[Linux]pthread学习笔记
<UNIX环境高级编程（第二版）> 线程学习P287-P297
#include <pthread.h> //新建线程 int pthread_create(pthread_t *restrict tidp, const pthread_attr_t *restrict attr, void *(*start_rtn)(void *), void *restrict arg); //线程终止 void pthread_exit(void *rval_ptr);//线程自身主动退出 int pthread_join(pthread_t tid, void **rval_ptr);//其他线程阻塞自身，等待tid退出 //线程清理 void pthread_cleanup_push(void (*rtn)(void *), void *arg); void pthread_cleanup_pop(int execute);
补充说明：
1. 线程创建
pthread_create()函数返回值0，表示创建成功，线程id保存载tidp中；失败则返回非零，需自行处理，不会修改errno值
2. 线程终止
a. 任一线程调用exit, _Exit, _exit都将导致整个进程终止；
b. 单个线程退出方式有三种：
1> 线程执行函数start_rtn()中使用return返回，返回值为线程退出码；
2> 被同一个进程的其他线程使用pthread_cancel()取消；
3> 线程自身调用了pthread_exit()；
说明：pthread_join(pthread_t tid, void **rval_ptr)函数会阻塞调用线程，直到tid线程通过上述三种方式终止退出，且return/pthread_exit()方式会设置相应线程退出码rval_ptr，而pthread_cancel()取消的线程，将退出码设置为PTHREAD_CANCELED.
3. 线程清理处理程序（thread cleanup handler）
3.a> pthread_cleanup_push()与pthread_cleanup_pop()均为<pthread.h>中实现的宏定义，具体实现如下：
pthread_cleanup_push and pthread_cleanup_pop are macros and must always
be used in matching pairs at the same nesting level of braces. */
# define pthread_cleanup_push(routine, arg) \
do { \
__pthread_cleanup_class __clframe (routine, arg)
/* Remove a cleanup handler installed by the matching pthread_cleanup_push.
If EXECUTE is non-zero, the handler function is called. */
# define pthread_cleanup_pop(execute) \
__clframe.__setdoit (execute); \
} while (0)
可见push/pop中的{/}是一一对应的，因此pthread_cleanup_push/pop()也应一一对应出现，否则编译出错。
3.b> 当线程执行下列之一操作时调用清理函数，thread_cleanup_push由栈结构实现，注意清理程序调用的顺序，先入后出。
1: 调用pthread_exit()时，而直接return不会出发清理函数；
2: 相应取消请求pthread_cancel()时；
3: 使用非零execute参数调用pthread_cleanup_pop()时；
尤其需注意pthread_cleanup_pop()参数不同及此语句所处位置不同而有不同效果。
看此代码实例，注意return或pthread_exit()位置不同导致pthread_cleanup_pop()不同参数的效果变化。
#include <pthread.h>
void testPointerSize()
{
void *tret;
printf("size of pointer in x86-64：%d\n",sizeof(tret));
//result is 8 in x86-64.
//which is 4 in x86-32.
printf("size of int in x86-64：%d\n",sizeof(int));
//result is 4 in x86-64.
//which is also 4 in x86-32.
}
void cleanup(void *arg)
{
printf("cleanup:%s\n",(char *)arg);
}
void * thr_fn1(void *arg)
{
printf("thread 1 start\n");
pthread_cleanup_push(cleanup, "thread 1 first handler");
pthread_cleanup_push(cleanup, "thread 1 second handler");
if(arg)
return ((void *)1);//arg !=0 ,return here.
// return here will not triger any cleanup.
pthread_cleanup_pop(0);
pthread_cleanup_pop(1);
return ((void *)2);//will not run this
}
void * thr_fn2(void *arg)
{
printf("thread 2 start\n");
pthread_cleanup_push(cleanup, "thread 2 first handler");
pthread_cleanup_push(cleanup, "thread 2 second handler");
pthread_cleanup_pop(0);
pthread_cleanup_pop(1);
return ((void *)2);
// return here can triger cleanup second handler;
}
void * thr_fn3(void *arg)
{
printf("thread 3 start\n");
pthread_cleanup_push(cleanup, "thread 3 first handler");
pthread_cleanup_push(cleanup, "thread 3 second handler");
if(arg)
pthread_exit((void *)3);
//pthread_exit() here will triger both cleanup first&second handler.
pthread_cleanup_pop(1);
pthread_cleanup_pop(0);
pthread_exit((void *)3);//wont run this
}
void * thr_fn4(void *arg)
{
printf("thread 4 start\n");
pthread_cleanup_push(cleanup, "thread 4 first handler");
pthread_cleanup_push(cleanup, "thread 4 second handler");
pthread_cleanup_pop(1);
pthread_cleanup_pop(0);
pthread_exit((void *)4);
//pthread_exit() here will triger cleanup second handler.
}
int main(void)
{
testPointerSize();
int err;
pthread_t tid1, tid2, tid3, tid4;
void *tret;
err = pthread_create(&tid1, NULL, thr_fn1, (void *)1);
err = pthread_join(tid1,&tret);
printf("thread 1 exit code %d\n",(int)tret);
err = pthread_create(&tid2, NULL, thr_fn2, (void *)2);
err = pthread_join(tid2, &tret);
printf("thread 2 exit code %d\n",(int)tret);
err = pthread_create(&tid3, NULL, thr_fn3, (void *)3);
err = pthread_join(tid3,&tret);
printf("thread 3 exit code %d\n",(int)tret);
err = pthread_create(&tid4, NULL, thr_fn4, (void *)4);
err = pthread_join(tid4, &tret);
printf("thread 4 exit code %d\n",(int)tret);
}
运行结果：
[root@hello testData]# ./test size of pointer in x86-64：8 size of int in x86-64：4 thread 1 start thread 1 exit code 1 thread 2 start cleanup:thread 2 first handler thread 2 exit code 2 thread 3 start cleanup:thread 3 second handler cleanup:thread 3 first handler thread 3 exit code 3 thread 4 start cleanup:thread 4 second handler thread 4 exit code 4
由上述测试程序总结如下：
1> push与pop间的return，将导致清理程序不被触发；
2> 位于pop之后return，由pop的参数确定是否触发清理程序，非零参数触发，零参数不触发；
3> push/pop间的pthread_exit()，将触发所有清理函数；
4>位于pop之后的pthread_exit()时，pop参数决定是否触发清理程序；
其实，上述四种情况只是测试验证了前文3.b所说三个条件，加深理解。
参考文献：
2. <UNIX环境高级编程（第2版）> P295-296程序
3. pthread_cleanup_push()/pthread_cleanup_pop()的详解
4. Linux中vim的列编辑实例 （Mark记录）
