reallocate() — netty Function Reference

Architecture documentation for the reallocate() function in PoolArena.java from the netty codebase.

Function java Buffer Telemetry calls 3

Entity Profile

Buffer→ Telemetry→ reallocate() — netty Function Reference

Dependency Diagram

graph TD
  41f1f758_db84_9e73_7e23_6c7d6ad2b5dd["reallocate()"]
  de926ba9_75e3_c416_27fc_3623234991a8["PoolArena"]
  41f1f758_db84_9e73_7e23_6c7d6ad2b5dd -->|defined in| de926ba9_75e3_c416_27fc_3623234991a8
  2476a64f_8776_d678_76d8_c4cd7055f5df["allocate()"]
  41f1f758_db84_9e73_7e23_6c7d6ad2b5dd -->|calls| 2476a64f_8776_d678_76d8_c4cd7055f5df
  1eb7867b_3257_ad29_cda0_1b8484056b67["free()"]
  41f1f758_db84_9e73_7e23_6c7d6ad2b5dd -->|calls| 1eb7867b_3257_ad29_cda0_1b8484056b67
  8355ca1b_dc45_7413_2560_d7dae2ffa914["memoryCopy()"]
  41f1f758_db84_9e73_7e23_6c7d6ad2b5dd -->|calls| 8355ca1b_dc45_7413_2560_d7dae2ffa914
  style 41f1f758_db84_9e73_7e23_6c7d6ad2b5dd fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

buffer/src/main/java/io/netty/buffer/PoolArena.java lines 292–339

    void reallocate(PooledByteBuf<T> buf, int newCapacity) {
        assert newCapacity >= 0 && newCapacity <= buf.maxCapacity();

        final int oldCapacity;
        final PoolChunk<T> oldChunk;
        final ByteBuffer oldNioBuffer;
        final long oldHandle;
        final T oldMemory;
        final int oldOffset;
        final int oldMaxLength;
        final PoolThreadCache oldCache;

        // We synchronize on the ByteBuf itself to ensure there is no "concurrent" reallocations for the same buffer.
        // We do this to ensure the ByteBuf internal fields that are used to allocate / free are not accessed
        // concurrently. This is important as otherwise we might end up corrupting our internal state of our data
        // structures.
        //
        // Also note we don't use a Lock here but just synchronized even tho this might seem like a bad choice for Loom.
        // This is done to minimize the overhead per ByteBuf. The time this would block another thread should be
        // relative small and so not be a problem for Loom.
        // See https://github.com/netty/netty/issues/13467
        synchronized (buf) {
            oldCapacity = buf.length;
            if (oldCapacity == newCapacity) {
                return;
            }

            oldChunk = buf.chunk;
            oldNioBuffer = buf.tmpNioBuf;
            oldHandle = buf.handle;
            oldMemory = buf.memory;
            oldOffset = buf.offset;
            oldMaxLength = buf.maxLength;
            oldCache = buf.cache;

            // This does not touch buf's reader/writer indices
            allocate(parent.threadCache(), buf, newCapacity);
        }
        int bytesToCopy;
        if (newCapacity > oldCapacity) {
            bytesToCopy = oldCapacity;
        } else {
            buf.trimIndicesToCapacity(newCapacity);
            bytesToCopy = newCapacity;
        }
        memoryCopy(oldMemory, oldOffset, buf, bytesToCopy);
        free(oldChunk, oldNioBuffer, oldHandle, oldMaxLength, oldCache);
    }