Linux C线程同步的三种方法
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Linux C线程同步的三种方法
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void* thr_fn1()
{printf ("111111");
}int main()
{int err;pthread_t tid;void *tret;err = pthread_create(&tid, NULL, thr_fn1, NULL);if (err != 0).........錯誤err = pthread_join(tid, &tret);if (err != 0).........錯誤exit(0);
}
初始化鎖。在Linux下，線程的互斥量數據類型是pthread_mutex_t。在使用前,要對它進行初始化。
靜態分配：pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
動態分配：int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutex_attr_t *mutexattr); 加鎖。對共享資源的訪問，要對互斥量進行加鎖，如果互斥量已經上了鎖，調用線程會阻塞，直到互斥量被解鎖。
int pthread_mutex_lock(pthread_mutex *mutex);
int pthread_mutex_trylock(pthread_mutex_t *mutex); 解鎖。在完成了對共享資源的訪問后，要對互斥量進行解鎖。
int pthread_mutex_unlock(pthread_mutex_t *mutex); 銷毀鎖。鎖在是使用完成后，需要進行銷毀以釋放資源。
int pthread_mutex_destroy(pthread_mutex *mutex);
#include?<cstdio>?? #include?<cstdlib>?? #include?<unistd.h>?? #include?<pthread.h>?? #include?"iostream"?? using?namespace?std;?? pthread_mutex_t?mutex?=?PTHREAD_MUTEX_INITIALIZER;?? int?tmp;?? void*?thread(void?*arg)?? {?? ????cout?<<?"thread?id?is?"?<<?pthread_self()?<<?endl;?? ????pthread_mutex_lock(&mutex);?? ????tmp?=?12;?? ????cout?<<?"Now?a?is?"?<<?tmp?<<?endl;?? ????pthread_mutex_unlock(&mutex);?? ????return?NULL;?? }?? int?main()?? {?? ????pthread_t?id;?? ????cout?<<?"main?thread?id?is?"?<<?pthread_self()?<<?endl;?? ????tmp?=?3;?? ????cout?<<?"In?main?func?tmp?=?"?<<?tmp?<<?endl;?? ????if?(!pthread_create(&id,?NULL,?thread,?NULL))?? ????{?? ????????cout?<<?"Create?thread?success!"?<<?endl;?? ????}?? ????else?? ????{?? ????????cout?<<?"Create?thread?failed!"?<<?endl;?? ????}?? ????pthread_join(id,?NULL);?? ????pthread_mutex_destroy(&mutex);?? ????return?0;?? }?? //編譯：g++?-o?thread?testthread.cpp?-lpthread?
初始化條件變量。
靜態態初始化，pthread_cond_t cond = PTHREAD_COND_INITIALIER;
動態初始化，int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *cond_attr); 等待條件成立。釋放鎖,同時阻塞等待條件變量為真才行。timewait()設置等待時間,仍未signal,返回ETIMEOUT(加鎖保證只有一個線程wait)
int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);
int pthread_cond_timewait(pthread_cond_t *cond,pthread_mutex *mutex,const timespec *abstime); 激活條件變量。pthread_cond_signal,pthread_cond_broadcast（激活所有等待線程）
int pthread_cond_signal(pthread_cond_t *cond);
int pthread_cond_broadcast(pthread_cond_t *cond); //解除所有線程的阻塞 清除條件變量。無線程等待,否則返回EBUSY
int pthread_cond_destroy(pthread_cond_t *cond);
#include?<stdio.h>?? #include?<pthread.h>?? #include?"stdlib.h"?? #include?"unistd.h"?? pthread_mutex_t?mutex;?? pthread_cond_t?cond;?? void?hander(void?*arg)?? {?? ????free(arg);?? ????(void)pthread_mutex_unlock(&mutex);?? }?? void?*thread1(void?*arg)?? {?? ????pthread_cleanup_push(hander,?&mutex);?? ????while(1)?? ????{?? ????????printf("thread1?is?running\n");?? ????????pthread_mutex_lock(&mutex);?? ????????pthread_cond_wait(&cond,?&mutex);?? ????????printf("thread1?applied?the?condition\n");?? ????????pthread_mutex_unlock(&mutex);?? ????????sleep(4);?? ????}?? ????pthread_cleanup_pop(0);?? }?? void?*thread2(void?*arg)?? {?? ????while(1)?? ????{?? ????????printf("thread2?is?running\n");?? ????????pthread_mutex_lock(&mutex);?? ????????pthread_cond_wait(&cond,?&mutex);?? ????????printf("thread2?applied?the?condition\n");?? ????????pthread_mutex_unlock(&mutex);?? ????????sleep(1);?? ????}?? }?? int?main()?? {?? ????pthread_t?thid1,thid2;?? ????printf("condition?variable?study!\n");?? ????pthread_mutex_init(&mutex,?NULL);?? ????pthread_cond_init(&cond,?NULL);?? ????pthread_create(&thid1,?NULL,?thread1,?NULL);?? ????pthread_create(&thid2,?NULL,?thread2,?NULL);?? ????sleep(1);?? ????do?? ????{?? ????????pthread_cond_signal(&cond);?? ????}while(1);?? ????sleep(20);?? ????pthread_exit(0);?? ????return?0;?? }??
#include?<pthread.h>?? #include?<unistd.h>?? #include?"stdio.h"?? #include?"stdlib.h"?? static?pthread_mutex_t?mtx?=?PTHREAD_MUTEX_INITIALIZER;?? static?pthread_cond_t?cond?=?PTHREAD_COND_INITIALIZER;?? struct?node?? {?? ????int?n_number;?? ????struct?node?*n_next;?? }*head?=?NULL;?? ?? static?void?cleanup_handler(void?*arg)?? {?? ????printf("Cleanup?handler?of?second?thread./n");?? ????free(arg);?? ????(void)pthread_mutex_unlock(&mtx);?? }?? static?void?*thread_func(void?*arg)?? {?? ????struct?node?*p?=?NULL;?? ????pthread_cleanup_push(cleanup_handler,?p);?? ????while?(1)?? ????{?? ????????//這個mutex主要是用來保證pthread_cond_wait的并發性?? ????????pthread_mutex_lock(&mtx);?? ????????while?(head?==?NULL)?? ????????{?? ????????????//這個while要特別說明一下，單個pthread_cond_wait功能很完善，為何?? ????????????//這里要有一個while?(head?==?NULL)呢？因為pthread_cond_wait里的線?? ????????????//程可能會被意外喚醒，如果這個時候head?!=?NULL，則不是我們想要的情況。?? ????????????//這個時候，應該讓線程繼續進入pthread_cond_wait?? ????????????//?pthread_cond_wait會先解除之前的pthread_mutex_lock鎖定的mtx，?? ????????????//然后阻塞在等待對列里休眠，直到再次被喚醒(大多數情況下是等待的條件成立?? ????????????//而被喚醒，喚醒后，該進程會先鎖定先pthread_mutex_lock(&mtx);，再讀取資源?? ????????????//用這個流程是比較清楚的?? ????????????pthread_cond_wait(&cond,?&mtx);?? ????????????p?=?head;?? ????????????head?=?head->n_next;?? ????????????printf("Got?%d?from?front?of?queue/n",?p->n_number);?? ????????????free(p);?? ????????}?? ????????pthread_mutex_unlock(&mtx);?//臨界區數據操作完畢，釋放互斥鎖?? ????}?? ????pthread_cleanup_pop(0);?? ????return?0;?? }?? int?main(void)?? {?? ????pthread_t?tid;?? ????int?i;?? ????struct?node?*p;?? ????//子線程會一直等待資源，類似生產者和消費者，但是這里的消費者可以是多個消費者，而?? ????//不僅僅支持普通的單個消費者，這個模型雖然簡單，但是很強大?? ????pthread_create(&tid,?NULL,?thread_func,?NULL);?? ????sleep(1);?? ????for?(i?=?0;?i?<?10;?i++)?? ????{?? ????????p?=?(struct?node*)malloc(sizeof(struct?node));?? ????????p->n_number?=?i;?? ????????pthread_mutex_lock(&mtx);?//需要操作head這個臨界資源，先加鎖，?? ????????p->n_next?=?head;?? ????????head?=?p;?? ????????pthread_cond_signal(&cond);?? ????????pthread_mutex_unlock(&mtx);?//解鎖?? ????????sleep(1);?? ????}?? ????printf("thread?1?wanna?end?the?line.So?cancel?thread?2./n");?? ????//關于pthread_cancel，有一點額外的說明，它是從外部終止子線程，子線程會在最近的取消點，退出?? ????//線程，而在我們的代碼里，最近的取消點肯定就是pthread_cond_wait()了。?? ????pthread_cancel(tid);?? ????pthread_join(tid,?NULL);?? ????printf("All?done?--?exiting/n");?? ????return?0;?? }?? 信號量初始化。
int sem_init (sem_t *sem , int pshared, unsigned int value);
這是對由sem指定的信號量進行初始化，設置好它的共享選項(linux 只支持為0，即表示它是當前進程的局部信號量)，然后給它一個初始值VALUE。 等待信號量。給信號量減1，然后等待直到信號量的值大于0。
int sem_wait(sem_t *sem); 釋放信號量。信號量值加1。并通知其他等待線程。
int sem_post(sem_t *sem); 銷毀信號量。我們用完信號量后都它進行清理。歸還占有的一切資源。
int sem_destroy(sem_t *sem);
#include?<stdlib.h>?? #include?<stdio.h>?? #include?<unistd.h>?? #include?<pthread.h>?? #include?<semaphore.h>?? #include?<errno.h>?? #define?return_if_fail(p)?if((p)?==?0){printf?("[%s]:func?error!/n",?__func__);return;}?? typedef?struct?_PrivInfo?? {?? ????sem_t?s1;?? ????sem_t?s2;?? ????time_t?end_time;?? }PrivInfo;?? ?? static?void?info_init?(PrivInfo*?thiz);?? static?void?info_destroy?(PrivInfo*?thiz);?? static?void*?pthread_func_1?(PrivInfo*?thiz);?? static?void*?pthread_func_2?(PrivInfo*?thiz);?? ?? int?main?(int?argc,?char**?argv)?? {?? ????pthread_t?pt_1?=?0;?? ????pthread_t?pt_2?=?0;?? ????int?ret?=?0;?? ????PrivInfo*?thiz?=?NULL;?? ????thiz?=?(PrivInfo*?)malloc?(sizeof?(PrivInfo));?? ????if?(thiz?==?NULL)?? ????{?? ????????printf?("[%s]:?Failed?to?malloc?priv./n");?? ????????return?-1;?? ????}?? ????info_init?(thiz);?? ????ret?=?pthread_create?(&pt_1,?NULL,?(void*)pthread_func_1,?thiz);?? ????if?(ret?!=?0)?? ????{?? ????????perror?("pthread_1_create:");?? ????}?? ????ret?=?pthread_create?(&pt_2,?NULL,?(void*)pthread_func_2,?thiz);?? ????if?(ret?!=?0)?? ????{?? ????????perror?("pthread_2_create:");?? ????}?? ????pthread_join?(pt_1,?NULL);?? ????pthread_join?(pt_2,?NULL);?? ????info_destroy?(thiz);?? ????return?0;?? }?? static?void?info_init?(PrivInfo*?thiz)?? {?? ????return_if_fail?(thiz?!=?NULL);?? ????thiz->end_time?=?time(NULL)?+?10;?? ????sem_init?(&thiz->s1,?0,?1);?? ????sem_init?(&thiz->s2,?0,?0);?? ????return;?? }?? static?void?info_destroy?(PrivInfo*?thiz)?? {?? ????return_if_fail?(thiz?!=?NULL);?? ????sem_destroy?(&thiz->s1);?? ????sem_destroy?(&thiz->s2);?? ????free?(thiz);?? ????thiz?=?NULL;?? ????return;?? }?? static?void*?pthread_func_1?(PrivInfo*?thiz)?? {?? ????return_if_fail(thiz?!=?NULL);?? ????while?(time(NULL)?<?thiz->end_time)?? ????{?? ????????sem_wait?(&thiz->s2);?? ????????printf?("pthread1:?pthread1?get?the?lock./n");?? ????????sem_post?(&thiz->s1);?? ????????printf?("pthread1:?pthread1?unlock/n");?? ????????sleep?(1);?? ????}?? ????return;?? }?? static?void*?pthread_func_2?(PrivInfo*?thiz)?? {?? ????return_if_fail?(thiz?!=?NULL);?? ????while?(time?(NULL)?<?thiz->end_time)?? ????{?? ????????sem_wait?(&thiz->s1);?? ????????printf?("pthread2:?pthread2?get?the?unlock./n");?? ????????sem_post?(&thiz->s2);?? ????????printf?("pthread2:?pthread2?unlock./n");?? ????????sleep?(1);?? ????}?? ????return;?? }??
帶返回值
#include <stdio.h> #include <pthread.h> #include <unistd.h> #include <string.h>extern void* threadFun(void* arg);int main() {char pNameA[20] = "I'am thread A";pthread_t pid;pthread_create(&pid, NULL, threadFun, pNameA);char* retStr = 0;pthread_join(pid, (void**)&retStr);printf("Main process:%s.\r\n", retStr);delete[] retStr;return 0; }void* threadFun(void* arg) {char* pName = (char*)arg;int count = 0;while(count < 5){printf("%s, count:%d\r\n", pName, count);sleep(1);count++;}char* retVal = new char[32];sprintf(retVal, "%s, final count is:%d.", pName, count);return ((void*)retVal); }結構體：
具體例子#ifdef HAVE_CONFIG_H #include <config.h> #endif#include <stdio.h> #include <stdlib.h> #include <pthread.h> #include <string.h>// 參數結構體 struct argument {int num;char string[30]; };// 聲明兩個線程函數 void *thread1_func( void * ); void *thread2_func( void * );int main(int argc, char *argv[]) {//定義兩個線程標識符pthread_t thread1, thread2;//定義用來接收兩個線程退出后的返回值,用作pthread_join的第二個參數void *thread1_return, *thread2_return;//傳遞的參數結構體struct argument arg1, arg2;int i;int wait_thread_end; //判斷線程退出成功與否//參數結構體值初始化arg1.num = 1949;strcpy( arg1.string, "中華人民共和國" );arg2.num = 2012;strcpy( arg2.string, "建國63周年" );// 創建兩個線程pthread_create(&thread1, NULL, thread1_func, (void*)&arg1 );pthread_create( &thread2, NULL, thread2_func, (void*)&arg2 );for( i = 0; i < 2; i++ ){printf("我是最初的進程！\n");sleep(2); //主統線程睡眠，調用其他線程}//等待第一個線程退出，并接收它的返回值(返回值存儲在thread1_return)wait_thread_end = pthread_join( thread1, &thread1_return );if( wait_thread_end != 0 ) {printf("調用 pthread_join 獲取線程1的返回值出現錯誤!\n");}else{printf("調用 pthread_join 成功！線程1退出后的返回值是 %d\n", (int)thread1_return);}//等待第二個線程退出，并接收它的返回值(返回值存儲在thread2_return)wait_thread_end = pthread_join( thread2, &thread2_return);if( wait_thread_end != 0 ) {printf("調用 pthread_join 獲取線程2的返回值出現錯誤!\n");}else{printf("調用 pthread_join 成功！線程2退出后的返回值是 %d\n",(int)thread2_return );}return EXIT_SUCCESS; }/***線程1函數實現 */void *thread1_func( void *arg ) {int i;struct argument *arg_thread1; // 接收傳遞過來的參數結構體arg_thread1 = ( struct argument * )arg;for( i = 0; i < 3; i++){printf( "我來自線程1，傳遞給我的參數是 %d, %s\n", arg_thread1->num, arg_thread1->string);sleep(2); // 投入睡眠，調用其它線程}return (void *)123; }void *thread2_func( void *arg ) {int i;struct argument *arg_thread2; // 接收傳遞過來的參數結構體arg_thread2 = ( struct argument * )arg;for( i = 0; i < 3; i++){printf( "我來自線程2，傳遞給我的參數是 %d, %s\n", arg_thread2->num, arg_thread2->string);sleep(2); // 投入睡眠，調用其它線程}return (void *)456; }?
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線程的最大特點是資源的共享性，但資源共享中的同步問題是多線程編程的難點。linux下提供了多種方式來處理線程同步，最常用的是互斥鎖、條件變量和信號量。
一、互斥鎖(mutex)
通過鎖機制實現線程間的同步。
靜態分配：pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
動態分配：int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutex_attr_t *mutexattr);
int pthread_mutex_lock(pthread_mutex *mutex);
int pthread_mutex_trylock(pthread_mutex_t *mutex);
int pthread_mutex_unlock(pthread_mutex_t *mutex);
int pthread_mutex_destroy(pthread_mutex *mutex);
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二、條件變量(cond)
互斥鎖不同，條件變量是用來等待而不是用來上鎖的。條件變量用來自動阻塞一個線程，直到某特殊情況發生為止。通常條件變量和互斥鎖同時使用。條件變量分為兩部分: 條件和變量。條件本身是由互斥量保護的。線程在改變條件狀態前先要鎖住互斥量。條件變量使我們可以睡眠等待某種條件出現。條件變量是利用線程間共享的全局變量進行同步的一種機制，主要包括兩個動作：一個線程等待"條件變量的條件成立"而掛起；另一個線程使"條件成立"（給出條件成立信號）。條件的檢測是在互斥鎖的保護下進行的。如果一個條件為假，一個線程自動阻塞，并釋放等待狀態改變的互斥鎖。如果另一個線程改變了條件，它發信號給關聯的條件變量，喚醒一個或多個等待它的線程，重新獲得互斥鎖，重新評價條件。如果兩進程共享可讀寫的內存，條件變量可以被用來實現這兩進程間的線程同步。
靜態態初始化，pthread_cond_t cond = PTHREAD_COND_INITIALIER;
動態初始化，int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *cond_attr);
int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);
int pthread_cond_timewait(pthread_cond_t *cond,pthread_mutex *mutex,const timespec *abstime);
int pthread_cond_signal(pthread_cond_t *cond);
int pthread_cond_broadcast(pthread_cond_t *cond); //解除所有線程的阻塞
int pthread_cond_destroy(pthread_cond_t *cond);
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三、信號量(sem)
如同進程一樣，線程也可以通過信號量來實現通信，雖然是輕量級的。信號量函數的名字都以"sem_"打頭。線程使用的基本信號量函數有四個。
int sem_init (sem_t *sem , int pshared, unsigned int value);
這是對由sem指定的信號量進行初始化，設置好它的共享選項(linux 只支持為0，即表示它是當前進程的局部信號量)，然后給它一個初始值VALUE。
int sem_wait(sem_t *sem);
int sem_post(sem_t *sem);
int sem_destroy(sem_t *sem);
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