Skip to content

exit data delete on data that is not present

A common pattern is to tear down device data with !$acc exit data delete(var). But what should happen if var is not present on the device at the point of the delete — either because it was never copied in, or because a previous delete already removed it?

The OpenACC 3.3 specification answers this in the definition of the delete clause (section 2.7.11):

OpenACC 3.3 section 2.7.11 
For each var in var-list, if var is in shared memory, no action is taken; if var is not in shared
memory, the delete clause behaves as follows:
• If the dynamic reference counter for var is zero, no action is taken.
• Otherwise, a detach action is performed if var is a pointer reference, and the dynamic
  reference counter is updated if var is not a null pointer:
  – On an exit data directive with a finalize clause, the dynamic reference counter is set to zero.
  – Otherwise, a present decrement action with the dynamic reference counter is performed.
If both structured and dynamic reference counters are zero, a delete action is performed.

If var was never placed on the device, its dynamic reference counter is zero, so the rule is explicit: "no action is taken." The delete is a silent no-op. This is reinforced by the Delete Action definition, which states "A delete action for a var occurs only when var is present in device memory."

The data clause errors in section 2.7.3 confirm that there is no not-present error for delete: acc_error_not_present is only issued for a var in a present clause, never for delete. So per the specification, both programs below should run to completion and print OK.

exit data delete on never-present data

Here host_mem is never copied to the device, yet it is immediately deleted:

Code 
program main
  use openacc
  implicit none
  real :: host_mem

  host_mem = 4
  !$acc exit data delete(host_mem)
  write(*,*) "OK"
end program
Compiler Result Correctness Notes
Cray Fortran 19.0.0 ❌ Crash Not per spec — should be a no-op Runtime abort: CRAY_ACC_ERROR - Variable not found in present table; exits with code 1.
nvfortran 25.3-0 ❌ Crash Not per spec — should be a no-op Segmentation fault in __pgi_uacc_dataexitstart2. nvfortran 24.9 behaves identically.

The Cray runtime error:

Error 
ACC:            find_in_present_table failed for 'host_mem' (...) from exit_data_not_present.f90:7
ACC: libcrayacc/acc_runtime.c:890 CRAY_ACC_ERROR - Variable not found in present table

Double exit data delete

Here host_mem is copied in once, then deleted twice. The first delete brings the dynamic reference counter to zero and frees the device copy; the second delete then sees a reference counter of zero and should take no action:

Code 
program main
  use openacc
  implicit none
  real :: host_mem

  host_mem = 4
  !$acc enter data copyin(host_mem)
  !$acc exit data delete(host_mem)
  !$acc exit data delete(host_mem)
  write(*,*) "OK"
end program
Compiler Result Correctness Notes
Cray Fortran 19.0.0 ❌ Crash Not per spec — the second delete should be a no-op First delete frees the data; the second aborts with CRAY_ACC_ERROR - Variable not found in present table at line 9.
nvfortran 25.3-0 ✅ OK Per spec — the second delete is correctly a no-op Prints OK.

Note the inconsistency: nvfortran tolerates deleting an already-deleted variable (where it was present at least once), but crashes when the variable was never present. Cray aborts whenever a delete targets a variable that is absent from the present table, in either scenario.