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RE: Bug in HTTimer.c

From: Jens Meggers <jens.meggers@firepad.com>
Date: Wed, 28 Feb 2001 11:05:58 -0800
Message-ID: <DDF913B74F07D411B22500B0D0206D9F1853B9@FIREPLUG>
To: "'www-lib@w3.org'" <www-lib@w3.org>
Hi,

I applied the patch to my source base. It fixes a lot of problems apprearing
under high load when processing requests loaded from a file (HTFile.c) mixed
up with requests loading from the network (HTTCP.c). As the HTCache is using
such kind of system, it also make the cache reliable.

Thanks for finding the bug,

Jens


-----Original Message-----
From: Stefan Wiesner [mailto:sw@ais-ag.de]
Sent: Montag, 26. Februar 2001 06:11
To: www-lib@w3.org
Subject: Bug in HTTimer.c


Hi,

I think there is a bug in the code of function HTTimer_new if a timer
is already expired when HTTimer_new is called. See description below:


>>> ...
>>>    /*
>>>    **  Sort new element into list
>>>    */
>>>    for (cur = last; 
>>>	    (pres = (HTTimer *) HTList_nextObject(cur)) != NULL &&
pres->expires < expires; 
>>>	    last = cur);

       last                     cur
   	|                        |
   	|                        |
   	V                        |
     --------                    |
     |object|--->timer1          V
     |      |                 --------
     |next  |---------------->|object|--->timer2
     --------                 |      |
   			      |next  |--->...
   			      --------

>>> ...
>>>    /*
>>>    **	add to list if timer is new
>>>    */
>>>    HTList_addObject(last, (void *)timer);

       last                                               cur
   	|                                                  |
   	|                                                  |
   	V                                                  |
     --------                                              | 
     |object|--->timer1                                    |
     |      |                 --------                     |
     |next  |---------------->|object|--->timer_new        V
     --------                 |      |                  --------
   			      |next  |----------------->|object|--->timer2
   			      --------                  |      |
                                                        |next  |--->...
                                                        --------

>>> ...
>>>    /* Check if the timer object has already expired. If so then dispatch
*/
>>>    if (timer->expires <= now) Timer_dispatch(cur, last);
>>> ...

If the 'if' evaluates to 'TRUE', function 'Timer_dispatch' is called
with wrong parameters. As the result, the HTList object pointing to
timer_new gets lost and the callback function of timer2 is called.

To fix this, the previous call of function
'HTList_addObject(last, (void *)timer);' should be replaced by
'cur = HTList_addList(last, (void *)timer);'


One other thing to the Timer handling:
Although it is a good idea to dispatch the timer in function
'HTTimer_new'
when it has already expired, (I think) there is no way to get this
information
from the parameter the function returns. This behaviour may lead to
errors in a calling program. (In fact it has in my program.)


Greetings


Stefan Wiesner

-- 
Stefan Wiesner
AIS Automations- und Informationssysteme GmbH
Rheinweg 7, 34131 Kassel, Germany
Telefon: +49-561/30859-24, Telefax: +49-561/30859-39
Received on Wednesday, 28 February 2001 14:15:54 GMT

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