如何从主上下文中中断线程的执行？

在下面的代码片段中——如何在不破坏线程的情况下停止线程的操作？

class ReadFileThread extends Thread
{
    public function __construct($file, $chunk = 1024)
    {
        $this->file = $file;

        $this->chunk = $chunk;
    }

    public function run()
    {
        if(is_file($this->file) && is_readable($this->file))
        {
            $fh = fopen($this->file, 'rb');

            while(!feof($fh))
            {
                $content = fread($fh, $this->chunk);
            }

            fclose($fh);
        }
    }
}

$num = 10;
$threads = [];

for($i = 0; $i < $num; $i++)
{
    $thread = new ReadFileThread('/path/to/10gig_file.txt', 1024);

    $threads[] = $thread;

    // I start the thread, now it's detached from the main context and is reading the file asynchronously
    $thread->start();
}

// The interesting part - I want to random 1 thread whose operation of file reading I want to interrupt
$to_interrupt = $threads[rand(0, $num)];

// How to interrupt the thread without destroying it? I want its context preserved

最佳答案

RandomSeeds 答案很接近，但对竞争条件开放。

<?php
class FileReader extends Thread {
    public $file;
    public $pause;

    public function __construct($file) {
        $this->file = $file;
        $this->pause = false;
    }

    public function run() {
        if (($handle = fopen($this->file, "rb"))) {
            $len = 0;
            do {
                $this->synchronized(function(){
                    if ($this->paused) {
                        printf(
                            "\npausing %lu ...\n", $this->getThreadId());
                        $this->wait();
                    }
                });

                $data = fread($handle, 1024);
                $len += strlen($data);

                if (($len % 2) == 0) {
                    printf( 
                        "\r\rread %lu", $len);
                }
            } while (!feof($handle));

            fclose($handle);
        }
    }

    public function pause() {
        return $this->synchronized(function(){
            return ($this->paused = true);
        });
    }

    public function unpause() {
        return $this->synchronized(function(){
            $this->paused = false;      
            if ($this->isWaiting()) {
                return $this->notify();
            }
        });
    }
}

function do_something($time) {
    $start = time();

    while (($now = time()) < ($start + $time)) {
        usleep(100);
        if (($now % 2) == 0) {
            echo ".";
        }
    }

    echo "\n";
}

$reader = new FileReader("/path/to/big/file.ext");
$reader->start();

sleep(2);
$reader->pause();
do_something(rand(2, 4));
$reader->unpause();
sleep(2);
$reader->pause();
do_something(rand(2, 4));
$reader->unpause();
sleep(2);
$reader->pause();
do_something(rand(2, 4));
$reader->unpause();
?>

重要的是，用于同步目的的变量只能在同步块(synchronized block)中访问，我省略了停止/退出函数的实现，但它的逻辑大致相同，如 RandomSeeds 示例所示。

竞争条件潜伏在:

public function mine($data) {
    /* anyone can set doSynchronization at any time */
    if ($this->doSynchronization) {

        $this->synchronize(function(){
            /* checking the predicate in here is safer */
            $this->wait();
        });
    }
}

好:

public function mine($data) {
    $this->synchronize(function(){
        if ($this->doSynchronization) {
            $this->wait();
        }
    });
}

极端:

public function mine($data) {
    $this->synchronize(function(){
        while ($this->doSynchronization) {
            $this->wait();
        }
    });
}

posix 标准总是让你以极端的方式编写它，我不那么大惊小怪，任何适合你的。这种极端代码的原因是，必须允许线程接收信号而不是它正在等待的信号，许多低级别信号可能导致线程从调用 pthread_cond_wait 中唤醒；在这样的循环中检查谓词可以防止规范中所谓的虚假唤醒……但这种极端措施也会导致不良的副作用；这些线程收到低电平信号的原因是因为他们有必要采取某种行动，忽略它很容易导致堆栈的不同部分死锁，因为它希望你的线程死掉(或做其他事情， die 是一个例子)当它被发出信号时......

关于PHP - 中断或暂停 pthread 的执行，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/20195956/