pthread_create的使用方法.doc

pthread_create的使用方法.txt人生重要的不是所站的位置，而是所朝的方向。不要用自己的需求去衡量别人的给予，否则永远是抱怨。1：pthread_create 函数的安全使用问题 做过linux多线程开发的人都会用过pthread_create函数，但是很少人会注意到：主线程在使用pthread_create创建线程时，如果pthread_create 函数的第四个参数（指针参数）传入的值会被主线程随时修改时，这时我们的线程从pthread_create 函数的第四个参数获取的值可能就不是我们想要传入的值了。 看看下面代码：在 main 函数的 for 循环中创建10个线程；每创建一个线程时都把循环变量 i 的值通过 pthread_create 函数的第四个参数传入线程函数中；但是线程获取的值可能不并不是我们想传入的值。#include #include void * threadFunc( void * pm_iPthreadId ) unsigned int iId = * ( unsigned int * ) pm_iPthreadId; printf( # No.%d pthread start exec; pthread id = %u !n, iId, pthread_self() ); time_t iStartTime = time( NULL ); while(1) time_t iTempTime = time( NULL ); if ( iTempTime - iStartTime 2 ) printf( $ NO.%d pthread cirle exec !n, * ( unsigned int * ) pm_iPthreadId ); iStartTime = time( NULL ); int main() pthread_t * pthreadId; pthreadId = new pthread_t10; for( unsigned int i = 0; i 10; i+ ) int iRet = pthread_create( pthreadId + i, NULL, threadFunc, &i ); if ( iRet = 0 ) printf( create No.%d pthread success; pthreadId = %u !n, i, pthreadId + i ); while(1) return 0;程序运行结果如下（结果是随机的，每次运行可能都不一样）： create No.0 pthread success; pthreadId = 138174472 !# No.1 pthread start exec; pthread id = 3076803472 !# No.1 pthread start exec; pthread id = 3087293328 ! create No.1 pthread success; pthreadId = 138174476 ! create No.2 pthread success; pthreadId = 138174480 !# No.3 pthread start exec; pthread id = 3055823760 !# No.3 pthread start exec; pthread id = 3066313616 ! create No.3 pthread success; pthreadId = 138174484 !# No.4 pthread start exec; pthread id = 3045333904 ! create No.4 pthread success; pthreadId = 138174488 ! create No.5 pthread success; pthreadId = 138174492 !# No.6 pthread start exec; pthread id = 3024354192 !# No.6 pthread start exec; pthread id = 3034844048 ! create No.6 pthread success; pthreadId = 138174496 ! create No.7 pthread success; pthreadId = 138174500 !# No.8 pthread start exec; pthread id = 3003374480 !# No.8 pthread start exec; pthread id = 3013864336 ! create No.8 pthread success; pthreadId = 138174504 ! create No.9 pthread success; pthreadId = 138174508 !# No.10 pthread start exec; pthread id = 2992884624 !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec ! 从以“#”开头的字符结果可以看出：以“#No.0”、“#No.2”、“#No.5、“#No.7”、“#No.7”的字符没有；从这可以看出，我们从pthread_create 函数的第四个参数传入的值是不安全的，应该受到安全保护。2：此问题原因 pthread_create 函数是非阻塞函数；会立即返回，主线程不会在创建线程后阻塞到线程函数执行完后返回，导致线程函数获取到循环变量 i 的值被主线程立即改变。3：此问题解决方法利用条件变量的保护，在线程函数中把 pthread_create 第四个参数传入的值保存为局部变量。#include #include pthread_cond_t m_Cond;pthread_mutex_t m_Locker;void * threadFunc( void * pm_iPthreadId ) pthread_mutex_lock(&m_Locker); unsigned int iId = * ( unsigned int * ) pm_iPthreadId; printf( # No.%d pthread start exec; pthread id = %u !n, iId, pthread_self() ); pthread_cond_signal(&m_Cond); pthread_mutex_unlock(&m_Locker); time_t iStartTime = time( NULL ); while(1) time_t iTempTime = time( NULL ); if ( iTempTime - iStartTime 2 ) printf( $ NO.%d pthread cirle exec !n, * ( unsigned int * ) pm_iPthreadId ); iStartTime = time( NULL ); int main() pthread_mutex_init(&m_Locker, NULL); pthread_cond_init(&m_Cond, NULL); pthread_t * pthreadId; pthreadId = new pthread_t10; for( unsigned int i = 0; i 10; i+ ) pthread_mutex_lock(&m_Locker); int iRet = pthread_create( pthreadId + i, NULL, threadFunc, &i ); if ( iRet = 0 ) printf( create No.%d pthread success; pthreadId = %u !n, i, pthreadId + i ); pthread_cond_wait(&m_Cond, &m_Locker); pthread_mutex_unlock(&m_Locker); while(1) return 0;上面代码运行结果： create No.0 pthread success; pthreadId = 147902472 !# No.0 pthread start exec; pthread id = 3087563664 ! create No.1 pthread success; pthreadId = 147902476 !# No.1 pthread start exec; pthread id = 3077073808 ! create No.2 pthread success; pthreadId = 147902480 !# No.2 pthread start exec; pthread id = 3066583952 ! create No.3 pthread success; pthreadId = 147902484 !# No.3 pthread start exec; pthread id = 3056094096 ! create No.4 pthread success; pthreadId = 147902488 !# No.4 pthread start exec; pthread id = 3045604240 ! create No.5 pthread success; pthreadId = 147902492 !# No.5 pthread start exec; pthread id = 3035114384 ! create No.6 pthread success; pthreadId = 147902496 !# No.6 pthread start exec; pthread id = 3024624528 ! create No.7 pthread success; pthreadId = 147902500 !# No.7 pthread start exec; pthread id = 3014134672 ! create No.8 pthread success; pthreadId = 147902504 !# No.8 pthread start exec; pthread id = 3003644816 ! create No.9 pthread success; pthreadId = 147902508 !# No.9 pthread start exec; pthread id = 2993154960 !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cirle exec !$ NO.10 pthread cir