omp task bug with private and firstprivate

[Patrice_l_]

Hi,

I think there is a bug with the following simplified code, ifort is giving forrtl: severe (151): allocatable array is already allocated, when compiled with ifort -fopenmp -O2. when compiled with -C it seems to give the good results.

module toto
implicit none
type t
double precision,dimension(:),allocatable :: a
      contains
      procedure,pass :: copy_t
      generic,public :: assignment(=) => copy_t
end type t
contains
subroutine copy_t(t1,t2)
      class(t),intent(in) :: t2
      class(t),intent(out) :: t1
      allocate(t1%a(size(t2%a)),source=t2%a)
end subroutine
end module toto

program foo

use toto
use omp_lib
implicit none
type(t) :: g1,g2,g3
      integer :: i,j

!$omp parallel
!$omp master      
allocate(g2%a(10),g3%a(10))
g2%a=-1
do i=1,10
      !$omp task shared(g2,g3) private(g1)
      !$ print *,omp_get_thread_num(),allocated(g1%a)
        g1=g2
        do j=1,20
                g3%a=g1%a+j
        end do   
        !$omp end task   
        g2%a=i
        !$omp taskwait
        g1=g2
        !$omp task shared(g3) firstprivate(g1)
      !$ print *,omp_get_thread_num(),allocated(g1%a)
        do j=1,20
                g3%a=g1%a+j
        end do   
        !$omp end task   
        g2%a=i+1
        !$omp taskwait

end do
print *,'g3a',g3%a
!$omp end master      
!$omp end parallel

end program foo

[jimdempseyatthecove]

you may need to add COPYIN(g1) or firstprivate(g1) on line 12 to assure you receive a copy of the not-allocated array descriptor of g1%a. IOW you need to copy in the state of the array descriptor.

There was some discussion elsewhere, where private(x) should imply any constructors involved with x but that some cases were overlooked.

Jim Dempsey

[Patrice_l_]

Actually firstprivate gives worst result :

*** Error in `./a.out': double free or corruption (fasttop): 0x0000000000708e30 ***
           0 T
           2 T
           6 T
======= Backtrace: =========
/lib64/libc.so.6(+0x7d1fd)[0x2aaaab5ab1fd]
./a.out[0x4255e0]
./a.out[0x40b26b]
./a.out[0x40bbf8]
./a.out[0x4086e1]
./a.out[0x4059f6]
/data/apps/Intel/2016/lib/intel64/libiomp5.so(+0x98d3a)[0x2aaaab069d3a]
/data/apps/Intel/2016/lib/intel64/libiomp5.so(+0x99666)[0x2aaaab06a666]
/data/apps/Intel/2016/lib/intel64/libiomp5.so(+0x49a6f)[0x2aaaab01aa6f]
/data/apps/Intel/2016/lib/intel64/libiomp5.so(+0x4ad59)[0x2aaaab01bd59]
/data/apps/Intel/2016/lib/intel64/libiomp5.so(+0x74f20)[0x2aaaab045f20]
/data/apps/Intel/2016/lib/intel64/libiomp5.so           3 T
/lib64/libpthread.so.0(+0x7df5)[0x2aaaab319df5]

I think its more complicated than that, since the first iteration works, but not the later.

[jimdempseyatthecove]

Place a print statement in your copy_t assignment function. Also add "Task 1" and "Task 2" to the trace lines such that they can be disambiguated by the reader of your log files. Also add to the trace line LOC(g1).

From the first line of your output above, it indicates that the private(g1) is calling your copy_t function. The firstprivate(g1) may also exhibit this behavior too.

Jim Dempsey

[Patrice_l_]

Hi jim,

Here, is a modified version, still triggers the bug. Note that if the omp waittask is commented it goes without error.

module toto
use omp_lib
implicit none
type t
double precision,dimension(:),allocatable :: a
      contains
      procedure,pass :: copy_t
      generic,public :: assignment(=) => copy_t
end type t
contains
subroutine copy_t(t1,t2)
      class(t),intent(in) :: t2
      class(t),intent(out) :: t1
      print *,'copy_t',omp_get_thread_num(),LOC(t1)
      allocate(t1%a(size(t2%a)),source=t2%a)
end subroutine
end module toto


program foo
use toto
use omp_lib
implicit none
type(t) :: g1,g2,g3
integer :: i,j

!$omp parallel
!$omp master      
allocate(g2%a(10),g3%a(10))
g2%a=-1
do i=1,10
      !$omp task shared(g2,g3) private(g1) 
      !$ print *,'task1',omp_get_thread_num(),i,allocated(g1%a),LOC(g1)
        g1=g2
        do j=1,20
                g3%a=g1%a+j
        end do   
        !$omp end task   
        g2%a=i
        !!omp taskwait
        g1=g2
        !$omp task shared(g3) firstprivate(g1)
      !$ print *,'task2',omp_get_thread_num(),allocated(g1%a),LOC(g1)
        do j=1,20
                g3%a=g1%a+j
        end do   
        !$omp end task   
        g2%a=i+1
        !$omp taskwait

end do
        !$omp taskwait
print *,'g3a',g3%a
!$omp end master      
!$omp end parallel

end program foo

Compiled with -fopenmp -O2 -C -g -traceback , the error log is : 

 ./a.out 
 task1           2           1 F        46912614975672
 copy_t           0       140737488343616
 copy_t           2        46912614975672
 task2           4 T        46912614973464
 task1           4           2 F        46912614971192
 copy_t           0       140737488343616
 copy_t           4        46912614971192
 task2           3 T        46912614968984
 copy_t           0       140737488343616
 task1           1           3 F        46912614966712
 task2           0 T        46912614964504
 copy_t           1        46912614966712
 copy_t           0       140737488343616
 task1           4           4 F        46912614964536
 copy_t           4        46912614964536
 task2           3 T        46912614962200
forrtl: severe (151): allocatable array is already allocated
Image              PC                Routine            Line        Source             
a.out              0000000000421057  Unknown               Unknown  Unknown
a.out              000000000040465E  toto_mp_copy_t_            15  bugomptask.f90
a.out              0000000000403824  MAIN__                     34  bugomptask.f90
libiomp5.so        00002AAAAB069D3A  Unknown               Unknown  Unknown
libiomp5.so        00002AAAAB06A666  Unknown               Unknown  Unknown
libiomp5.so        00002AAAAB01AA6F  Unknown               Unknown  Unknown
libiomp5.so        00002AAAAB01BD59  Unknown               Unknown  Unknown
libiomp5.so        00002AAAAB045F20  Unknown               Unknown  Unknown
libiomp5.so        00002AAAAB074EE3  Unknown               Unknown  Unknown
libpthread.so.0    00002AAAAB319DF5  Unknown               Unknown  Unknown
libc.so.6          00002AAAAB8281AD  Unknown               Unknown  Unknown