services/surfaceflinger/HwcSlotGenerator.cpp

/*
 * Copyright 2022 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.
 */

#undef LOG_TAG
#define LOG_TAG "HwcSlotGenerator"
#define ATRACE_TAG ATRACE_TAG_GRAPHICS

#include <gui/BufferQueue.h>

#include "HwcSlotGenerator.h"

namespace android {

HwcSlotGenerator::HwcSlotGenerator() {
    for (int i = 0; i < BufferQueue::NUM_BUFFER_SLOTS; i++) {
        mFreeHwcCacheSlots.push(i);
    }
}

void HwcSlotGenerator::bufferErased(const client_cache_t& clientCacheId) {
    std::lock_guard lock(mMutex);
    if (!clientCacheId.isValid()) {
        ALOGE("invalid process, failed to erase buffer");
        return;
    }
    eraseBufferLocked(clientCacheId);
}

int HwcSlotGenerator::getHwcCacheSlot(const client_cache_t& clientCacheId) {
    std::lock_guard<std::mutex> lock(mMutex);
    auto itr = mCachedBuffers.find(clientCacheId);
    if (itr == mCachedBuffers.end()) {
        return addCachedBuffer(clientCacheId);
    }
    auto& [hwcCacheSlot, counter] = itr->second;
    counter = mCounter++;
    return hwcCacheSlot;
}

int HwcSlotGenerator::addCachedBuffer(const client_cache_t& clientCacheId) REQUIRES(mMutex) {
    if (!clientCacheId.isValid()) {
        ALOGE("invalid process, returning invalid slot");
        return BufferQueue::INVALID_BUFFER_SLOT;
    }

    ClientCache::getInstance().registerErasedRecipient(clientCacheId,
                                                       wp<ErasedRecipient>::fromExisting(this));

    int hwcCacheSlot = getFreeHwcCacheSlot();
    mCachedBuffers[clientCacheId] = {hwcCacheSlot, mCounter++};
    return hwcCacheSlot;
}

int HwcSlotGenerator::getFreeHwcCacheSlot() REQUIRES(mMutex) {
    if (mFreeHwcCacheSlots.empty()) {
        evictLeastRecentlyUsed();
    }

    int hwcCacheSlot = mFreeHwcCacheSlots.top();
    mFreeHwcCacheSlots.pop();
    return hwcCacheSlot;
}

void HwcSlotGenerator::evictLeastRecentlyUsed() REQUIRES(mMutex) {
    uint64_t minCounter = UINT_MAX;
    client_cache_t minClientCacheId = {};
    for (const auto& [clientCacheId, slotCounter] : mCachedBuffers) {
        const auto& [hwcCacheSlot, counter] = slotCounter;
        if (counter < minCounter) {
            minCounter = counter;
            minClientCacheId = clientCacheId;
        }
    }
    eraseBufferLocked(minClientCacheId);

    ClientCache::getInstance().unregisterErasedRecipient(minClientCacheId,
                                                         wp<ErasedRecipient>::fromExisting(this));
}

void HwcSlotGenerator::eraseBufferLocked(const client_cache_t& clientCacheId) REQUIRES(mMutex) {
    auto itr = mCachedBuffers.find(clientCacheId);
    if (itr == mCachedBuffers.end()) {
        return;
    }
    auto& [hwcCacheSlot, counter] = itr->second;

    // TODO send to hwc cache and resources

    mFreeHwcCacheSlots.push(hwcCacheSlot);
    mCachedBuffers.erase(clientCacheId);
}

} // namespace android