[Openmp-dev] Status of detached tasks in Clang

[Joseph Schuchart via Openmp-dev]

Johannes, Alexey,

Thanks for the pointers. I will try to call in to the telco tomorrow.

In the meantime: I was able to install trunk and run tests with detached 
tasks. However, every once in a while I end up in an assert inside libomp:

OMP: Error #13: Assertion failure at kmp_tasking.cpp(920).

The relevant code is in __kmp_task_finish:

   if (taskdata->td_flags.destructors_thunk) {
     kmp_routine_entry_t destr_thunk = task->data1.destructors;
     KMP_ASSERT(destr_thunk); // <- this assert triggers
     destr_thunk(gtid, task);
   }


My first suspicion is that there is a race condition when one thread 
fulfills the event while the executing task completes it. I have not 
been able to spot this issue in the code but maybe someone familiar with 
it has an idea about what might be going wrong?

Thanks,
Joseph

On 4/4/20 6:20 PM, Johannes Doerfert wrote:
> Hi Joseph,
> 
> 
> I'm not sure who is working on this but we might be able to figure this 
> out on our bi-weekly call Wednesday.
> 
> Feel free to call but we should figure this out either way.
> 
> 
> Apologies for the delay,
> 
>    Johannes
> 
> 
> 
> On 4/3/20 7:18 AM, Joseph Schuchart via Openmp-dev wrote:
>> Dear all,
>>
>> I am eager to play around with detached tasks in OpenMP. It seems that 
>> support has gone into the runtime about a year ago [1] but even with 
>> Clang 10 I get a warning that the detach clause is ignored:
>>
>> $ clang-10 -fopenmp test_detached.c
>> test_detached.c:25:47: warning: extra tokens at the end of '#pragma 
>> omp task' are ignored [-Wextra-tokens]
>>   #pragma omp task detach(event)
>>
>> The status website lists detached tasks as work in progress [2]. Is 
>> there a way to try detached tasks in some experimental version of 
>> Clang? Or am I just missing a flag to enable them in the Clang release?
>>
>> Thanks a lot,
>> Joseph
>>
>> [1] https://reviews.llvm.org/D62485
>> [2] https://clang.llvm.org/docs/OpenMPSupport.html
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