Global incremen in thread PHP - php

Question

I am running 4 threads running in same time. (Threads are running work() function in same time in this case)
global $i;
$i = 1;
function work($address) {
while($i < 1000) {
$i++;
----
if($i == something) some job...
----
}
}
For some reason this don't do the job.
Threads do sometimes same circle in while, so I have later some duplicate values. (probably they have some critical section)
Any idea how to fix this ?

Answer 1

The counter object must be thread safe, it must also employ synchronized methods.
Follows is an example of such code:
<?php
class Counter extends Threaded {
public function __construct($value = 0) {
$this->value = $value;
}
/** protected methods are synchronized in pthreads **/
protected function increment() { return ++$this->value; }
protected function decrement() { return --$this->value; }
protected $value;
}
class My extends Thread {
/** all threads share the same counter dependency */
public function __construct(Counter $counter) {
$this->counter = $counter;
}
/** work will execute from job 1 to 1000, and no more, across all threads **/
public function run() {
while (($job = $this->counter->increment()) <= 1000) {
printf("Thread %lu doing job %d\n",
Thread::getCurrentThreadId(), $job);
}
}
protected $counter;
}
$counter = new Counter();
$threads = [];
while (($tid = count($threads)) < 4) {
$threads[$tid] = new My($counter);
$threads[$tid]->start();
}
foreach ($threads as $thread)
$thread->join();
?>
work() seems superfluous, this logic should be in the ::run function most likely.