SoundPool: Fix WeakRef lifetime

    return getSoundPoolManager().set(env, thiz, soundPool);

}

/**

 * ConcurrentHashMap is a locked hash map

 *

 * As from the name, this class is thread_safe.

 *

 * The type V must have 3 properties in the current implementation.

 *    1) A V{} default constructor which represents a nullValue.

 *    2) V::operator bool() const efficient detection of such a nullValue.

 *    3) V must be copyable.

 *

 * Note: The Key cannot be a Java LocalRef, as those change between JNI calls.

 * The Key could be the raw native object pointer if one wanted to associate

 * extra data with a native object.

 *

 * Using set() with a nullValue V results in erasing the key entry.

 * A nullValue V is returned by get() if there is no underlying entry.

 *

 * Design notes:

 * 1) For objects of type V that do not naturally have a "nullValue",

 *    wrapping VOpt = std::optional<V> or VShared = std::shared<V> is recommended.

 *

 * 2) An overload for an explicit equality comparable nullValue such as

 *    get(..., const V& nullValue) or set(..., const V& nullValue)

 *    is omitted.  An alternative is to pass a fixed nullValue into a special

 *    constructor (omitted) for equality comparisons and return value.

 *

 * 3) This ConcurrentHashMap currently allows only one thread at a time.

 *    It is not optimized for heavy multi-threaded use.

 */

template <typename K, typename V>

class ConcurrentHashMap

{

public:

    // Sets the value and returns the old one.

    //

    // If the old value doesn't exist, then nullValue V is returned.

    // If the new value is false by operator bool(), the internal value is destroyed.

    // Note: The old value is returned so if V is a smart pointer, it can be held

    // by the caller to be deleted outside of any external lock.

    V set(const K& key, const V& value) {

        std::lock_guard lg(mLock);

        auto it = mMap.find(key);

        if (it == mMap.end()) {

            if (value) {

                mMap[key] = value;

            }

            return {};

        }

        V oldValue = std::move(it->second);

        if (value) {

            it->second = value;

        } else {

            mMap.erase(it);

        }

        return oldValue;

    }

    // Retrieves the associated object, returns nullValue V if not available.

    V get(const K& key) const {

        std::lock_guard lg(mLock);

        auto it = mMap.find(key);

        return it != mMap.end() ? it->second : V{};

    }

private:

    mutable std::mutex mLock;

    std::unordered_map<K, V> mMap GUARDED_BY(mLock);

};

// *jobject is needed to fit the jobject into a std::shared_ptr.

// This is the Android type _jobject, but we derive this type as JObjectValue.

using JObjectValue = std::remove_pointer_t<jobject>; // _jobject

// Check that jobject is really a pointer to JObjectValue.

// The JNI contract is that jobject is NULL comparable,

// so jobject is pointer equivalent; we check here to be sure.

// Note std::remove_ptr_t<NonPointerType> == NonPointerType.

static_assert(std::is_same_v<JObjectValue*, jobject>);

// We store the ancillary data associated with a SoundPool object in a concurrent

// hash map indexed on the SoundPool native object pointer.

auto& getSoundPoolJavaRefManager() {

    static ConcurrentHashMap<SoundPool *, std::shared_ptr<JObjectValue>> concurrentHashMap;

    return concurrentHashMap;

}

// make_shared_globalref_from_localref() creates a sharable Java global

// reference from a Java local reference. The equivalent type is

// std::shared_ptr<_jobject> (where _jobject is JObjectValue,

// and _jobject * is jobject),

// and the jobject may be retrieved by .get() or pointer dereference.

// This encapsulation gives the benefit of std::shared_ptr

// ref counting, weak_ptr, etc.

//

// The Java global reference should be stable between JNI calls.  It is a limited

// quantity so sparingly use global references.

//

// The Android JNI implementation is described here:

// https://developer.android.com/training/articles/perf-jni

// https://android-developers.googleblog.com/2011/11/jni-local-reference-changes-in-ics.html

//

inline auto make_shared_globalref_from_localref(JNIEnv *env, jobject localRef) {

    return std::shared_ptr<JObjectValue>(

            env->NewGlobalRef(localRef),

            [](JObjectValue* object) { // cannot cache env as don't know which thread we're on.

                if (object != nullptr) AndroidRuntime::getJNIEnv()->DeleteGlobalRef(object);

            });

}

} // namespace

static const char* const kAudioAttributesClassPathName = "android/media/AudioAttributes";

static void android_media_callback(SoundPoolEvent event, SoundPool* soundPool, void* user)

{

    ALOGV("callback: (%d, %d, %d, %p, %p)", event.mMsg, event.mArg1, event.mArg2, soundPool, user);

    auto weakRef = getSoundPoolJavaRefManager().get(soundPool); // shared_ptr to WeakRef

    if (weakRef == nullptr) {

        ALOGD("%s: no weak ref, object released, ignoring callback", __func__);

        return;

    }

    JNIEnv *env = AndroidRuntime::getJNIEnv();

    env->CallStaticVoidMethod(

            fields.mSoundPoolClass, fields.mPostEvent, user, event.mMsg, event.mArg1, event.mArg2,

            fields.mSoundPoolClass, fields.mPostEvent,

            weakRef.get(), event.mMsg, event.mArg1, event.mArg2,

            nullptr /* object */);

    if (env->ExceptionCheck() != JNI_FALSE) {

        ALOGE("%s: Uncaught exception returned from Java callback", __func__);

        env->ExceptionDescribe();

        env->ExceptionClear(); // Just clear it, hopefully all is ok.

    }

}

static jint

    ALOGV("android_media_SoundPool_native_setup");

    ScopedUtfChars opPackageNameStr(env, opPackageName);

    auto soundPool = std::make_shared<SoundPool>(maxChannels, paa, opPackageNameStr.c_str());

    // set callback with weak reference

    jobject globalWeakRef = env->NewGlobalRef(weakRef);

    soundPool->setCallback(android_media_callback, globalWeakRef);

    soundPool->setCallback(android_media_callback, nullptr /* user */);

    // register with SoundPoolManager.

    auto oldSoundPool = setSoundPool(env, thiz, soundPool);

    // register Java SoundPool WeakRef using native SoundPool * as the key, for the callback.

    auto oldSoundPoolJavaRef = getSoundPoolJavaRefManager().set(

            soundPool.get(), make_shared_globalref_from_localref(env, weakRef));

    ALOGW_IF(oldSoundPool != nullptr, "%s: Aliased SoundPool object %p",

            __func__, oldSoundPool.get());

    ALOGV("android_media_SoundPool_release");

    // Remove us from SoundPoolManager.

    auto oldSoundPool = setSoundPool(env, thiz, nullptr);

    // Caution: Deleting the weakRef is not race free from invoking

    // the Java callback because we may not have the last remaining

    // reference to the SoundPool object - another method could still

    // be in progress.

    auto oldSoundPool = setSoundPool(env, thiz, nullptr);

    if (oldSoundPool != nullptr) {

        // release weak reference and clear callback

        auto weakRef = (jobject) oldSoundPool->getUserData();

        oldSoundPool->setCallback(nullptr /* callback */, nullptr /* user */);

        if (weakRef != nullptr) {

            env->DeleteGlobalRef(weakRef);

        }

        // Note: setting the weak ref is thread safe in case there is a callback

        // simultaneously occurring.

        auto oldSoundPoolJavaRef = getSoundPoolJavaRefManager().set(oldSoundPool.get(), nullptr);

    }

    // destructor to oldSoundPool should occur at exit.

}