pthread参数的值已更改 [英] pthread argument's value changed

问题描述

这是我的主要功能，其中 NO_RECIEVERS = 3 .我正在尝试使用我发送的 i 的值来区分编写者线程和读取者线程.

This is my main function, where NO_RECIEVERS = 3. I am trying to differentiate between the writer and reader threads using the value of i that i send.

int main() {
    int status, i;
    pthread_t tr[NO_RECIEVERS], tw[NO_SENDERS], bd;
    i=1;

    for(i=1; i<=NO_SENDERS; i++) {
        pthread_create(&tw[i-1], NULL, writer, &i);
    }

    for(i=1; i<=NO_RECIEVERS; i++) {
        printf("%d\n", i);
        pthread_create(&tr[i-1], NULL, reader, &i);
    }

    pthread_create(&bd, NULL ,daemon_thread, NULL);

    for(i=1; i<=NO_SENDERS; i++) {
        pthread_join(tw[i-1], NULL);
    }

    for(i=1; i<=NO_RECIEVERS; i++) {
        pthread_join(tr[i-1], NULL);
    }
    pthread_join(bd, NULL);

    return 0;
}

我的阅读器功能如下

void* reader(void *val) {
    int ret, fd, id;
    struct mssg data;
    id = *(int*)val;
    printf("id: %d %d\n", id, *(int*)val);
    while(1) {

但是此函数似乎正在创建ID为一些随机值的线程..我得到了这样的日志

But this function seems to be creating threads with id some random values.. i get a log like this

...
id: 1 1
...
id: 2 2
...
id: 1 1

下次我得到..它是随机的

Next time i get.. its kind of random

...
id: 1 1
...
2
id: 2 2
...
id: 4 4

但是我分配的值仅限于1,2,3

But the values i am assigning are limited to 1,2,3

推荐答案

您将& i 传递给了您创建的所有线程...因此，每个线程都有一个指向 i ，然后当他们取消引用以读取 i 的值时，所读取的就是当时的 i .

You passed &i to all the threads you created... so each one has a pointer to i, and when they dereference that to read the value of i, and what they read is whatever i happens to be at the time.

如果要在 pthread_create 时传递 i 的值，我建议 malloc()占用一小段内存，将 i 复制到其中，然后将已分配的内容传递给线程(线程可以读取该内容，并可以将 free()传递给内存.)或其他任何提供<为创建的每个线程在不同位置放置code> i .

If you want to pass the value of i at the time of the pthread_create, I suggest malloc() a small piece of memory, copy i to it and pass the malloced thing to the thread (which can read it and the free() the memory. Or any other method that provides a copy of i in a different location for each thread created.

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