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RE: Problem using PThreads TLS from a DLL.
- From: "Aurelio Medina" <AMedina at xcaliber dot com>
- To: <hanasim at yahoo dot com>
- Cc: "Ross Johnson" <rpj at ise dot canberra dot edu dot au>,<pthreads-win32 at sources dot redhat dot com>,"Pat Bacon" <pbacon at xcaliber dot com>
- Date: Thu, 7 Feb 2002 12:27:18 -0600
- Subject: RE: Problem using PThreads TLS from a DLL.
I didn't write specific test code.
The second argument was a function declared in MY-DLL that called free().
From: mmh [mailto:email@example.com]
Sent: Thursday, February 07, 2002 11:20 AM
To: Aurelio Medina
Cc: Ross Johnson; firstname.lastname@example.org; Pat Bacon
Subject: Re: Problem using PThreads TLS from a DLL.
If you have written the test code which you explained, it would be
great if you could post the code.
I was just wondering what was specified as the second argument to
function pthread_key_create(). Was it a function in MY-DLL or just free()?
>I have found the real problem and a resolution for this problem. I will summarize the problem and the solution that applies only if you are using the PThreads DLL from within another DLL.
>[MY-APP] uses [MY-DLL] which uses [PTHREADS-DLL]
>For simplicity assume you have only one thread, that is the MY-APP/MY-DLL/PTHREAD-DLL address spaces are all within the same thread.
>1) MY-APP implicitly loads MY-DLL and PTHREADS-DLL.
>2) MY-DLL allocates TLS data (calloc()) and sets up a destructor (pthread_key_create()).
>3) MY-APP does some work.
>4) MY-APP calls exit().
>5) MY-DLL is unloaded and therfore its address space is invalidated.
>6) PTHREADS-DLL calls the TLS destructor on memory that was in MY-DLL's address space.
>7) MY-APP crashes :(
>When MY-DLL receives a DLL_PROCESS_DETACH in DllMain() (i.e. Step 5) I free() the TLS data and unset the destructor (pthread_key_delete()). Therefore when PTHREADS-DLL unloads it won't call my invalid destructor function which tries to delete invalid memory. MY-DLL unloads before PTHREADS-DLL because it is dependent on it.
>PS If you know of a better way please let me know.
>Anyhow hope this may help others later,
>From: Ross Johnson [mailto:email@example.com]
>Sent: Wednesday, February 06, 2002 9:06 PM
>To: Aurelio Medina
>Cc: firstname.lastname@example.org; Pat Bacon
>Subject: Re: Problem using PThreads TLS from a DLL.
>Aurelio Medina wrote:
>>I've encountered a problem when using the PThreads-Win32 (PThreadVCE)
>>thread local storage (TLS) routines from within my own DLL. Before I
>>dig any deeper I would like to know if anyone has seen this and/or has
>>a workaround. My DLL is calloc'ing TLS data and I believe the TLS
>>destructors (which I have calling free) are firing within the main app
>>and not within my DLL. This causes the app that uses my DLL to crash
>>in the TLS destructor when calling free. It crashes beacuse the app is
>>trying to free CRT memory allocated by my DLL. Is there some PThread
>>function that I can call in my DLLMain to cause the TLS destructors to
>>fire when my DLL is detached?
>Do I understand the problem correctly: is this because the memory is
>unallocated when your DLL is unloaded and therefore free()
>Are you able to join those threads before unloading
>your DLL? Pthread_join() will call the destructors
>for you when the threads exit.
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