在 Linux 系統(tǒng)中，進程和線程是兩種重要的并發(fā)執(zhí)行單元。本文將詳細介紹它們的區(qū)別、使用場景、以及多線程編程中的關鍵API和示例代碼。

進程與線程的區(qū)別

進程

• 進程是程序運行的一個實例，承擔分配系統(tǒng)資源的基本單位。
• 每個進程都有獨立的地址空間，一個進程崩潰不會影響其他進程。
• 進程的創(chuàng)建和切換消耗較多資源。

線程

• 線程是進程中的一個執(zhí)行路徑，是CPU調度的基本單位。
• 線程共享進程的地址空間，但每個線程有自己的堆棧和局部變量。
• 線程的創(chuàng)建和切換開銷較小。
• 如果一個線程崩潰，會導致整個進程崩潰。

使用線程的理由

1. 節(jié)省資源：創(chuàng)建進程需要分配獨立的地址空間，建立多個數據表來維護其代碼段、數據段和堆棧段，這種方式十分昂貴。線程共享同一進程的地址空間和大部分數據，啟動一個線程比啟動一個進程要快很多。一個進程的開銷大約是一個線程的30倍。
2. 方便的通信機制：不同進程之間的數據傳遞需要通過通信機制，如管道、信號等，這種方式耗時且復雜。而線程共享進程的數據空間，數據共享非常方便和快捷，但需要注意數據同步的問題。

多線程開發(fā)及API

多線程開發(fā)主要包含三點：線程、互斥鎖、條件變量。以下是具體的操作和API介紹：

線程操作

線程的創(chuàng)建

#include <pthread.h>
int pthread_create(pthread_t *restrict tidp, const pthread_attr_t *restrict attr, void *(*start_rtn)(void *), void *restrict arg);
// 返回：若成功返回0，否則返回錯誤編號

線程的獲取和比較

#include <pthread.h>
pthread_t pthread_self(void);

線程的等待

#include <pthread.h>
int pthread_join(pthread_t thread, void **rval_ptr);
// 參數：
// pthread_t thread：等待的線程
// void **rval：線程退出狀態(tài)的收回，NULL表示不收回

線程的退出

#include <pthread.h>
int pthread_exit(void *rval_ptr);

線程的創(chuàng)建、退出、等待示例

#include <stdio.h>
#include <pthread.h>void *func1(void *arg)
{static int ret = 10;printf("t1:%ld thread is created\n", (unsigned long)pthread_self());printf("t1: parameter is %d\n", *((int *)arg));pthread_exit((void*)&ret); // 線程退出
}int main()
{int ret;int param = 100;int *pret = NULL;pthread_t t1;ret = pthread_create(&t1, NULL, func1, (void*)&param); // 創(chuàng)建線程if(ret == 0){printf("main: create t1 success\n");}printf("main: %ld\n", (unsigned long)pthread_self()); // 獲取線程IDpthread_join(t1, (void**)&pret); // 等待線程退出printf("main: t1 quit with %d\n", *pret);return 0;
}

傳入一個結構體的線程創(chuàng)建示例

#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>struct data
{int a;char *s;
};void *func1(void *arg)
{static char *x = "t1 run out";struct data *temp;temp = (struct data*)arg;printf("t1:%ld pthread is created\n", (unsigned long)pthread_self());printf("t1: %d\n", temp->a);printf("t1: %s\n", temp->s);pthread_exit((void*)x);
}int main()
{int ret;pthread_t t1;char *pret = NULL;struct data *p = (struct data*)malloc(sizeof(struct data));p->a = 1;p->s = "xiancheng";ret = pthread_create(&t1, NULL, func1, (void*)p);if(ret == 0){printf("main: create t1 success\n");}printf("main: %ld\n", (unsigned long)pthread_self());pthread_join(t1, (void**)&pret);printf("main: t1 quit with %s\n", pret);free(p);return 0;
}

線程共享空間驗證示例

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>int g_data = 10;void *func1(void *arg)
{printf("t1:%ld thread is created\n", (unsigned long)pthread_self());printf("t1: parameter is %d\n", *((int*)arg));while(1){printf("%d\n", g_data++);sleep(1);if(g_data == 3){pthread_exit(NULL);}}
}void *func2(void *arg)
{printf("t2:%ld thread is created\n", (unsigned long)pthread_self());printf("t2: parameter is %d\n", *((int*)arg));while(1){printf("%d\n", g_data++);sleep(1);}
}int main()
{int ret;int param = 100;pthread_t t1;pthread_t t2;ret = pthread_create(&t1, NULL, func1, (void*)&param);if(ret == 0){printf("main: create t1 success\n");}ret = pthread_create(&t2, NULL, func2, (void*)&param);if(ret == 0){printf("main: create t2 success\n");}printf("main: %ld\n", (unsigned long)pthread_self());while(1){printf("%d\n", g_data++);sleep(1);} pthread_join(t1, NULL);pthread_join(t2, NULL);return 0;
}

互斥鎖（Mutex）

互斥鎖API

創(chuàng)建及銷毀互斥鎖

#include <pthread.h>
int pthread_mutex_init(pthread_mutex_t *restrict mutex, const pthread_mutexattr_t *restrict attr);
int pthread_mutex_destroy(pthread_mutex_t *restrict mutex);

加鎖及解鎖

#include <pthread.h>
int pthread_mutex_lock(pthread_mutex_t *restrict mutex);
int pthread_mutex_trylock(pthread_mutex_t *restrict mutex);
int pthread_mutex_unlock(pthread_mutex_t *restrict mutex);

使用互斥鎖的示例

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>int g_data = 0;
pthread_mutex_t mutex; // 定義鎖void *func1(void *arg)
{pthread_mutex_lock(&mutex); // 加鎖for(int i = 0; i < 5; i++){printf("t1: %ld thread is created\n", (unsigned long)pthread_self());printf("t1: parameter is %d\n", *((int*)arg));sleep(1);}pthread_mutex_unlock(&mutex); // 解鎖
}void *func2(void *arg)
{pthread_mutex_lock(&mutex);for(int i = 0; i < 5; i++){printf("t2: %ld thread is created\n", (unsigned long)pthread_self());printf("t2: parameter is %d\n", *((int*)arg));sleep(1);}pthread_mutex_unlock(&mutex);
}void *func3(void *arg)
{pthread_mutex_lock(&mutex);for(int i = 0; i < 5; i++){printf("t3: %ld thread is created\n", (unsigned long)pthread_self());printf("t3: parameter is %d\n", *((int*)arg));sleep(1);}pthread_mutex_unlock(&mutex);
}int main()
{int ret;int param = 100;pthread_t t1;pthread_t t2;pthread_t t3;pthread_mutex_init(&mutex, NULL); // 初始化鎖ret = pthread_create(&t1, NULL, func1, (void*)&param);if(ret == 0){printf("main: create t1 success\n");}ret = pthread_create(&t2, NULL, func2, (void*)&param);if(ret == 0){printf("main: create t2 success\n");}ret = pthread_create(&t3, NULL, func3, (void*)&param);if(ret == 0){printf("main: create t3 success\n");}printf("main: %ld\n", (unsigned long)pthread_self());pthread_join(t1, NULL);pthread_join(t2, NULL);pthread_join(t3, NULL);pthread_mutex_destroy(&mutex); // 收回鎖return 0;
}

互斥鎖限制共享資源的訪問示例

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>int g_data = 0;
pthread_mutex_t mutex;void *func1(void *arg)
{printf("t1: %ld pthread is created\n", (unsigned long)pthread_self());printf("t1: parameter is %d\n", *((int*)arg));while(1){pthread_mutex_lock(&mutex);printf("%d\n", g_data++);sleep(1);if(g_data == 3){pthread_mutex_unlock(&mutex);pthread_exit(NULL);}}
}void *func2(void *arg)
{printf("t2: %ld pthread is created\n", (unsigned long)pthread_self());printf("t2: parameter is %d\n", *((int*)arg));while(1){printf("%d\n", g_data);pthread_mutex_lock(&mutex);g_data++;pthread_mutex_unlock(&mutex);sleep(1); }
}int main()
{int ret;int param = 100;pthread_t t1;pthread_t t2;pthread_mutex_init(&mutex, NULL);ret = pthread_create(&t1, NULL, func1, (void*)&param);if(ret == 0){printf("main: create t1 success\n");}ret = pthread_create(&t2, NULL, func2, (void*)&param);if(ret == 0){printf("main: create t2 success\n");}printf("main: %ld\n", (unsigned long)pthread_self());pthread_join(t1, NULL);pthread_join(t2, NULL);pthread_mutex_destroy(&mutex);return 0;
}

死鎖示例

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>pthread_mutex_t mutex;
pthread_mutex_t mutex2;void *func1(void *arg)
{pthread_mutex_lock(&mutex);sleep(1);pthread_mutex_lock(&mutex2);for(int i = 0; i < 5; i++){printf("t1: %ld\n", (unsigned long)pthread_self());printf("t1: parameter is %d\n", *((int *)arg));sleep(1);}pthread_mutex_unlock(&mutex);pthread_mutex_unlock(&mutex2);
}void *func2(void *arg)
{pthread_mutex_lock(&mutex2);sleep(1);pthread_mutex_lock(&mutex);for(int i = 0; i < 5; i++){printf("t2: %ld\n", (unsigned long)pthread_self());printf("t2: parameter is %d\n", *((int *)arg));sleep(1);}pthread_mutex_unlock(&mutex2);pthread_mutex_unlock(&mutex);
}void *func3(void *arg)
{pthread_mutex_lock(&mutex);for(int i = 0; i < 5; i++){printf("t3: %ld\n", (unsigned long)pthread_self());printf("t3: parameter is %d\n", *((int *)arg));sleep(1);}pthread_mutex_unlock(&mutex);
}int main()
{int ret;int param = 100;pthread_t t1;pthread_t t2;pthread_t t3;pthread_mutex_init(&mutex, NULL);pthread_mutex_init(&mutex2, NULL);ret = pthread_create(&t1, NULL, func1, (void*)&param);if(ret == 0){printf("main: create t1 success\n");}ret = pthread_create(&t2, NULL, func2, (void*)&param);if(ret == 0){printf("main: create t2 success\n");}ret = pthread_create(&t3, NULL, func3, (void*)&param);if(ret == 0){printf("main: create t3 success\n");}printf("main: %ld\n", (unsigned long)pthread_self());pthread_join(t1, NULL);pthread_join(t2, NULL);pthread_join(t3, NULL);pthread_mutex_destroy(&mutex);pthread_mutex_destroy(&mutex2);return 0;
}

條件變量實現線程同步

條件變量API

創(chuàng)建及銷毀條件變量

#include <pthread.h>
int pthread_cond_init(pthread_cond_t *restrict cond, const pthread_condattr_t *restrict attr);
int pthread_cond_destroy(pthread_cond_t cond);

等待

#include <pthread.h>
int pthread_cond_wait(pthread_cond_t *restrict cond, pthread_mutex_t *restrict mutex);
int pthread_cond_timedwait(pthread_cond_t *restrict cond, pthread_mutex_t *restrict mutex, const struct timespec *restrict timeout);

觸發(fā)

#include <pthread.h>
int pthread_cond_signal(pthread_cond_t *restrict cond);
int pthread_cond_broadcast(pthread_cond_t cond);

使用條件變量的示例

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <stdlib.h>int g_data = 0;
pthread_mutex_t mutex;
pthread_cond_t cond;void *func1(void *arg)
{static int cnt = 10;printf("t1: %ld pthread is created\n", (unsigned long)pthread_self());printf("t1: parameter is %d\n", *((int*)arg));while(1){pthread_cond_wait(&cond, &mutex); // 等待if(g_data == 3){printf("t1 run=========================\n");}printf("t1: %d\n", g_data);g_data = 0;sleep(1);if(cnt++ == 10){exit(1);}}
}void *func2(void *arg)
{printf("t2: %ld pthread is created\n", (unsigned long)pthread_self());printf("t2: parameter is %d\n", *((int*)arg));while(1){printf("t2: %d\n", g_data);pthread_mutex_lock(&mutex);printf("%d\n", g_data++);if(g_data == 3){pthread_cond_signal(&cond); // 觸發(fā)}pthread_mutex_unlock(&mutex);sleep(1);}
}int main()
{int ret;int param = 100;pthread_t t1;pthread_t t2;pthread_cond_init(&cond, NULL);pthread_mutex_init(&mutex, NULL);ret = pthread_create(&t1, NULL, func1, (void *)&param);if(ret == 0){printf("main: create t1 success\n");}ret = pthread_create(&t2, NULL, func2, (void *)&param);if(ret == 0){printf("main: create t2 success\n");}pthread_join(t1, NULL);pthread_join(t2, NULL);pthread_mutex_destroy(&mutex);pthread_cond_destroy(&cond);return 0;
}

通過上述示例和API的講解，本文詳細介紹了Linux下進程與線程的區(qū)別、多線程開發(fā)的基本操作以及常見問題和解決方案。希望能夠幫助大家更好地理解和使用多線程編程。