[Omp] Critical Section deadlock

[Andreas Gajda]

Dear cOMPunity!

I have a question about nested critical sections. Supposed a subroutine sub1 is enclosing a critical section and in this section another subroutine sub2 is called, which contains another critical sections (with the same or a different name).

Is this causing a deadlock or not?

Specification 2.5. says: "A thread waits at the beginning of a critical region until no other thread is executing a critical region with the same name"

Does this mean, the thread must be able to decide, that he already is executing the named critical section and enter the second "part" of the same critical section? On the other hand, if he tests if the critical section is already entered by any thread, he have to wait until "he" is leaving the section. This is the deadlock.

I tested it with two programs and the Intel 9.1 Fortran compiler on a linux platform. Program 1 caused a deadlock and program 2 haven't caused a deadlock. (see below)

The second one is expected, because the critical sections have different names. 

Maybe someone can tell me, if my first interpretation of the specification is correct or not. Or if this is already discussed somewhere.

Thank you very much in advance.

Andreas Gajda

#####################################################################
      program deadlocktest1
      use omp_lib

      call omp_set_num_threads(4)
      print  *,"start test"
      call sub1
      print  *,"test passed. No deadlocks occured!"
      stop
      contains

      subroutine sub1()
      integer       :: me
!$OMP PARALLEL PRIVATE (me)
      me=omp_get_thread_num()
      print *,me
!$OMP CRITICAL
      print *,"First critical section entered by thread: ", me
      call sub2(me)
      print *,"First critical section is left by thread: ", me
!$OMP END CRITICAL
!$OMP END PARALLEL
      return
      end subroutine

      subroutine sub2(me)
      integer me
!$OMP CRITICAL
      print *,"If you can read this, thread ", me," is not deadlocked."
!$OMP END CRITICAL
      return
      end subroutine

      end program

#####################################################################
      program deadlocktest2
      use omp_lib

      call omp_set_num_threads(4)
      print  *,"start test"
      call sub1
      print  *,"test passed. No deadlocks occured!"
      stop
      contains

      subroutine sub1()
      integer       :: me
!$OMP PARALLEL PRIVATE (me)
      me=omp_get_thread_num()
      print *,me
!$OMP CRITICAL (first)
      print *,"First critical section entered by thread: ", me
      call sub2(me)
      print *,"First critical section is left by thread: ", me
!$OMP END CRITICAL (first)
!$OMP END PARALLEL
      return
      end subroutine

      subroutine sub2(me)
      integer me
!$OMP CRITICAL (second)
      print *,"If you can read this, thread ", me," is not deadlocked."
!$OMP END CRITICAL (second)
      return
      end subroutine

      end program

#####################################################################
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.openmp.org/pipermail/omp/attachments/20060802/15035765/attachment.html