Question

如何从主上下文中断线程的执行？

在下面的代码段中 - 如何在不破坏线程的情况下停止线程执行的操作？

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

Answer 1

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中访问，我省略了stop / quit函数的实现，但它的逻辑与RandomSeeds示例显示的大致相同。

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();
        }
    });
}

极限：

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写它，我不是那么讨厌，不管你有什么用。这种极端代码的原因是，必须允许线程接收除正在等待的信号之外的信号，许多低电平信号可能导致线程从调用pthread_cond_wait唤醒;检查循环中的谓词就像防止规范所谓的虚假唤醒......但是这种极端措施也会导致不良副作用;这些线程接收低电平信号的原因是因为它们需要采取某种行动，忽略这很容易导致堆栈的不同部分死锁，因为它期望你的线程死掉（或做其他事情，当它被发出信号时，就是一个例子......

Answer 2

AFAIK您不能随意暂停并发线程，但您可以向其发送通知。另一个线程必须合作并在收到通知时自愿暂停。

示例：

<?php

class MyThread extends Thread {

    private $pauseRequested = false;
    private $stopRequested = false;

    public function pause() {
        $this->synchronized(function($thread){
            $thread->pauseRequested = true;
        }, $this);
    }

    public function resume() {
        $this->synchronized(function($thread){
            $thread->pauseRequested = false;
            $thread->notify();
        }, $this);

    }

    public function stop() {
        $this->synchronized(function($thread){
            $thread->stopRequested = true;
        }, $this);
    }

    public function run() {
        echo 'Thread started!' . PHP_EOL;
        while (!$this->stopRequested) {

            // do the actual work
            echo 'Working...';
            sleep(1);

            // check if we have been requested to pause
            $this->synchronized(function($thread){
                if ($this->pauseRequested) {
                    echo 'Paused...';
                    $thread->wait(); // this is where the magic happens
                }
            }, $this);
        }

        if ($this->stopRequested) {
            echo PHP_EOL . 'Stopped!' . PHP_EOL;
        }
    }
}


$t = new MyThread();
$t->start();
sleep(5);

$t->pause();
sleep(2);

$t->resume();
sleep(5);

$t->stop();

// wait for $t to complete
$t->join(); 

?>

Answer 3

从未使用过pthreads，tbh，但您是否尝试在线程类中创建一个公共布尔标志？

PHP - 中断或暂停pthread的执行

3 个答案: