From 98a779bdc1a742a6d636e0d7f3a395f751271a73 Mon Sep 17 00:00:00 2001
From: Sam Caldwell <samc@ccs.neu.edu>
Date: Fri, 24 May 2019 11:42:21 -0400
Subject: [PATCH] resolve mutual dependency in flink via dataflow

---
 racket/typed/examples/roles/flink.rkt | 58 ++++++++++++++-------------
 1 file changed, 31 insertions(+), 27 deletions(-)

diff --git a/racket/typed/examples/roles/flink.rkt b/racket/typed/examples/roles/flink.rkt
index e8dbce6..8e6c4f0 100644
--- a/racket/typed/examples/roles/flink.rkt
+++ b/racket/typed/examples/roles/flink.rkt
@@ -369,22 +369,8 @@ The JobManager then performs the job and, when finished, asserts (job-finished I
          (match-define (task $this-id $desc) t)
          (log "JM begins on task ~a" this-id)
 
-         (define (∀ (ρ2) (select-a-task-manager [assign-task : (proc ID -> ★/t
-                                                                     #:roles (ρ2))]))
-           (start-facet this-facet
-            (begin/dataflow
-              (define mngr?
-                (for/first ([(id slots) (ref task-managers)]
-                            #:when (positive? (- slots (hash-ref/failure (ref requests-in-flight) id 0))))
-                  id))
-              (match mngr?
-                [(some $mngr)
-                 (take-slot! mngr)
-                 (stop this-facet
-                       (assign-task mngr))]
-                [none
-                 #f])
-              #f)))
+         (define not-a-real-task-manager (gensym 'FAKE))
+         (field [task-mngr ID not-a-real-task-manager])
 
          ;; ID -> ...
          (define (assign-task [mngr : ID])
@@ -392,16 +378,17 @@ The JobManager then performs the job and, when finished, asserts (job-finished I
             (assert (task-assignment mngr job-id t))
             (on (retracted (task-manager mngr discard))
                 ;; our task manager has crashed
-                (stop this-facet #;(select-a-task-manager)))
+                (stop this-facet
+                      (set! task-mngr not-a-real-task-manager)))
             (on start
-             ;; N.B. when this line was here, and not after `(when mngr ...)` above,
-             ;; things didn't work. I think that due to script scheduling, all ready
-             ;; tasks were being assigned to the manager
-             #;(take-slot! mngr)
-             (start-facet take-slot
-               (on (asserted (task-state mngr job-id this-id _))
-                   (stop take-slot
-                         (received-answer! mngr)))))
+                ;; N.B. when this line was here, and not after `(when mngr ...)` above,
+                ;; things didn't work. I think that due to script scheduling, all ready
+                ;; tasks were being assigned to the manager
+                #;(take-slot! mngr)
+                (start-facet take-slot
+                  (on (asserted (task-state mngr job-id this-id _))
+                      (stop take-slot
+                            (received-answer! mngr)))))
             (on (asserted (task-state mngr job-id this-id $status))
                 (match status
                   [ACCEPTED #f]
@@ -411,12 +398,29 @@ The JobManager then performs the job and, when finished, asserts (job-finished I
                    ;; don't think we need a release-slot! here, because if we've heard back from a task manager,
                    ;; they should have told us a different slot count since we tried to give them work
                    (log "JM overloaded manager ~a with task ~a" mngr this-id)
-                   (stop this-facet #;(select-a-task-manager))]
+                   (stop this-facet
+                         (set! task-mngr not-a-real-task-manager))]
                   [(finished $results)
                    (log "JM receives the results of task ~a" this-id)
                    (stop perform (k this-id results))]))))
 
-         (on start (select-a-task-manager assign-task))))
+           (define (select-a-task-manager)
+             (start-facet this-facet
+              (begin/dataflow
+                (when (equal? (ref task-mngr) not-a-real-task-manager)
+                  (define mngr?
+                    (for/first ([(id slots) (ref task-managers)]
+                                #:when (positive? (- slots (hash-ref/failure (ref requests-in-flight) id 0))))
+                      id))
+                  (match mngr?
+                    [(some $mngr)
+                     (take-slot! mngr)
+                     (set! task-mngr mngr)
+                     (assign-task mngr)]
+                    [none
+                     #f])))))
+
+         (on start (select-a-task-manager))))
 
       (begin/dataflow
         (define slots (slots-available))