[flang-commits] [flang] [Flang][runtime] Distinguish CPU time and elapsed time for cpu_time and system_clock (PR #96652)

[Kareem Ergawy via flang-commits]

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@@ -0,0 +1,27 @@
+! RUN: %flang -o %t %s
+! RUN: %t
+
+program system_clock_test
+    use iso_fortran_env, only: int64, real64
+    implicit none
+
+    integer, parameter :: delta = 1
+    real(kind=real64), parameter :: epsilon = 0.001
+
+    integer(kind=int64) :: t_start, t_end
+    integer(kind=int64) :: rate
+    real(kind=real64) :: diff
+
+    call system_clock(count_rate=rate)
+
+    call system_clock(t_start)
+    call sleep(delta)
+    call system_clock(t_end)
+
+    diff = real(t_end - t_start, kind=real64) / real(rate, kind=real64)
+
+    if (abs(diff - real(delta, kind=real64)) <= epsilon) then
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ergawy wrote:

Isn't that check flakey? `delta` is the minimum amount of time the thread will sleep but there is not guranatee the actual sleep will be longer than that if the CPU is busy, right? Or did I miss something?

https://github.com/llvm/llvm-project/pull/96652