#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
#include <errno.h>
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
int lock_var=1;
time_t end_time;
void pthread1(void *arg);
void pthread2(void *arg);
int main(int argc, char *argv[])
{
pthread_t id1,id2;
pthread_t mon_th_id;
int ret;
end_time = time(NULL)+10;
pthread_mutex_init(&mutex,NULL);
ret=pthread_create(&id1,NULL,(void *)pthread1, NULL);
if(ret!=0)
perror("pthread cread1");
ret=pthread_create(&id2,NULL,(void *)pthread2, NULL);
if(ret!=0)
perror("pthread cread2");
pthread_join(id1,NULL);
pthread_join(id2,NULL);
exit(0);
}
void pthread1(void *arg)
{
int i;
while(time(NULL) < end_time)
{
if(pthread_mutex_lock(&mutex)!=0)
{
perror("pthread_mutex_lock");
}
else
{
printf("pthread1:pthread1 lock the variable\n");
}
for(i=0;i<1;i++)
{
sleep(1);
lock_var+=2;
}
if(pthread_mutex_unlock(&mutex)!=0)
{
perror("pthread_mutex_unlock");
}
else
{
printf("pthread1:pthread1 unlock the variable\n");
}
sleep(1);
}
}
void pthread2(void *arg)
{
int nolock=0;
int ret;
while(time(NULL) < end_time)
{
ret=pthread_mutex_lock(&mutex);
if(ret==EBUSY)
{
printf("pthread2:the variable is locked by pthread1\n");
}
else
{
if(ret!=0)
{
perror("pthread-mutex_trylock");
exit(1);
}
else
{
printf("pthread2 got lock.the variable is %d\n",lock_var);
}
if(pthread_mutex_unlock(&mutex)!=0)
{
perror("pthread_mutex_unlock");
}
else
{
printf("pthread2:pthread2 unlock the variable\n");
}
}
sleep(2);
}
}
上面是一个简单的互斥锁，但是有一点不明白，为什么两个线程同时得到了同一个锁，打印如下
pthread1:pthread1 lock the variable
pthread1:pthread1 unlock the variable
pthread2 got lock.the variable is 3
pthread2:pthread2 unlock the variable
pthread1:pthread1 lock the variable
pthread2 got lock.the variable is 5
pthread2:pthread2 unlock the variable
pthread1:pthread1 unlock the variable
pthread1:pthread1 lock the variable
pthread2 got lock.the variable is 7
pthread2:pthread2 unlock the variable
pthread1:pthread1 unlock the variable
pthread1:pthread1 lock the variable
pthread2 got lock.the variable is 9
pthread2:pthread2 unlock the variable
pthread1:pthread1 unlock the variable
pthread1:pthread1 lock the variable
pthread2 got lock.the variable is 11
pthread2:pthread2 unlock the variable
pthread1:pthread1 unlock the variable
求解释。。。。 越详细越好！！！
