例子：利用两个子进程从50进行降序输出
int g_num=50;
//偶数
void *threadEven(void *lParam)
{
while(g_num>0)
{
if(!(g_num&1))
{
printf("even:%d\n",g_num);
}
g_num--;
usleep(1);
}
return NULL;
}
//奇数
void *threadOdd(void *lParam)
{
while(g_num>0)
{
if(g_num&1)
{
printf("odd:%d\n",g_num);
}
g_num--;
usleep(1);
}
return NULL;
}
void testMutex()
{
pthread_t thread1,thread2;
int nRet1=pthread_create(&thread1,NULL,threadOdd,NULL);
int nRet2=pthread_create(&thread2,NULL,threadEven,NULL);
printf("thread1 id:%d\t thread2 id:%d\n",(int)thread1,(int)thread2);
if(nRet1||nRet2)
{
fprintf(stderr,"fail to create thread!");
return ;
}
pthread_join(thread1,NULL);
pthread_join(thread2,NULL);
}
int main(int argc,char**argv)
{
testMutex();
return 0;
}
上面的代码表示，创建两个子进程，子进程threadOdd输出奇数，子进程threadEven输出偶数。并且奇偶数是交替输出。即从50降序输出。
如果实现奇偶数分开输出，如：先把50内的奇数或偶数输出。此时就要加锁。
线程互斥
多线程共享进程资源，访问共享资源时候，需要进行互斥操作确保数据的有效性
什么是锁操作：
比如:两人进屋子拿东西，A先进去反锁屋子，那么B就进不去。只有等A开锁出来后，才轮到B进去。
锁类型设置/获取
int pthread_mutexattr_settype(pthread_mutexattr_t* attr, int type);
int pthread_mutexattr_gettype(pthread_mutexattr_t* attr, int *type);
type参数:
mutex 锁类型 PTHREAD_MUTEX_XXX
NORMAL: 普通锁，不提供死锁检测，可能出现死锁
ERRORCHECK: 检错锁，同一线程对已锁的互斥锁加锁会返回错误
RECURSIVE: 嵌套锁，允许同一线程多次锁定而不产生死锁，多次释放才能被别的线程锁定
DEFAULT: 默认为普通锁，排队获取锁
创建互斥锁
pthread_mutex_init(pthread_mutex_t *mutex, pthread_mutexattr_t *attr)
注意：
attr == NULL 初始化的线程锁 mutex
等价于 mutex = PTHREAD_MUTEX_INITIALIZER
互斥锁加锁
pthread_mutex_lock(pthread_mutex_t *mutex)
对互斥锁加锁
同一线程内对已经加锁的互斥锁，进行再次加锁，会造成死锁
互斥锁解锁
pthread_mutex_unlock(pthread_mutex_t *mutex)
释放互斥锁
对未锁定的互斥锁，进行释放操作，会产生不确定的行为
尝试解除有其他线程创建的互斥锁，会产生不确定的行为
pthread_mutex_trylock(pthread_mutex_t *mutex)
试图锁住互斥体，不阻塞
1： 互斥体未上锁，锁定并返回成功
2： 互斥体已经上锁，不阻塞直接返回失败
3： 锁类型为嵌套锁 RECURSIVE, 已上锁，则锁计数器自加
问题：若使用man无法查询文档？pthread_mutex_* 函数族 man 无显示解决办法
解决方式：$ sudo apt-get install manpages-posix-dev
例子：利用互斥锁，两个子进程分开输出50的奇偶数
pthread_mutex_t mutex;
int g_num=50;
void *threadEven(void *lParam)
{
//加锁
pthread_mutex_lock(&mutex);
while(g_num>0)
{
if(!(g_num&1))
{
printf("even:%d\n",g_num);
}
g_num--;
usleep(1);
}
g_num=50;
//解锁
pthread_mutex_unlock(&mutex);
return NULL;
}
void *threadOdd(void *lParam)
{
//加锁
pthread_mutex_lock(&mutex);
while(g_num>0)
{
if(g_num&1)
{
printf("odd:%d\n",g_num);
}
g_num--;
usleep(1);
}
g_num=50;
//解锁
pthread_mutex_unlock(&mutex);
return NULL;
}
void testMutex()
{
pthread_t thread1,thread2;
//初始化互斥锁
pthread_mutex_init(&mutex,NULL);
int nRet1=pthread_create(&thread1,NULL,threadOdd,NULL);
int nRet2=pthread_create(&thread2,NULL,threadEven,NULL);
printf("thread1 id:%d\t thread2 id:%d\n",(int)thread1,(int)thread2);
if(nRet1||nRet2)
{
fprintf(stderr,"fail to create thread!");
return ;
}
pthread_join(thread1,NULL);
pthread_join(thread2,NULL);
}
int main(int argc,char**argv)
{
testMutex();
return 0;
}
以上是实现，奇偶数分开输出。
ERRORCHECK和RECURSIVE属性：
例子：锁上加锁，ERRORCHECK错误返回
#include<stdio.h>
#include<pthread.h>
#include<stdlib.h>
#include<unistd.h>
#include<string.h>
pthread_mutex_t mutex;
int g_num=50;
//验证死锁
void *thread()
{
int nRet=pthread_mutex_lock(&mutex);
if(nRet)
{
printf("repeat lock!\n");
return NULL;
}
printf("test:%d\n",g_num);
pthread_mutex_unlock(&mutex);
return NULL;
}
void *threadEven(void *lParam)
{
int nRet=pthread_mutex_lock(&mutex);
if(nRet)
{
printf("repeat lock!\n");
return NULL;
}
while(g_num>0)
{
if(!(g_num&1))
{
printf("even:%d\n",g_num);
}
g_num--;
usleep(1);
}
g_num=50;
thread();
pthread_mutex_unlock(&mutex);
return NULL;
}
void *threadOdd(void *lParam)
{
int nRet=pthread_mutex_lock(&mutex);
if(nRet)
{
printf("repeat lock!\n");
return NULL;
}
while(g_num>0)
{
if(g_num&1)
{
printf("odd:%d\n",g_num);
}
g_num--;
usleep(1);
}
g_num=50;
thread();
pthread_mutex_unlock(&mutex);
return NULL;
}
void testMutex()
{
pthread_t thread1,thread2;
pthread_mutexattr_t attr;
//设置锁的属性
//pthread_mutexattr_settype(&attr,PTHREAD_MUTEX_RECURSIVE);
pthread_mutexattr_settype(&attr,PTHREAD_MUTEX_ERRORCHECK);
//默认排队锁
//pthread_mutex_init(&mutex,NULL);
pthread_mutex_init(&mutex,&attr);
int nRet1=pthread_create(&thread1,NULL,threadOdd,NULL);
int nRet2=pthread_create(&thread2,NULL,threadEven,NULL);
printf("thread1 id:%d\t thread2 id:%d\n",(int)thread1,(int)thread2);
if(nRet1||nRet2)
{
fprintf(stderr,"fail to create thread!");
return ;
}
pthread_join(thread1,NULL);
pthread_join(thread2,NULL);
}
int main(int argc,char**argv)
{
testMutex();
return 0;
}