Re: [Boost-users] boost::thread join() and DLL unloading

Subject: Re: [Boost-users] boost::thread join() and DLL unloading
From: Christopher Pisz (cpisz_at_[hidden])
Date: 2011-09-15 11:15:12

John M. Dlugosz <mpbecey7gu <at> snkmail.com> writes:

> 
> On 9/14/2011 4:48 PM, Christopher Pisz wrote:
> > I've googled for a few hours and seen people mention something to the 
effect
> > of "you cannot call join from DllMain" and "while DLL is unloading", but no
> > explanation or alternative.
> >
> > How would I go about fixing this problem?
> > I don't think I can guarentee noone will ever make a global instance of my
> > class....
> 
> As I recall, the DLLMain's as well as process startup code in the main EXE 
is called with 
> a process mutex, so threads cannot be started until the normal main is 
called.  Likewise 
> at shut-down, but I don't know what happens to other threads.  I suspect 
they are halted 
> before the unloading process begins.  Once your main() returns, at some 
point threads are 
> halted so ensure that threading is done before that!
> 
> I assume you mean the DLL is unloading because the process is terminating.  
I don't know 
> if that's still the case for dynamic LoadLibrary.
> 

Yes, at process terminatation, the dll gets unloaded, which calls a 
constructor, which attempts to join a thread in a class that has created a 
thread with its constructor. I get deadlock.

I did some reading on MSDN and it seems there are severe restrictions on what 
can be done at dll load and unload time. So, I think the solution is to 
implement a c-style init() and shutdown() methods for the DLL to take care of 
any resources it has internally.