Cancelling a PTHREAD_CANCEL_DISABLE thread

[Neale.Ferguson@SoftwareAG-USA.com]

Title: Cancelling a PTHREAD_CANCEL_DISABLE thread





I have a test program that creates a thread which has the attribute of "PTHREAD_CANCEL_DISABLE". This child thread will issue a pthread_cond_wait for a condition to be raised (i.e. it will enqueue(&cond->__c_waiting, self)). The main program attempts (and expects to fail) to pthread_cancel() this thread before waking it with a pthread_cond_signal(). However, pthread_cancel() is calling the extricate function below without checking if the thread is cancellable. The extricate function removes the entry from &cond->__c_waiting. The pthread_cond_wait()is woken by the cancel but, correctly, determines that the thread is not cancellable and ignores the signal. The main routine then issues the pthread_cond_signal() but because the queue entry has been removed by the extricate function it is effectively a no-op. The process is now dead in the water.  

Should cancel.c be changed to detect that the thread is not cancellable or should that test be performed in the extricate routine?

/* If the thread has registered an extrication interface, then          
   invoke the interface. If it returns 1, then we succeeded in          
   dequeuing the thread from whatever waiting object it was enqueued    
   with. In that case, it is our responsibility to wake it up.          
   And also to set the p_woken_by_cancel flag so the woken thread       
   can tell that it was woken by cancellation. */                       
                                                                        
if (pextricate != NULL) {                                               
  dorestart = pextricate->pu_extricate_func(pextricate->pu_object, th); 
  th->p_woken_by_cancel = dorestart;                                    
}                                                                     ÂÂ