读/dev/urandom是线程安全的吗? [英] Is reading /dev/urandom thread-safe?

问题描述

这是代码:

如果没有，我如何使其成为线程安全的?

解决方案

只要函数的每次执行都在其自己的线程中(即，不共享局部变量number，urandom，bytes_read)在线程之间)，我看不到任何线程安全问题.每个线程将在/dev/urandom中拥有自己的文件描述符.可以同时从多个进程中打开/dev/urandom，这没关系.

顺便说一句，/dev/urandom可能无法打开，您的代码应该处理它.某些原因是:用尽了可用的文件描述符； /dev没有正确安装(尽管在这种情况下，您有更大的问题)；您的程序正在特殊的chroot中运行，它拒绝访问任何设备；等

This is the code:

  unsigned int number;
  FILE* urandom = fopen("/dev/urandom", "r");
  if (urandom) {
    size_t bytes_read = fread(&number, 1, sizeof(number), urandom);
    DCHECK(bytes_read == sizeof(number));
    fclose(urandom);
  } else {
    NOTREACHED();
  }

If not, how do I make it thread-safe?

解决方案

As long as each execution of the function is in its own thread (i.e., the local variables number, urandom, bytes_read are not shared between threads), I don't see any thread-safety problems. Each thread will then have its own file descriptor into /dev/urandom. /dev/urandom can be opened simultaneously from multiple processes, so that's okay.

By the way, /dev/urandom can fail to open, and your code should deal with it. Some causes are: running out of available file descriptors; /dev not properly mounted (although in this case you have bigger problems); your program is being run in a special chroot which denies access to any devices; etc.

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