PooledByteBufAllocator Class — netty Architecture

Source Code

buffer/src/main/java/io/netty/buffer/PooledByteBufAllocator.java lines 38–859

public class PooledByteBufAllocator extends AbstractByteBufAllocator implements ByteBufAllocatorMetricProvider {

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(PooledByteBufAllocator.class);
    private static final int DEFAULT_NUM_HEAP_ARENA;
    private static final int DEFAULT_NUM_DIRECT_ARENA;

    private static final int DEFAULT_PAGE_SIZE;
    private static final int DEFAULT_MAX_ORDER; // 8192 << 9 = 4 MiB per chunk
    private static final int DEFAULT_SMALL_CACHE_SIZE;
    private static final int DEFAULT_NORMAL_CACHE_SIZE;
    static final int DEFAULT_MAX_CACHED_BUFFER_CAPACITY;
    private static final int DEFAULT_CACHE_TRIM_INTERVAL;
    private static final long DEFAULT_CACHE_TRIM_INTERVAL_MILLIS;
    private static final boolean DEFAULT_USE_CACHE_FOR_ALL_THREADS;
    private static final int DEFAULT_DIRECT_MEMORY_CACHE_ALIGNMENT;
    static final int DEFAULT_MAX_CACHED_BYTEBUFFERS_PER_CHUNK;
    private static final boolean DEFAULT_DISABLE_CACHE_FINALIZERS_FOR_FAST_THREAD_LOCAL_THREADS;

    private static final int MIN_PAGE_SIZE = 4096;
    private static final int MAX_CHUNK_SIZE = (int) (((long) Integer.MAX_VALUE + 1) / 2);

    private static final int CACHE_NOT_USED = 0;

    private final Runnable trimTask = new Runnable() {
        @Override
        public void run() {
            PooledByteBufAllocator.this.trimCurrentThreadCache();
        }
    };

    static {
        int defaultAlignment = SystemPropertyUtil.getInt(
                "io.netty.allocator.directMemoryCacheAlignment", 0);
        int defaultPageSize = SystemPropertyUtil.getInt("io.netty.allocator.pageSize", 8192);
        Throwable pageSizeFallbackCause = null;
        try {
            validateAndCalculatePageShifts(defaultPageSize, defaultAlignment);
        } catch (Throwable t) {
            pageSizeFallbackCause = t;
            defaultPageSize = 8192;
            defaultAlignment = 0;
        }
        DEFAULT_PAGE_SIZE = defaultPageSize;
        DEFAULT_DIRECT_MEMORY_CACHE_ALIGNMENT = defaultAlignment;

        int defaultMaxOrder = SystemPropertyUtil.getInt("io.netty.allocator.maxOrder", 9);
        Throwable maxOrderFallbackCause = null;
        try {
            validateAndCalculateChunkSize(DEFAULT_PAGE_SIZE, defaultMaxOrder);
        } catch (Throwable t) {
            maxOrderFallbackCause = t;
            defaultMaxOrder = 9;
        }
        DEFAULT_MAX_ORDER = defaultMaxOrder;

        // Determine reasonable default for nHeapArena and nDirectArena.
        // Assuming each arena has 3 chunks, the pool should not consume more than 50% of max memory.
        final Runtime runtime = Runtime.getRuntime();

        /*
         * We use 2 * available processors by default to reduce contention as we use 2 * available processors for the
         * number of EventLoops in NIO and EPOLL as well. If we choose a smaller number we will run into hot spots as
         * allocation and de-allocation needs to be synchronized on the PoolArena.
         *
         * See https://github.com/netty/netty/issues/3888.
         */
        final int defaultMinNumArena = NettyRuntime.availableProcessors() * 2;
        final int defaultChunkSize = DEFAULT_PAGE_SIZE << DEFAULT_MAX_ORDER;
        DEFAULT_NUM_HEAP_ARENA = Math.max(0,
                SystemPropertyUtil.getInt(
                        "io.netty.allocator.numHeapArenas",
                        (int) Math.min(
                                defaultMinNumArena,
                                runtime.maxMemory() / defaultChunkSize / 2 / 3)));
        DEFAULT_NUM_DIRECT_ARENA = Math.max(0,
                SystemPropertyUtil.getInt(
                        "io.netty.allocator.numDirectArenas",
                        (int) Math.min(
                                defaultMinNumArena,
                                PlatformDependent.maxDirectMemory() / defaultChunkSize / 2 / 3)));