如何使用互斥锁 [英] How to use mutex

问题描述

我应该在哪里放置互斥锁，以便线程可以交替打印?谢谢:D

执行一个创建两个线程的程序.线程将打印其ID(pthread_self)10次，然后停止.确保打印的ID始终交替(即A，B，A，B，...)

#include <stdio.h>
#include <pthread.h>

#define N 2
pthread_mutex_t mtx;
void* func (void* arg) {
    int i=0;
    int f=1;

    for(i=0; i<10; i++) {
        printf("%d%s%d\n",f ,":  ", (int)pthread_self());
        f++;
    }

    return NULL;
}

int main() {
    int i;
    pthread_t thr[N];
    pthread_mutex_init(&mtx, NULL);


    for(i=0; i<N; i++) {

        pthread_create(&thr[i], NULL, func, NULL);
    }

    for(i=0; i<N; i++) {
        pthread_join(thr[i], NULL);
    }
    pthread_mutex_destroy(&mtx);
    return 0;
}

解决方案

如果要获得可预测的有序输出A，B，A，B，A，B，则最适合使用的工具是单控制线程. /p>

要在两个线程上浪费时间，可以定义一个共享变量"turn"，该变量指示要打印哪些内容.每个线程都在等待条件变量，直到"turn"变量等于其自身为止.然后执行顺序任务，将"turn"变量设置为另一个线程并发出条件信号.

Where should i put the lock and unlock mutex in order for the threads to print alternatively? Thanks:D

Implement a program that creates two threads. The threads will print their ID (pthread_self) 10 times and then stop. Insure that the printed IDs alternate always (ie A, B, A, B, ...)

#include <stdio.h>
#include <pthread.h>

#define N 2
pthread_mutex_t mtx;
void* func (void* arg) {
    int i=0;
    int f=1;

    for(i=0; i<10; i++) {
        printf("%d%s%d\n",f ,":  ", (int)pthread_self());
        f++;
    }

    return NULL;
}

int main() {
    int i;
    pthread_t thr[N];
    pthread_mutex_init(&mtx, NULL);


    for(i=0; i<N; i++) {

        pthread_create(&thr[i], NULL, func, NULL);
    }

    for(i=0; i<N; i++) {
        pthread_join(thr[i], NULL);
    }
    pthread_mutex_destroy(&mtx);
    return 0;
}

解决方案

If you want the predictably ordered output A, B, A, B, A, B, the most appropriate tool to use is a single thread of control.

To do it wastefully with two threads, you can define a shared variable called "turn" which indicates whose turn it is to print something. Each thread waits on a condition variable until the "turn" variable is equal to itself. Then it carries out the sequential task, sets the "turn" variable to another thread and signals the condition.

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