diff --git a/autowiring/DispatchQueue.h b/autowiring/DispatchQueue.h index bd273d7f9..bc67fd768 100644 --- a/autowiring/DispatchQueue.h +++ b/autowiring/DispatchQueue.h @@ -186,6 +186,9 @@ class DispatchQueue { /// /// If DispatchQueue::Abort() is called before the dispatcher has been completed, this method will throw an exception. /// If a dispatcher on the underlying DispatchQueue throws an exception, this method will also throw an exception. + /// + /// If zero is passed as the timeout value, this method will return true if and only if the queue was empty at the time + /// of the call, ignoring any delayed dispatchers. /// bool Barrier(std::chrono::nanoseconds timeout); diff --git a/src/autowiring/DispatchQueue.cpp b/src/autowiring/DispatchQueue.cpp index ec143ce1b..9d68a2835 100644 --- a/src/autowiring/DispatchQueue.cpp +++ b/src/autowiring/DispatchQueue.cpp @@ -177,15 +177,33 @@ void DispatchQueue::AddExisting(DispatchThunkBase* pBase) { } bool DispatchQueue::Barrier(std::chrono::nanoseconds timeout) { - // Set up the lambda: - auto complete = std::make_shared(false); - *this += [complete] { *complete = true; }; + static const char text [] = "Dispatch queue was aborted while a barrier was invoked"; - // Obtain the lock, wait until our variable is satisfied, which might be right away: + // Optimistic check first: std::unique_lock lk(m_dispatchLock); + + // Short-circuit if dispatching has been aborted + if (m_aborted) + throw dispatch_aborted_exception("Dispatch queue was aborted before a timed wait was attempted"); + + // Short-circuit if the queue is already empty + if (m_dispatchQueue.empty()) + return true; + + // Also short-circuit if zero is specified as the timeout value + if (timeout.count() == 0) + return false; + + // Set up the lambda. Note that the queue size CANNOT be 1, because we just checked to verify + // that it is non-empty. Thus, we do not need to signal the m_queueUpdated condition variable. + auto complete = std::make_shared(false); + auto lambda = [complete] { *complete = true; }; + m_dispatchQueue.push_back(new DispatchThunk(std::move(lambda))); + + // Wait until our variable is satisfied, which might be right away: bool rv = m_queueUpdated.wait_for(lk, timeout, [&] { return m_aborted || *complete; }); if (m_aborted) - throw dispatch_aborted_exception("Dispatch queue was aborted while a barrier was invoked"); + throw dispatch_aborted_exception("Dispatch queue was aborted during a timed wait"); return rv; } diff --git a/src/autowiring/test/DispatchQueueTest.cpp b/src/autowiring/test/DispatchQueueTest.cpp index 18157b0a5..0116c8208 100644 --- a/src/autowiring/test/DispatchQueueTest.cpp +++ b/src/autowiring/test/DispatchQueueTest.cpp @@ -69,6 +69,13 @@ TEST_F(DispatchQueueTest, PathologicalStartAndStop){ ASSERT_TRUE(t4->WaitFor(std::chrono::seconds(10))); } +TEST_F(DispatchQueueTest, TrivialBarrier) { + AutoCurrentContext()->Initiate(); + AutoRequired ct; + + ASSERT_TRUE(ct->Barrier(std::chrono::seconds(0))) << "Zero-time barrier on a zero-length queue did not pass as expected"; +} + TEST_F(DispatchQueueTest, Barrier) { AutoCurrentContext()->Initiate(); AutoRequired ct; @@ -110,7 +117,6 @@ TEST_F(DispatchQueueTest, BarrierWithAbort) { }; // Launch something that will barrier: - auto exception = std::make_shared(false); auto f = std::async( std::launch::async, [=] { @@ -118,8 +124,9 @@ TEST_F(DispatchQueueTest, BarrierWithAbort) { ct->Barrier(std::chrono::seconds(5)); } catch (autowiring_error&) { - *exception = true; + return false; } + return true; } ); @@ -129,5 +136,5 @@ TEST_F(DispatchQueueTest, BarrierWithAbort) { // Now abandon the queue, this should cause the async thread to quit: ct->Abort(); ASSERT_EQ(std::future_status::ready, f.wait_for(std::chrono::seconds(5))) << "Barrier did not abort fast enough"; - ASSERT_TRUE(*exception) << "Exception should have been thrown inside the Barrier call"; + ASSERT_TRUE(f.get()) << "Exception should have been thrown inside the Barrier call"; }