linux_POSIX线程

原创：https://blog.csdn.net/ndzjx/article/details/88965748

线程：在一个程序中的多个执行路线。更准确一点：线程是一个进程内部的一个控制序列。

线程有关的函数库，函数名都以pthread_开头，必须定义宏_REENTRANT，包含头文件pthread.h，编译时要用选项-lpthread来链接线程库。

_REENTRANT宏做了三件事：

1：对部分函数重新定义可安全重入的版本，如gethostbyname变为gethostbyname_r

2：stdio.h中原以宏的形式实现的一些函数将变成可安全重入的函数。

3：errno.h中定义的errno变量将成为一个函数调用。

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创建线程

int pthread_create(pthread_t *thread, pthread_attr_t *attr, void *(*start_routine)(void *), void *arg);

void pthread_exit(void *retval)

线程通过pthread_exit函数终止执行，如同进程调用exit，注意，绝不能用它返回一个指向局部变量的指针。

等待线程：

int pthread_join(pthread_t th, void **thread_return);

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

void *thread_function(void *arg);

char message[] = "Hello World";

int main() {
    int res;
    pthread_t a_thread;
    void *thread_result;
    res = pthread_create(&a_thread, NULL, thread_function, (void *)message);
    if (res != 0) {
        perror("Thread creation failed");
        exit(EXIT_FAILURE);
    }
    printf("Waiting 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, it returned %s\n", (char *)thread_result);
    printf("Message is now %s\n", message);
    exit(EXIT_SUCCESS);
}

void *thread_function(void *arg) {
    printf("thread_function is running. Argument was %s\n", (char *)arg);
    sleep(3);
    strcpy(message, "Bye!");
    pthread_exit("Thank you for the CPU time");
}

信号量：

#include <semaphore.h>

int sem_init(sem_t *sem, int pshared, unsigned int value)

int sem_wait(sem_t *sem); // 信号量减1

int sem_post(sem_t *sem); // 信号量加1

int sem_destroy(sem_t *sem);

互斥量：

#include <pthread.h>

int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *mutexattr);

int pthread_mutex_lock(pthread_mutex_t *mutex);

int pthread_mutex_unlock(pthread_mutex_t *mutex);

int pthread_mutex_destroy(pthread_mutex_t *mutex);

线程的属性：

int pthread_attr_init (pthread_attr_t *__attr)
int pthread_attr_destroy (pthread_attr_t *__attr)
int pthread_attr_getstacksize (。。。。)

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

void *thread_function(void *arg);

char message[] = "Hello World";
int thread_finished = 0;

int main() {
    int res;
    pthread_t a_thread;
    void *thread_result;
    pthread_attr_t thread_attr;

    res = pthread_attr_init(&thread_attr);
    if (res != 0) {
        perror("Attribute creation failed");
        exit(EXIT_FAILURE);
    }
    res = pthread_attr_setdetachstate(&thread_attr, PTHREAD_CREATE_DETACHED);
    if (res != 0) {
        perror("Setting detached attribute failed");
        exit(EXIT_FAILURE);
    }
    res = pthread_create(&a_thread, &thread_attr, thread_function, (void *)message);
    if (res != 0) {
        perror("Thread creation failed");
        exit(EXIT_FAILURE);
    }
    (void)pthread_attr_destroy(&thread_attr);
    while(!thread_finished) {
        printf("Waiting for thread to say it's finished...\n");
        sleep(1);
    }
    printf("Other thread finished, bye!\n");
    exit(EXIT_SUCCESS);
}

void *thread_function(void *arg) {
    printf("thread_function is running. Argument was %s\n", (char *)arg);
    sleep(4);
    printf("Second thread setting finished flag, and exiting now\n");
    thread_finished = 1;
    pthread_exit(NULL);
}

取消一个线程：

int pthread_cancel(pthread_t thread);

int pthread_setcanelstate(int state, int *oldstate);

int pthread_setcanceltype(int type, int *oldtype);

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

void *thread_function(void *arg);

int main() {
    int res;
    pthread_t a_thread;
    void *thread_result;

    res = pthread_create(&a_thread, NULL, thread_function, NULL);
    if (res != 0) {
        perror("Thread creation failed");
        exit(EXIT_FAILURE);
    }
    sleep(3);
    printf("Canceling thread...\n");
    res = pthread_cancel(a_thread);
    if (res != 0) {
        perror("Thread cancelation failed");
        exit(EXIT_FAILURE);
    }
    printf("Waiting for thread to finish...\n");
    res = pthread_join(a_thread, &thread_result);
    if (res != 0) {
        perror("Thread join failed");
        exit(EXIT_FAILURE);
    }
    exit(EXIT_SUCCESS);
}

void *thread_function(void *arg) {
    int i, res, j;
    res = pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
    if (res != 0) {
        perror("Thread pthread_setcancelstate failed");
        exit(EXIT_FAILURE);
    }
    res = pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, NULL);
    if (res != 0) {
        perror("Thread pthread_setcanceltype failed");
        exit(EXIT_FAILURE);
    }
    printf("thread_function is running\n");
    for(i = 0; i < 10; i++) {
        printf("Thread is still running (%d)...\n", i);
        sleep(1);
    }
    pthread_exit(0);
}

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