John Davidson

fork - Why doesn't PHP pcntl_fork run more than two child processes in parallel?

0 comments
Message:


I understand how fork() works at a high level and the pcntl_fork() wrapper, but for some reason in my environment PHP only runs two child processes at a time. Take for example this simple code:


<?php
for ($i = 1; $i <= 5; ++$i) {
$pid = pcntl_fork();
if ($pid === -1) {
print "Could not fork!\n";
exit(1);
}
if (!$pid) {
print "-In child $i\n";
sleep(1);
print "In child $i\n";
exit($i);
} else {
print "Parent: forked $i\n";
}
}

while (pcntl_waitpid(0, $status) != -1) {
$status = pcntl_wexitstatus($status);
echo "Child $status completed\n";
}

The output I expect is something like this with total time around 1 second:


Parent: forked 1
-In child 1
Parent: forked 2
-In child 2
Parent: forked 3
-In child 3
Parent: forked 4
-In child 4
Parent: forked 5
-In child 5
In child 1
In child 2
In child 3
In child 4
In child 5
Child 1 completed
Child 2 completed
Child 3 completed
Child 4 completed
Child 5 completed

But what I actually get is this, with total execution time around 3.5 seconds:


Parent: forked 1
Parent: forked 2
Parent: forked 3
Parent: forked 4
Parent: forked 5
-In child 2
-In child 1
In child 2
Child 2 completed
-In child 3
In child 1
Child 1 completed
-In child 4
In child 3
Child 3 completed
-In child 5
In child 4
Child 4 completed
In child 5
Child 5 completed

So it appears that only two child processes are actually running at any given time. I can't find any explanation for this behavior...


When running the test on a production system which is Docker on a native Linux host I get the expected result, but why can't I reproduce it with the exact same container on my WSL2 host?


System Information



  • I'm running this test in a very recent version of Docker Desktop via WSL2 on Windows 11.

  • My system has 12 CPU cores (20 with hyperthreading - nproc prints "20" from both the WSL2 hostand from inside the docker container).

  • I have not changed the defaults in Docker Desktop or WSL config or used any resource control flags on the Docker container so CPU should not be restricted in any way.



My Answer:
are you asking about forks? Forks are commonly used utensils for eating food, especially foods that are difficult to eat with just a knife or spoon. They have multiple prongs that help to pick up and hold food securely. Forks are an essential tool in dining etiquette and are used in various cultures around the world.

Rate this post

3 of 5 based on 9741 votes

Comments




© 2024 Hayatsk.info - Personal Blogs Platform. All Rights Reserved.
Create blog  |  Privacy Policy  |  Terms & Conditions  |  Contact Us