InputTracer: Separate the threading logic into a wrapper backend
InputTracer writes to the tracing backend interface. However, since
perfetto expects events to be written from a single thread, InputTracer
would write the events from a separate thread.
To simplify the logic inside InputTracer, remove the threading logic.
Instead, we introduce the ThreadingBackend class, which wraps around an
abitrary backend and forwards events to the inner backend from a new
thread.
Another benefit of this is that we no longer have to use the threaded
backend for tests, which makes the tracing part of InputDispatcher_test
deterministic.
Bug: 210460522
Test: atest inputflinger_tests
Change-Id: If7bbc912c05bc975ec9585f0a0ebce68683925bb
diff --git a/services/inputflinger/dispatcher/trace/InputTracer.h b/services/inputflinger/dispatcher/trace/InputTracer.h
index 9fe395d..c8b25c9 100644
--- a/services/inputflinger/dispatcher/trace/InputTracer.h
+++ b/services/inputflinger/dispatcher/trace/InputTracer.h
@@ -18,14 +18,7 @@
#include "InputTracerInterface.h"
-#include <android-base/thread_annotations.h>
-#include <gui/WindowInfo.h>
-
#include <memory>
-#include <mutex>
-#include <thread>
-#include <unordered_set>
-#include <vector>
#include "../Entry.h"
#include "InputTracingBackendInterface.h"
@@ -35,17 +28,16 @@
/**
* The tracer implementation for InputDispatcher.
*
- * InputTracer is thread-safe, so it can be called from any thread. Upon construction, InputTracer
- * will start its own thread that it uses for write events into the tracing backend. That is the
- * one and only thread that will interact with the tracing backend, since the Perfetto backend
- * uses thread-local storage.
+ * InputTracer's responsibility is to keep track of events as they are processed by InputDispatcher,
+ * and to write the events to the tracing backend when enough information is collected. InputTracer
+ * is not thread-safe.
*
* See the documentation in InputTracerInterface for the API surface.
*/
class InputTracer : public InputTracerInterface {
public:
explicit InputTracer(std::unique_ptr<InputTracingBackendInterface>);
- ~InputTracer() override;
+ ~InputTracer() = default;
InputTracer(const InputTracer&) = delete;
InputTracer& operator=(const InputTracer&) = delete;
@@ -55,10 +47,6 @@
void traceEventDispatch(const DispatchEntry&, const EventTrackerInterface*) override;
private:
- std::mutex mLock;
- std::thread mTracerThread;
- bool mThreadExit GUARDED_BY(mLock){false};
- std::condition_variable mThreadWakeCondition;
std::unique_ptr<InputTracingBackendInterface> mBackend;
// The state of a tracked event.
@@ -67,14 +55,12 @@
// TODO(b/210460522): Add additional args for tracking event sensitivity and
// dispatch target UIDs.
};
- std::vector<const EventState> mTraceQueue GUARDED_BY(mLock);
- using WindowDispatchArgs = InputTracingBackendInterface::WindowDispatchArgs;
- std::vector<const WindowDispatchArgs> mDispatchTraceQueue GUARDED_BY(mLock);
- // Provides thread-safe access to the state from an event tracker cookie.
- std::optional<EventState>& getState(const EventTrackerInterface&) REQUIRES(mLock);
+ // Get the event state associated with a tracking cookie.
+ std::optional<EventState>& getState(const EventTrackerInterface&);
- // Implementation of the event tracker cookie.
+ // Implementation of the event tracker cookie. The cookie holds the event state directly for
+ // convenience to avoid the overhead of tracking the state separately in InputTracer.
class EventTrackerImpl : public EventTrackerInterface {
public:
explicit EventTrackerImpl(InputTracer&, TracedEvent&& entry);
@@ -84,16 +70,10 @@
InputTracer& mTracer;
// This event tracker cookie will only hold the state as long as it has not been written
// to the trace. The state is released when the event is written to the trace.
- mutable std::optional<EventState> mLockedState;
+ mutable std::optional<EventState> mState;
- // Only allow InputTracer access to the locked state through getTrackerState() to ensure
- // that the InputTracer lock is held when this is accessed.
friend std::optional<EventState>& InputTracer::getState(const EventTrackerInterface&);
};
-
- void threadLoop();
- void writeEventsToBackend(const std::vector<const EventState>& events,
- const std::vector<const WindowDispatchArgs>& dispatchEvents);
};
} // namespace android::inputdispatcher::trace::impl