此時(shí)互斥鎖的作用，只有在時(shí)間足夠的情況下才能體現(xiàn)出來，即有時(shí)線程內(nèi)需要延時(shí)；
否則只有第一個(gè)線程不斷解鎖和獲鎖，別的線程在第一個(gè)線程執(zhí)行完前無法獲得互斥鎖。
三 pthread_join pthread_exit
函數(shù)pthread_join用來等待一個(gè)線程的結(jié)束。函數(shù)原型為：
extern int pthread_join __P ((pthread_t __th, void **__thread_return));
第一個(gè)參數(shù)為被等待的線程標(biāo)識(shí)符，第二個(gè)參數(shù)為一個(gè)用戶定義的指針，它可以用來存儲(chǔ)被等待線程的返回值。這個(gè)函數(shù)是一個(gè)線程阻塞的函數(shù)，調(diào)用它的函數(shù)將 一直等待到被等待的線程結(jié)束為止，當(dāng)函數(shù)返回時(shí)，被等待線程的資源被收回。一個(gè)線程的結(jié)束有兩種途徑，一種是象我們上面的例子一樣，函數(shù)結(jié)束了，調(diào)用它的 線程也就結(jié)束了；另一種方式是通過函數(shù)pthread_exit來實(shí)現(xiàn)。它的函數(shù)原型為：
extern void pthread_exit __P ((void *__retval)) __attribute__ ((__noreturn__));
唯一的參數(shù)是函數(shù)的返回代碼，只要pthread_join中的第二個(gè)參數(shù)thread_return不是NULL，這個(gè)值將被傳遞給 thread_return。最后要說明的是，一個(gè)線程不能被多個(gè)線程等待，否則第一個(gè)接收到信號(hào)的線程成功返回，其余調(diào)用pthread_join的線 程則返回錯(cuò)誤代碼ESRCH。
在這一節(jié)里，我們編寫了一個(gè)最簡單的線程，并掌握了最常用的三個(gè)函數(shù)pthread_create，pthread_join和pthread_exit。下面，我們來了解線程的一些常用屬性以及如何設(shè)置這些屬性。
///////////////////////////////////////////////////////////////////////////
源程序：
/*thread_example.c : c multiple thread programming in linux
*/
#include
#include
#include
#include
#define MAX1 10
#define MAX2 30
pthread_t thread[2];
pthread_mutex_t mut;
int number=0, i;
void *thread1()
{
printf ("thread1 : I'm thread 1\n");
for (i = 0; i < MAX1; i++)
{
printf("thread1 : number = %d i=%d\n",number,i);
pthread_mutex_lock(&mut);
number++;
pthread_mutex_unlock(&mut);
sleep(2);
}
printf("thread1 :Is main function waiting for me acomplishing task? \n");
pthread_exit(NULL);
}
void *thread2()
{
printf("thread2 : I'm thread 2\n");
for (i = 0; i < MAX2; i++)
{
printf("thread2 : number = %d i=%d\n",number,i);
pthread_mutex_lock(&mut);
number++;
pthread_mutex_unlock(&mut);
sleep(3);
}
printf("thread2 :Is main function waiting for me to acomplish task ?\n");
pthread_exit(NULL);
}
void thread_create(void)
{
int temp;
memset(&thread, 0, sizeof(thread)); //comment1
/*創(chuàng)建線程*/
if((temp = pthread_create(&thread[0], NULL, thread1, NULL)) != 0) //comment2
printf("線程1創(chuàng)建失敗!\n");
else
printf("Thread 1 is established\n");
if((temp = pthread_create(&thread[1], NULL, thread2, NULL)) != 0) //comment3
printf("線程2創(chuàng)建失敗");
else
printf("Thread 2 is established\n");
}
void thread_wait(void)
{
/*等待線程結(jié)束*/
if(thread[0] !=0) { //comment4
pthread_join(thread[0],NULL);
printf("Thread 1 is over \n");
}
if(thread[1] !=0) { //comment5
pthread_join(thread[1],NULL);
printf("Thread 2 is over\n");
}
}
int main()
{
/*用默認(rèn)屬性初始化互斥鎖*/
pthread_mutex_init(&mut,NULL);
printf("I am the main funtion,and I am establishing threads. Ha-ha\n");
thread_create();
printf("I am the main funtion,and I am waiting for thread to accomplish task. Ha-ha\n");
thread_wait();
return 0;
}
///////////////////////////////////////////////////////////
執(zhí)行情況1(linux終端)：
[root@localhost root]# gcc -o joint joint.c -lpthread
[root@localhost root]# ./joint
I am the main funtion,and I am establishing threads. Ha-ha
thread1 : I'm thread 1
thread1 : number = 0 i=0
Thread 1 is established
thread2 : I'm thread 2
thread2 : number = 1 i=0
Thread 2 is established
I am the main funtion,and I am waiting for thread to accomplish task. Ha-ha
thread1 : number = 2 i=1
thread2 : number = 3 i=2
thread1 : number = 4 i=3
thread2 : number = 5 i=4
thread1 : number = 6 i=5
thread1 : number = 7 i=6
thread2 : number = 8 i=7
thread1 : number = 9 i=8
thread2 : number = 10 i=9
thread1 :Is main function waiting for me acomplishing task?
Thread 1 is over
thread2 : number = 11 i=11
thread2 : number = 12 i=12
thread2 : number = 13 i=13
thread2 : number = 14 i=14
thread2 : number = 15 i=15
thread2 : number = 16 i=16
thread2 : number = 17 i=17
thread2 : number = 18 i=18
thread2 : number = 19 i=19
thread2 : number = 20 i=20
thread2 : number = 21 i=21
thread2 : number = 22 i=22
thread2 : number = 23 i=23
thread2 : number = 24 i=24
thread2 : number = 25 i=25
thread2 : number = 26 i=26
thread2 : number = 27 i=27
thread2 : number = 28 i=28
thread2 : number = 29 i=29
thread2 :Is main function waiting for me to acomplish task ?
Thread 2 is over
