Subj : Re: Answer David Schwartz 's question
To   : comp.programming.threads
From : David Schwartz
Date : Tue Apr 05 2005 01:09 pm


"David Hopwood" <david.nospam.hopwood@blueyonder.co.uk> wrote in message 
news:o1z4e.32961$C12.3726@fe1.news.blueyonder.co.uk...
> Oliver Battenfeld wrote:
>> David Schwartz wrote:
>>
>>>>Can't main thread do anything after STOP other threads?
>>>
>>>    Nope. Suppose another thread was in the middle of 'malloc' when you
>>>stopped it.
>>
>> Question then: What happens, if one such thread is preempted "in the 
>> middle
>> of malloc" by the main thread?
>
> If the main thread needs the malloc lock, it blocks at that point, and the
> thread that holds the lock eventually gets rescheduled and releases it.
>
> (The reply by David Schwartz misunderstood what you meant by "preempt", I 
> think.)

    Perhaps. If by "pre-empt" he just means the normal scheduling mechanism, 
then there's no problem because the thread will run later and nothing any 
other thread can do will stop it from finishing its call to 'malloc' and 
releasing the lock. If by "pre-empt" he means the thread is stopped some way 
by another thread and only that thread can release it, then if that thread 
calls 'malloc' (which any function might call 'under-the-hood' unbeknownst 
to you) then we have a fatal deadlock.

    DS

.