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Thread-Topic: Safe timeout handling
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Date: Wed, 20 Apr 2016 10:58:00 +0000
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Subject: Safe timeout handling
From: dmitry@zend.com (Dmitry Stogov)

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Hi,


It's a well known PHP problem, that exceeding of execution time-out (max_ex=
ecution_time) may lead to unexpected crashes.

They occur because PHP may be interrupted in inconsistent state, and attemp=
t 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 inter=
preter.

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 (becau=
se of long running internal function), PHP process will be terminated witho=
ut 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" i=
nstead.

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 TIC=
K and signal handling.


Thanks. Dmitry.

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