如何通过PHP多线程加速大文件下载

<?php

$file_url = 'http://example.com/large_file.zip'; // 大文件的URL
$num_threads = 4; // 线程数

// 获取文件大小
$file_size = intval(get_headers($file_url, true)['Content-Length']);

// 计算每个线程下载的字节数
$bytes_per_thread = ceil($file_size / $num_threads);

// 创建多个子进程
$pid_array = array();
for ($i = 0; $i < $num_threads; $i++) {
    $start_byte = $i * $bytes_per_thread;
    $end_byte = min(($i + 1) * $bytes_per_thread - 1, $file_size - 1);
    
    $pid = pcntl_fork();
    
    if ($pid == -1) {
        exit('Fork failed');
    } elseif ($pid) {
        // 父进程
        $pid_array[] = $pid;
    } else {
        // 子进程
        $range = "bytes=$start_byte-$end_byte";
        $options = array(
            'http' => array(
                'header' => "Range: $range
"
            )
        );
        $context = stream_context_create($options);
        $stream = fopen($file_url, 'r', false, $context);
        file_put_contents("part_$i", stream_get_contents($stream));
        fclose($stream);
        exit(0);
    }
}

// 等待所有子进程完成
foreach ($pid_array as $pid) {
    pcntl_waitpid($pid, $status);
}

// 合并所有下载的部分文件
$merged_file = 'merged_file.zip';
$merged_stream = fopen($merged_file, 'wb');
for ($i = 0; $i < $num_threads; $i++) {
    $part_file = "part_$i";
    $part_stream = fopen($part_file, 'rb');
    stream_copy_to_stream($part_stream, $merged_stream);
    fclose($part_stream);
    unlink($part_file);
}
fclose($merged_stream);

echo "文件下载完成！";

?>