\n", (int)pthread_self(), t, ++counter);
    pthread_rwlock_unlock(&rwlock);
  }
}

void *th_read(void *arg)
{
  while (1) 
  {
    usleep(100);
    pthread_rwlock_rdlock(&rwlock);
    printf("read %x : %d\n", (int)pthread_self(), counter);
    pthread_rwlock_unlock(&rwlock);
  }
}
int main(void)
{
  int i;
  pthread_t tid[8];
  pthread_rwlock_init(&rwlock, NULL);
  for (i = 0; i < 3; i++)
    pthread_create(&tid[i], NULL, th_write, NULL);
  for (i = 0; i < 5; i++)
    pthread_create(&tid[i+3], NULL, th_read, NULL);
    
  pthread_rwlock_destroy(&rwlock);
  for (i = 0; i < 8; i++)
    pthread_join(tid[i], NULL);
  return 0;
}