;1. 初始化: 在Linux下, 線程的互斥量數(shù)據(jù)類型是pthread_mutex_t. 在使用前, 要對(duì)它進(jìn)行初始化: 對(duì)于靜態(tài)分配的互斥量, 可以把它設(shè)置為PTHREAD_MUTEX_INITIALIZER, 或者調(diào)用pthread_mutex_init. 對(duì)于動(dòng)態(tài)分配的互斥量, 在申請(qǐng)內(nèi)存(malloc)之后, 通過pthread_mutex_init進(jìn)行初始化, 并且在釋放內(nèi)存(free)前需要調(diào)用pthread_mutex_destroy. 原型: int pthread_mutex_init(pthread_mutex_t *restrict mutex, const pthread_mutexattr_t *restric attr); int pthread_mutex_destroy(pthread_mutex_t *mutex); 頭文件: 返回值: 成功則返回0, 出錯(cuò)則返回錯(cuò)誤編號(hào). 說(shuō)明: 如果使用默認(rèn)的屬性初始化互斥量, 只需把a(bǔ)ttr設(shè)為NULL. 其他值在以后講解. 2. 互斥操作: 對(duì)共享資源的訪問, 要對(duì)互斥量進(jìn)行加鎖, 如果互斥量已經(jīng)上了鎖, 調(diào)用線程會(huì)阻塞, 直到互斥量被解鎖. 在完成了對(duì)共享資源的訪問后, 要對(duì)互斥量進(jìn)行解鎖. 首先說(shuō)一下加鎖函數(shù): 頭文件: 原型: int pthread_mutex_lock(pthread_mutex_t *mutex); int pthread_mutex_trylock(pthread_mutex_t *mutex); 返回值: 成功則返回0, 出錯(cuò)則返回錯(cuò)誤編號(hào). 說(shuō)明: 具體說(shuō)一下trylock函數(shù), 這個(gè)函數(shù)是非阻塞調(diào)用模式, 也就是說(shuō), 如果互斥量沒被鎖住, trylock函數(shù)將把互斥量加鎖, 并獲得對(duì)共享資源的訪問權(quán)限; 如果互斥量被鎖住了, trylock函數(shù)將不會(huì)阻塞等待而直接返回EBUSY, 表示共享資源處于忙狀態(tài). 再說(shuō)一下解所函數(shù): 頭文件: 原型: int pthread_mutex_unlock(pthread_mutex_t *mutex); 返回值: 成功則返回0, 出錯(cuò)則返回錯(cuò)誤編號(hào). 3. 死鎖: 死鎖主要發(fā)生在有多個(gè)依賴鎖存在時(shí), 會(huì)在一個(gè)線程試圖以與另一個(gè)線程相反順序鎖住互斥量時(shí)發(fā)生. 如何避免死鎖是使用互斥量應(yīng)該格外注意的東西. 總體來(lái)講, 有幾個(gè)不成文的基本原則: 對(duì)共享資源操作前一定要獲得鎖. 完成操作以后一定要釋放鎖. 盡量短時(shí)間地占用鎖. 如果有多鎖, 如獲得順序是ABC連環(huán)扣, 釋放順序也應(yīng)該是ABC. 線程錯(cuò)誤返回時(shí)應(yīng)該釋放它所獲得的鎖. 示例： #include #include #include #include 【Linux操作系統(tǒng)多線程同步Mutex詳細(xì)介紹】#include pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;int lock_var;time_t end_time;int sum;void pthread1(void *arg);void pthread2(void *arg);void pthread3(void *arg);int main(int argc, char *argv[]){pthread_t id1,id2,id3;pthread_t mon_th_id;int ret;sum=10;end_time = time(NULL) 10;pthread_mutex_init(&mutex,NULL);ret=pthread_create(&id1,NULL,(void *)pthread1, NULL);if(ret!=0)perror("pthread cread1");ret=pthread_create(&id2,NULL,(void *)pthread2, NULL);if(ret!=0)perror("pthread cread2");ret=pthread_create(&id3,NULL,(void *)pthread3, NULL);if(ret!=0)perror("pthread cread3");pthread_join(id1,NULL);pthread_join(id2,NULL);pthread_join(id3,NULL);exit(0);}void pthread1(void *arg){int i;while(time(NULL) < end_time){if(pthread_mutex_lock(&mutex)!=0) //lock{perror("pthread_mutex_lock");}elseprintf("pthread1:pthread1 lock the variablen");for(i=0;i<2;i){sleep(2);lock_var;}if(pthread_mutex_unlock(&mutex)!=0) //unlock{perror("pthread_mutex_unlock");}elseprintf("pthread1:pthread1 unlock the variablen");sleep(1);}}void pthread2(void *arg){int nolock=0;int ret;while(time(NULL) < end_time){ret=pthread_mutex_trylock(&mutex);//try lockif(ret==EBUSY)printf("pthread2:the variable is locked by pthread1n");else{if(ret!=0){perror("pthread_mutex_trylock");exit(1);}elseprintf("pthread2:pthread2 got lock.The variable is %dn",lock_var);if(pthread_mutex_unlock(&mutex)!=0)//unlock{perror("pthread_mutex_unlock");}elseprintf("pthread2:pthread2 unlock the variablen");}sleep(1);}}void pthread3(void *arg){/*int nolock=0;int ret;while(time(NULL) < end_time){ret=pthread_mutex_trylock(&mutex);if(ret==EBUSY)printf("pthread3:the variable is locked by pthread1 or 2n");else{if(ret!=0){perror("pthread_mutex_trylock");exit(1);}elseprintf("pthread3:pthread3 got lock.The variable is %dn",lock_var);if(pthread_mutex_unlock(&mutex)!=0){perror("pthread_mutex_unlock");}elseprintf("pthread3:pthread2 unlock the variablen");}sleep(3);}*/}
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