SF: Introduce background task executor

Extract logic to execute work outside of the main thread
from TransactionCallbackInvoker so we can reuse the
thread for other tasks that are not critical to drawing.

Bug: 206380307
Test: presubmit
Change-Id: I8128d2f333e3aab5639cd1200e820de39f0b3191

5 files changed, 113 insertions, 43 deletions

diff --git a/services/surfaceflinger/Android.bp b/services/surfaceflinger/Android.bp
index fb42cc02eb..2a9e2e7f0d 100644
--- a/services/surfaceflinger/Android.bp
+++ b/services/surfaceflinger/Android.bp
@@ -144,6 +144,7 @@ cc_library_headers {
 filegroup {
     name: "libsurfaceflinger_sources",
     srcs: [
+        "BackgroundExecutor.cpp",
         "BufferLayer.cpp",
         "BufferLayerConsumer.cpp",
         "BufferQueueLayer.cpp",
diff --git a/services/surfaceflinger/BackgroundExecutor.cpp b/services/surfaceflinger/BackgroundExecutor.cpp
new file mode 100644
index 0000000000..3663cdb0ec
--- /dev/null
+++ b/services/surfaceflinger/BackgroundExecutor.cpp
@@ -0,0 +1,65 @@
+/*
+ * Copyright 2021 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_NDEBUG 0
+#undef LOG_TAG
+#define LOG_TAG "BackgroundExecutor"
+#define ATRACE_TAG ATRACE_TAG_GRAPHICS
+
+#include "BackgroundExecutor.h"
+
+namespace android {
+
+ANDROID_SINGLETON_STATIC_INSTANCE(BackgroundExecutor);
+
+BackgroundExecutor::BackgroundExecutor() : Singleton<BackgroundExecutor>() {
+    mThread = std::thread([&]() {
+        bool done = false;
+        while (!done) {
+            std::vector<std::function<void()>> tasks;
+            {
+                std::unique_lock lock(mMutex);
+                mWorkAvailableCv.wait(lock, [&]() { return mDone || !mTasks.empty(); });
+                tasks = std::move(mTasks);
+                mTasks.clear();
+                done = mDone;
+            } // unlock mMutex
+
+            for (auto& task : tasks) {
+                task();
+            }
+        }
+    });
+}
+
+BackgroundExecutor::~BackgroundExecutor() {
+    {
+        std::unique_lock lock(mMutex);
+        mDone = true;
+        mWorkAvailableCv.notify_all();
+    }
+    if (mThread.joinable()) {
+        mThread.join();
+    }
+}
+
+void BackgroundExecutor::execute(std::function<void()> task) {
+    std::unique_lock lock(mMutex);
+    mTasks.emplace_back(std::move(task));
+    mWorkAvailableCv.notify_all();
+}
+
+} // namespace android
\ No newline at end of file
diff --git a/services/surfaceflinger/BackgroundExecutor.h b/services/surfaceflinger/BackgroundExecutor.h
new file mode 100644
index 0000000000..6f6d305280
--- /dev/null
+++ b/services/surfaceflinger/BackgroundExecutor.h
@@ -0,0 +1,42 @@
+/*
+ * Copyright 2021 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.
+ */
+
+#pragma once
+
+#include <utils/Singleton.h>
+#include <condition_variable>
+#include <mutex>
+#include <queue>
+#include <thread>
+
+namespace android {
+
+// Executes tasks off the main thread.
+class BackgroundExecutor : public Singleton<BackgroundExecutor> {
+public:
+    BackgroundExecutor();
+    ~BackgroundExecutor();
+    void execute(std::function<void()>);
+
+private:
+    std::mutex mMutex;
+    std::condition_variable mWorkAvailableCv;
+    std::thread mThread;
+    bool mDone = false;
+    std::vector<std::function<void()>> mTasks;
+};
+
+} // namespace android
diff --git a/services/surfaceflinger/TransactionCallbackInvoker.cpp b/services/surfaceflinger/TransactionCallbackInvoker.cpp
index f3d46ea061..b705d9cf7b 100644
--- a/services/surfaceflinger/TransactionCallbackInvoker.cpp
+++ b/services/surfaceflinger/TransactionCallbackInvoker.cpp
@@ -24,6 +24,7 @@
 #define ATRACE_TAG ATRACE_TAG_GRAPHICS
 
 #include "TransactionCallbackInvoker.h"
+#include "BackgroundExecutor.h"
 
 #include <cinttypes>
 
@@ -49,31 +50,6 @@ static bool containsOnCommitCallbacks(const std::vector<CallbackId>& callbacks)
     return !callbacks.empty() && callbacks.front().type == CallbackId::Type::ON_COMMIT;
 }
 
-TransactionCallbackInvoker::TransactionCallbackInvoker() {
-    mThread = std::thread([&]() {
-          std::unique_lock lock(mCallbackThreadMutex);
-
-        while (mKeepRunning) {
-          while (mCallbackThreadWork.size() > 0) {
-              mCallbackThreadWork.front()();
-              mCallbackThreadWork.pop();
-          }
-          mCallbackConditionVariable.wait(lock);
-        }
-    });
-}
-
-TransactionCallbackInvoker::~TransactionCallbackInvoker() {
-    {
-          std::unique_lock lock(mCallbackThreadMutex);
-          mKeepRunning = false;
-          mCallbackConditionVariable.notify_all();
-    }
-    if (mThread.joinable()) {
-        mThread.join();
-    }
-}
-
 void TransactionCallbackInvoker::addEmptyTransaction(const ListenerCallbacks& listenerCallbacks) {
     auto& [listener, callbackIds] = listenerCallbacks;
     auto& transactionStatsDeque = mCompletedTransactions[listener];
@@ -242,15 +218,10 @@ void TransactionCallbackInvoker::sendCallbacks(bool onCommitOnly) {
                 // keep it as an IBinder due to consistency reasons: if we
                 // interface_cast at the IPC boundary when reading a Parcel,
                 // we get pointers that compare unequal in the SF process.
-                {
-                    std::unique_lock lock(mCallbackThreadMutex);
-                    mCallbackThreadWork.push(
-                        [stats = std::move(listenerStats)]() {
-                          interface_cast<ITransactionCompletedListener>(stats.listener)
-                              ->onTransactionCompleted(stats);
-                    });
-                    mCallbackConditionVariable.notify_all();
-                }
+                BackgroundExecutor::getInstance().execute([stats = std::move(listenerStats)]() {
+                    interface_cast<ITransactionCompletedListener>(stats.listener)
+                            ->onTransactionCompleted(stats);
+                });
             }
         }
         completedTransactionsItr++;
diff --git a/services/surfaceflinger/TransactionCallbackInvoker.h b/services/surfaceflinger/TransactionCallbackInvoker.h
index e203d41bd9..5ef54757d7 100644
--- a/services/surfaceflinger/TransactionCallbackInvoker.h
+++ b/services/surfaceflinger/TransactionCallbackInvoker.h
@@ -61,9 +61,6 @@ public:
 
 class TransactionCallbackInvoker {
 public:
-    TransactionCallbackInvoker();
-    ~TransactionCallbackInvoker();
-
     status_t addCallbackHandles(const std::deque<sp<CallbackHandle>>& handles,
                                 const std::vector<JankData>& jankData);
     status_t addOnCommitCallbackHandles(const std::deque<sp<CallbackHandle>>& handles,
@@ -94,12 +91,6 @@ private:
         mCompletedTransactions;
 
     sp<Fence> mPresentFence;
-
-    std::mutex mCallbackThreadMutex;
-    std::condition_variable mCallbackConditionVariable;
-    std::thread mThread;
-    bool mKeepRunning = true;
-    std::queue<std::function<void()>> mCallbackThreadWork;
 };
 
 } // namespace android