The Pool class

Please note, when using the collect function, it's important that you extend the pool class so you can keep checking for finished threads until they're all done.
<?php
class TestWork extends Threaded {
 protected $complete;
 //$pData is the data sent to your worker thread to do it's job.
 public function __construct($pData){
 //transfer all the variables to local variables
 $this->complete = false;
 $this->testData = $pData;
 }
 //This is where all of your work will be done.
 public function run(){
 usleep(2000000); //sleep 2 seconds to simulate a large job
 $this->complete = true;
 }
 public function isGarbage() {
 return $this->complete;
 }
}
class ExamplePool extends Pool
{
 public $data = array();
 public function process()
 {
 // Run this loop as long as we have
 // jobs in the pool
 while (count($this->work)) {
 $this->collect(function (TestWork $task) {
 // If a task was marked as done
 // collect its results
 if ($task->isGarbage()) {
 $tmpObj = new stdclass();
 $tmpObj->complete = $task->complete;
 //this is how you get your completed data back out [accessed by $pool->process()]
 $this->data[] = $tmpObj;
 }
 return $task->isGarbage();
 });
 }
 // All jobs are done
 // we can shutdown the pool
 $this->shutdown();
 return $this->data;
 }
}
$pool = new ExamplePool(3);
$testData = 'asdf';
for($i=0;$i<5;$i++) {
 $pool->submit(new TestWork($testData));
}
$retArr = $pool->process(); //get all of the results
echo '<pre>';
print_r($retArr); //return the array of results (and maybe errors)
echo '</pre>';
?>

In this example, it shows how to use a pool to get an array of results, using pThreads v3.2.1 and php 7.3.23
<?php
class TestWork extends Threaded {
//updated version that works with pThreads v3.2.1 and php 7.3.23
 protected $complete;
 //$pData is the data sent to your worker thread to do it's job.
 public function __construct($pData) {
 //transfer all the variables to local variables
 $this->complete = false;
 $this->testData = $pData;
 }
 //This is where all of your work will be done.
 public function run() {
 usleep(2000000); //sleep 2 seconds to simulate a large job
 $this->complete = true;
 }
 public function isDone() {
 return $this->complete;
 }
}
class ExamplePool extends Pool {
 public $data = array(); // used to return data after we're done
 private $numTasks = 0; // counter used to know when we're done
 /**
 * override the submit function from the parent
 * to keep track of our jobs
 */
 public function submit(Threaded $task) {
 $this->numTasks++;
 parent::submit($task);
 }
 /**
 * used to wait until all workers are done
 */
 public function process() {
 // Run this loop as long as we have
 // jobs in the pool
 while (count($this->data) < $this->numTasks) {
 $this->collect(function (TestWork $task) {
 // If a task was marked as done, collect its results
 if ($task->isDone()) {
 $tmpObj = new stdclass();
 $tmpObj->complete = $task->complete;
 //this is how you get your completed data back out [accessed by $pool->process()]
 $this->data[] = $tmpObj;
 }
 return $task->isDone();
 });
 }
 // All jobs are done
 // we can shutdown the pool
 $this->shutdown();
 return $this->data;
 }
}
$pool = new ExamplePool(3);
$testData = 'asdf';
for($i=0;$i<5;$i++) {
 $pool->submit(new TestWork($testData));
}
$retArr = $pool->process(); //get all of the results
echo '<pre>';
print_r($retArr); //return the array of results (and maybe errors)
echo '</pre>';
?>

Simple example with Collectable (basically Thread meant for Pool) and Pool
<?php
class job extends Collectable {
 public $val;
 public function __construct($val){
 // init some properties
 $this->val = $val;
 }
 public function run(){
 // do some work
 $this->val = $this->val . file_get_contents('http://www.example.com/', null, null, 3, 20);
 $this->setGarbage();
 }
}
// At most 3 threads will work at once
$p = new Pool(3);
$tasks = array(
 new job('0'),
 new job('1'),
 new job('2'),
 new job('3'),
 new job('4'),
 new job('5'),
 new job('6'),
 new job('7'),
 new job('8'),
 new job('9'),
 new job('10'),
);
// Add tasks to pool queue
foreach ($tasks as $task) {
 $p->submit($task);
}
// shutdown will wait for current queue to be completed
$p->shutdown();
// garbage collection check / read results
$p->collect(function($checkingTask){
 echo $checkingTask->val;
 return $checkingTask->isGarbage();
});
?>