How can I throttle the # of php threads accessing a resource?

[JonBlockBoston]

Inside of go.php I have a function called doSomethingCrazy().

My go.php file gets a lot of requests, but I want to ensure that doSomethingCrazy() will only be running in up to 5 concurrent requests.

In other words, I'd like to write some kind of "manager" that would check to see if doSomethingCrazy() is already in use by 5 other php threads. If so, I do not want to call doSomethingCrazy().

Are there any types of thread managers or pool connection managers or something I can use to help throttle access to this resource?

Thank you,
Jon

[sneakyimp]

PHP apparently has some built-in functionality to support semaphores and other concurrent programming features, but I haven't heard of any tools anyone has written to support this sort of thing.

Have you considered using a MySQL table. Your function could LOCK a table, count how many records are in it, and if there are 5 or more, then it could die. Otherwise, it could add a record and then unlock the table.