services/inputflinger/dispatcher/trace/ThreadedBackend.cpp

/*
 * Copyright 2024 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define LOG_TAG "InputTracer"

#include "ThreadedBackend.h"

#include "InputTracingPerfettoBackend.h"

#include <android-base/logging.h>
#include <utils/AndroidThreads.h>

namespace android::inputdispatcher::trace::impl {

namespace {

// Helper to std::visit with lambdas.
template <typename... V>
struct Visitor : V... {
    using V::operator()...;
};

} // namespace

// --- ThreadedBackend ---

template <typename Backend>
ThreadedBackend<Backend>::ThreadedBackend(Backend&& innerBackend)
      : mTracerThread(&ThreadedBackend::threadLoop, this), mBackend(std::move(innerBackend)) {}

template <typename Backend>
ThreadedBackend<Backend>::~ThreadedBackend() {
    {
        std::scoped_lock lock(mLock);
        mThreadExit = true;
    }
    mThreadWakeCondition.notify_all();
    mTracerThread.join();
}

template <typename Backend>
void ThreadedBackend<Backend>::traceMotionEvent(const TracedMotionEvent& event) {
    std::scoped_lock lock(mLock);
    mQueue.emplace_back(event);
    mThreadWakeCondition.notify_all();
}

template <typename Backend>
void ThreadedBackend<Backend>::traceKeyEvent(const TracedKeyEvent& event) {
    std::scoped_lock lock(mLock);
    mQueue.emplace_back(event);
    mThreadWakeCondition.notify_all();
}

template <typename Backend>
void ThreadedBackend<Backend>::traceWindowDispatch(const WindowDispatchArgs& dispatchArgs) {
    std::scoped_lock lock(mLock);
    mQueue.emplace_back(dispatchArgs);
    mThreadWakeCondition.notify_all();
}

template <typename Backend>
void ThreadedBackend<Backend>::threadLoop() {
    androidSetThreadName("InputTracer");

    std::vector<std::variant<TracedKeyEvent, TracedMotionEvent, WindowDispatchArgs>> events;

    while (true) {
        { // acquire lock
            std::unique_lock lock(mLock);
            base::ScopedLockAssertion assumeLocked(mLock);

            // Wait until we need to process more events or exit.
            mThreadWakeCondition.wait(lock, [&]() REQUIRES(mLock) {
                return mThreadExit || !mQueue.empty();
            });
            if (mThreadExit) {
                return;
            }

            mQueue.swap(events);
        } // release lock

        // Trace the events into the backend without holding the lock to reduce the amount of
        // work performed in the critical section.
        for (const auto& event : events) {
            std::visit(Visitor{[&](const TracedMotionEvent& e) { mBackend.traceMotionEvent(e); },
                               [&](const TracedKeyEvent& e) { mBackend.traceKeyEvent(e); },
                               [&](const WindowDispatchArgs& args) {
                                   mBackend.traceWindowDispatch(args);
                               }},
                       event);
        }
        events.clear();
    }
}

// Explicit template instantiation for the PerfettoBackend.
template class ThreadedBackend<PerfettoBackend>;

} // namespace android::inputdispatcher::trace::impl