On Wed, 9 Aug 2006, Nitin Hande wrote:
> C, Kiran (STSD) wrote:
>>
>> HI,
>>
>> I have a doubt in mdb.
>>
>> When I do, ::threadlist -v it will list all the kernel threads
>>
>> In the Solaris OS, the WCHAN column is the address of a synchronization
>> variable on which the thread is blocked.
>>
>> Say, There is a thread called abcd() which is blocked, and the address
>> of the sychronization variable say xxxx
>>
>> I want to know which function in this thread is holding this lock so
>> that I can look into that function in more detail.
>>
>
> But threadlist -v also shows the stacktrace of the thread doing wait...or am
> I not understanding your question ?
Misunderstanding on both parts :)
Condition variables are not locks. They're a "synchronization primitive"
(as are semaphores, mutexes, rwlocks, spinlocks, ...), but not every
synchronization primitive has/needs an owner ...
When a thread is waiting on a condition variable, there will not be an
"owner" of the lock. Blocking on a condition variable is an indication of
state - the thread has an expectation about an event/statechange to happen
that hasn't happened yet. Code that waits on condition variables always
looks like this:
mutex_enter(somelock);
while (cond_not_met)
cv_wait(condvar, somelock);
[ ... perform action now ... ]
mutex_exit(somelock);
That cv_wait(9f) requires a mutex is for synchronizing wakeups (avoid
thundering herds). While threads sleep on a condvar the lock is unheld.
It'll be pure coincidence if during that time another thread happens to
hold that lock. Unless, of course, you have a systematic problem where the
thread that is supposed to perform the wakeup, aka call either of the two
cv_signal(9f)/cv_broadcast(9f), has acquired the mutex already but is now
stuck/looping itself somewhere.
Condition variables have no owners. They only have waiters.
The mutex required for going to sleep on a condvar may have an owner. But
it will only while a thread is in such a critical section, and that will,
usually, not be true for 99.99% of the time the waiters are blocked on the
condvar.
FrankH.
>
> Thanks
> Nitin
>
>> Or is there any other command in mdb where we can find who is holding
>> the lock in a blocked thread
>>
>>
>>
>> Regards
>>
>> Kiran
>> _______________________________________________
>> mdb-discuss mailing list
>> mdb-discuss at opensolaris.org
>>
>
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>
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