If you are working on a project which requires fair amount of background work to be done, then you must have seen the requirement of keeping background threads separate. Unfortunately, there is no explicit way of threading in php (there are a number of way around to do this, but those to me look like hacks rather a supported feature). Such needs are normally seen in a project which requires some work to be done which is not needed immediately. For example, if a user uploads a picture and you want to crop that picture, or, you want to send some sort of notification email etc. This is a classical case of having a worker thread doing all these tasks in parallel. There are a number of open source libraries available which take care of such things e.g. https://github.com/pda/pheanstalk . But if you want to do this yourself, then here is a simple strategy.
First two points are fairly simple. So, lets talk about third point now. How would you run the php script as a background thread. There are two ways in linux to do this. One is to run the script as a cron. To know how to run a script as a cron job, refer to my post here => http://saadnawaz.blogspot.com/2012/05/create-cron-job-in-linux.html. Now, if you think that your job is something which can run after 1 minute, then simply write the php script and add entry in the crontab. Though, in most of cases, 1 minute is just a bit too much delay. So, the next option is creating a daemon. Daemon is a process which runs in the background. What you should be doing is running the worker php script as a daemon. Follow the following steps to do that:(this is just one way of creating a daemon, there are other ways as well, but this seems simplest to me)
1. Create a shell script which executes the php script file, which is gonna be something like:
What this shell script is doing is fairly straight forward. You have an infinite loop which runs a php script file, and after than sleeps for 5 seconds. So, basically you are achieving something like cron, but you are executing the script every 5 seconds (which cron can't do, since, the granularity is upto minutes).
Since, this is treated as an executable, therefore, make sure you have given appropriate rights on the script and php worker file.
2. Run the shell script as a daemon:
The "&" at the end runs this as a daemon.
Now, keep in mind, it's always better to use an existing solution rather reinventing the wheel. But, if your problem is not big enough to use open source solutions, then the above strategy should get you started.
- Create a queue in memcache or add the jobs in some table in DB
- Create a php script which takes a job out from memcache queue to from the table in DB and executes the job
- Run the php script as a background thread.
First two points are fairly simple. So, lets talk about third point now. How would you run the php script as a background thread. There are two ways in linux to do this. One is to run the script as a cron. To know how to run a script as a cron job, refer to my post here => http://saadnawaz.blogspot.com/2012/05/create-cron-job-in-linux.html. Now, if you think that your job is something which can run after 1 minute, then simply write the php script and add entry in the crontab. Though, in most of cases, 1 minute is just a bit too much delay. So, the next option is creating a daemon. Daemon is a process which runs in the background. What you should be doing is running the worker php script as a daemon. Follow the following steps to do that:(this is just one way of creating a daemon, there are other ways as well, but this seems simplest to me)
1. Create a shell script which executes the php script file, which is gonna be something like:
while true
do
php /pathtofile/filename.php
sleep 5
done
What this shell script is doing is fairly straight forward. You have an infinite loop which runs a php script file, and after than sleeps for 5 seconds. So, basically you are achieving something like cron, but you are executing the script every 5 seconds (which cron can't do, since, the granularity is upto minutes).
Since, this is treated as an executable, therefore, make sure you have given appropriate rights on the script and php worker file.
2. Run the shell script as a daemon:
/completePathToFile/shell.sh &
The "&" at the end runs this as a daemon.
Now, keep in mind, it's always better to use an existing solution rather reinventing the wheel. But, if your problem is not big enough to use open source solutions, then the above strategy should get you started.
