[osg-users] OpenThreads threading bug on creation/deletion (leads to crashes)

Adam Coates acoates at stanford.edu
Thu Sep 20 04:26:26 PDT 2007

Hi, Robert,

The following is sufficient (basically what you said):

#include <OpenThreads/Thread>

class MyThread : public OpenThreads::Thread {
  void run(void) { }

int main(int argc, char* argv[]) {
    MyThread thread;
  while(1) ;
  return 0;

You need the while(1) ; to prevent the process from dying and cleaning
up the thread before it wrecks.  This alone wouldn't reproduce the bug
because the interleaving doesn't happen (it's a very short window in
which it can happen).  To force the bug, I added  ::usleep(1000000) at
the beginning of ThreadPrivateActions::StartThread().


On 9/20/07, Robert Osfield <robert.osfield at gmail.com> wrote:
> Hi Adam,
> On 9/20/07, Adam Coates <acoates at stanford.edu> wrote:
> > So, I just realized that the OSG folks are not synonymous with the
> > OpenThreads folks.  ^_^  Sorry for dropping this on the wrong list
> > then.
> Well OpenThreads list is a flat line, almost  all (99.9%) OpenThreads
> activity and development is done by members of the OpenSceneGraph
> community.  So this is probably the best place to raise issues like
> this.  Responsibility for maintaining OpenThreads has also fallen on
> my shoulders as it effectively became an orphaned project when the
> original project lead got sucked into non coding management.
> >In that light, it may not even be considered a bug in OT,
> > since, theoretically, it might be unfair to call the Thread destructor
> > while the thread is running (even though I'm pretty sure they intended
> > isRunning() to work as we'd expect).
> Well this type of usage is kinda abusing the Thread class, but I'd
> still say this way a bug.
> > It should be possible to add a workaround in the following way:
> >
> > 1.  Before starting the thread, set a flag to indicate that the thread
> > is "starting up".
> > 2.  Have the thread's run() routine unset this flag.
> >
> > Before deleting the Thread, make sure that both the "starting up" flag
> > and the isRunning flag are false.  One of these will have to be true
> > if the thread has not reached the run() method yet, or has not
> > completely exited from run() -- thus avoiding the problem.
> I'll have ponder in this issue, I'm more inclined to use a mutex in
> some way that just a straight flag.
> > My question:  does somebody want me to implement this workaround and
> > submit it to you?  Alternatively, I can just point out the break to
> > the OpenThreads people and we can wait for a patch...
> It's best to just roll your sleeves up and get stuck in.  First up we
> need a test that can reliably reproduce the error.  Would the
> following code block do the trick?
>   {
>        OpenThreads::Thread thread;
>        thread.startThread();
>    }
> Robert.
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