如何从主上下文中断线程的执行？
在下面的片段中，如何在不破坏线程的情况下停止线程所做的操作？
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
RandomSeeds的答案很接近，但对比赛条件开放。
<?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));
$reader->unpause();
?>
重要的是，用于同步目的的变量只能在同步块中访问，我省略了停止/退出函数的实现，但它的逻辑基本相同，正如RandomSeeds示例所示。
种族状况潜伏在：
public function mine($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标准总是让你用极端的方式来写，我不那么担心，不管什么对你有用。出现这种极端代码的原因是，必须允许线程接收与其正在等待的信号不同的信号，许多低电平信号可能导致线程从对pthread_cond_wait的调用中唤醒；在这样的循环中检查谓词可以防止规范所称的虚假唤醒。。。但这种极端措施也可能导致不良副作用；这些线程接收到低电平信号的原因是，它们有必要采取某种行动，忽略这一点很容易导致堆栈的另一部分死锁，因为它预计线程在收到信号时会死亡（或者做其他事情，死亡就是一个例子）。。。
AFAIK你不能任意暂停一个并发线程，但你可以向它发送通知。另一个线程必须合作，并在收到通知时自愿暂停自己。
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();
?>
从未使用过pthreads，tbh，但您尝试过在线程类中创建公共布尔标志吗？