Firestore: use C++ Executor for user queue. (#1238)

FSTDispatchQueue enforces serial execution, which is inappropriate for
user queue, because a user may configure usage of a concurrent queue in
settings, breaking FSTDispatchQueue invariants. Instead, use C++
ExecutorLibdispatch directly.

1 files changed, 19 insertions, 14 deletions

diff --git a/Firestore/Example/Tests/Core/FSTQueryListenerTests.mm b/Firestore/Example/Tests/Core/FSTQueryListenerTests.mm
index 7ae9704..5629075 100644
--- a/Firestore/Example/Tests/Core/FSTQueryListenerTests.mm
+++ b/Firestore/Example/Tests/Core/FSTQueryListenerTests.mm
@@ -15,6 +15,7 @@
  */
 
 #import <XCTest/XCTest.h>
+#include <memory>
 
 #import "Firestore/Source/Core/FSTEventManager.h"
 #import "Firestore/Source/Core/FSTQuery.h"
@@ -23,23 +24,29 @@
 #import "Firestore/Source/Model/FSTDocumentSet.h"
 #import "Firestore/Source/Remote/FSTRemoteEvent.h"
 #import "Firestore/Source/Util/FSTAsyncQueryListener.h"
-#import "Firestore/Source/Util/FSTDispatchQueue.h"
 
 #import "Firestore/Example/Tests/Util/FSTHelpers.h"
 
+#include "Firestore/core/src/firebase/firestore/util/executor_libdispatch.h"
+#include "absl/memory/memory.h"
+
+using firebase::firestore::util::internal::ExecutorLibdispatch;
 using firebase::firestore::model::DocumentKeySet;
 
 NS_ASSUME_NONNULL_BEGIN
 
 @interface FSTQueryListenerTests : XCTestCase
-@property(nonatomic, strong, readonly) FSTDispatchQueue *asyncQueue;
 @end
 
-@implementation FSTQueryListenerTests
+@implementation FSTQueryListenerTests {
+  std::unique_ptr<ExecutorLibdispatch> _executor;
+}
 
 - (void)setUp {
-  _asyncQueue = [FSTDispatchQueue
-      queueWith:dispatch_queue_create("FSTQueryListenerTests Queue", DISPATCH_QUEUE_SERIAL)];
+  // TODO(varconst): moving this test to C++, it should be possible to store Executor as a value,
+  // not a pointer, and initialize it in the constructor.
+  _executor = absl::make_unique<ExecutorLibdispatch>(
+      dispatch_queue_create("FSTQueryListenerTests Queue", DISPATCH_QUEUE_SERIAL));
 }
 
 - (void)testRaisesCollectionEvents {
@@ -131,12 +138,12 @@ NS_ASSUME_NONNULL_BEGIN
   FSTDocument *doc1 = FSTTestDoc("rooms/Eros", 3, @{@"name" : @"Eros"}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/Eros", 4, @{@"name" : @"Eros2"}, NO);
 
-  __block FSTAsyncQueryListener *listener = [[FSTAsyncQueryListener alloc]
-      initWithDispatchQueue:self.asyncQueue
-            snapshotHandler:^(FSTViewSnapshot *snapshot, NSError *error) {
-              [accum addObject:snapshot];
-              [listener mute];
-            }];
+  __block FSTAsyncQueryListener *listener =
+      [[FSTAsyncQueryListener alloc] initWithExecutor:_executor.get()
+                                      snapshotHandler:^(FSTViewSnapshot *snapshot, NSError *error) {
+                                        [accum addObject:snapshot];
+                                        [listener mute];
+                                      }];
 
   FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTViewSnapshot *viewSnapshot1 = FSTTestApplyChanges(view, @[ doc1 ], nil);
@@ -148,9 +155,7 @@ NS_ASSUME_NONNULL_BEGIN
 
   // Drain queue
   XCTestExpectation *expectation = [self expectationWithDescription:@"Queue drained"];
-  [self.asyncQueue dispatchAsync:^{
-    [expectation fulfill];
-  }];
+  _executor->Execute([=] { [expectation fulfill]; });
 
   [self waitForExpectationsWithTimeout:4.0
                                handler:^(NSError *_Nullable expectationError) {