聊聊flink的MemoryPool

序

本文主要研究一下flink的MemoryPool

MemoryPool

flink-runtime_2.11-1.7.2-sources.jar!/org/apache/flink/runtime/memory/MemoryManager.java

    abstract static class MemoryPool {

        abstract int getNumberOfAvailableMemorySegments();

        abstract MemorySegment allocateNewSegment(Object owner);

        abstract MemorySegment requestSegmentFromPool(Object owner);

        abstract void returnSegmentToPool(MemorySegment segment);

        abstract void clear();
    }

• MemoryPool定义了getNumberOfAvailableMemorySegments、allocateNewSegment、requestSegmentFromPool、returnSegmentToPool、clear这几个抽象方法；它有HybridHeapMemoryPool、HybridOffHeapMemoryPool这两个子类

HybridHeapMemoryPool

flink-runtime_2.11-1.7.2-sources.jar!/org/apache/flink/runtime/memory/MemoryManager.java

    static final class HybridHeapMemoryPool extends MemoryPool {

        /** The collection of available memory segments. */
        private final ArrayDeque<byte[]> availableMemory;

        private final int segmentSize;

        HybridHeapMemoryPool(int numInitialSegments, int segmentSize) {
            this.availableMemory = new ArrayDeque<>(numInitialSegments);
            this.segmentSize = segmentSize;

            for (int i = 0; i < numInitialSegments; i++) {
                this.availableMemory.add(new byte[segmentSize]);
            }
        }

        @Override
        MemorySegment allocateNewSegment(Object owner) {
            return MemorySegmentFactory.allocateUnpooledSegment(segmentSize, owner);
        }

        @Override
        MemorySegment requestSegmentFromPool(Object owner) {
            byte[] buf = availableMemory.remove();
            return  MemorySegmentFactory.wrapPooledHeapMemory(buf, owner);
        }

        @Override
        void returnSegmentToPool(MemorySegment segment) {
            if (segment.getClass() == HybridMemorySegment.class) {
                HybridMemorySegment heapSegment = (HybridMemorySegment) segment;
                availableMemory.add(heapSegment.getArray());
                heapSegment.free();
            }
            else {
                throw new IllegalArgumentException("Memory segment is not a " + HybridMemorySegment.class.getSimpleName());
            }
        }

        @Override
        protected int getNumberOfAvailableMemorySegments() {
            return availableMemory.size();
        }

        @Override
        void clear() {
            availableMemory.clear();
        }
    }

• HybridHeapMemoryPool继承了MemoryPool，它使用的是jvm的heap内存；构造器接收numInitialSegments、segmentSize两个参数用于初始化availableMemory这个ArrayDeque，该queue的元素类型为byte[]
• allocateNewSegment方法调用的是MemorySegmentFactory.allocateUnpooledSegment，用于分配unpooled memory；requestSegmentFromPool方法调用的是availableMemory.remove()，然后调用MemorySegmentFactory.wrapPooledHeapMemory包装为MemorySegment，这个方法没有判断ArrayDeque的大小就直接remove，需要注意
• returnSegmentToPool方法只对HybridMemorySegment类型进行处理，首先将它的byte[]归还到availableMemory，之后调用heapSegment.free()释放；getNumberOfAvailableMemorySegments方法返回的是availableMemory.size()；clear方法调用的是availableMemory.clear()

HybridOffHeapMemoryPool

flink-runtime_2.11-1.7.2-sources.jar!/org/apache/flink/runtime/memory/MemoryManager.java

    static final class HybridOffHeapMemoryPool extends MemoryPool {

        /** The collection of available memory segments. */
        private final ArrayDeque<ByteBuffer> availableMemory;

        private final int segmentSize;

        HybridOffHeapMemoryPool(int numInitialSegments, int segmentSize) {
            this.availableMemory = new ArrayDeque<>(numInitialSegments);
            this.segmentSize = segmentSize;

            for (int i = 0; i < numInitialSegments; i++) {
                this.availableMemory.add(ByteBuffer.allocateDirect(segmentSize));
            }
        }

        @Override
        MemorySegment allocateNewSegment(Object owner) {
            return MemorySegmentFactory.allocateUnpooledOffHeapMemory(segmentSize, owner);
        }

        @Override
        MemorySegment requestSegmentFromPool(Object owner) {
            ByteBuffer buf = availableMemory.remove();
            return MemorySegmentFactory.wrapPooledOffHeapMemory(buf, owner);
        }

        @Override
        void returnSegmentToPool(MemorySegment segment) {
            if (segment.getClass() == HybridMemorySegment.class) {
                HybridMemorySegment hybridSegment = (HybridMemorySegment) segment;
                ByteBuffer buf = hybridSegment.getOffHeapBuffer();
                availableMemory.add(buf);
                hybridSegment.free();
            }
            else {
                throw new IllegalArgumentException("Memory segment is not a " + HybridMemorySegment.class.getSimpleName());
            }
        }

        @Override
        protected int getNumberOfAvailableMemorySegments() {
            return availableMemory.size();
        }

        @Override
        void clear() {
            availableMemory.clear();
        }
    }

• HybridOffHeapMemoryPool继承了MemoryPool，它使用的是OffHeap；构造器接收numInitialSegments、segmentSize两个参数用于初始化availableMemory这个ArrayDeque，该queue的元素类型为ByteBuffer
• allocateNewSegment方法调用的是MemorySegmentFactory.allocateUnpooledOffHeapMemory，用于分配unpooled off-heap memory；requestSegmentFromPool方法调用的是availableMemory.remove()，然后调用MemorySegmentFactory.wrapPooledOffHeapMemory包装为MemorySegment，这个方法没有判断ArrayDeque的大小就直接remove，需要注意
• returnSegmentToPool方法只对HybridMemorySegment类型进行处理，首先将它的ByteBuffer归还到availableMemory，之后调用heapSegment.free()释放；getNumberOfAvailableMemorySegments方法返回的是availableMemory.size()；clear方法调用的是availableMemory.clear()

小结

• MemoryPool定义了getNumberOfAvailableMemorySegments、allocateNewSegment、requestSegmentFromPool、returnSegmentToPool、clear这几个抽象方法；它有HybridHeapMemoryPool、HybridOffHeapMemoryPool这两个子类
• HybridHeapMemoryPool继承了MemoryPool，它使用的是jvm的heap内存；构造器接收numInitialSegments、segmentSize两个参数用于初始化availableMemory这个ArrayDeque，该queue的元素类型为byte[]；allocateNewSegment方法调用的是MemorySegmentFactory.allocateUnpooledSegment，用于分配unpooled memory；requestSegmentFromPool方法调用的是availableMemory.remove()，然后调用MemorySegmentFactory.wrapPooledHeapMemory包装为MemorySegment，这个方法没有判断ArrayDeque的大小就直接remove，需要注意；returnSegmentToPool方法只对HybridMemorySegment类型进行处理，首先将它的byte[]归还到availableMemory，之后调用heapSegment.free()释放；getNumberOfAvailableMemorySegments方法返回的是availableMemory.size()；clear方法调用的是availableMemory.clear()
• HybridOffHeapMemoryPool继承了MemoryPool，它使用的是OffHeap；构造器接收numInitialSegments、segmentSize两个参数用于初始化availableMemory这个ArrayDeque，该queue的元素类型为ByteBuffer；allocateNewSegment方法调用的是MemorySegmentFactory.allocateUnpooledOffHeapMemory，用于分配unpooled off-heap memory；requestSegmentFromPool方法调用的是availableMemory.remove()，然后调用MemorySegmentFactory.wrapPooledOffHeapMemory包装为MemorySegment，这个方法没有判断ArrayDeque的大小就直接remove，需要注意；returnSegmentToPool方法只对HybridMemorySegment类型进行处理，首先将它的ByteBuffer归还到availableMemory，之后调用heapSegment.free()释放；getNumberOfAvailableMemorySegments方法返回的是availableMemory.size()；clear方法调用的是availableMemory.clear()

doc

• MemoryManager