pthread_mutex_init(&main_wait, NULL);什么意识
时间: 2024-04-12 11:12:29 浏览: 23
pthread_mutex_t *mutex, const pthread_mutexattr_t *attr)
The pthread_mutex_init() function initializes a mutex object specified by the mutex parameter. The attr parameter can be used to specify additional attributes for the mutex object, such as whether it is a recursive mutex or a shared mutex.
The function returns zero on success and a non-zero error code on failure. Once a mutex object has been initialized, it can be used to synchronize access to shared resources between multiple threads.
Note: This function is part of the POSIX threads (pthread) library, which is a standard for thread programming in Unix-like operating systems.
相关问题
pthread_mutex_init(&main_wait, NULL)中main_wait是什么
pthread_mutex_t *mutex, const pthread_mutexattr_t *attr);
The pthread_mutex_init() function initializes a mutex object referenced by the mutex parameter with the attributes specified by the attr parameter. If attr is NULL, the mutex is initialized with default attributes. The mutex object can be used for synchronization between threads.
The function returns 0 on success and an error number on failure.
编写一个2线程程序:主线程每秒输出依次偶数0,2,4,8等偶数,另外一个线程每秒一次输出1、2、3、5等奇数,并且通过同步方法实现总的输出结果为 0、1、2、3、4按大小顺序一次输出。(提示:可以使用互斥锁实现同步)//参考例题2:thread2.c#include <stdio.h>#include <unistd.h>#include <stdlib.h>#include <string.h>#include <pthread.h>#include <semaphore.h>void *thread_function(void *arg);pthread_mutex_t work_mutex; /* protects both work_area and time_to_exit */#define WORK_SIZE 1024char work_area[WORK_SIZE];int time_to_exit = 0;int main() { int res; pthread_t a_thread; void *thread_result; res = pthread_mutex_init(&work_mutex, NULL); if (res != 0) { perror("Mutex initialization failed"); exit(EXIT_FAILURE); } res = pthread_create(&a_thread, NULL, thread_function, NULL); if (res != 0) { perror("Thread creation failed"); exit(EXIT_FAILURE); } pthread_mutex_lock(&work_mutex); printf("Input some text. Enter 'end' to finish\n"); while(!time_to_exit) { fgets(work_area, WORK_SIZE, stdin); pthread_mutex_unlock(&work_mutex); while(1) { pthread_mutex_lock(&work_mutex); if (work_area[0] != '\0') { pthread_mutex_unlock(&work_mutex); sleep(1); } else { break; } } } pthread_mutex_unlock(&work_mutex); printf("\nWaiting for thread to finish...\n"); res = pthread_join(a_thread, &thread_result); if (res != 0) { perror("Thread join failed"); exit(EXIT_FAILURE); } printf("Thread joined\n"); pthread_mutex_destroy(&work_mutex); exit(EXIT_SUCCESS);}void *thread_function(void *arg) { sleep(1); pthread_mutex_lock(&work_mutex); while(strncmp("end", work_area, 3) != 0) { printf("You input %d characters\n", strlen(work_area) -1); work_area[0] = '\0'; pthread_mutex_unlock(&work_mutex); sleep(1); pthread_mutex_lock(&work_mutex); while (work_area[0] == '\0' ) { pthread_mutex_unlock(&work_mutex); sleep(1); pthread_mutex_lock(&work_mutex); } } time_to_exit = 1; work_area[0] = '\0'; pthread_mutex_unlock(&work_mutex); pthread_exit(0);}
这是一个参考程序,实现了一个主线程和一个子线程,主线程等待用户输入字符串,子线程每秒输出用户输入字符串的长度。你需要根据题目要求编写一个新的程序。
以下是一个参考答案,你可以参考一下:
```c
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
pthread_mutex_t mutex;
pthread_cond_t cond;
int even_num = 0;
int odd_num = 1;
int stop = 0;
void *even_thread(void *arg) {
while (!stop) {
pthread_mutex_lock(&mutex);
while (even_num <= odd_num) {
pthread_cond_wait(&cond, &mutex);
}
printf("%d ", even_num);
even_num -= 2;
pthread_cond_signal(&cond);
pthread_mutex_unlock(&mutex);
sleep(1);
}
pthread_exit(0);
}
void *odd_thread(void *arg) {
while (!stop) {
pthread_mutex_lock(&mutex);
while (odd_num <= even_num) {
pthread_cond_wait(&cond, &mutex);
}
printf("%d ", odd_num);
odd_num += 2;
pthread_cond_signal(&cond);
pthread_mutex_unlock(&mutex);
sleep(1);
}
pthread_exit(0);
}
int main() {
pthread_t even_tid, odd_tid;
pthread_mutex_init(&mutex, NULL);
pthread_cond_init(&cond, NULL);
pthread_create(&even_tid, NULL, even_thread, NULL);
pthread_create(&odd_tid, NULL, odd_thread, NULL);
pthread_join(even_tid, NULL);
pthread_join(odd_tid, NULL);
pthread_mutex_destroy(&mutex);
pthread_cond_destroy(&cond);
return 0;
}
```
程序中创建了两个线程,一个线程每秒输出一个偶数,另一个线程每秒输出一个奇数。两个线程通过互斥锁和条件变量来实现同步输出。具体实现方式是,每个线程输出一个数后,通过条件变量通知另一个线程输出下一个数。同时,线程在输出前会先判断当前应该输出的数是否合法,如果不合法则等待条件变量通知。最后,在主线程中调用 pthread_join 阻塞等待两个子线程结束,销毁互斥锁和条件变量并退出程序。