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Commit 9dee501c authored by Atneya Nair's avatar Atneya Nair
Browse files

Add move only type erased function 

std::function does not permit move only function objects, which is
necessary for convenient usage of std::packaged_task. move_only_function
is being added in a subsequent version of the standard.

Add a Runnable class which is a limited move only no-param function
object with SBO only for typical double pointer types, which also erases
the return value of the type. This is useful for constructing executors.

Test: atest runnable_tests
Flag: EXEMPT util
Bug: 391668615
Change-Id: I44c25992465956e33944060cc0dcc07a768cb768
parent e36cbc11

media/utils/include/mediautils/Runnable.h

0 → 100644
+111 −0
Original line number Diff line number Diff line 
/*

 * Copyright (C) 2025 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 <cstddef>

#include <future>

#include <memory>



namespace android::mediautils {



// Essentially std::function <void()>, but supports moveable types (and binds to any return type).

// The lack of moveable is fixed in C++23, but we don't yet have it.

// Also, SBO for std::packaged_task size, which is what we are using this for

class Runnable {

  private:

    // src == nullptr => destroy the dest, otherwise move from src storage to dst, destroying src

    using move_destroy_fptr_t = void (*)(std::byte* dest, std::byte* src) noexcept;

    using call_fptr_t = void (*)(std::byte* storage);



    struct VTable {

        move_destroy_fptr_t move_destroy;

        call_fptr_t invoke;

    };



    static void empty_move_destroy(std::byte*, std::byte*) noexcept {}

    static constexpr VTable empty_vtable{.move_destroy = empty_move_destroy, .invoke = nullptr};



    template <typename T>

    static T& transmogrify(std::byte* addr) {

        return *std::launder(reinterpret_cast<T*>(addr));

    }



    template <typename T>

    static void move_destroy_impl(std::byte* dest, std::byte* src) noexcept {

        if (src) {

            std::construct_at(&transmogrify<T>(dest), std::move(transmogrify<T>(src)));

            transmogrify<T>(src).~T();

        } else {

            transmogrify<T>(dest).~T();

        }

    }



    template <typename T>

    static void call_impl(std::byte* addr) {

        std::invoke(transmogrify<T>(addr));

    }



  public:

    static constexpr size_t STORAGE_SIZE = sizeof(std::packaged_task<int()>);



    Runnable() = default;



    Runnable(std::nullptr_t) {}



    Runnable(const Runnable& o) = delete;



    Runnable(Runnable&& o) noexcept {

        // ask other vtable to move their storage into ours

        o.v.move_destroy(storage_, o.storage_);

        std::swap(v, o.v);

    }



    template <typename F>

        requires(std::is_invocable_v<std::decay_t<F>> &&

                 !std::is_same_v<std::decay_t<F>, Runnable> &&

                 std::is_move_constructible_v<std::decay_t<F>> &&

                 sizeof(std::decay_t<F>) <= STORAGE_SIZE)

    explicit Runnable(F&& task)

        : v{move_destroy_impl<std::decay_t<F>>, call_impl<std::decay_t<F>>} {

        std::construct_at(&transmogrify<std::decay_t<F>>(storage_), std::forward<F>(task));

    }



    Runnable& operator=(const Runnable& o) = delete;



    Runnable& operator=(Runnable&& o) {

        // destroy ourselves

        v.move_destroy(storage_, nullptr);

        v = empty_vtable;

        // ask other vtable to move their storage into ours

        o.v.move_destroy(storage_, o.storage_);

        std::swap(v, o.v);

        return *this;

    }



    ~Runnable() { v.move_destroy(storage_, nullptr); }



    operator bool() const { return v.invoke != nullptr; }



    void operator()() {

        if (*this) v.invoke(storage_);

    }



  private:

    VTable v = empty_vtable;

    alignas(alignof(std::max_align_t)) std::byte storage_[STORAGE_SIZE];

};

}  // namespace android::mediautils

media/utils/tests/Android.bp

+1 −0
Original line number Diff line number Diff line
@@ -285,5 +285,6 @@ cc_test { 
    defaults: ["libmediautils_tests_defaults"],

    srcs: [

        "jthread_tests.cpp",

        "runnable_tests.cpp",

    ],

}

media/utils/tests/runnable_tests.cpp

0 → 100644
+139 −0
Original line number Diff line number Diff line 
/*

 * Copyright (C) 2025 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 "runnable_tests"



#include <mediautils/Runnable.h>



#include <gtest/gtest.h>



using namespace android::mediautils;



struct Func {

    inline static int sMoveCtor = 0;

    inline static int sDtor = 0;

    // accumulator for call operator of this object

    inline static int sSum = 0;

    static constexpr int VAL1 = 7;

    static constexpr int VAL2 = 4;



    Func(int v) : value(v) {}

    Func(const Func&) = delete;

    Func(Func&& other) : value(other.value) { sMoveCtor++; }

    Func& operator=(const Func&) = delete;

    ~Func() { sDtor++; }



    void operator()() { sSum += value; }



  private:

    const int value;

};



class RunnableTests : public ::testing::Test {

  protected:

    void SetUp() override {

        Func::sMoveCtor = 0;

        Func::sDtor = 0;

        Func::sSum = 0;

    }

};



TEST_F(RunnableTests, testEmpty) {

    Runnable r1{};

    Runnable r2{nullptr};

    // empty func should do nothing, instead of crash

    r1();

    r2();

    EXPECT_FALSE(r1);

    EXPECT_FALSE(r2);

}



static int foo() {

    return 5;

}



struct Copy {

    Copy() {}

    Copy(const Copy&) {}

    Copy(Copy&&) {}

    void operator()(){}

};



TEST_F(RunnableTests, testCompile) {

    const Copy b{};

    Runnable r1{std::move(b)};

    Runnable r2{b};

    Runnable r4{foo};

    std::unique_ptr<int> ptr;

    auto move_only = [ptr = std::move(ptr)](){};

    Runnable r5{std::move(move_only)};

    auto copyable = [](){};

    Runnable r6{copyable};

}



TEST_F(RunnableTests, testBool) {

    Runnable r1{[]() {}};

    EXPECT_TRUE(r1);

}



TEST_F(RunnableTests, testCall) {

    Runnable r1{Func{Func::VAL1}};

    EXPECT_TRUE(r1);

    r1();

    EXPECT_EQ(Func::sSum, Func::VAL1);

}



TEST_F(RunnableTests, testDtor) {

    {

        Runnable r1{Func{Func::VAL1}};

    }

    EXPECT_EQ(Func::sDtor, 2);

}



TEST_F(RunnableTests, testMoveCtor) {

    {

        Runnable moved_from{Func{Func::VAL1}};

        EXPECT_EQ(Func::sMoveCtor, 1);

        EXPECT_EQ(Func::sDtor, 1);

        Runnable r1{std::move(moved_from)};

        EXPECT_EQ(Func::sDtor, 2);  // impl detail that we destroy internal obj after move

        EXPECT_EQ(Func::sMoveCtor, 2);

        EXPECT_TRUE(r1);

        EXPECT_FALSE(moved_from);

        r1();

        EXPECT_EQ(Func::sSum, Func::VAL1);

    }

    EXPECT_EQ(Func::sDtor, 3);

}



TEST_F(RunnableTests, testMoveAssign) {

    {

        Runnable r1{Func{Func::VAL2}};

        Runnable moved_from{Func{Func::VAL1}};

        EXPECT_EQ(Func::sMoveCtor, 2);

        EXPECT_EQ(Func::sDtor, 2);

        r1();

        EXPECT_EQ(Func::sSum, 4);

        r1 = std::move(moved_from);

        EXPECT_EQ(Func::sDtor, 4);  // impl detail that we destroy internal obj after move

        EXPECT_EQ(Func::sMoveCtor, 3);

        EXPECT_TRUE(r1);

        EXPECT_FALSE(moved_from);

        r1();  // value should now hold Func::VAL1

        EXPECT_EQ(Func::sSum, Func::VAL2 + Func::VAL1);

    }

    EXPECT_EQ(Func::sDtor, 5);

}