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(cuò)誤err = pthread_join(tid, &tret);if (err != 0).........錯(cuò)誤exit(0);
}
初始化鎖。在Linux下，線(xiàn)程的互斥量數(shù)據(jù)類(lèi)型是pthread_mutex_t。在使用前,要對(duì)它進(jìn)行初始化。
靜態(tài)分配：pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
動(dòng)態(tài)分配：int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutex_attr_t *mutexattr); 加鎖。對(duì)共享資源的訪(fǎng)問(wèn)，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(xiàn)程會(huì)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(duì)共享資源的訪(fǎng)問(wèn)后，要對(duì)互斥量進(jìn)行解鎖。
int pthread_mutex_unlock(pthread_mutex_t *mutex); 銷(xiāo)毀鎖。鎖在是使用完成后，需要進(jìn)行銷(xiāo)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(tài)態(tài)初始化，pthread_cond_t cond = PTHREAD_COND_INITIALIER;
動(dòng)態(tài)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(shí)阻塞等待條件變量為真才行。timewait()設(shè)置等待時(shí)間,仍未signal,返回ETIMEOUT(加鎖保證只有一個(gè)線(xiàn)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(xiàn)程）
int pthread_cond_signal(pthread_cond_t *cond);
int pthread_cond_broadcast(pthread_cond_t *cond); //解除所有線(xiàn)程的阻塞 清除條件變量。無(wú)線(xiàn)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(gè)mutex主要是用來(lái)保證pthread_cond_wait的并發(fā)性?? ????????pthread_mutex_lock(&mtx);?? ????????while?(head?==?NULL)?? ????????{?? ????????????//這個(gè)while要特別說(shuō)明一下，單個(gè)pthread_cond_wait功能很完善，為何?? ????????????//這里要有一個(gè)while?(head?==?NULL)呢？因?yàn)閜thread_cond_wait里的線(xiàn)?? ????????????//程可能會(huì)被意外喚醒，如果這個(gè)時(shí)候head?!=?NULL，則不是我們想要的情況。?? ????????????//這個(gè)時(shí)候，應(yīng)該讓線(xiàn)程繼續(xù)進(jìn)入pthread_cond_wait?? ????????????//?pthread_cond_wait會(huì)先解除之前的pthread_mutex_lock鎖定的mtx，?? ????????????//然后阻塞在等待對(duì)列里休眠，直到再次被喚醒(大多數(shù)情況下是等待的條件成立?? ????????????//而被喚醒，喚醒后，該進(jìn)程會(huì)先鎖定先pthread_mutex_lock(&mtx);，再讀取資源?? ????????????//用這個(gè)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(qū)數(shù)據(jù)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(xiàn)程會(huì)一直等待資源，類(lèi)似生產(chǎn)者和消費(fèi)者，但是這里的消費(fèi)者可以是多個(gè)消費(fèi)者，而?? ????//不僅僅支持普通的單個(gè)消費(fèi)者，這個(gè)模型雖然簡(jiǎn)單，但是很強(qiáng)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(gè)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(guān)于pthread_cancel，有一點(diǎn)額外的說(shuō)明，它是從外部終止子線(xiàn)程，子線(xiàn)程會(huì)在最近的取消點(diǎn)，退出?? ????//線(xiàn)程，而在我們的代碼里，最近的取消點(diǎn)肯定就是pthread_cond_wait()了。?? ????pthread_cancel(tid);?? ????pthread_join(tid,?NULL);?? ????printf("All?done?--?exiting/n");?? ????return?0;?? }?? 信號(hào)量初始化。
int sem_init (sem_t *sem , int pshared, unsigned int value);
這是對(duì)由sem指定的信號(hào)量進(jìn)行初始化，設(shè)置好它的共享選項(xiàng)(linux 只支持為0，即表示它是當(dāng)前進(jìn)程的局部信號(hào)量)，然后給它一個(gè)初始值VALUE。 等待信號(hào)量。給信號(hào)量減1，然后等待直到信號(hào)量的值大于0。
int sem_wait(sem_t *sem); 釋放信號(hào)量。信號(hào)量值加1。并通知其他等待線(xiàn)程。
int sem_post(sem_t *sem); 銷(xiāo)毀信號(hào)量。我們用完信號(hào)量后都它進(jìn)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(jié)構(gòu)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(shù)結(jié)構(gòu)體 struct argument {int num;char string[30]; };// 聲明兩個(gè)線(xiàn)程函數(shù) void *thread1_func( void * ); void *thread2_func( void * );int main(int argc, char *argv[]) {//定義兩個(gè)線(xiàn)程標(biāo)識(shí)符pthread_t thread1, thread2;//定義用來(lái)接收兩個(gè)線(xiàn)程退出后的返回值,用作pthread_join的第二個(gè)參數(shù)void *thread1_return, *thread2_return;//傳遞的參數(shù)結(jié)構(gòu)體struct argument arg1, arg2;int i;int wait_thread_end; //判斷線(xiàn)程退出成功與否//參數(shù)結(jié)構(gòu)體值初始化arg1.num = 1949;strcpy( arg1.string, "中華人民共和國(guó)" );arg2.num = 2012;strcpy( arg2.string, "建國(guó)63周年" );// 創(chuàng)建兩個(gè)線(xiàn)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(jìn)程！\n");sleep(2); //主統(tǒng)線(xiàn)程睡眠，調(diào)用其他線(xiàn)程}//等待第一個(gè)線(xiàn)程退出，并接收它的返回值(返回值存儲(chǔ)在thread1_return)wait_thread_end = pthread_join( thread1, &thread1_return );if( wait_thread_end != 0 ) {printf("調(diào)用 pthread_join 獲取線(xiàn)程1的返回值出現(xiàn)錯(cuò)誤!\n");}else{printf("調(diào)用 pthread_join 成功！線(xiàn)程1退出后的返回值是 %d\n", (int)thread1_return);}//等待第二個(gè)線(xiàn)程退出，并接收它的返回值(返回值存儲(chǔ)在thread2_return)wait_thread_end = pthread_join( thread2, &thread2_return);if( wait_thread_end != 0 ) {printf("調(diào)用 pthread_join 獲取線(xiàn)程2的返回值出現(xiàn)錯(cuò)誤!\n");}else{printf("調(diào)用 pthread_join 成功！線(xiàn)程2退出后的返回值是 %d\n",(int)thread2_return );}return EXIT_SUCCESS; }/***線(xiàn)程1函數(shù)實(shí)現(xiàn) */void *thread1_func( void *arg ) {int i;struct argument *arg_thread1; // 接收傳遞過(guò)來(lái)的參數(shù)結(jié)構(gòu)體arg_thread1 = ( struct argument * )arg;for( i = 0; i < 3; i++){printf( "我來(lái)自線(xiàn)程1，傳遞給我的參數(shù)是 %d, %s\n", arg_thread1->num, arg_thread1->string);sleep(2); // 投入睡眠，調(diào)用其它線(xiàn)程}return (void *)123; }void *thread2_func( void *arg ) {int i;struct argument *arg_thread2; // 接收傳遞過(guò)來(lái)的參數(shù)結(jié)構(gòu)體arg_thread2 = ( struct argument * )arg;for( i = 0; i < 3; i++){printf( "我來(lái)自線(xiàn)程2，傳遞給我的參數(shù)是 %d, %s\n", arg_thread2->num, arg_thread2->string);sleep(2); // 投入睡眠，調(diào)用其它線(xiàn)程}return (void *)456; }?
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線(xiàn)程的最大特點(diǎn)是資源的共享性，但資源共享中的同步問(wèn)題是多線(xiàn)程編程的難點(diǎn)。linux下提供了多種方式來(lái)處理線(xiàn)程同步，最常用的是互斥鎖、條件變量和信號(hào)量。
一、互斥鎖(mutex)
通過(guò)鎖機(jī)制實(shí)現(xiàn)線(xiàn)程間的同步。
靜態(tài)分配：pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
動(dòng)態(tài)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(lái)等待而不是用來(lái)上鎖的。條件變量用來(lái)自動(dòng)阻塞一個(gè)線(xiàn)程，直到某特殊情況發(fā)生為止。通常條件變量和互斥鎖同時(shí)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(hù)的。線(xiàn)程在改變條件狀態(tài)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(xiàn)。條件變量是利用線(xiàn)程間共享的全局變量進(jìn)行同步的一種機(jī)制，主要包括兩個(gè)動(dòng)作：一個(gè)線(xiàn)程等待"條件變量的條件成立"而掛起；另一個(gè)線(xiàn)程使"條件成立"（給出條件成立信號(hào)）。條件的檢測(cè)是在互斥鎖的保護(hù)下進(jìn)行的。如果一個(gè)條件為假，一個(gè)線(xiàn)程自動(dòng)阻塞，并釋放等待狀態(tài)改變的互斥鎖。如果另一個(gè)線(xiàn)程改變了條件，它發(fā)信號(hào)給關(guān)聯(lián)的條件變量，喚醒一個(gè)或多個(gè)等待它的線(xiàn)程，重新獲得互斥鎖，重新評(píng)價(jià)條件。如果兩進(jìn)程共享可讀寫(xiě)的內(nèi)存，條件變量可以被用來(lái)實(shí)現(xiàn)這兩進(jìn)程間的線(xiàn)程同步。
靜態(tài)態(tài)初始化，pthread_cond_t cond = PTHREAD_COND_INITIALIER;
動(dòng)態(tài)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(xiàn)程的阻塞
int pthread_cond_destroy(pthread_cond_t *cond);
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三、信號(hào)量(sem)
如同進(jìn)程一樣，線(xiàn)程也可以通過(guò)信號(hào)量來(lái)實(shí)現(xiàn)通信，雖然是輕量級(jí)的。信號(hào)量函數(shù)的名字都以"sem_"打頭。線(xiàn)程使用的基本信號(hào)量函數(shù)有四個(gè)。
int sem_init (sem_t *sem , int pshared, unsigned int value);
這是對(duì)由sem指定的信號(hào)量進(jìn)行初始化，設(shè)置好它的共享選項(xiàng)(linux 只支持為0，即表示它是當(dāng)前進(jìn)程的局部信號(hào)量)，然后給它一個(gè)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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