PHP running as a FastCGI application (php-cgi) - how to issue concurrent requests?

php concurrency fastcgi
Waleed Amjad picture Waleed Amjad · May 8, 2010 · Viewed 8.6k times · Source

EDIT: Update - scroll down
EDIT 2: Update - problem solved

Some background information:

I'm writing my own webserver in Java and a couple of days ago I asked on SO how exactly Apache interfaces with PHP, so I can implement PHP support. I learnt that FastCGI is the best approach (since mod_php is not an option). So I have looked at the FastCGI protocol specification and have managed to write a working FastCGI wrapper for my server. I have tested phpinfo() and it works, in fact all PHP functions seem to work just fine (posting data, sessions, date/time, etc etc).

My webserver is able to serve requests concurrently (ie user1 can retrieve file1.html at the same time as user2 requesting some_large_binary_file.zip), it does this by spawning a new Java thread for each user request (terminating when completed or user connection with client is cancelled).

However, it cannot deal with 2 (or more) FastCGI requests at the same time. What it does is, it queues them up, so when request 1 is completed immediately thereafter it starts processing request 2. I tested this with 2 PHP pages, one contains sleep(10) and the other phpinfo().

How would I go about dealing with multiple requests as I know it can be done (PHP under IIS runs as FastCGI and it can deal with multiple requests just fine).

Some more info:

I am coding under windows and my batch file used to execute php-cgi.exe contains:

set PHP_FCGI_CHILDREN=8
set PHP_FCGI_MAX_REQUESTS=500
php-cgi.exe -b 9000

But it does not spawn 8 children, the service simply terminates after 500 requests.

I have done research and from Wikipedia:

Processing of multiple requests simultaneously is achieved either by using a single connection with internal multiplexing (ie. multiple requests over a single connection) and/or by using multiple connections

Now clearly the multiple connections isn't working for me, as everytime a client requests something that involves FastCGI it creates a new socket to the FastCGI application, but it does not work concurrently (it queues them up instead).

I know that internal multiplexing of FastCGI requests under the same connection is accomplished by issuing each unique FastCGI request with a different request ID. (also see the last 3 paragraphs of 'The Communication Protocol' heading in this article).

I have not tested this, but how would I go about implementing that? I take it I need some kind of FastCGI Java thread which contains a Map of some sort and a static function which I can use to add requests to. Then in the Thread's run() function it would have a while loop and for every cycle it would check whether the Map contains new requests, if so it would assign them a request ID and write them to the FastCGI stream. And then wait for input etc etc, As you can see this becomes too complicated.

Does anyone know the correct way of doing this? Or any thoughts at all? Thanks very much.

Note, if required I can supply the code for my FastCGI wrapper.

Update:

Basically, I downloaded nginx and set it up to use PHP as a FastCGI application and it too suffered from the same problem as my server. It could not handle concurrent PHP requests. This is leads me to believe my code is in fact correct. So something is wrong with PHP or I am not setting it up correctly. Maybe it is because I am using Windows because some lighttpd users claim Windows can't handle FastCGI properly (this doesn't make much sense). I'll install Linux sometime soon and report any progress with that.

Answer

Waleed Amjad picture Waleed Amjad · Aug 13, 2010

Okay, I managed to find the cause of the problem. It wasn't my code at all. It's PHP, it cannot spawn additional php-cgi's under Windows when running as FastCGI mode, under Linux it works perfectly, I simply pointed my server to my linux box IP and it had no problems with concurrent FCGI requests. Sucks, but I guess that's the way it is...

I did look deeper into the PHP source code after that and found that the section of code which responds to PHP_FCGI_CHILDREN has been encapsulated by #ifndef WIN32 So the developers must be aware of the issue

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