DispatchQueue delayed callback improvements + testing (#784)

Basically a port of https://github.com/firebase/firebase-js-sdk/commit/a1e346ff93c6cbcc0a1b3b33f0fbc3a7b66e7e12 and https://github.com/firebase/firebase-js-sdk/commit/fce4168309f42aa038125f39818fbf654b65b05f

* Introduces a DelayedCallback helper class in FSTDispatchQueue to encapsulate delayed callback logic.
* Adds cancellation support.
* Updates the idle timer in FSTStream to use new cancellation support.
* Adds a FSTTimerId enum for identifying delayed operations on the queue and uses it to identify our existing backoff and idle timers.
* Added containsDelayedCallback: and runDelayedCallbacksUntil: methods to FSTDispatchQueue which can be used from tests to check for the presence of a callback or to schedule them to run early.
* Removes FSTTestDispatchQueue and changes idle tests to use new test methods.

2 files changed, 14 insertions, 6 deletions

diff --git a/Firestore/Example/Tests/Integration/API/FIRDatabaseTests.mm b/Firestore/Example/Tests/Integration/API/FIRDatabaseTests.mm
index 3b6a67e..751e7ff 100644
--- a/Firestore/Example/Tests/Integration/API/FIRDatabaseTests.mm
+++ b/Firestore/Example/Tests/Integration/API/FIRDatabaseTests.mm
@@ -21,6 +21,7 @@
 #import "Firestore/Example/Tests/Util/FSTIntegrationTestCase.h"
 #import "Firestore/Source/API/FIRFirestore+Internal.h"
 #import "Firestore/Source/Core/FSTFirestoreClient.h"
+#import "Firestore/Source/Util/FSTDispatchQueue.h"
 
 @interface FIRDatabaseTests : FSTIntegrationTestCase
 @end
@@ -926,7 +927,7 @@
   FIRFirestore *firestore = doc.firestore;
 
   [self writeDocumentRef:doc data:@{@"foo" : @"bar"}];
-  [self waitForIdleFirestore:firestore];
+  [[self queueForFirestore:firestore] runDelayedCallbacksUntil:FSTTimerIDWriteStreamIdle];
   [self writeDocumentRef:doc data:@{@"foo" : @"bar"}];
 }
 
@@ -935,7 +936,7 @@
   FIRFirestore *firestore = doc.firestore;
 
   [self readSnapshotForRef:[self documentRef] requireOnline:YES];
-  [self waitForIdleFirestore:firestore];
+  [[self queueForFirestore:firestore] runDelayedCallbacksUntil:FSTTimerIDListenStreamIdle];
   [self readSnapshotForRef:[self documentRef] requireOnline:YES];
 }
 
diff --git a/Firestore/Example/Tests/Integration/FSTStreamTests.mm b/Firestore/Example/Tests/Integration/FSTStreamTests.mm
index 6259aff..a36361a 100644
--- a/Firestore/Example/Tests/Integration/FSTStreamTests.mm
+++ b/Firestore/Example/Tests/Integration/FSTStreamTests.mm
@@ -20,7 +20,6 @@
 
 #import "Firestore/Example/Tests/Util/FSTHelpers.h"
 #import "Firestore/Example/Tests/Util/FSTIntegrationTestCase.h"
-#import "Firestore/Example/Tests/Util/FSTTestDispatchQueue.h"
 #import "Firestore/Source/Auth/FSTEmptyCredentialsProvider.h"
 #import "Firestore/Source/Remote/FSTDatastore.h"
 #import "Firestore/Source/Remote/FSTStream.h"
@@ -133,7 +132,7 @@ using firebase::firestore::model::DatabaseId;
 
 @implementation FSTStreamTests {
   dispatch_queue_t _testQueue;
-  FSTTestDispatchQueue *_workerDispatchQueue;
+  FSTDispatchQueue *_workerDispatchQueue;
   DatabaseInfo _databaseInfo;
   FSTEmptyCredentialsProvider *_credentials;
   FSTStreamStatusDelegate *_delegate;
@@ -150,7 +149,7 @@ using firebase::firestore::model::DatabaseId;
                          DatabaseId::kDefaultDatabaseId);
 
   _testQueue = dispatch_queue_create("FSTStreamTestWorkerQueue", DISPATCH_QUEUE_SERIAL);
-  _workerDispatchQueue = [[FSTTestDispatchQueue alloc] initWithQueue:_testQueue];
+  _workerDispatchQueue = [[FSTDispatchQueue alloc] initWithQueue:_testQueue];
 
   _databaseInfo = DatabaseInfo(database_id, "test-key", util::MakeStringView(settings.host),
                                settings.sslEnabled);
@@ -272,10 +271,14 @@ using firebase::firestore::model::DatabaseId;
     [writeStream writeHandshake];
   }];
 
-  [_delegate awaitNotificationFromBlock:^{
+  [_workerDispatchQueue dispatchAsync:^{
     [writeStream markIdle];
+    XCTAssertTrue(
+        [_workerDispatchQueue containsDelayedCallbackWithTimerID:FSTTimerIDWriteStreamIdle]);
   }];
 
+  [_workerDispatchQueue runDelayedCallbacksUntil:FSTTimerIDWriteStreamIdle];
+
   dispatch_sync(_testQueue, ^{
     XCTAssertFalse([writeStream isOpen]);
   });
@@ -299,7 +302,11 @@ using firebase::firestore::model::DatabaseId;
   // Mark the stream idle, but immediately cancel the idle timer by issuing another write.
   [_delegate awaitNotificationFromBlock:^{
     [writeStream markIdle];
+    XCTAssertTrue(
+        [_workerDispatchQueue containsDelayedCallbackWithTimerID:FSTTimerIDWriteStreamIdle]);
     [writeStream writeMutations:_mutations];
+    XCTAssertFalse(
+        [_workerDispatchQueue containsDelayedCallbackWithTimerID:FSTTimerIDWriteStreamIdle]);
   }];
 
   dispatch_sync(_testQueue, ^{