php and cgi

thesilencer5

two questions about php and cgi:
Following situation: I read many URLs out of my DB, and want to ping each of them. But I have to ping them simultaneously to decrease needed time. So I can´t do that directly with PHP. I already tried with forking PHP, but that won´t work on my server. So I want to send each of the URLs to a CGI, that pings the URLs and writes the results back into my DB.

Question1: Are CGIs capable for multithreading? If I do so, will an instance of the cgi be opened on the server for each one of the URLs?

Question2: Is ist possible wiht PHP to send data to the CGI and forget about the rest? (without having to wait for the ping results to send the next URL)

Thanks in advance
thesilencer

swr

You may be able to do what you want with fsockopen. Open multiple connections, send the requests on each, don't wait for response. You will still have to wait on the TCP handshakes though, just not the HTTP response. This requires implementing HTTP protocol yourself (which fortunately is not difficult). You might be able to get away with just passing a URL to fopen and not reading any data; not sure though as fopen might wait for an HTTP response code which would reduce your parallelism.

Another way to do it would be to invoke the PHP multiple times in parallel, and each instance could process a portion of your URL list. Each PHP would be running in its own web server process so it would be truely parallel. The down side is that you need to load multiple pages simultaneously to start the processes.

You could combine the two approaches. Have one .php file that the user accesses, that uses fsockopen to make parallel requests to .php files that each process a portion of the list one URL at a time. This should be able to do exactly what you want.

This is all very kludgy though. If you really need to write a multithreaded app, PHP is not a very good choice.

thesilencer5

...OK, the combined Solution looks good. But slowly, I´m not a PHP professional yet. Let´s see if I understood it right ;-)

The whole thing should run as a cronjob on my server, which starts phpFile1.
phpFile1 starts phpFile2, phpFile3 via fsockopen..... right?

The Script in file2 and 3 I have already written. That Files will ping the servers, and write back the results into my DB. No screen output will be done.

But I dont know how to code the File1. Do you have a bit of example-code? I never worked with socket-functions yet.

Thanks

swr

Oh, you didn't mention you'd be running it from a cron job. That simplifies things, as you can use shell script, which has good process forking capabilities.

See "Using PHP from the command line" for how to run PHP scripts from the command line or shell script:
http://www.php.net/manual/en/features.commandline.php

Create a shell script that looks like this:

#!/bin/sh
php /path/to/script.php args1 &
php /path/to/script.php args2 &
php /path/to/script.php args3 &

chmod it to be executable, then tell cron to run it (as if it were an executable binary). It executes each line as if you entered it at the command prompt. The "&" on the end tells it to put the job into the background, so the above will create three instances of the script running simultaneously.

thesilencer5

OK, the shell script works. But there is still the problem, that I previously don´t know how many URLs I have to ping. That information is provided dynamically by my DB.....

swr

Don't know why I didn't think of this when I was posting the shell script...

Instead of writing the master script in shell, write it in PHP, starting it from cron the way the shell script started the other scripts. Use system("php /path/to/script/script.php args &") from within the master script to start the worker scripts (not sure if safe mode might interfere with that though).

With the master script written in PHP, you can make whatever database requests you want using the usual PHP function calls.

If you're thinking of having each background process ping one site and starting one background process per site, don't - it'll really hurt your server and will eventually fail due to resource limits. The best way to handle it is to start a fixed number of processes, say 10, and instruct each of them to process one tenth of your list.

thesilencer5

Oh yeah, now a lot time later, I got a solution. If you´d need it in the future, here it is: www.fping.com

pings unlimited amount of servers at the same time.
Thanks for help!!