Python子进程返回错误的退出代码

我编写了一个脚本来启动一些并行运行的进程(简单的单元测试)。可以了 N 具有的作业 num_workers 一次并行处理。

我的第一个实现以批处理的方式运行流程 num\u工人 而且似乎工作得很好(我使用了 false 命令测试行为)

import subprocess

errors = 0
num_workers = 10
N = 100
i = 0

while i < N:
    processes = []
    for j in range(i, min(i+num_workers, N)):
        p = subprocess.Popen(['false'])
        processes.append(p)

    [p.wait() for p in processes]
    exit_codes = [p.returncode for p in processes]

    errors += sum(int(e != 0) for e in exit_codes)
    i += num_workers

print(f"There were {errors}/{N} errors")

然而,这些测试花费的时间并不相等,所以我有时会等待一个缓慢的测试完成。因此,我重写了它,以便在任务完成时继续分配任务

import subprocess
import os


errors = 0
num_workers = 40
N = 100
assigned = 0
completed = 0
processes = set()

while completed < N:
    if assigned < N:
        p = subprocess.Popen(['false'])
        processes.add((assigned, p))
        assigned += 1
    if len(processes) >= num_workers or assigned == N:
        os.wait()

    for i, p in frozenset(processes):
        if p.poll() is not None:
            completed += 1
            processes.remove((i, p))
            err = p.returncode
            print(i, err)
            if err != 0:
                errors += 1

print(f"There were {errors}/{N} errors")

然而,这会在最后几个过程中产生错误的结果。例如,在上面的示例中,它产生98/100个错误,而不是100个错误。我检查了,这与并发无关;出于某种原因,返回了2个最新作业,退出代码为0。

为什么会发生这种情况?