libuv之线程池的坑，注意避免

在使用libuv线程池时遇到一个坑，查了很久发现不是我们产品项目的问题，记录一下！

libuv线程池的使用简单例子如下：

uv_loop_t *loop;

loop = uv_default_loop();

uv_work_t req;
int size = 10240;
req.data = (void*) &size;

uv_queue_work(loop, &req, fake_download, after);

这样没问题，但是有一种情况会出问题，

主进程使用了uv_queue_work之后， fork得到一个子进程，在子进程中再次使用uv_queue_work，无效，工作回调函数fake_download不会执行，

原因未知，请有了解的给我发信息，万分感谢！

附上我的测试代码

#include "uv.h"
#include "stdio.h"

uv_loop_t *loop;
uv_async_t async;


void hare(void *arg)
{
    int tracklen = *((int *) arg);
    while (tracklen) {
        tracklen--;
        sleep(1);
        fprintf(stderr, "Hare ran another step\n");
    }
    fprintf(stderr, "Hare done running!\n");
}

void work_cb1(uv_work_t *req) {
    int size = *((int*) req->data);
    fprintf(stderr, "work_cb1 \n");
}
void work_cb2(uv_work_t *req, int status) {
    fprintf(stderr, "work_cb2   \n");
}



void print_progress(uv_async_t *handle) {
    double percentage = *((double*) handle->data);
    fprintf(stderr, "Downloaded %.2f%%\n", percentage);
}

void after(uv_work_t *req, int status) {
    fprintf(stderr, "Download complete\n");
    uv_close((uv_handle_t*) &async, NULL);
}

void fake_download(uv_work_t *req) {
    int size = *((int*) req->data);
    int downloaded = 0;
    double percentage;
    while (downloaded < size) {
        percentage = downloaded*100.0/size;
        async.data = (void*) &percentage;
        uv_async_send(&async);

        sleep(1);
        downloaded += (200+random())%1000; // can only download max 1000bytes/sec,
                                           // but at least a 200;
        //fprintf(stderr, "---- downloaded:%d\n", downloaded);
        if(downloaded < 600)
        {
                pid_t pid,pc;
                pid = fork();
                if(pid == -1)
                {
                        printf("fork err\n");
                }else if(pid == 0)
                {
                        fprintf(stderr, "fork child process ...\n");
                        uv_work_t req;
                        int size = 10240;
                        req.data = (void*) &size;
                        fprintf(stderr, "fork child process ...1\n");
                        uv_queue_work(loop, &req, work_cb1, work_cb2); //fork的子进程再使用
                        fprintf(stderr, "fork child process ...2\n");
                }else
                {
                }
        }


     }
}
int main()
{

        loop = uv_default_loop();

    uv_work_t req;
    int size = 10240;
    req.data = (void*) &size;

    uv_async_init(loop, &async, print_progress);
    uv_queue_work(loop, &req, fake_download, after); //主进程先使用一次

    return uv_run(loop, UV_RUN_DEFAULT);

  return 0;
}