Merge pull request grpc#1580 from murgatroid99/grpc-js_event_loop_liveness

grpc-js: Add a timer that holds the event loop open while there are pending calls

Author: murgatroid99

packages/grpc-js/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@grpc/grpc-js",
-  "version": "1.1.6",
+  "version": "1.1.7",
   "description": "gRPC Library for Node - pure JS implementation",
   "homepage": "https://grpc.io/",
   "repository": "https://github.com/grpc/grpc-node/tree/master/packages/grpc-js",

packages/grpc-js/src/channel.ts

@@ -48,6 +48,11 @@ export enum ConnectivityState {
   SHUTDOWN,
 }
 
+/**
+ * See https://nodejs.org/api/timers.html#timers_setinterval_callback_delay_args
+ */
+const MAX_TIMEOUT_TIME = 2147483647;
+
 let nextCallNumber = 0;
 
 function getNewCallNumber(): number {
@@ -137,6 +142,14 @@ export class ChannelImplementation implements Channel {
   private defaultAuthority: string;
   private filterStackFactory: FilterStackFactory;
   private target: GrpcUri;
+  /**
+   * This timer does not do anything on its own. Its purpose is to hold the
+   * event loop open while there are any pending calls for the channel that
+   * have not yet been assigned to specific subchannels. In other words,
+   * the invariant is that callRefTimer is reffed if and only if pickQueue
+   * is non-empty.
+   */
+  private callRefTimer: NodeJS.Timer;
   constructor(
     target: string,
     private readonly credentials: ChannelCredentials,
@@ -177,6 +190,10 @@ export class ChannelImplementation implements Channel {
         `Could not find a default scheme for target name "${target}"`
       );
     }
+
+    this.callRefTimer = setInterval(() => {}, MAX_TIMEOUT_TIME);
+    this.callRefTimer.unref?.();
+
     if (this.options['grpc.default_authority']) {
       this.defaultAuthority = this.options['grpc.default_authority'] as string;
     } else {
@@ -206,6 +223,7 @@ export class ChannelImplementation implements Channel {
       updateState: (connectivityState: ConnectivityState, picker: Picker) => {
         this.currentPicker = picker;
         const queueCopy = this.pickQueue.slice();
+        this.callRefTimer.unref?.();
         this.pickQueue = [];
         for (const { callStream, callMetadata } of queueCopy) {
           this.tryPick(callStream, callMetadata);
@@ -232,6 +250,11 @@ export class ChannelImplementation implements Channel {
     ]);
   }
 
+  private pushPick(callStream: Http2CallStream, callMetadata: Metadata) {
+    this.callRefTimer.ref?.();
+    this.pickQueue.push({ callStream, callMetadata });
+  }
+
   /**
    * Check the picker output for the given call and corresponding metadata,
    * and take any relevant actions. Should not be called while iterating
@@ -276,7 +299,7 @@ export class ChannelImplementation implements Channel {
                 ' has state ' +
                 ConnectivityState[pickResult.subchannel!.getConnectivityState()]
             );
-            this.pickQueue.push({ callStream, callMetadata });
+            this.pushPick(callStream, callMetadata);
             break;
           }
           /* We need to clone the callMetadata here because the transparent
@@ -367,11 +390,11 @@ export class ChannelImplementation implements Channel {
         }
         break;
       case PickResultType.QUEUE:
-        this.pickQueue.push({ callStream, callMetadata });
+        this.pushPick(callStream, callMetadata);
         break;
       case PickResultType.TRANSIENT_FAILURE:
         if (callMetadata.getOptions().waitForReady) {
-          this.pickQueue.push({ callStream, callMetadata });
+          this.pushPick(callStream, callMetadata);
         } else {
           callStream.cancelWithStatus(
             pickResult.status!.code,
@@ -433,6 +456,7 @@ export class ChannelImplementation implements Channel {
   close() {
     this.resolvingLoadBalancer.destroy();
     this.updateState(ConnectivityState.SHUTDOWN);
+    clearInterval(this.callRefTimer);
 
     this.subchannelPool.unrefUnusedSubchannels();
   }