c - Linux 2.6.30 uClibc 0.9.29 pthread_create 两个线程只安装一个

Question

线程创建绝对奇怪的情况，这里是测试代码:

#include <stdint.h>         /* C99 types */
#include <stdbool.h>        /* bool type */
#include <stdio.h>          /* printf, fprintf, snprintf, fopen, fputs */

#include <string.h>         /* memset */
#include <signal.h>         /* sigaction */
#include <time.h>           /* time, clock_gettime, strftime, gmtime */
#include <sys/time.h>       /* timeval */
#include <unistd.h>         /* getopt, access */
#include <stdlib.h>         /* atoi, exit */
#include <errno.h>          /* error messages */
#include <math.h>           /* modf */
#include <assert.h>

#include <sys/socket.h>     /* socket specific definitions */
#include <netinet/in.h>     /* INET constants and stuff */
#include <arpa/inet.h>      /* IP address conversion stuff */
#include <netdb.h>          /* gai_strerror */

#include <pthread.h>
void thread_up(void) {
        printf("thread ....\n");
        int loop=0;
        while(loop<=7)
        {
                printf("loop...\n");
                sleep(10);
                loop++;
        }
        printf("Exit loop\n");
}
int main()
{
pthread_t thrid_up=0;

        int i = pthread_create( &thrid_up, NULL, (void * (*)(void *))thread_up, NULL);
        if (i != 0) {
                printf("ERROR: [main] impossible to create upstream thread\n");
                exit(1);
        }
        while(1)
        {
                sleep(10);
        }

}

该代码在 ps 命令上产生以下输出(在 ./test& 启动之后):

30214 root        704 S   ./test
30215 root        704 S   ./test
30216 root        704 S   ./test

有什么提示吗？

Answer 1

只是一个注释。 man 7 pthreads

LinuxThreads

The notable features of this implementation are the following:

• In addition to the main (initial) thread, and the threads that the program creates using pthread_create(3), the implementation creates a "manager" thread. This thread handles thread creation and termination. (Problems can result if this thread is inadvertently killed.)
• Threads do not share process IDs. (In effect, LinuxThreads threads are implemented as processes which share more information than usual, but which do not share a common process ID.) LinuxThreads threads (including the manager thread) are visible as separate processes using ps(1).

不管这个文档是关于 Glibc 的，你的 uClibc 版本可能使用 LinuxThreads 作为 pthread“后端”。因此从技术上讲，您的代码可能会创建三个调度实体。

但首先您确实必须确保 ps 打印线程，而不仅仅是进程，并仔细检查在探测期间是否只有一个已启动的程序实例。

附言您还应该检查您的 uClibc 是否真的使用 LinuxThreads 而不是 NPTL。因此 IMO 观察到三个线程的机会是存在的，但它非常小。