PHP :: Bug #49340 :: Signals not catchable when certain functions are in execution

[2009-08-23 22:12 UTC] alexmontoanelli at gmail dot com

Description:
------------
After executions of certain functions,
the handler configured by
posix_singal, are not called where the 
funcion are in execution - like freads.

Reproduce code:
---------------
#!/usr/bin/php
<?php

declare(ticks = 1);

function handler($a){
    echo "Calling handler on signal :  $a\n";
}

//define handlers for signals
pcntl_signal(SIGTERM, 'handler');
pcntl_signal(SIGINT, 'handler');

//if you send a signal, the function fgets are waiting for a user input, he is not called, until you enter something
$foo = fgets(STDIN);

echo $foo;


Expected result:
----------------
alexmm tmp # php a.php 
^C
Calling handler on signal :  2


Actual result:
--------------
alexmm tmp # php a.php 
^C MY_INPUT_AFTER_SEND_CTRL_C
Calling handler on signal :  2
 MY_INPUT_AFTER_SEND_CTRL_C

[2009-08-24 08:54 UTC] sjoerd@php.net

Thank you for your bug report.

I don't fully understand the problem.

Is the problem that you have to hit enter for the signal handler to run? Or that the line with 'echo $foo' is ran after the fgets?

[2009-08-24 11:41 UTC] alexmontoanelli at gmail dot com

The problem is that I need hit enter - exit from fgets - to run the signal handler - but this is not the correct way - in python for example, the signal handler are calling when the function are waiting for a user input.

I found this page - http://br2.php.net/manual/en/function.pcntl-signal.php - the commentary above:

'28-Mar-2006 07:26
Process handling is not available when using a blocking socket! Bear this in mind.'

There is true?

Regards

[2009-08-24 13:04 UTC] alexmontoanelli at gmail dot com

Where I say:

'There is true?',

is

'That's true?'

Regards

[2009-08-27 11:28 UTC] alexmontoanelli at gmail dot com

some position ?

[2009-08-27 19:30 UTC] sjoerd@php.net

PHP signals are implemented with ticks (http://us3.php.net/manual/en/control-structures.declare.php). Ticks are events that occur every so much statements in a script. Since fgets() blocks, no more statements are executed and no more ticks are fired. This means that no signal arrives.

I do not know whether the current behavior is by design or by mistake, so I cannot determine whether it is a bug or not. It would certainly be desirable to be able to interrupt a blocking read by doing Ctrl-C.

[2009-08-31 13:42 UTC] alexmontoanelli at gmail dot com

Ok.But I guess that this behavior is not that anyone expect.

Some one else can give the final word ?

Regards

[2012-01-31 13:53 UTC] nasretdinov at gmail dot com

Actually it is due to syscall restarting by default. You should pass third 
argument as "false" to pcntl_signal and you will be able to catch SIGINT, but 
only after second attempt. The other bug I created (https://bugs.php.net/bug.php?
id=52121) addresses more severe case, I suppose

[2016-07-13 00:24 UTC] anthonyryan1 at gmail dot com

Just encountered this in PHP 7.0.6. The fgets blocking operation still prevents signal handlers from firing.

[2017-01-01 21:53 UTC] dave at mudsite dot com

Another oddity with this is that using pcntl_async_signals() rather than declare(ticks=1) results with no handling of your ^C's

[2018-06-12 12:20 UTC] dnt at gmx dot gom

I also stumbled upon this, I as well think this is not the expected behavior. There exists a third party extension that should work with blocking PHP scripts. I haven't tested it, though. 
https://github.com/rstgroup/php-signal-handler

[2021-07-08 10:17 UTC] cmb@php.net

Related To: Bug #55614

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