一、互斥鎖

1. 函數原型

pthread_mutex_init(pthread_mutex_t *restrict mutex, const pthread_mutexattr_t *restrict attr);  
pthread_mutex_destroy(pthread_mutex_t *mutex); 

分析：

• pthread_mutex_t 類型，其本質是一個結構體，為簡化理解，應用時可忽略其實現細節，簡單當成整數看待。
• pthread_mutex_t??mutex：變量mutex只有兩種取值0、1；

函數一參數1：傳出參數，調用時應傳&mutex

• restrict關鍵字：只用于限制指針，告訴編譯器，所有修改該指針指向內存中內容的操作，只能通過本指針完成。不能通過除本指針以外的其他變量或指針修改。

函數一參數2：互斥屬性。是一個傳入參數，通常傳NULL，選用默認屬性(線程間共享).

• 靜態初始化：如果互斥鎖mutex是靜態分配的(定義在全局，或加了static關鍵字修飾），可以直接使用宏進行初始化。pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
• 動態初始化：局部變量應采用動態初始化, pthread_mutex_init(&mutex, NULL);
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2. 函數原型：

pthread_mutex_lock(pthread_mutex_t *mutex);
pthread_mutex_unlock(pthread_mutex_t *mutex);                                        

分析：

• 函數1：沒有被上鎖，當前線程會將這把鎖鎖上；被鎖上了，當前線程阻塞，鎖被打開之后，線程解除阻塞（加鎖。可理解為將mutex--（或-1））。
• 函數2：同時將阻塞在該鎖上的所有線程全部喚醒解鎖(可理解為將mtex++（或+1)).

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二、代碼清單

1. 測試代碼

#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>void *tfn(void *arg)
{srand(time(NULL));while(1) {printf("hello ");sleep(rand() % 3); //模擬長時間操作共享資源，導致cpu易主，產生與時間有關的錯誤printf("word\n");sleep(rand() % 3);}return NULL;
}int main()
{pthread_t tid;srand(time(NULL));pthread_create(&tid, NULL, tfn, NULL);while(1) {printf("HELLO ");sleep(rand() % 3);printf("WORLD\n");sleep(rand() % 3);}return 0;
}

輸出結果?

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2. 測試代碼?

#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>void *tfn(void *arg)
{srand(time(NULL));while(1) {printf("hello ");sleep(rand() % 3); //模擬長時間操作共享資源，導致cpu易主，產生與時間有關的錯誤printf("word\n");sleep(rand() % 3);}return NULL;
}int main()
{pthread_t tid;srand(time(NULL));pthread_create(&tid, NULL, tfn, NULL);while(1) {printf("HELLO ");sleep(rand() % 3);printf("WORLD\n");sleep(rand() % 3);}return 0;
}

輸出結果

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#include<pthread.h>
#include<stdlib.h>
#include<unistd.h>pthread_mutex_t mutex;void* tfn(void* arg)
{srand(time(NULL));while (1) {pthread_mutex_lock(&mutex);printf("hello ");sleep(rand() % 3);  //模擬長時間共享資源，導致cpu易主。產生于時間有關的錯誤 printf("word\n");pthread_mutex_unlock(&mutex);sleep(rand() % 3);}return NULL;
}int main()
{pthread_t tid;srand(time(NULL));pthread_mutex_init(&mutex, NULL);pthread_create(&tid, NULL, tfn, NULL);  //mutex == 1while (1) {pthread_mutex_lock(&mutex);printf("HELLO ");sleep(rand() % 3);printf("WORLD\n");pthread_mutex_unlock(&mutex);sleep(rand() % 3);}pthread_mutex_destroy(&mutex);return 0;
}

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#include<stdlib.h>
#include<unistd.h>
#include<pthread.h>
#include<errno.h>
#include<stdio.h>pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t *mp;void add(void)
{int i = 10;i = i + 1;i = i + 2;i = i + 3;printf("sum is %d\n", i);
}void thread1(void)
{{pthread_mutex_lock(mp);add();pthread_mutex_unlock(mp);sleep(1);}
}
void thread2(void)
{{pthread_mutex_lock(mp);add();pthread_mutex_unlock(mp);sleep(2);}
}int main(void)
{pthread_t id1, id2;int ret;mp = (pthread_mutex_t*)malloc(sizeof(pthread_mutex_t));pthread_mutex_init(mp, NULL);ret = pthread_create(&id1, NULL, (void*)thread1, NULL);if(ret < 0){perror("pthread_create id1");exit(1);}ret = pthread_create(&id2, NULL, (void*)thread2, NULL);if(ret <0){perror("pthread_create id2");exit(1);}pthread_join(id1, NULL);    pthread_join(id2, NULL);    pthread_mutex_destroy(mp);free(mp);return 0;
}	

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