From 262a8d74522ae5a9899e9b5fcfb4595fd7ffc646 Mon Sep 17 00:00:00 2001
From: Emery Hemingway <ehmry@posteo.net>
Date: Fri, 9 Jul 2021 11:38:53 +0200
Subject: [PATCH] Track external tasks that will drive dataspace

---
 src/syndicate.nim            |  2 ++
 src/syndicate/dataspaces.nim | 41 +++++++++++++++++++++++++++++-------
 2 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/src/syndicate.nim b/src/syndicate.nim
index c575f1f..1af72e1 100644
--- a/src/syndicate.nim
+++ b/src/syndicate.nim
@@ -14,7 +14,9 @@ export dataspaces.`==`
 export dataspaces.addEndpoint
 export dataspaces.addStartScript
 export dataspaces.addStopScript
+export dataspaces.beginExternalTask
 export dataspaces.defineObservableProperty
+export dataspaces.endExternalTask
 export dataspaces.generateId
 export dataspaces.hash
 export dataspaces.recordDamage
diff --git a/src/syndicate/dataspaces.nim b/src/syndicate/dataspaces.nim
index 002b210..b7b10df 100644
--- a/src/syndicate/dataspaces.nim
+++ b/src/syndicate/dataspaces.nim
@@ -92,6 +92,8 @@ type
     dataspace: Dataspace
     stopHandlers: seq[StopHandler]
     future: Future[void]
+    externalTaskCount: int
+    stepScheduled: bool
 
   ParentFacet = Option[Facet]
 
@@ -524,16 +526,39 @@ proc stop*(facet; continuation: Script[void] = nil) =
 proc addStopHandler*(g: Ground; h: StopHandler) =
   g.stopHandlers.add(h)
 
-proc step(g: Ground) =
-  if g.dataspace.runTasks():
+proc step(g: Ground) {.gcsafe.}
+
+proc scheduleStep(g: Ground) =
+  if not g.stepScheduled:
+    g.stepScheduled = true
     asyncdispatch.callSoon: step(g)
+
+proc beginExternalTask*(facet) =
+  ## Inform the ``Ground`` dataspace of a pending external task.
+  ## The dataspace will continue to operate until all internal
+  ## and external tasks have completed. See ``endExternalTask``.
+  inc facet.actor.dataspace.ground.externalTaskCount
+
+proc endExternalTask*(facet) =
+  ## Inform the ``Ground`` dataspace that an external task has completed.
+  # TODO: automatically do this when the facet stops?
+  let g = facet.actor.dataspace.ground
+  dec g.externalTaskCount
+  scheduleStep g
+
+proc step(g: Ground) =
+  # TODO: backgroundtasks
+  g.stepScheduled = false
+  if g.dataspace.runTasks():
+    scheduleStep g
   else:
-    for actor in g.dataspace.actors.values:
-      terminate(actor, false)
-    for sh in g.stopHandlers:
-      sh(g.dataspace)
-    reset g.stopHandlers
-    complete(g.future)
+    if g.externalTaskCount < 1:
+      for actor in g.dataspace.actors.values:
+        terminate(actor, false)
+      for sh in g.stopHandlers:
+        sh(g.dataspace)
+      reset g.stopHandlers
+      complete(g.future)
 
 proc bootModule*(name: string; bootProc: ActivationScript): Future[void] =
   # TODO: better integration with the async dispatcher