Introduce current_task_*_time_ns for non-racy continuous metrics

for the running task only.
Other tasks report metrics that are non-continuous
but updated only on task switches.

base/experimental.jl

@@ -511,13 +511,30 @@ See [`Base.Experimental.task_metrics`](@ref).
 """
 function task_cpu_time_ns(t::Task)
     t.metrics_enabled || return nothing
-    if t.last_started_running_at == 0
-        return Int(t.cpu_time_ns)
+    if t == current_task()
+        current_task_cpu_time_ns()
     else
-        return Int(t.cpu_time_ns + (time_ns() - t.last_started_running_at))
+        return Int(t.cpu_time_ns)
     end
 end
 
+"""
+    Base.Experimental.current_task_cpu_time_ns() -> Union{Int, Nothing}
+
+Return the total nanoseconds that the current task `t` has spent running.
+
+Like [`Base.Experimental.task_cpu_time_ns`](@ref), but returns an up-to-date value for the
+currently running task, whereas `task_cpu_time_ns(t)` for another task `t` only updates when
+`t` yields or completes.
+"""
+function current_task_cpu_time_ns()
+    t = current_task()
+    t.metrics_enabled || return nothing
+    # These metrics fields can't update while we're running.
+    # But since we're running we need to include the time since we last started running!
+    return Int(t.cpu_time_ns + (time_ns() - t.last_started_running_at))
+end
+
 """
     Base.Experimental.task_wall_time_ns(t::Task) -> Union{Int, Nothing}
 
@@ -541,4 +558,12 @@ function task_wall_time_ns(t::Task)
     return Int(end_at - start_at)
 end
 
+"""
+    Base.Experimental.current_task_wall_time_ns() -> Union{Int, Nothing}
+
+Report the total wall time that the current task has been running.
+See [`Base.Experimental.task_wall_time_ns`](@ref) for more details.
+"""
+current_task_wall_time_ns() = task_wall_time_ns(current_task())
+
 end # module

test/threads_exec.jl

@@ -1439,15 +1439,11 @@ end
             schedule(t2)
             yield()
             @assert istaskstarted(t1) && !istaskdone(t2)
-            cpu1 = Base.Experimental.task_cpu_time_ns(t2)
-            wall1 = Base.Experimental.task_wall_time_ns(t2)
-            @test cpu1 > 0
-            @test wall1 > 0
             schedule(t2, 1)
             yield()
             @assert istaskfailed(t2)
-            @test Base.Experimental.task_cpu_time_ns(t2) > cpu1
-            @test Base.Experimental.task_wall_time_ns(t2) > wall1
+            @test Base.Experimental.task_cpu_time_ns(t2) > 0
+            @test Base.Experimental.task_wall_time_ns(t2) > 0
         finally
             Base.Experimental.task_metrics(false)
         end
@@ -1458,14 +1454,14 @@ end
             last_cpu_time = Ref(typemax(Int))
             last_wall_time = Ref(typemax(Int))
             t = Threads.@spawn begin
-                cpu_time = Base.Experimental.task_cpu_time_ns(current_task())
-                wall_time = Base.Experimental.task_wall_time_ns(current_task())
+                cpu_time = Base.Experimental.current_task_cpu_time_ns()
+                wall_time = Base.Experimental.current_task_wall_time_ns()
                 for _ in 1:5
                     x = time_ns()
                     while time_ns() < x + 100
                     end
-                    new_cpu_time = Base.Experimental.task_cpu_time_ns(current_task())
-                    new_wall_time = Base.Experimental.task_wall_time_ns(current_task())
+                    new_cpu_time = Base.Experimental.current_task_cpu_time_ns()
+                    new_wall_time = Base.Experimental.current_task_wall_time_ns()
                     @test new_cpu_time > cpu_time
                     @test new_wall_time > wall_time
                     cpu_time = new_cpu_time