PHP中fork子进程时CURL返回异常计时结果的原因及修复方案咨询

我正在尝试用PHP复刻ApacheBench（ab）压力测试工具，这样就能根据响应内容实现更定制化的控制逻辑。但在使用pcntl_fork()创建子进程发起请求时，得到的响应计时结果非常异常，和单进程非fork的情况差距很大。想请教各位大佬这是什么原因，以及该怎么修复才能得到fork执行时的真实请求耗时？

我的测试代码 #

<?php
$start_time = microtime(true);

function makeRequest(int $id) {
    $time = 0;
    $url = 'http://localhost:8080/';
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_FRESH_CONNECT, true);
    curl_setopt($ch, CURLOPT_FORBID_REUSE, true);
    curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 1);
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    
    curl_exec($ch);
    $code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
    $info = curl_getinfo($ch);
    $time = $info['total_time'];
    
    curl_close($ch);
    echo "#$id. Response code: " . $code . ' in ' . $time * 1000 . ' ms' . PHP_EOL;
}

$repeat = 100;

// 发起fork的请求
for ($i = 1; $i <= $repeat; ++$i) {
    $pid = pcntl_fork();
    if (!$pid) {
        makeRequest($i);
        exit($i);
    }
}

while (pcntl_waitpid(0, $status) != -1) {
    $status = pcntl_wexitstatus($status);
    echo "\tChild $status completed" . PHP_EOL;
}

// 发起非fork的请求做对比
for ($i = 1; $i <= $repeat; ++$i) {
    makeRequest($i);
}

$finished = microtime(true);
echo 'Finished all in ' . ($finished - $start_time) * 1000 . ' ms' . PHP_EOL;

测试环境 #

• 系统：MacOS
• PHP版本：8.4.4
• 执行命令：php -f test_request.php

测试结果对比 #

非fork单进程请求（结果正常）

所有请求耗时都在1ms以内，输出如下：

#1. Response code: 200 in 0.737 ms
#2. Response code: 200 in 0.586 ms
#3. Response code: 200 in 0.516 ms
#4. Response code: 200 in 0.575 ms
#5. Response code: 200 in 0.557 ms
...
#95. Response code: 200 in 0.351 ms
#96. Response code: 200 in 0.348 ms
#97. Response code: 200 in 0.389 ms
#98. Response code: 200 in 0.394 ms
#99. Response code: 200 in 0.345 ms
#100. Response code: 200 in 0.323 ms

fork多进程请求（结果异常）

响应耗时随着请求数量增加而持续变长，部分请求甚至达到60ms以上，而且因为子进程并行输出，顺序也混乱了：

#1. Response code: 200 in 1.045 ms
#2. Response code: 200 in 0.911 ms
#3. Response code: 200 in 1.546 ms
#4. Response code: 200 in 1.236 ms
#5. Response code: 200 in 1.916 ms
...
#93. Response code: 200 in 63.043 ms
#92. Response code: 200 in 64.184 ms
Child 95 completed
Child 89 completed
Child 88 completed
#94. Response code: 200 in 65.008 ms
Child 96 completed
Child 97 completed
#98. Response code: 200 in 60.779 ms
#100. Response code: 200 in 54.383 ms

我的疑问 #

1. 为什么fork子进程发起请求时，响应耗时会随着请求数增加而变长？这是真实的请求耗时还是计时逻辑有问题？
2. 我的代码中有没有什么错误导致了这个异常结果？该怎么修改才能得到fork执行时的真实请求耗时？

内容来源于stack exchange