1 files changed, 613 insertions, 0 deletions
diff --git a/xpcom/tests/gtest/TestThrottledEventQueue.cpp b/xpcom/tests/gtest/TestThrottledEventQueue.cpp
new file mode 100644
index 0000000000..64f34ff14f
--- /dev/null
+++ b/xpcom/tests/gtest/TestThrottledEventQueue.cpp
@@ -0,0 +1,613 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <functional>
+#include <queue>
+#include <string>
+#include <utility>
+
+#include "MainThreadUtils.h"
+#include "gtest/gtest.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/CondVar.h"
+#include "mozilla/gtest/MozAssertions.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/ThrottledEventQueue.h"
+#include "nsCOMPtr.h"
+#include "nsError.h"
+#include "nsIRunnable.h"
+#include "nsISerialEventTarget.h"
+#include "nsIThread.h"
+#include "nsThreadUtils.h"
+#include "prinrval.h"
+
+using mozilla::CondVar;
+using mozilla::MakeRefPtr;
+using mozilla::Mutex;
+using mozilla::MutexAutoLock;
+using mozilla::ThrottledEventQueue;
+using std::function;
+using std::string;
+
+namespace TestThrottledEventQueue {
+
+// A simple queue of runnables, to serve as the base target of
+// ThrottledEventQueues in tests.
+//
+// This is much simpler than mozilla::TaskQueue, and so better for unit tests.
+// It's about the same as mozilla::EventQueue, but that doesn't implement
+// nsIEventTarget, so it can't be the base target of a ThrottledEventQueue.
+struct RunnableQueue : nsISerialEventTarget {
+  std::queue<nsCOMPtr<nsIRunnable>> runnables;
+
+  bool IsEmpty() { return runnables.empty(); }
+  size_t Length() { return runnables.size(); }
+
+  [[nodiscard]] nsresult Run() {
+    while (!runnables.empty()) {
+      auto runnable = std::move(runnables.front());
+      runnables.pop();
+      nsresult rv = runnable->Run();
+      if (NS_FAILED(rv)) return rv;
+    }
+
+    return NS_OK;
+  }
+
+  // nsIEventTarget methods
+
+  [[nodiscard]] NS_IMETHODIMP Dispatch(already_AddRefed<nsIRunnable> aRunnable,
+                                       uint32_t aFlags) override {
+    MOZ_ALWAYS_TRUE(aFlags == nsIEventTarget::DISPATCH_NORMAL);
+    runnables.push(aRunnable);
+    return NS_OK;
+  }
+
+  [[nodiscard]] NS_IMETHODIMP DispatchFromScript(nsIRunnable* aRunnable,
+                                                 uint32_t aFlags) override {
+    RefPtr<nsIRunnable> r = aRunnable;
+    return Dispatch(r.forget(), aFlags);
+  }
+
+  NS_IMETHOD_(bool)
+  IsOnCurrentThreadInfallible(void) override { return NS_IsMainThread(); }
+
+  [[nodiscard]] NS_IMETHOD IsOnCurrentThread(bool* retval) override {
+    *retval = IsOnCurrentThreadInfallible();
+    return NS_OK;
+  }
+
+  [[nodiscard]] NS_IMETHODIMP DelayedDispatch(
+      already_AddRefed<nsIRunnable> aEvent, uint32_t aDelay) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  NS_IMETHOD RegisterShutdownTask(nsITargetShutdownTask*) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  NS_IMETHOD UnregisterShutdownTask(nsITargetShutdownTask*) override {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  // nsISupports methods
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+ private:
+  virtual ~RunnableQueue() = default;
+};
+
+NS_IMPL_ISUPPORTS(RunnableQueue, nsIEventTarget, nsISerialEventTarget)
+
+static void Enqueue(nsIEventTarget* target, function<void()>&& aCallable) {
+  nsresult rv = target->Dispatch(
+      NS_NewRunnableFunction("TEQ GTest", std::move(aCallable)));
+  MOZ_ALWAYS_TRUE(NS_SUCCEEDED(rv));
+}
+
+}  // namespace TestThrottledEventQueue
+
+using namespace TestThrottledEventQueue;
+
+TEST(ThrottledEventQueue, RunnableQueue)
+{
+  string log;
+
+  RefPtr<RunnableQueue> queue = MakeRefPtr<RunnableQueue>();
+  Enqueue(queue, [&]() { log += 'a'; });
+  Enqueue(queue, [&]() { log += 'b'; });
+  Enqueue(queue, [&]() { log += 'c'; });
+
+  ASSERT_EQ(log, "");
+  ASSERT_NS_SUCCEEDED(queue->Run());
+  ASSERT_EQ(log, "abc");
+}
+
+TEST(ThrottledEventQueue, SimpleDispatch)
+{
+  string log;
+
+  auto base = MakeRefPtr<RunnableQueue>();
+  RefPtr<ThrottledEventQueue> throttled =
+      ThrottledEventQueue::Create(base, "test queue 1");
+
+  Enqueue(throttled, [&]() { log += 'a'; });
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_EQ(log, "a");
+
+  ASSERT_TRUE(base->IsEmpty());
+  ASSERT_TRUE(throttled->IsEmpty());
+}
+
+TEST(ThrottledEventQueue, MixedDispatch)
+{
+  string log;
+
+  auto base = MakeRefPtr<RunnableQueue>();
+  RefPtr<ThrottledEventQueue> throttled =
+      ThrottledEventQueue::Create(base, "test queue 2");
+
+  // A ThrottledEventQueue limits its impact on the base target by only queuing
+  // its next event on the base once the prior event has been run. What it
+  // actually queues on the base is a sort of proxy event called an
+  // "executor": the base running the executor draws an event from the
+  // ThrottledEventQueue and runs that. If the ThrottledEventQueue has further
+  // events, it re-queues the executor on the base, effectively "going to the
+  // back of the line".
+
+  // Queue an event on the ThrottledEventQueue. This also queues the "executor"
+  // event on the base.
+  Enqueue(throttled, [&]() { log += 'a'; });
+  ASSERT_EQ(throttled->Length(), 1U);
+  ASSERT_EQ(base->Length(), 1U);
+
+  // Add a second event to the throttled queue. The executor is already queued.
+  Enqueue(throttled, [&]() { log += 'b'; });
+  ASSERT_EQ(throttled->Length(), 2U);
+  ASSERT_EQ(base->Length(), 1U);
+
+  // Add an event directly to the base, after the executor.
+  Enqueue(base, [&]() { log += 'c'; });
+  ASSERT_EQ(throttled->Length(), 2U);
+  ASSERT_EQ(base->Length(), 2U);
+
+  // Run the base target. This runs:
+  // - the executor, which runs the first event from the ThrottledEventQueue,
+  //   and re-enqueues itself
+  // - the event queued directly on the base
+  // - the executor again, which runs the second event from the
+  // ThrottledEventQueue.
+  ASSERT_EQ(log, "");
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_EQ(log, "acb");
+
+  ASSERT_TRUE(base->IsEmpty());
+  ASSERT_TRUE(throttled->IsEmpty());
+}
+
+TEST(ThrottledEventQueue, EnqueueFromRun)
+{
+  string log;
+
+  auto base = MakeRefPtr<RunnableQueue>();
+  RefPtr<ThrottledEventQueue> throttled =
+      ThrottledEventQueue::Create(base, "test queue 3");
+
+  // When an event from the throttled queue dispatches a new event directly to
+  // the base target, it is queued after the executor, so the next event from
+  // the throttled queue will run before it.
+  Enqueue(base, [&]() { log += 'a'; });
+  Enqueue(throttled, [&]() {
+    log += 'b';
+    Enqueue(base, [&]() { log += 'c'; });
+  });
+  Enqueue(throttled, [&]() { log += 'd'; });
+
+  ASSERT_EQ(log, "");
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_EQ(log, "abdc");
+
+  ASSERT_TRUE(base->IsEmpty());
+  ASSERT_TRUE(throttled->IsEmpty());
+}
+
+TEST(ThrottledEventQueue, RunFromRun)
+{
+  string log;
+
+  auto base = MakeRefPtr<RunnableQueue>();
+  RefPtr<ThrottledEventQueue> throttled =
+      ThrottledEventQueue::Create(base, "test queue 4");
+
+  // Running the event queue from within an event (i.e., a nested event loop)
+  // does not stall the ThrottledEventQueue.
+  Enqueue(throttled, [&]() {
+    log += '(';
+    // This should run subsequent events from throttled.
+    ASSERT_NS_SUCCEEDED(base->Run());
+    log += ')';
+  });
+
+  Enqueue(throttled, [&]() { log += 'a'; });
+
+  ASSERT_EQ(log, "");
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_EQ(log, "(a)");
+
+  ASSERT_TRUE(base->IsEmpty());
+  ASSERT_TRUE(throttled->IsEmpty());
+}
+
+TEST(ThrottledEventQueue, DropWhileRunning)
+{
+  string log;
+
+  auto base = MakeRefPtr<RunnableQueue>();
+
+  // If we drop the event queue while it still has events, they still run.
+  {
+    RefPtr<ThrottledEventQueue> throttled =
+        ThrottledEventQueue::Create(base, "test queue 5");
+    Enqueue(throttled, [&]() { log += 'a'; });
+  }
+
+  ASSERT_EQ(log, "");
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_EQ(log, "a");
+}
+
+TEST(ThrottledEventQueue, AwaitIdle)
+{
+  Mutex mutex MOZ_UNANNOTATED("TEQ AwaitIdle");
+  CondVar cond(mutex, "TEQ AwaitIdle");
+
+  string dequeue_await;           // mutex
+  bool threadFinished = false;    // mutex & cond
+  bool runnableFinished = false;  // main thread only
+
+  auto base = MakeRefPtr<RunnableQueue>();
+  RefPtr<ThrottledEventQueue> throttled =
+      ThrottledEventQueue::Create(base, "test queue 6");
+
+  // Put an event in the queue so the AwaitIdle might block.
+  Enqueue(throttled, [&]() { runnableFinished = true; });
+
+  // Create a separate thread that waits for the queue to become idle, and
+  // then takes observable action.
+  nsCOMPtr<nsIRunnable> await = NS_NewRunnableFunction("TEQ AwaitIdle", [&]() {
+    throttled->AwaitIdle();
+    MutexAutoLock lock(mutex);
+    dequeue_await += " await";
+    threadFinished = true;
+    cond.Notify();
+  });
+
+  nsCOMPtr<nsIThread> thread;
+  nsresult rv =
+      NS_NewNamedThread("TEQ AwaitIdle", getter_AddRefs(thread), await);
+  ASSERT_NS_SUCCEEDED(rv);
+
+  // We can't guarantee that the thread has reached the AwaitIdle call, but we
+  // can get pretty close. Either way, it shouldn't affect the behavior of the
+  // test.
+  PR_Sleep(PR_MillisecondsToInterval(100));
+
+  // Drain the queue.
+  {
+    MutexAutoLock lock(mutex);
+    ASSERT_EQ(dequeue_await, "");
+    dequeue_await += "dequeue";
+    ASSERT_FALSE(threadFinished);
+  }
+  ASSERT_FALSE(runnableFinished);
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_TRUE(runnableFinished);
+
+  // Wait for the thread to finish.
+  {
+    MutexAutoLock lock(mutex);
+    while (!threadFinished) cond.Wait();
+    ASSERT_EQ(dequeue_await, "dequeue await");
+  }
+
+  ASSERT_NS_SUCCEEDED(thread->Shutdown());
+}
+
+TEST(ThrottledEventQueue, AwaitIdleMixed)
+{
+  // Create a separate thread that waits for the queue to become idle, and
+  // then takes observable action.
+  nsCOMPtr<nsIThread> thread;
+  ASSERT_TRUE(NS_SUCCEEDED(
+      NS_NewNamedThread("AwaitIdleMixed", getter_AddRefs(thread))));
+
+  Mutex mutex MOZ_UNANNOTATED("AwaitIdleMixed");
+  CondVar cond(mutex, "AwaitIdleMixed");
+
+  // The following are protected by mutex and cond, above.
+  string log;
+  bool threadStarted = false;
+  bool threadFinished = false;
+
+  auto base = MakeRefPtr<RunnableQueue>();
+  RefPtr<ThrottledEventQueue> throttled =
+      ThrottledEventQueue::Create(base, "test queue 7");
+
+  Enqueue(throttled, [&]() {
+    MutexAutoLock lock(mutex);
+    log += 'a';
+  });
+
+  Enqueue(throttled, [&]() {
+    MutexAutoLock lock(mutex);
+    log += 'b';
+  });
+
+  nsCOMPtr<nsIRunnable> await = NS_NewRunnableFunction("AwaitIdleMixed", [&]() {
+    {
+      MutexAutoLock lock(mutex);
+
+      // Note that we are about to begin awaiting. When the main thread sees
+      // this notification, it will begin draining the queue.
+      log += '(';
+      threadStarted = true;
+      cond.Notify();
+    }
+
+    // Wait for the main thread to drain the TEQ.
+    throttled->AwaitIdle();
+
+    {
+      MutexAutoLock lock(mutex);
+
+      // Note that we have finished awaiting.
+      log += ')';
+      threadFinished = true;
+      cond.Notify();
+    }
+  });
+
+  {
+    MutexAutoLock lock(mutex);
+    ASSERT_EQ(log, "");
+  }
+
+  ASSERT_NS_SUCCEEDED(thread->Dispatch(await.forget()));
+
+  // Wait for the thread to be ready to await. We can't be sure it will actually
+  // be blocking before we get around to draining the event queue, but that's
+  // the nature of the API; this test should work even if we drain the queue
+  // before it awaits.
+  {
+    MutexAutoLock lock(mutex);
+    while (!threadStarted) cond.Wait();
+    ASSERT_EQ(log, "(");
+  }
+
+  // Let the queue drain.
+  ASSERT_NS_SUCCEEDED(base->Run());
+
+  {
+    MutexAutoLock lock(mutex);
+    // The first runnable must always finish before AwaitIdle returns. But the
+    // TEQ notifies the condition variable as soon as it dequeues the last
+    // runnable, without waiting for that runnable to complete. So the thread
+    // and the last runnable could run in either order. Or, we might beat the
+    // thread to the mutex.
+    //
+    // (The only combination excluded here is "(a)": the 'b' runnable should
+    // definitely have run.)
+    ASSERT_TRUE(log == "(ab" || log == "(a)b" || log == "(ab)");
+    while (!threadFinished) cond.Wait();
+    ASSERT_TRUE(log == "(a)b" || log == "(ab)");
+  }
+
+  ASSERT_NS_SUCCEEDED(thread->Shutdown());
+}
+
+TEST(ThrottledEventQueue, SimplePauseResume)
+{
+  string log;
+
+  auto base = MakeRefPtr<RunnableQueue>();
+  RefPtr<ThrottledEventQueue> throttled =
+      ThrottledEventQueue::Create(base, "test queue 8");
+
+  ASSERT_FALSE(throttled->IsPaused());
+
+  Enqueue(throttled, [&]() { log += 'a'; });
+
+  ASSERT_EQ(log, "");
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_EQ(log, "a");
+
+  ASSERT_NS_SUCCEEDED(throttled->SetIsPaused(true));
+  ASSERT_TRUE(throttled->IsPaused());
+
+  Enqueue(throttled, [&]() { log += 'b'; });
+
+  ASSERT_EQ(log, "a");
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_EQ(log, "a");
+
+  ASSERT_NS_SUCCEEDED(throttled->SetIsPaused(false));
+  ASSERT_FALSE(throttled->IsPaused());
+
+  ASSERT_EQ(log, "a");
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_EQ(log, "ab");
+
+  ASSERT_TRUE(base->IsEmpty());
+  ASSERT_TRUE(throttled->IsEmpty());
+}
+
+TEST(ThrottledEventQueue, MixedPauseResume)
+{
+  string log;
+
+  auto base = MakeRefPtr<RunnableQueue>();
+  RefPtr<ThrottledEventQueue> throttled =
+      ThrottledEventQueue::Create(base, "test queue 9");
+
+  ASSERT_FALSE(throttled->IsPaused());
+
+  Enqueue(base, [&]() { log += 'A'; });
+  Enqueue(throttled, [&]() {
+    log += 'b';
+    MOZ_ALWAYS_TRUE(NS_SUCCEEDED(throttled->SetIsPaused(true)));
+  });
+  Enqueue(throttled, [&]() { log += 'c'; });
+  Enqueue(base, [&]() { log += 'D'; });
+
+  ASSERT_EQ(log, "");
+  ASSERT_NS_SUCCEEDED(base->Run());
+  // Since the 'b' event paused the throttled queue, 'c' should not have run.
+  // but 'D' was enqueued directly on the base, and should have run.
+  ASSERT_EQ(log, "AbD");
+  ASSERT_TRUE(base->IsEmpty());
+  ASSERT_FALSE(throttled->IsEmpty());
+  ASSERT_TRUE(throttled->IsPaused());
+
+  Enqueue(base, [&]() { log += 'E'; });
+  ASSERT_NS_SUCCEEDED(throttled->SetIsPaused(false));
+  Enqueue(base, [&]() { log += 'F'; });
+  ASSERT_FALSE(throttled->IsPaused());
+
+  ASSERT_NS_SUCCEEDED(base->Run());
+  // Since we've unpaused, 'c' should be able to run now. The executor should
+  // have been enqueued between 'E' and 'F'.
+  ASSERT_EQ(log, "AbDEcF");
+
+  ASSERT_TRUE(base->IsEmpty());
+  ASSERT_TRUE(throttled->IsEmpty());
+}
+
+TEST(ThrottledEventQueue, AwaitIdlePaused)
+{
+  Mutex mutex MOZ_UNANNOTATED("AwaitIdlePaused");
+  CondVar cond(mutex, "AwaitIdlePaused");
+
+  string dequeue_await;           // mutex
+  bool threadFinished = false;    // mutex & cond
+  bool runnableFinished = false;  // main thread only
+
+  auto base = MakeRefPtr<RunnableQueue>();
+  RefPtr<ThrottledEventQueue> throttled =
+      ThrottledEventQueue::Create(base, "test queue 10");
+
+  ASSERT_NS_SUCCEEDED(throttled->SetIsPaused(true));
+
+  // Put an event in the queue so the AwaitIdle might block. Since throttled is
+  // paused, this should not enqueue an executor in the base target.
+  Enqueue(throttled, [&]() { runnableFinished = true; });
+  ASSERT_TRUE(base->IsEmpty());
+
+  // Create a separate thread that waits for the queue to become idle, and
+  // then takes observable action.
+  nsCOMPtr<nsIRunnable> await =
+      NS_NewRunnableFunction("AwaitIdlePaused", [&]() {
+        throttled->AwaitIdle();
+        MutexAutoLock lock(mutex);
+        dequeue_await += " await";
+        threadFinished = true;
+        cond.Notify();
+      });
+
+  nsCOMPtr<nsIThread> thread;
+  nsresult rv =
+      NS_NewNamedThread("AwaitIdlePaused", getter_AddRefs(thread), await);
+  ASSERT_NS_SUCCEEDED(rv);
+
+  // We can't guarantee that the thread has reached the AwaitIdle call, but we
+  // can get pretty close. Either way, it shouldn't affect the behavior of the
+  // test.
+  PR_Sleep(PR_MillisecondsToInterval(100));
+
+  // The AwaitIdle call should be blocked, even though there is no executor,
+  // because throttled is paused.
+  {
+    MutexAutoLock lock(mutex);
+    ASSERT_EQ(dequeue_await, "");
+    dequeue_await += "dequeue";
+    ASSERT_FALSE(threadFinished);
+  }
+
+  // A paused TEQ contributes no events to its base target. (This is covered by
+  // other tests...)
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_TRUE(base->IsEmpty());
+  ASSERT_FALSE(throttled->IsEmpty());
+
+  // Resume and drain the queue.
+  ASSERT_FALSE(runnableFinished);
+  ASSERT_NS_SUCCEEDED(throttled->SetIsPaused(false));
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_TRUE(base->IsEmpty());
+  ASSERT_TRUE(throttled->IsEmpty());
+  ASSERT_TRUE(runnableFinished);
+
+  // Wait for the thread to finish.
+  {
+    MutexAutoLock lock(mutex);
+    while (!threadFinished) cond.Wait();
+    ASSERT_EQ(dequeue_await, "dequeue await");
+  }
+
+  ASSERT_NS_SUCCEEDED(thread->Shutdown());
+}
+
+TEST(ThrottledEventQueue, ExecutorTransitions)
+{
+  string log;
+
+  auto base = MakeRefPtr<RunnableQueue>();
+  RefPtr<ThrottledEventQueue> throttled =
+      ThrottledEventQueue::Create(base, "test queue 11");
+
+  ASSERT_NS_SUCCEEDED(throttled->SetIsPaused(true));
+
+  // Since we're paused, queueing an event on throttled shouldn't queue the
+  // executor on the base target.
+  Enqueue(throttled, [&]() { log += 'a'; });
+  ASSERT_EQ(throttled->Length(), 1U);
+  ASSERT_EQ(base->Length(), 0U);
+
+  // Resuming throttled should create the executor, since throttled is not
+  // empty.
+  ASSERT_NS_SUCCEEDED(throttled->SetIsPaused(false));
+  ASSERT_EQ(throttled->Length(), 1U);
+  ASSERT_EQ(base->Length(), 1U);
+
+  // Pausing can't remove the executor from the base target since we've already
+  // queued it there, but it can ensure that it doesn't do anything.
+  ASSERT_NS_SUCCEEDED(throttled->SetIsPaused(true));
+
+  ASSERT_EQ(log, "");
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_EQ(log, "");
+  ASSERT_EQ(throttled->Length(), 1U);
+  ASSERT_EQ(base->Length(), 0U);
+
+  // As before, resuming must create the executor, since throttled is not empty.
+  ASSERT_NS_SUCCEEDED(throttled->SetIsPaused(false));
+  ASSERT_EQ(throttled->Length(), 1U);
+  ASSERT_EQ(base->Length(), 1U);
+
+  ASSERT_EQ(log, "");
+  ASSERT_NS_SUCCEEDED(base->Run());
+  ASSERT_EQ(log, "a");
+  ASSERT_EQ(throttled->Length(), 0U);
+  ASSERT_EQ(base->Length(), 0U);
+
+  // Since throttled is empty, pausing and resuming now should not enqueue an
+  // executor.
+  ASSERT_NS_SUCCEEDED(throttled->SetIsPaused(true));
+  ASSERT_NS_SUCCEEDED(throttled->SetIsPaused(false));
+  ASSERT_EQ(throttled->Length(), 0U);
+  ASSERT_EQ(base->Length(), 0U);
+}