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Message Queue problems (?)

From: Tanmay Patwardhan <tpthesis@hotmail.com>
Date: Thu, 08 May 2003 09:35:12 -0500
To: www-lib@w3.org
Message-ID: <Law14-F603zCParqjPi0000251b@hotmail.com>

Hi,

I use libwww as an underlying http library, in a COM dll. When COM is used 
in STA (single threaded apartments), there seems to be some issue with 
libwww and COM win32 message queues.

If libwww in the midst of processing a post request, and a second COM 
request is done, the libwww event loop seems to crash. Now, according to 
STA, this second COM call would be waiting in queue for the first one to 
complete, but since the libwww event loop crashes, this "pair" of calls 
fails.

I am not entirely certain this is the cause of the problem, and was 
wondering whether anyone could throw some light on this.

Thanks and regards,
Tanmay


-----------------------
Tanmay Patwardhan
Applications Developer,
UBS Warburg,
Chicago, IL.
-----------------------





>From: Timothee Besset <ttimo@idsoftware.com>
>To: Timothee Besset <ttimo@idsoftware.com>
>CC: www-lib@w3.org, richard@list03.atterer.net
>Subject: Re: HTLoadToFile crashing after load on FTP URLs,     
>HTRequest_bytesRead  inoperant
>Date: Tue, 6 May 2003 15:00:12 +0200
>
>
>Finally fixed those two bugs by using a few workarounds. I'll post
>something more detailed later, but basically:
>
>For no progress bug:
>added HTFTP_setRawBytesCount and HTFTP_getDNetRawBytesCount to HTFTP.c
>- forcing the raw count to YES (it's already set once at init, but that 
>gets wiped out somehow)
>- using HTFTP_getDNetRawBytesCount, otherwise we get the byte count of 
>control connection and not data conn
>
>For timeout crash:
>
>solution is to disable timeouts while login in so that control socket is 
>not
>affected by timeout, then re-enable to do the download (that way we have 
>timeout on
>data connection, and not on control).
>
>We're in crunch atm, would post something more detailed later
>
>TTimo
>
>On Tue, 6 May 2003 02:19:38 +0200
>Timothee Besset <ttimo@idsoftware.com> wrote:
>
> >
> > Still trying to understand and fix that bug. It is very easy to 
>reproduce,
> > you just need the command line client and an anonymous ftp on which
> > there's a file that will take more than the default timeout to download
> > (20s).
> >
> > I use this for instance
> > w3c -v 
>'ftp://ftp.idsoftware.com/idstuff/wolf/linux/wolf-linux-1.32-1.33-up.x86.run' 
>-o foo.bar
> >
> > Download goes fine, you see timeout expire, and when it triggers the
> > download is aborted. File is incomplete, says timeout reading from host,
> > which is not true.
> >
> > I am suspecting that the problem would be related to
> > HTRequest_bytesRead(request) being broken also (i.e. download keeps 
>going,
> > but request says nothing was read). Because I found those few lines of
> > code in HTFTP.c's FTPEvent function:
> >
> > 	/*
> > 	** Don't time out the control connection if we are actually recieving 
>data
> > 	** on the data connection
> > 	*/
> > 	if (!(soc == HTNet_socket(cnet) && !(data->complete & 1) && 
>HTNet_bytesRead(ctrl->dnet)>0)) {
> > 	    HTRequest_addError(request, ERR_FATAL, NO, HTERR_TIME_OUT, NULL, 0, 
>"HTLoadHTTP");
> > 	    FTPCleanup(request, HT_TIMEOUT);
> > 	}
> >
> > The problem with that, is that when the control connection timeout
> > triggers, the data connection still says bytesRead 0 .. so instead of
> > hacking the timeout and keep going, it fails..
> >
> > TTimo
> >
> > On Mon, 5 May 2003 21:44:12 +0200
> > Timothee Besset <ttimo@idsoftware.com> wrote:
> >
> > >
> > > Below is the trace when the initial timeout reaches 0 (testing with 
>w3c
> > > command line). There is something utterly screwed going on there. It 
>tries
> > > to unregister a socket it can't find, does a few hickups .. then keeps
> > > going as if nothing. Only problem, at the end of the complete 
>download, it
> > > will crash.
> > >
> > > TTimo
> > >
> > > FTP Event... now in state FTP_NEED_DATA
> > > FTP Get Data now in state NEED_BODY
> > > Read Socket. 1400 bytes read from socket 6
> > > Memory Free. 0x80ea828
> > > Memory Free. 0x80e21c8
> > > Event Loop.. calling select: maxfds is 6
> > > ............ READ : 4 6
> > > ............ WRITE:
> > > ............ OOB  :
> > > ............ Timeout is 0 s, 1000 microsecs
> > > Event Loop.. select returns 0
> > > ............ READ :
> > > ............ WRITE:
> > > ............ OOB  :
> > > ............ Timeout is 0 s, 0 microsecs
> > > Memory Free. 0x80e21e0
> > > Timer....... Found timer 0x80e2298 with callback 0x804f1c5, context 
>0x80e2150, and relative timeout 20000
> > > Timer....... Dispatch timer 0x80e2298
> > > Event....... READ timed out on 4.
> > > Host kill... Pipeline due to HTEvent_TIMEOUT event
> > > Host kill... Terminating net object 0x80d8290 from pipe line
> > > Channel..... Semaphore set to 0 for channel 0x80da0a0
> > > Memory Free. 0x80e21e0
> > > Timer....... Deleted active timer 0x80e2298
> > > Memory Free. 0x80e2298
> > > Event....... No more events registered for socket 4
> > > Memory Free. 0x80e2150
> > > Memory Free. 0x80e21a8
> > > Event....... Socket 4 unregistered for HTEvent_READ
> > > Event....... Couldn't find socket 4. Can't unregister type 
>HTEvent_WRITE
> > > Channel..... Delete 0x80da0a0 with semaphore 0, status -902
> > > Channel..... Delete input stream 0x80da0e0 from channel 0x80da0a0
> > > Memory Free. 0x80e2190
> > > Memory Free. 0x80e21f0
> > > FTPStatus... ABORTING...
> > > Channel..... Delete input stream 0x80da0e0 from channel 0x80da0a0
> > > Memory Free. 0x80da0d0
> > > Socket read. FREEING....
> > > Memory Free. 0x80da0e0
> > > Socket write FREEING....
> > > Memory Free. 0x80e2100
> > > Net Manager. Decreasing active sockets to 1, 1 persistent sockets
> > > Channel..... Deleted 0x80da0a0, socket 4
> > > Memory Free. 0x80da0a0
> > > Net Manager. 1 active sockets, decreasing persistent sockets to 0
> > > Host info... removed host 0x80d8f60 as persistent
> > > Event Loop.. calling select: maxfds is 6
> > > ............ READ : 6
> > > ............ WRITE:
> > > ............ OOB  :
> > > ............ Timeout is 19 s, 997000 microsecs
> > > Event Loop.. select returns 1
> > > ............ READ : 6
> > > ............ WRITE:
> > > ............ OOB  :
> > > ............ Timeout is 19 s, 990000 microsecs
> > > Memory Free. 0x80ea808
> > > Timer....... Found timer 0x80e22e0 with callback 0x804f1c5, context 
>0x80ea5b0, and relative timeout 20000
> > > EventOrder.. execute ordered events
> > > Memory Free. 0x80da0d0
> > > EventList... calling socket 6, request 0x80d1810 handler 0x80863fc 
>type HTEvent_READ
> > > Host Event.. READ passed to `ftp://<.......>'
> > > FTP Event... now in state FTP_NEED_DATA
> > > FTP Get Data now in state NEED_BODY
> > > Read Socket. 1400 bytes read from socket 6
> > > Memory Free. 0x80e2190
> > >
> > >
> > > On Mon, 5 May 2003 20:25:24 +0200
> > > Timothee Besset <ttimo@idsoftware.com> wrote:
> > >
> > > >
> > > > I have reproduced the crash with the w3c command line client, and 
>found
> > > > out it is related to timeouts. If the file is small enough to get
> > > > downloaded below the default 20s timeout of w3c command line client
> > > > (ComLine/src/w3c), then we are fine.
> > > >
> > > > When it runs I see the timeout go down, and not being reset to 20s 
>each
> > > > time there is data read from the socket. Once it reaches 0, it gets 
>set
> > > > again to 20s and stops decreasing, it looks like it's properly 
>maintain at
> > > > 20s at this point. But then at the end of the download the crash 
>situation
> > > > I described happens.
> > > >
> > > > I am still looking at what is going on with the timeout thing.
> > > >
> > > > TTimo
> > > >
> > > > On Mon, 5 May 2003 19:53:15 +0200
> > > > Richard Atterer <richard@list03.atterer.net> wrote:
> > > >
> > > > >
> > > > > On Mon, May 05, 2003 at 05:10:02PM +0200, Timothee Besset wrote:
> > > > > > I keep calling HTRequest_bytesRead on each HT_PROG_READ alert 
>callback,
> > > > > > but it remains 0. I can see the file being downloaded and 
>growing though.
> > > > >
> > > > > Hmm, my code uses HTResponse_length(HTRequest_response(request)). 
>I'm not
> > > > > sure whether that works though, since I'm keeping track of the 
>length
> > > > > myself regardless of what libwww says about it.
> > > > >
> > > > > > - After the download has completed, it crashes. Here's what the 
>end of the
> > > > > > trace says:
> > > > > [...]
> > > > >
> > > > > It works for me! See the end of this mail for the debug output I 
>get (with
> > > > > the OpenBSD ftpd and my respective FTP patch applied).  Your FTP 
>server
> > > > > seems to close the connection on you, mine doesn't. Maybe that 
>makes a
> > > > > difference.
> > > > >
> > > > > [This FTP patch of mine is unlikely to affect your problem, it 
>only
> > > > > influences libwww's behaviour before the FTP GET. Check the list 
>archives
> > > > > if you need it.]
> > > > >
> > > > > > HTDoClose... Close 20
> > > > > > Net Manager. Decreasing active sockets to 0, 0 persistent 
>sockets
> > > > > > FTP Get Data now in state NEED_BODY
> > > > >
> > > > > Are you maybe making "recursive" calls to libwww? libwww doesn't 
>like it at
> > > > > all e.g. if you start/stop requests from within callbacks which 
>you
> > > > > registered with it.
> > > > >
> > > > > > Actually, I know how the crash happens, but I haven't thought of 
>a
> > > > > > solution. I thought for a while that it could be related to the 
>ftp
> > > > > > daemon, but I tried a win32 daemon and proftp, and they both 
>cause the
> > > > > > same crash.
> > > > >
> > > > > If you want to have an envious look at Code That Works (woohoo!), 
>look at
> > > > > the things in src/net inside 
><http://atterer.net/jigdo/jigdo-0.7.0.tar.bz2>
> > > > > ;-)
> > > > >
> > > > > [...]
> > > > > > status is HT_CLOSED
> > > > > > ctrl->repcode is 150
> > > > > > data->complete is 1
> > > > >
> > > > > FTP code 150 is "File status okay; about to open data connection", 
>looks
> > > > > like this is still the last status code *before* the error.
> > > > >
> > > > > > But the data->complete |= 2 doesn't trigger. If it would, I 
>*think* that
> > > > > > HTFTP.c would finish the job and exit cleanly.
> > > > >
> > > > > I'm not sure what the problem is - please find out whether the 
>server is
> > > > > using active FTP, whether using passive FTP makes a difference, 
>and whether
> > > > > the socket that's unexpectedly being closed by the remote end is 
>for the
> > > > > control or the data connection.
> > > > >
> > > > > Cheers,
> > > > >
> > > > >   Richard
> > > > >
> > > > > --
> > > > >   __   _
> > > > >   |_) /|  Richard Atterer     |  CS student at the Technische  |  
>GnuPG key:
> > > > >   | \/¯|  http://atterer.net  |  Universität München, Germany  |  
>0x888354F7
> > > > >   ¯ '` ¯
> > > > > ...
> > > > > Read Socket. 2669 bytes read from socket 7
> > > > > Host Event.. READ passed to `ftp://localhost/image'
> > > > > FTP Event... now in state FTP_NEED_DATA
> > > > > FTP Get Data now in state NEED_BODY
> > > > > Read Socket. FIN received on socket 7
> > > > > HTDoClose... Close 7
> > > > > Net Manager. Decreasing active sockets to 1, 1 persistent sockets
> > > > > FTP Get Data now in state SUB_SUCCESS
> > > > > FTP Event... now in state FTP_SUCCESS
> > > > > Channel..... Delete input stream 0x8247078 from channel 0x82248f0
> > > > > Channel..... Delete input stream 0x8247078 from channel 0x82248f0
> > > > > Net Object.. Delete 0x8225a70 and call AFTER filters
> > > > > Host info... Remove 0x8225a70 from pipe
> > > > > Host Object. closing socket -1
> > > > > Channel..... Semaphore set to 0 for channel 0x82248f0
> > > > > Channel..... Delete 0x82248f0 with semaphore 0, status 900
> > > > > Channel..... Semaphore decreased to 0 for channel 0x82248f0
> > > > > Host info... removed host 0x8237f98 as persistent
> > > > > Net Object.. Check for pending Net objects
> > > > > Net Object.. Freeing object 0x8225a70
> > > > > Net Object.. Delete 0x823ccc8 and call AFTER filters
> > > > > Host info... Remove 0x823ccc8 from pipe
> > > > > Host Object. keeping persistent socket 5
> > > > > Channel..... Delete 0x822c598 with semaphore 1, status 200
> > > > > Channel..... Delete input stream 0x823f058 from channel 0x822c598
> > > > > Channel..... Delete input stream 0x823f058 from channel 0x822c598
> > > > > Channel..... Semaphore decreased to 0 for channel 0x822c598
> > > > > Timer....... Created one shot timer 0x822cb10 with callback 
>0x809e9e8,
> > > > > context 0x8224940, and relative timeout 60000
> > > > > Host........ Object 0x8224940 going idle...
> > > > > Net Object.. Check for pending Net objects
> > > > > Net Object.. Freeing object 0x823ccc8
> > > > > Net After... calling 0x809363c (request 0x8224a60, response 
>0x823a4c8,
> > > > > status 200, context (nil))
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> >
> >
>

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Received on Thursday, 8 May 2003 10:35:19 GMT

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