[Tcl-bugs] [ tcl-Bugs-1909647 ] TclStackFree: incorrect freePtr. Call out of sequence?

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Bugs item #1909647, was opened at 2008-03-07 16:47
Message generated for change (Comment added) made by ctasada
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Category: 69. Other
Group: current: 8.5.1
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Carlos Tasada (ctasada)
Assigned to: miguel sofer (msofer)
Summary: TclStackFree: incorrect freePtr. Call out of sequence?

Initial Comment:
Hi guys,

We're using ActiveTcl 8.5.1, bytecoded with tbcload1.7. From time to time, the application crashes with a "TclStackFree: incorrect freePtr. Call out of sequence?", but so far this happens only in Linux.

We're using threads and sockets actively and usually the crash appears just after a "puts" in a file or after a socket is closed.

I don't even known how to start debugging the problem.

I've been looking into Tcl sourcecode and the first think that I see regarding the use of TclStackFree is that it's used in the Linux version of TclpCreateProcess, but not in Windows. Following this lead I finished in the Tcl_OpenCommandChannel, the one used to process the tcl exec command.

Am I in drunks o could be that some error or wrongly synched command in the Tcl_OpenCommandChannel could be producing this problem?

Any help is more than welcome.

Cheers,
Carlos

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>Comment By: Carlos Tasada (ctasada)
Date: 2008-03-11 14:14

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Hi Miguel,

What do you mean by "wrong timing"? Some "after"? or maybe some async
thread that's released too early? Can the problem be related with some
"exec" command as I said before?

Regarding you questions

1) I already though about that. I doing some changes in the sourcecode and
I have a client that volunteer to test it running from source. Hope I'll
have something new in a couple of days.

2) I'm using threads from scripts.

3) That's the bad part. I'm trying to find how to simplify the problem as
much as possible to have a nice test case. Anyway seems that's related with
some other problem that's leaking memory (I'm looking into that right now).
At the moment that I "puts" to a file, seems that the used memory is too
much and the application crashes.

Best Regards,
Carlos Tasada.

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Comment By: miguel sofer (msofer)
Date: 2008-03-11 13:48

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This definitely looks like a threading problem: wrong timing within the
same thread will cause TclStackFree to bomb reliably.

First let us try to reduce the problem a bit:

(1) tbcload should have nothing to do with this; can you confirm by using
the script sources instead of the precompiled version? I do not know if you
have them available or not, it might be 3rd party code

(2) You are using threads: script or C api? If C: are you respecting Tcl's
threading model, "no calls to an interp from a different thread"? 

(3) Can you reduce the problem to some smallish demo that we can study?

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