Simplify the new tests for measuring compilation time.

base/timing.jl

@@ -55,10 +55,10 @@ function gc_alloc_count(diff::GC_Diff)
  diff.malloc + diff.realloc + diff.poolalloc + diff.bigalloc
 end
 
-# cumulative total time spent on compilation
+# cumulative total time spent on compilation, in nanoseconds
 cumulative_compile_time_ns_before() = ccall(:jl_cumulative_compile_time_ns_before, UInt64, ())
 cumulative_compile_time_ns_after() = ccall(:jl_cumulative_compile_time_ns_after, UInt64, ())
-# cumulative total time this thread has spent on compilation since process start.
+# cumulative total time the process has spent on compilation while measurement was enabled.
 cumulative_compile_time_ns() = ccall(:jl_cumulative_compile_time_ns, UInt64, ())
 
 # total time spend in garbage collection, in nanoseconds

src/jitlayers.cpp

@@ -78,12 +78,14 @@ void jl_jit_globals(std::map<void *, GlobalVariable*> &globals)
 extern "C" JL_DLLEXPORT
 uint64_t jl_cumulative_compile_time_ns_before()
 {
+ // Increment the flag to allow reentrant callers to `@time`.
  jl_atomic_fetch_add(&jl_measure_compile_time, 1);
  return jl_atomic_load(&jl_cumulative_compile_time);
 }
 extern "C" JL_DLLEXPORT
 uint64_t jl_cumulative_compile_time_ns_after()
 {
+ // Decrement the flag when done measuring, allowing other callers to continue measuring.
  jl_atomic_fetch_add(&jl_measure_compile_time, -1);
  return jl_atomic_load(&jl_cumulative_compile_time);
 }

test/misc.jl

@@ -263,6 +263,8 @@ function timev_macro_scope()
 end
 @test timev_macro_scope() == 1
 
+before = Base.cumulative_compile_time_ns_before();
+
 # exercise concurrent calls to `@time` for reentrant compilation time measurement.
 t1 = @async @time begin
  sleep(2)
@@ -274,8 +276,9 @@ t2 = @async begin
  @time 2 + 2
 end
 
-# Test that the total compilation time across all threads is including at least this thread.
-@test Base.process_cumulative_compile_time_ns() >= Base.cumulative_compile_time_ns()
+after = Base.cumulative_compile_time_ns_after();
+@test after >= before;
+@test Base.cumulative_compile_time_ns() >= after;
 
 # interactive utilities