Q:

pthreads hangs / stuck on pool->submit

I'm trying to get Pthreads to work, but unfortunately with all of the outdated documentation it is really hard to figure out what is current and what has changed. As well as not getting any errors returned.
Running PHP7.2.0-dev with the latest version of pthreads and xDebug
Currently I have
<?php

$THREADS = 3;

class UptimeWorker extends Worker {
    public function start(?int $options = null) {
        return parent::start(PTHREADS_INHERIT_CLASSES | PTHREADS_INHERIT_CONSTANTS | PTHREADS_INHERIT_FUNCTIONS);
    }
}

class UptimeWork extends Threaded {

    private $i;

    public function __construct(int $i) {
        $this->i = $i;
    }

    public function run() {
        echo "I am ".$i.PHP_EOL;
        $this->setGarbage();
    }

}

$pool = new Pool($THREADS, UptimeWorker::class);

for($i=0;$i<10;$i++) {
    var_dump($i);
    $pool->submit(new UptimeWork($i));
}

echo "pre-shutdown".PHP_EOL;

$pool->shutdown();

echo "finished".PHP_EOL;

and the only output is int(0) from the first var_dump call in the for statement, from there the process just seems to hang, it doesn't exit and no further output is given.
What is going wrong here and what needs to happen in order for this to work?

A:

I get two errors in your code, both in
 public function run() {
    echo "I am ".$i.PHP_EOL;
    $this->setGarbage();
}

First it should the $this->i  (simple typo)
Second is that setGarbage is not found as it's a property of Collectable (http://php.net/manual/en/collectable.setgarbage.php - Note: the manual documents the old PHP 5/API version 2 classes, this has changed to an interface for PHP 7/API version 3). Therefore you need 
class UptimeWork extends Threaded  Implements Collectable {

to get access to setGarbage(). As Collectable is an interface, you also need to write the interface methods. 
Here is your working code:
$THREADS = 3;

class UptimeWorker extends Worker {
    public function start(?int $options = null) {
        return parent::start(PTHREADS_INHERIT_CLASSES | PTHREADS_INHERIT_CONSTANTS | PTHREADS_INHERIT_FUNCTIONS);
    }
}

class UptimeWork extends Threaded  Implements Collectable {

    private $i;
    private $isGarbage = false;

    public function __construct(int $i) {
        $this->i = $i;
    }

    public function run() {
        echo "I am ".$this->i.PHP_EOL;
        $this->setGarbage();
    }

    public function setGarbage() {
        echo "Setting garbage ".$this->i.PHP_EOL;
        $this->isGarbage = true;
    }

    public function isGarbage() : bool {
        return $this->isGarbage;
    }

}

$pool = new Pool($THREADS, UptimeWorker::class);

for($i=0;$i<10;$i++) {
    var_dump($i);
    $pool->submit(new UptimeWork($i));
}

echo "pre-shutdown".PHP_EOL;

$pool->shutdown();

echo "finished".PHP_EOL;

