Re: Bug: Spawning short-lived threads may crash the memory allocator

[Wolfram Gloger]

Hello,

> We like to report a bug we call "Spawning short-lived threads may crash the
> memory allocator".  
> The bug most probably resides in pthreads.

Sorry, but it's in your program.

> Main part of the memtester program:
> 
> class TSecondThread : public TDetachThread{
> private:
>   TBinarySignal* Signal;
>   char MemoryBlock[TEST_BLOCK_SIZE];
> protected:
>   // Overloads pure virtual function in base class.
>   virtual void Execute() throw ();
> public:
>   TSecondThread(TBinarySignal& signal);
> };
> 
> TSecondThread::TSecondThread(TBinarySignal& signal){
>   Signal = &signal;
> }
> 
> void TSecondThread::Execute() throw (){
>   TBinarySignal* s = Signal;
>   delete this;

Here is the problem.  "delete this" is almost always suspicious.  Here
you are implicitly deallocating the space for the pthread_t descriptor
in your base class TDetachThread.  Note that pthread_create() does
_not_ guarantee that the setting of the pthread_t descriptor occurs
before the thread actually starts running.  Hence the pthread_create()
call in your TDetachThread::Dispatch() method can (and sometimes does)
crash when it finally tries to write the pthread_t descriptor value.

You could for example delete your TSecondThread from the main loop
rather than from the thread itself, then the problem does not occur.
alternatively, make the pthread_t variable local to
TDetachThread::Start().

Regards,
Wolfram.