NPTL将最大线程数限制为65528吗? [英] NPTL caps maximum threads at 65528?

问题描述

下面的代码应该可以创建100,000个线程:

The following code is supposed to make 100,000 threads:

/* compile with:   gcc -lpthread -o thread-limit thread-limit.c */
/* originally from: http://www.volano.com/linuxnotes.html */

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

#define MAX_THREADS 100000
int i;

void run(void) {
  sleep(60 * 60);
}

int main(int argc, char *argv[]) {
  int rc = 0;
  pthread_t thread[MAX_THREADS];
  printf("Creating threads ...\n");
  for (i = 0; i < MAX_THREADS && rc == 0; i++) {
    rc = pthread_create(&(thread[i]), NULL, (void *) &run, NULL);
    if (rc == 0) {
      pthread_detach(thread[i]);
      if ((i + 1) % 100 == 0)
    printf("%i threads so far ...\n", i + 1);
    }
    else
    {
      printf("Failed with return code %i creating thread %i (%s).\n",
         rc, i + 1, strerror(rc));

      // can we allocate memory?
      char *block = NULL;
      block = malloc(65545);
      if(block == NULL)
        printf("Malloc failed too :( \n");
      else
        printf("Malloc worked, hmmm\n");
    }
  }
sleep(60*60); // ctrl+c to exit; makes it easier to see mem use
  exit(0);
}

这是在具有32GB RAM的64位计算机上运行的；已安装Debian 5.0，所有库存.

This is running on a 64bit machine with 32GB of RAM; Debian 5.0 installed, all stock.

• ulimit -s 512以减小堆栈大小
• /proc/sys/kernel/pid_max设置为1,000,000(默认情况下，上限为32k pid).
• ulimit -u 1000000以增加最大进程(一点也不重要)
• /proc/sys/kernel/threads-max设置为1,000,000(默认情况下，完全没有设置)

运行此命令会吐出以下内容:

Running this spits out the following:

65500 threads so far ...
Failed with return code 12 creating thread 65529 (Cannot allocate memory).
Malloc worked, hmmm

我当然不会用完公羊.我什至可以启动多个同时运行的程序，它们都启动其65k线程.

I'm certainly not running out of ram; I can even launch several more of these programs all running at the same time and they all start their 65k threads.

((请避免建议我不要尝试启动100,000个以上的线程.这是对应该可以正常工作的测试).我当前的基于epoll的服务器始终具有大约200k +的连接，而各种论文都表明线程可能只是一个更好的选择--谢谢:))

(Please refrain from suggesting I not try to launch 100,000+ threads. This is simple testing of something which should work. My current epoll-based server has roughly 200k+ connections at all times and various papers would suggest that threads just might be a better option. - Thanks :) )

推荐答案

pilcrow对/proc/sys/vm/max_map_count的提及是正确的；增大该值将允许打开更多线程；不确定所涉及的确切公式，但是1mil +的值允许大约300k +线程.

pilcrow's mention of /proc/sys/vm/max_map_count is right on track; raising this value allows more threads to be opened; not sure of the exact formula involved, but a 1mil+ value allows for some 300k+ threads.

(对于尝试使用100k +线程的其他人，请查看 pthread_create的mmap 问题...当内存不足时，使新线程变得非常慢.)

(For anyone else experimenting with 100k+ threads, do look at pthread_create's mmap issues... making new threads gets really slow really fast when lower memory is used up.)

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