Synchronized functions using PHP

Question

How to make functions in PHP synchronized so that same function won\'t be executed concurrently ? 2nd user must wait till 1st user is done with the function. Then 2nd user

Answer 1

This basically comes down to setting a flag somewhere that the function is locked and cannot be executed until the first caller returns from that function. This can be done in a number of ways:

• use a lock file (first function locks a file name "f.lok", second function checks if the lock file exists and executes or doesn't based on that evaluation)
• set a flag in the database (not recomended)
• use semaphores as @JvdBerg suggested (the fastest)

When coding concurrent application always beware of race conditions and deadlocks!

UPDATE using semaphores (not tested):

PHP needs to be compiled with sysvsem support in order to use sem_* functions

Here's a more in depth tutorial for using semaphores in PHP:

http://www.re-cycledair.com/php-dark-arts-semaphores