1：pthread_create 函式的安全使用問題
做過linux多執行緒開發的人都會用過pthread_create函式，但是很少人會注意到：主線程在使用pthread_create建立執行緒時，如果pthread_create 函式的第四個引數（指標引數）傳入的值會被主線程隨時修改時，這時我們的執行緒從pthread_create 函式的第四個引數獲取的值可能就不是我們想要傳入的值了。
看看下面**：在 main 函式的 for 迴圈中建立10個執行緒；每建立乙個執行緒時都把迴圈變數 i 的值通過 pthread_create 函式的第四個引數傳入執行緒函式中；但是執行緒獲取的值可能不並不是我們想傳入的值。
#include
#include
void * threadfunc( void * pm_ipthreadid )}}
int main()
}while(1)
return 0;
}程式執行結果如下（結果是隨機的，每次執行可能都不一樣）：
@@@ 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 !
$$$ no.10 pthread cirle exec !
從以「###」開頭的字元結果可以看出：以「###no.0」、「###no.2」、「###no.5、「###no.7」、「###no.7」 的字元沒有；從這可以看出，我們從pthread_create 函式的第四個引數傳入的值是不安全的，應該受到安全保護。
2：此問題原因
pthread_create 函式是非阻塞函式；會立即返回，主線程不會在建立執行緒後阻塞到執行緒函式執行完後返回，導致執行緒函式獲取到迴圈變數 i 的值被主線程立即改變。
3：此問題解決方法
#include
#include
pthread_cond_t m_cond;
pthread_mutex_t m_locker;
void * threadfunc( void * pm_ipthreadid )}}
int main()
pthread_cond_wait(&m_cond, &m_locker);
pthread_mutex_unlock(&m_locker);
}while(1)
return 0;
}上面**執行結果：
@@@ create no.0 pthread success; pthreadid = 147902472 !
### no.0 pthread start exec; pthread id = 3087563664 !
@@@ create no.1 pthread success; pthreadid = 147902476 !
### no.1 pthread start exec; pthread id = 3077073808 !
@@@ create no.2 pthread success; pthreadid = 147902480 !
### no.2 pthread start exec; pthread id = 3066583952 !
@@@ create no.3 pthread success; pthreadid = 147902484 !
### no.3 pthread start exec; pthread id = 3056094096 !
@@@ create no.4 pthread success; pthreadid = 147902488 !
### no.4 pthread start exec; pthread id = 3045604240 !
@@@ create no.5 pthread success; pthreadid = 147902492 !
### no.5 pthread start exec; pthread id = 3035114384 !
@@@ create no.6 pthread success; pthreadid = 147902496 !
### no.6 pthread start exec; pthread id = 3024624528 !
@@@ create no.7 pthread success; pthreadid = 147902500 !
### no.7 pthread start exec; pthread id = 3014134672 !
@@@ create no.8 pthread success; pthreadid = 147902504 !
### no.8 pthread start exec; pthread id = 3003644816 !
@@@ create no.9 pthread success; pthreadid = 147902508 !
### no.9 pthread start exec; pthread id = 2993154960 !
$$$ no.10 pthread cirle exec !
$$$ no.10 pthread cirle exec !
$$$ no.10 pthread cirle exec !
$$$ no.10 pthread cirle exec !
$$$ 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 !
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