Port of the existing profiler to Chronos V4

chronos.nimble

@@ -70,6 +70,14 @@ task test_libbacktrace, "test with libbacktrace":
       run args & " --mm:refc", "tests/testall"
     run args, "tests/testall"
 
+task test_profiler, "test with profiler instrumentation":
+  var allArgs = @[
+      "-d:release -d:chronosFutureId -d:chronosProfiling",
+    ]
+
+  for args in allArgs:
+    run args, "tests/testall"
+
 task docs, "Generate API documentation":
   exec "mdbook build docs"
   exec nimc & " doc " & "--git.url:https://github.com/status-im/nim-chronos --git.commit:master --outdir:docs/book/api --project chronos"

chronos/config.nim

@@ -40,7 +40,12 @@ const
   chronosStackTrace* {.booldefine.}: bool = defined(chronosDebug)
     ## Include stack traces in futures for creation and completion points
 
-  chronosFutureId* {.booldefine.}: bool = defined(chronosDebug)
+  chronosProfiling* {.booldefine.} = defined(chronosProfiling)
+    ## Enable instrumentation callbacks which are called at
+    ## the start, pause, or end of a Future's lifetime.
+    ## Useful for implementing metrics or other instrumentation.
+
+  chronosFutureId* {.booldefine.}: bool = defined(chronosDebug) or chronosProfiling
     ## Generate a unique `id` for every future - when disabled, the address of
     ## the future will be used instead
 

chronos/futures.nim

@@ -111,6 +111,13 @@ when chronosFutureTracking:
 
   var futureList* {.threadvar.}: FutureList
 
+when chronosProfiling:
+  type AsyncFutureState* {.pure.} = enum
+    Running, Paused
+
+  var onBaseFutureEvent* {.threadvar.}: proc (fut: FutureBase, state: FutureState): void {.nimcall, gcsafe, raises: [].}
+  var onAsyncFutureEvent* {.threadvar.}: proc(fut: FutureBase, state: AsyncFutureState): void {.nimcall, gcsafe, raises: [].}
+
 # Internal utilities - these are not part of the stable API
 proc internalInitFutureBase*(fut: FutureBase, loc: ptr SrcLoc,
                              state: FutureState, flags: FutureFlags) =
@@ -144,6 +151,10 @@ proc internalInitFutureBase*(fut: FutureBase, loc: ptr SrcLoc,
         futureList.head = fut
       futureList.count.inc()
 
+  when chronosProfiling:
+    if not isNil(onBaseFutureEvent):
+      onBaseFutureEvent(fut, state)
+
 # Public API
 template init*[T](F: type Future[T], fromProc: static[string] = ""): Future[T] =
   ## Creates a new pending future.

chronos/internal/asyncfutures.nim

@@ -192,6 +192,11 @@ proc finish(fut: FutureBase, state: FutureState) =
   # 1. `finish()` is a private procedure and `state` is under our control.
   # 2. `fut.state` is checked by `checkFinished()`.
   fut.internalState = state
+
+  when chronosProfiling:
+    if not isNil(onBaseFutureEvent):
+      onBaseFutureEvent(fut, state)
+
   fut.internalCancelcb = nil # release cancellation callback memory
   for item in fut.internalCallbacks.mitems():
     if not(isNil(item.function)):
@@ -376,6 +381,10 @@ proc futureContinue*(fut: FutureBase) {.raises: [], gcsafe.} =
   #
   # Every call to an `{.async.}` proc is redirected to call this function
   # instead with its original body captured in `fut.closure`.
+  when chronosProfiling:
+    if not isNil(onAsyncFutureEvent):
+      onAsyncFutureEvent(fut, Running)
+
   while true:
     # Call closure to make progress on `fut` until it reaches `yield` (inside
     # `await` typically) or completes / fails / is cancelled
@@ -393,6 +402,10 @@ proc futureContinue*(fut: FutureBase) {.raises: [], gcsafe.} =
       GC_ref(fut)
       next.addCallback(CallbackFunc(internalContinue), cast[pointer](fut))
 
+      when chronosProfiling:
+        if not isNil(onAsyncFutureEvent):
+          onAsyncFutureEvent(fut, Paused)
+
       # return here so that we don't remove the closure below
       return