U++ framework: U++ MT-multithreading and servers

Home » U++ Library support » U++ MT-multithreading and servers » MT again

Show: Today's Messages :: Polls :: Message Navigator
E-mail to friend

Re: MT again (SOLVED!) [message #28174 is a reply to message #24029]

Fri, 20 August 2010 11:45

mdelfede
Messages: 1313
Registered: September 2007

Ultimate Contributor

Well, just for reference I'll post a bug that drove me crazy for long time Smile

Here the sample code :

void ThreadCb(void)
{
    INTERLOCKED_(mutex) {
        inThread = true;
    }

    << DO SOME TIME CONSUMING STUFFS>

    INTERLOCKED_(mutex) {
        inThread = false;
}

bool StartThread(void)
{
    bool inTh;
    INTERLOCKED_(mutex) {
        inTh = inThread;
    }
    if(inTh)
        return false;
    myThread.Run(ThreadCb);
    return true;
}

Purpose is clear, just start the thread *ONLY* if not already running, return true if success or false if thread was already running.
Where's the caveat ? It's simply in the time BETWEEN the start of ThreadCb() callback and the setting of 'inThread' variable to true. If code calls fast enough the StartThread() routine, it can happen that the Thread callback is in the middle of startup code BUT has still NOT SET the 'inThread' flag; so the StartThread() routine believes thread isn't running and calls it again.
The solution :

void ThreadCb(void)
{
    << DO SOME TIME CONSUMING STUFFS>

    INTERLOCKED_(mutex) {
        inThread = false;
}

bool StartThread(void)
{
    bool inTh;
    INTERLOCKED_(mutex) {
        inTh = inThread;
    }

    if(inTh)
        return false;
    inThread = true;
    myThread.Run(ThreadCb);
    return true;
}

So, I've moved the 'inThread' flag SETTING from the thread routine to its caller; the reset still belong to thread routine.
Now it's the caller that has the responsibility of setting the variable, so it can't happen that thread routine performs some stuffs between check and launch.

Ciao

Max

Report message to a moderator

[Message index]

		MT again By: mdelfede on Fri, 18 December 2009 12:03
		Re: MT again (SOLVED!) By: mdelfede on Fri, 18 December 2009 12:51
		Re: MT again (SOLVED!) By: mirek on Sat, 19 December 2009 11:55
		Re: MT again (SOLVED!) By: mdelfede on Fri, 20 August 2010 11:45
		Re: MT again (SOLVED!) By: koldo on Fri, 20 August 2010 12:22
		Re: MT again (SOLVED!) By: mdelfede on Fri, 20 August 2010 16:42

Previous Topic:	HttpQuery - not working?
Next Topic:	CGI-BIN bug with Apache Server

Goto Forum:

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Fri Sep 18 15:39:01 GMT+2 2026

Total time taken to generate the page: 0.00633 seconds