ACC008 timer-without-acc-wait

warning enabled by default

A timer is read while asynchronous OpenACC work may still be running.

Why

async compute and data constructs return immediately: reading the clock right after them measures only the launch, not the work. Put !$acc wait (or call acc_wait(...)) before every stop-time read.

Reported

!$acc parallel loop async(1)
...
call system_clock(t1)

Preferred

!$acc parallel loop async(1)
...
!$acc wait
call system_clock(t1)

Suppressing

For one occurrence, with the reason on the same line (or alone on the line before the statement):

! fobis: ignore[ACC008] <why this occurrence is fine>

For the whole project, ignore = ACC008 in the fobos [lint] section.

References

Sections of the shipped knowledge packs behind this rule:

• hpc-practice:gpu-practice#gpu-benchmark-timing (fobis kb show hpc-practice:gpu-practice#gpu-benchmark-timing)
• openacc:ch07-procedures-async-fortran#anti-patterns (fobis kb show openacc:ch07-procedures-async-fortran#anti-patterns)