Safe timeout handling

Hi Dmitry,

----- Original Message -----
From: "Dmitry Stogov"
Sent: Wednesday, April 20, 2016

Hi,

It's a well known PHP problem, that exceeding of execution time-out
(max_execution_time) may lead to unexpected crashes.

They occur because PHP may be interrupted in inconsistent state, and
attempt
to release allocated by request resources leads to failure.

Almost any big site sees these crashes from time to time.

I propose to delay actual request termination until a "safe" point in
interpreter.

Signal handler will just set EG(timed_out) flag.

Interpreter will check this time from time to time (on jumps and calls
that
may make loops or recursion) and perform the actual termination.

This approach already works in PHP for Windows.

I was thinking about this, checking for things like EG(exception)
"constantly," a few months ago for another reason...

What about instead of adding additional checks in the same place(s) in VM,
we just limit it to 1 check, for multiple things? Just have
EG(something_unexpected_to_check), and behind that (or in a function, I
guess), the actual rare/unexpected thing gets checked: timed_out, exception,
etc.

It seems Bob had a similar idea in the PR comment, except literally using
exceptions...

In addition I introduce hard_timeout (default value 2 seconds).

In case the "soft" timeout wasn't handled "safely" in that 2 seconds
(because of long running internal function), PHP process will be
terminated
without attempt to free any resources.

ZTS build will ignore "hard_timeout" (in the same way as PHP on Windows
do).

The PR: https://github.com/php/php-src/pull/1876

It removes "exit_on_timeout" ini directive, and introduces "hard_timeout"
instead.

Additional checks in VM make 0.5-1% slowdown in term of instruction
retired
reported by callgrind.

A single check would save those additional instructions and branches, and
would actually improve things on Windows (since this PR doesn't change
anything there).

I think we don't need RFC for this. This is a long time desired fix.

The same "interrupt" handling mechanism in the future may be reused for
TICK
and signal handling.

Thanks. Dmitry.

• Matt

Hi Dmitry,

-----Original Message-----
From: Dmitry Stogov [mailto:dmitry@zend.com]
Sent: Wednesday, April 20, 2016 12:58 PM
To: Nikita Popov nikita.ppv@gmail.com; Rasmus Lerdorf
rasmus@lerdorf.com; Anatol Belski ab@php.net; Antony Dovgal
antony.dovgal@gmail.com; Zeev Suraski zeev@zend.com; Xinchen Hui
laruence@php.net
Cc: internals internals@lists.php.net
Subject: [PHP-DEV] Safe timeout handling

Hi,

It's a well known PHP problem, that exceeding of execution time-out
(max_execution_time) may lead to unexpected crashes.

They occur because PHP may be interrupted in inconsistent state, and
attempt
to release allocated by request resources leads to failure.

Almost any big site sees these crashes from time to time.

I propose to delay actual request termination until a "safe" point in
interpreter.

Signal handler will just set EG(timed_out) flag.

Interpreter will check this time from time to time (on jumps and calls
that may
make loops or recursion) and perform the actual termination.

This approach already works in PHP for Windows.

In addition I introduce hard_timeout (default value 2 seconds).

In case the "soft" timeout wasn't handled "safely" in that 2 seconds
(because of
long running internal function), PHP process will be terminated without
attempt
to free any resources.

ZTS build will ignore "hard_timeout" (in the same way as PHP on Windows
do).

The PR: https://github.com/php/php-src/pull/1876

It removes "exit_on_timeout" ini directive, and introduces "hard_timeout"
instead.

Additional checks in VM make 0.5-1% slowdown in term of instruction
retired
reported by callgrind.

I think we don't need RFC for this. This is a long time desired fix.

The same "interrupt" handling mechanism in the future may be reused for
TICK
and signal handling.

I've tested your patch with CLI, mpm_prefork, mpm_worker and mpm_winnt and
see no regressions. The existing tests in tests/*/timeout.phpt pass as
well. We'd probably need to add some more with respect to the new INI option
and more extensive testing under high load.

AFM it's a good step towards unifying the timeout handling and making it
safer. Even better if ticks and exceptions handling can be later improved by
the same approach.

Regards

Anatol

Hi,

It's a well known PHP problem, that exceeding of execution time-out (max_execution_time) may lead to unexpected crashes.

They occur because PHP may be interrupted in inconsistent state, and attempt to release allocated by request resources leads to failure.

Almost any big site sees these crashes from time to time.

I propose to delay actual request termination until a "safe" point in interpreter.

Signal handler will just set EG(timed_out) flag.

Interpreter will check this time from time to time (on jumps and calls that may make loops or recursion) and perform the actual termination.

This approach already works in PHP for Windows.

In addition I introduce hard_timeout (default value 2 seconds).

In case the "soft" timeout wasn't handled "safely" in that 2 seconds (because of long running internal function), PHP process will be terminated without attempt to free any resources.

ZTS build will ignore "hard_timeout" (in the same way as PHP on Windows do).

The PR: https://github.com/php/php-src/pull/1876

It removes "exit_on_timeout" ini directive, and introduces "hard_timeout" instead.

Additional checks in VM make 0.5-1% slowdown in term of instruction retired reported by callgrind.

I think we don't need RFC for this. This is a long time desired fix.

The same "interrupt" handling mechanism in the future may be reused for TICK and signal handling.

Thanks. Dmitry.

Hi !

Good new.

No RFC needed, but that breaks ABI and could impact extensions.
So, 7.1 as target is OK, not 7.0

Julien.P