Starting a PHP script in the background?

[Jonah Bishop]

What is the appropriate way to start a PHP script in the background? I
have a script that manipulates image data, and it takes a long time to
run. I'd like to send this process to the background at the appropriate
time, so that it can go do its job without holding up the user.

I've seen something like this used:

system("php myscript.php &");

But the PHP manual entry for the system() function call indicates the
following:

"Note: If you start a program using this function and want to leave it
running in the background, you have to make sure that the output of
that program is redirected to a file or some other output stream or
else PHP will hang until the execution of the program ends."

I don't expect this background script to output anything, but suppose
an error occurs during execution? Will PHP get tied up as a result
(trying to output an error message)?

How do I properly execute a PHP script in the background from another
PHP script?

Thanks in advance!
Jonah Bishop

[NC]

Jonah Bishop wrote:

>
I have a script that manipulates image data, and it takes
a long time to run. I'd like to send this process to the
background at the appropriate time, so that it can go do
its job without holding up the user.

I've seen something like this used:

system("php myscript.php &");

But the PHP manual entry for the system() function call
indicates the following:

"Note: If you start a program using this function and want
to leave it running in the background, you have to make
sure that the output of that program is redirected to a file
or some other output stream or else PHP will hang until
the execution of the program ends."

I don't expect this background script to output anything,
but suppose an error occurs during execution? Will PHP
get tied up as a result (trying to output an error message)?

There are at least two ways of dealing with this issue:

1. Redirect the script's output into a file:

system("php myscript.php & myscriptlog.txt");
system("php myscript.php & >myscriptlog.txt");

The former will write any output the script produces into
a newly created file myscriptlog.txt; the latter will append
output the script produces to myscriptlog.txt

2. Buffer the output at the beginning of the script and
discard it at the end:

@ob_start();
// the script goes here...
@ob_end_clean();

Cheers,
NC

[Colin McKinnon]

NC wrote:

Jonah Bishop wrote:

>>
But the PHP manual entry for the system() function call
indicates the following:

"Note: If you start a program using this function and want
to leave it running in the background, you have to make
sure that the output of that program is redirected to a file
or some other output stream or else PHP will hang until
the execution of the program ends."

There are at least two ways of dealing with this issue:

1. Redirect the script's output into a file:

system("php myscript.php & myscriptlog.txt");
system("php myscript.php & >myscriptlog.txt");

<snip>
almost right.

>
2. Buffer the output at the beginning of the script and
discard it at the end:

@ob_start();
// the script goes here...
@ob_end_clean();

wrong - this leaves stdout bound to the same file as the parent process so
will be ineffective.

Since the parent process must wait for a sig child, simply redirecting the
output is not a very clean solution. Really you want the new process to run
in a seperate session - its possible to this with fork() and
posix_setsid(), but a much simpler solution is to hand it off to daemon
like 'at':

`echo /usr/bin/php -q $my_php_script | at now`

C.