Lack of PID uniqueness in container environments makes prometheus_multiproc difficult to use

In environments where each container is running in its own PID namespace, multiple instances of the same container will quickly result in (silently) conflicting file names as any my-favorite-server.py process will likely have the same low, single or double digit PID in each of the multiple containers. As a result, the different processes will attempt to mmap the same file in the shared multiprocess metric directory, and various scary errors that aren't always easy to understand the root cause will occur.

It would be beneficial if something in addition to the PID was used to help ensure uniqueness across the files in the PROMETHEUS_MULTIPROC_DIR, or if a string could be passed in at initialization time to be embedded in the file names, such as a container or pod name, or another value determined by the application.

首先跟踪 prometheus_multiproc 如何为 PROMETHEUS_MULTIPROC_DIR 中的文件命名，以及它如何根据进程 ID 推导名称。比较多个共享该目录的容器之间的行为，然后确定适合该 issue 的唯一性机制或初始化值。当并发容器进程不再 mmap 发生冲突的文件，并且相关失败情况已由测试覆盖时，即表示完成。