Threads in PHP?

EDIT (thanks @Efazati, there seems to be new development in this direction)

http://php.net/manual/en/book.pthreads.php
Caution: (from here on the bottom):

pthreads was, and is, an experiment with pretty good results. Any of its limitations or features may change at any time; [...]

/EDIT

No threads in PHP!

The workaround is to store jobs in a queue (say rows in a table with the emails) and have a cronjob call your php script at a given interval (say 2 minutes) and poll for jobs. When jobs present fetch a few (depending on your php's install timeout) and send emails.

The main idea to defer execution:

• main script adds jobs in the queue
• cron script sends them in tiny slices

Gotchas:

• make sure u don't send an email without deleting from queue (worst case would be if a user rescieves some spam at 2 mins interval ...)
• make sure you don't delete a job without executing it first ...
• handle bouncing email using a score algorithm

You could look into using multiple processes, such as with fork. The communication between them wouldn't be as simple as with threads (but then, it won't come with all of its pitfalls either), but if you're just sending emails, it might not be necessary to communicate much, if at all.

Watch out for doing forks on an Apache process. You may get some behaviors that you are not expecting. If you are looking to do any kind of asynchronous execution it should be via some kind of queuing mechanism. Gearman is one. Zend Server Job Queue is another. I have some demo code at Do you queue? Introduction to the Zend Server Job Queue. Cron can be used, but you'll have the problem of depending on your cron scheduler to run tasks whereas asynchronous computing often needs to be run immediately. Using a queuing system allows you to do that without threading.