Cancel background work (#3063)

* cleanup

* cleanup

* diagnostics

* cleanup diagnostics

* even cleaner diagnostics

* cleanup diagnostics

* default tuning

* adjust tuning, more logging

* add test, fix whitespace

* cancel background steps

* reduce changes

src/fsharp/vs/Reactor.fs

@@ -19,7 +19,7 @@ type internal IReactorOperations =
 [<NoEquality; NoComparison>]
 type internal ReactorCommands = 
     /// Kick off a build.
-    | SetBackgroundOp of ( (* userOpName: *) string * (* opName: *) string * (* opArg: *) string * (CompilationThreadToken -> bool)) option
+    | SetBackgroundOp of ( (* userOpName: *) string * (* opName: *) string * (* opArg: *) string * (CompilationThreadToken -> CancellationToken -> bool)) option
     /// Do some work not synchronized in the mailbox.
     | Op of userOpName: string * opName: string * opArg: string * CancellationToken * (CompilationThreadToken -> unit) * (unit -> unit)
     /// Finish the background building
@@ -39,6 +39,7 @@ type Reactor() =
     // so that when the reactor picks up a thread from the threadpool we can set the culture
     let culture = new CultureInfo(CultureInfo.CurrentUICulture.Name)
 
+    let mutable bgOpCts = new CancellationTokenSource()
     /// Mailbox dispatch function.
     let builder = 
         MailboxProcessor<_>.Start <| fun inbox ->
@@ -74,6 +75,7 @@ type Reactor() =
                     | Some (SetBackgroundOp bgOpOpt) -> 
                         //Trace.TraceInformation("Reactor: --> set background op, remaining {0}", inbox.CurrentQueueLength)
                         return! loop (bgOpOpt, onComplete, false)
+
                     | Some (Op (userOpName, opName, opArg, ct, op, ccont)) -> 
                         if ct.IsCancellationRequested then ccont() else
                         Trace.TraceInformation("Reactor: {0:n3} --> {1}.{2} ({3}), remaining {4}", DateTime.Now.TimeOfDay.TotalSeconds, userOpName, opName, opArg, inbox.CurrentQueueLength)
@@ -92,13 +94,21 @@ type Reactor() =
                         | None -> ()
                         | Some (bgUserOpName, bgOpName, bgOpArg, bgOp) -> 
                             Trace.TraceInformation("Reactor: {0:n3} --> wait for background {1}.{2} ({3}), remaining {4}", DateTime.Now.TimeOfDay.TotalSeconds, bgUserOpName, bgOpName, bgOpArg, inbox.CurrentQueueLength)
-                            while bgOp ctok do 
+                            bgOpCts.Dispose()
+                            bgOpCts <- new CancellationTokenSource()
+                            while not bgOpCts.IsCancellationRequested && bgOp ctok bgOpCts.Token do 
                                 ()
+
+                            if bgOpCts.IsCancellationRequested then 
+                                Trace.TraceInformation("FCS: <-- wait for background was cancelled {0}.{1}", bgUserOpName, bgOpName)
+
                         channel.Reply(())
                         return! loop (None, onComplete, false)
+
                     | Some (CompleteAllQueuedOps channel) -> 
                         Trace.TraceInformation("Reactor: {0:n3} --> stop background work and complete all queued ops, remaining {1}", DateTime.Now.TimeOfDay.TotalSeconds, inbox.CurrentQueueLength)
                         return! loop (None, Some channel, false)
+
                     | None -> 
                         match bgOpOpt, onComplete with 
                         | _, Some onComplete -> onComplete.Reply()
@@ -106,7 +116,11 @@ type Reactor() =
                             Trace.TraceInformation("Reactor: {0:n3} --> background step {1}.{2} ({3})", DateTime.Now.TimeOfDay.TotalSeconds, bgUserOpName, bgOpName, bgOpArg)
                             let time = Stopwatch()
                             time.Start()
-                            let res = bgOp ctok
+                            bgOpCts.Dispose()
+                            bgOpCts <- new CancellationTokenSource()
+                            let res = bgOp ctok bgOpCts.Token
+                            if bgOpCts.IsCancellationRequested then 
+                                Trace.TraceInformation("FCS: <-- background step {0}.{1}, was cancelled", bgUserOpName, bgOpName)
                             time.Stop()
                             let taken = time.Elapsed.TotalMilliseconds
                             //if span.TotalMilliseconds > 100.0 then 
@@ -126,8 +140,13 @@ type Reactor() =
     // [Foreground Mailbox Accessors] -----------------------------------------------------------                
     member r.SetBackgroundOp(bgOpOpt) = 
         Trace.TraceInformation("Reactor: {0:n3} enqueue start background, length {1}", DateTime.Now.TimeOfDay.TotalSeconds, builder.CurrentQueueLength)
+        bgOpCts.Cancel()
         builder.Post(SetBackgroundOp bgOpOpt)
 
+    member r.CancelBackgroundOp() = 
+        Trace.TraceInformation("FCS: trying to cancel any active background work")
+        bgOpCts.Cancel()
+
     member r.EnqueueOp(userOpName, opName, opArg, op) =
         Trace.TraceInformation("Reactor: {0:n3} enqueue {1}.{2} ({3}), length {4}", DateTime.Now.TimeOfDay.TotalSeconds, userOpName, opName, opArg, builder.CurrentQueueLength)
         builder.Post(Op(userOpName, opName, opArg, CancellationToken.None, op, (fun () -> ()))) 

src/fsharp/vs/Reactor.fsi

@@ -26,7 +26,10 @@ type internal Reactor =
 
     /// Set the background building function, which is called repeatedly
     /// until it returns 'false'.  If None then no background operation is used.
-    member SetBackgroundOp : ( (* userOpName:*) string * (* opName: *) string * (* opArg: *) string *  (CompilationThreadToken -> bool)) option -> unit
+    member SetBackgroundOp : ( (* userOpName:*) string * (* opName: *) string * (* opArg: *) string *  (CompilationThreadToken -> CancellationToken -> bool)) option -> unit
+
+    /// Cancel any work being don by the background building function.
+    member CancelBackgroundOp : unit -> unit
 
     /// Block until the current implicit background build is complete. Unit test only.
     member WaitForBackgroundOpCompletion : unit -> unit