Remove old TaskManager system

Replace it with a newer, fancier, WorkQueue-inspired
one that's just a global common thread pool.

Test: hwuiunit passes
Change-Id: Ib5d03104a08bbac9a4ec67a1bfc0db2b35d6700f
diff --git a/libs/hwui/thread/CommonPool.h b/libs/hwui/thread/CommonPool.h
new file mode 100644
index 0000000..aef2990
--- /dev/null
+++ b/libs/hwui/thread/CommonPool.h
@@ -0,0 +1,115 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+
+#ifndef FRAMEWORKS_BASE_COMMONPOOL_H
+#define FRAMEWORKS_BASE_COMMONPOOL_H
+
+#include "utils/Macros.h"
+
+#include <log/log.h>
+
+#include <condition_variable>
+#include <functional>
+#include <future>
+#include <mutex>
+
+namespace android {
+namespace uirenderer {
+
+template <class T, int SIZE>
+class ArrayQueue {
+    PREVENT_COPY_AND_ASSIGN(ArrayQueue);
+    static_assert(SIZE > 0, "Size must be positive");
+
+public:
+    ArrayQueue() = default;
+    ~ArrayQueue() = default;
+
+    constexpr size_t capacity() const { return SIZE; }
+    constexpr bool hasWork() const { return mHead != mTail; }
+    constexpr bool hasSpace() const { return ((mHead + 1) % SIZE) != mTail; }
+    constexpr int size() const {
+        if (mHead > mTail) {
+            return mHead - mTail;
+        } else {
+            return mTail - mHead + SIZE;
+        }
+    }
+
+    constexpr void push(T&& t) {
+        int newHead = (mHead + 1) % SIZE;
+        LOG_ALWAYS_FATAL_IF(newHead == mTail, "no space");
+
+        mBuffer[mHead] = std::move(t);
+        mHead = newHead;
+    }
+
+    constexpr T&& pop() {
+        LOG_ALWAYS_FATAL_IF(mTail == mHead, "empty");
+        int index = mTail;
+        mTail = (mTail + 1) % SIZE;
+        return std::move(mBuffer[index]);
+    }
+
+private:
+    T mBuffer[SIZE];
+    int mHead = 0;
+    int mTail = 0;
+};
+
+class CommonPool {
+    PREVENT_COPY_AND_ASSIGN(CommonPool);
+
+public:
+    using Task = std::function<void()>;
+    static constexpr auto THREAD_COUNT = 2;
+    static constexpr auto QUEUE_SIZE = 128;
+
+    static void post(Task&& func);
+
+    template <class F>
+    static auto async(F&& func) -> std::future<decltype(func())> {
+        typedef std::packaged_task<decltype(func())()> task_t;
+        auto task = std::make_shared<task_t>(std::forward<F>(func));
+        post([task]() { std::invoke(*task); });
+        return task->get_future();
+    }
+
+    template <class F>
+    static auto runSync(F&& func) -> decltype(func()) {
+        std::packaged_task<decltype(func())()> task{std::forward<F>(func)};
+        post([&task]() { std::invoke(task); });
+        return task.get_future().get();
+    };
+
+private:
+    CommonPool();
+    ~CommonPool() {}
+
+    void enqueue(Task&&);
+
+    void workerLoop();
+
+    std::mutex mLock;
+    std::condition_variable mCondition;
+    int mWaitingThreads = 0;
+    ArrayQueue<Task, QUEUE_SIZE> mWorkQueue;
+};
+
+}  // namespace uirenderer
+}  // namespace android
+
+#endif  // FRAMEWORKS_BASE_COMMONPOOL_H