序
本文主要研究一下flink的MemorySegment
MemorySegment
flink-release-1.7.2/flink-core/src/main/java/org/apache/flink/core/memory/MemorySegment.java
@Internalpublic abstract class MemorySegment { @SuppressWarnings("restriction") protected static final sun.misc.Unsafe UNSAFE = MemoryUtils.UNSAFE; @SuppressWarnings("restriction") protected static final long BYTE_ARRAY_BASE_OFFSET = UNSAFE.arrayBaseOffset(byte[].class); private static final boolean LITTLE_ENDIAN = (ByteOrder.nativeOrder() == ByteOrder.LITTLE_ENDIAN); // ------------------------------------------------------------------------ protected final byte[] heapMemory; protected long address; protected final long addressLimit; protected final int size; private final Object owner; MemorySegment(byte[] buffer, Object owner) { if (buffer == null) { throw new NullPointerException("buffer"); } this.heapMemory = buffer; this.address = BYTE_ARRAY_BASE_OFFSET; this.size = buffer.length; this.addressLimit = this.address + this.size; this.owner = owner; } MemorySegment(long offHeapAddress, int size, Object owner) { if (offHeapAddress <= 0) { throw new IllegalArgumentException("negative pointer or size"); } if (offHeapAddress >= Long.MAX_VALUE - Integer.MAX_VALUE) { // this is necessary to make sure the collapsed checks are safe against numeric overflows throw new IllegalArgumentException("Segment initialized with too large address: " + offHeapAddress + " ; Max allowed address is " + (Long.MAX_VALUE - Integer.MAX_VALUE - 1)); } this.heapMemory = null; this.address = offHeapAddress; this.addressLimit = this.address + size; this.size = size; this.owner = owner; } // ------------------------------------------------------------------------ // Memory Segment Operations // ------------------------------------------------------------------------ public int size() { return size; } public boolean isFreed() { return address > addressLimit; } public void free() { // this ensures we can place no more data and trigger // the checks for the freed segment address = addressLimit + 1; } public boolean isOffHeap() { return heapMemory == null; } public byte[] getArray() { if (heapMemory != null) { return heapMemory; } else { throw new IllegalStateException("Memory segment does not represent heap memory"); } } public long getAddress() { if (heapMemory == null) { return address; } else { throw new IllegalStateException("Memory segment does not represent off heap memory"); } } public abstract ByteBuffer wrap(int offset, int length); public Object getOwner() { return owner; } // ------------------------------------------------------------------------ // Random Access get() and put() methods // ------------------------------------------------------------------------ //------------------------------------------------------------------------ // Notes on the implementation: We try to collapse as many checks as // possible. We need to obey the following rules to make this safe // against segfaults: // // - Grab mutable fields onto the stack before checking and using. This // guards us against concurrent modifications which invalidate the // pointers // - Use subtractions for range checks, as they are tolerant //------------------------------------------------------------------------ public abstract byte get(int index); public abstract void put(int index, byte b); public abstract void get(int index, byte[] dst); public abstract void put(int index, byte[] src); public abstract void get(int index, byte[] dst, int offset, int length); public abstract void put(int index, byte[] src, int offset, int length); public abstract boolean getBoolean(int index); public abstract void putBoolean(int index, boolean value); @SuppressWarnings("restriction") public final char getChar(int index) { final long pos = address + index; if (index >= 0 && pos <= addressLimit - 2) { return UNSAFE.getChar(heapMemory, pos); } else if (address > addressLimit) { throw new IllegalStateException("This segment has been freed."); } else { // index is in fact invalid throw new IndexOutOfBoundsException(); } } public final char getCharLittleEndian(int index) { if (LITTLE_ENDIAN) { return getChar(index); } else { return Character.reverseBytes(getChar(index)); } } public final char getCharBigEndian(int index) { if (LITTLE_ENDIAN) { return Character.reverseBytes(getChar(index)); } else { return getChar(index); } } @SuppressWarnings("restriction") public final void putChar(int index, char value) { final long pos = address + index; if (index >= 0 && pos <= addressLimit - 2) { UNSAFE.putChar(heapMemory, pos, value); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { // index is in fact invalid throw new IndexOutOfBoundsException(); } } public final void putCharLittleEndian(int index, char value) { if (LITTLE_ENDIAN) { putChar(index, value); } else { putChar(index, Character.reverseBytes(value)); } } public final void putCharBigEndian(int index, char value) { if (LITTLE_ENDIAN) { putChar(index, Character.reverseBytes(value)); } else { putChar(index, value); } } public final short getShort(int index) { final long pos = address + index; if (index >= 0 && pos <= addressLimit - 2) { return UNSAFE.getShort(heapMemory, pos); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { // index is in fact invalid throw new IndexOutOfBoundsException(); } } public final short getShortLittleEndian(int index) { if (LITTLE_ENDIAN) { return getShort(index); } else { return Short.reverseBytes(getShort(index)); } } public final short getShortBigEndian(int index) { if (LITTLE_ENDIAN) { return Short.reverseBytes(getShort(index)); } else { return getShort(index); } } public final void putShort(int index, short value) { final long pos = address + index; if (index >= 0 && pos <= addressLimit - 2) { UNSAFE.putShort(heapMemory, pos, value); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { // index is in fact invalid throw new IndexOutOfBoundsException(); } } public final void putShortLittleEndian(int index, short value) { if (LITTLE_ENDIAN) { putShort(index, value); } else { putShort(index, Short.reverseBytes(value)); } } public final void putShortBigEndian(int index, short value) { if (LITTLE_ENDIAN) { putShort(index, Short.reverseBytes(value)); } else { putShort(index, value); } } public final int getInt(int index) { final long pos = address + index; if (index >= 0 && pos <= addressLimit - 4) { return UNSAFE.getInt(heapMemory, pos); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { // index is in fact invalid throw new IndexOutOfBoundsException(); } } public final int getIntLittleEndian(int index) { if (LITTLE_ENDIAN) { return getInt(index); } else { return Integer.reverseBytes(getInt(index)); } } public final int getIntBigEndian(int index) { if (LITTLE_ENDIAN) { return Integer.reverseBytes(getInt(index)); } else { return getInt(index); } } public final void putInt(int index, int value) { final long pos = address + index; if (index >= 0 && pos <= addressLimit - 4) { UNSAFE.putInt(heapMemory, pos, value); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { // index is in fact invalid throw new IndexOutOfBoundsException(); } } public final void putIntLittleEndian(int index, int value) { if (LITTLE_ENDIAN) { putInt(index, value); } else { putInt(index, Integer.reverseBytes(value)); } } public final void putIntBigEndian(int index, int value) { if (LITTLE_ENDIAN) { putInt(index, Integer.reverseBytes(value)); } else { putInt(index, value); } } public final long getLong(int index) { final long pos = address + index; if (index >= 0 && pos <= addressLimit - 8) { return UNSAFE.getLong(heapMemory, pos); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { // index is in fact invalid throw new IndexOutOfBoundsException(); } } public final long getLongLittleEndian(int index) { if (LITTLE_ENDIAN) { return getLong(index); } else { return Long.reverseBytes(getLong(index)); } } public final long getLongBigEndian(int index) { if (LITTLE_ENDIAN) { return Long.reverseBytes(getLong(index)); } else { return getLong(index); } } public final void putLong(int index, long value) { final long pos = address + index; if (index >= 0 && pos <= addressLimit - 8) { UNSAFE.putLong(heapMemory, pos, value); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { // index is in fact invalid throw new IndexOutOfBoundsException(); } } public final void putLongLittleEndian(int index, long value) { if (LITTLE_ENDIAN) { putLong(index, value); } else { putLong(index, Long.reverseBytes(value)); } } public final void putLongBigEndian(int index, long value) { if (LITTLE_ENDIAN) { putLong(index, Long.reverseBytes(value)); } else { putLong(index, value); } } public final float getFloat(int index) { return Float.intBitsToFloat(getInt(index)); } public final float getFloatLittleEndian(int index) { return Float.intBitsToFloat(getIntLittleEndian(index)); } public final float getFloatBigEndian(int index) { return Float.intBitsToFloat(getIntBigEndian(index)); } public final void putFloat(int index, float value) { putInt(index, Float.floatToRawIntBits(value)); } public final void putFloatLittleEndian(int index, float value) { putIntLittleEndian(index, Float.floatToRawIntBits(value)); } public final void putFloatBigEndian(int index, float value) { putIntBigEndian(index, Float.floatToRawIntBits(value)); } public final double getDouble(int index) { return Double.longBitsToDouble(getLong(index)); } public final double getDoubleLittleEndian(int index) { return Double.longBitsToDouble(getLongLittleEndian(index)); } public final double getDoubleBigEndian(int index) { return Double.longBitsToDouble(getLongBigEndian(index)); } public final void putDouble(int index, double value) { putLong(index, Double.doubleToRawLongBits(value)); } public final void putDoubleLittleEndian(int index, double value) { putLongLittleEndian(index, Double.doubleToRawLongBits(value)); } public final void putDoubleBigEndian(int index, double value) { putLongBigEndian(index, Double.doubleToRawLongBits(value)); } // ------------------------------------------------------------------------- // Bulk Read and Write Methods // ------------------------------------------------------------------------- public abstract void get(DataOutput out, int offset, int length) throws IOException; public abstract void put(DataInput in, int offset, int length) throws IOException; public abstract void get(int offset, ByteBuffer target, int numBytes); public abstract void put(int offset, ByteBuffer source, int numBytes); public final void copyTo(int offset, MemorySegment target, int targetOffset, int numBytes) { final byte[] thisHeapRef = this.heapMemory; final byte[] otherHeapRef = target.heapMemory; final long thisPointer = this.address + offset; final long otherPointer = target.address + targetOffset; if ((numBytes | offset | targetOffset) >= 0 && thisPointer <= this.addressLimit - numBytes && otherPointer <= target.addressLimit - numBytes) { UNSAFE.copyMemory(thisHeapRef, thisPointer, otherHeapRef, otherPointer, numBytes); } else if (this.address > this.addressLimit) { throw new IllegalStateException("this memory segment has been freed."); } else if (target.address > target.addressLimit) { throw new IllegalStateException("target memory segment has been freed."); } else { throw new IndexOutOfBoundsException( String.format("offset=%d, targetOffset=%d, numBytes=%d, address=%d, targetAddress=%d", offset, targetOffset, numBytes, this.address, target.address)); } } // ------------------------------------------------------------------------- // Comparisons & Swapping // ------------------------------------------------------------------------- public final int compare(MemorySegment seg2, int offset1, int offset2, int len) { while (len >= 8) { long l1 = this.getLongBigEndian(offset1); long l2 = seg2.getLongBigEndian(offset2); if (l1 != l2) { return (l1 < l2) ^ (l1 < 0) ^ (l2 < 0) ? -1 : 1; } offset1 += 8; offset2 += 8; len -= 8; } while (len > 0) { int b1 = this.get(offset1) & 0xff; int b2 = seg2.get(offset2) & 0xff; int cmp = b1 - b2; if (cmp != 0) { return cmp; } offset1++; offset2++; len--; } return 0; } public final void swapBytes(byte[] tempBuffer, MemorySegment seg2, int offset1, int offset2, int len) { if ((offset1 | offset2 | len | (tempBuffer.length - len)) >= 0) { final long thisPos = this.address + offset1; final long otherPos = seg2.address + offset2; if (thisPos <= this.addressLimit - len && otherPos <= seg2.addressLimit - len) { // this -> temp buffer UNSAFE.copyMemory(this.heapMemory, thisPos, tempBuffer, BYTE_ARRAY_BASE_OFFSET, len); // other -> this UNSAFE.copyMemory(seg2.heapMemory, otherPos, this.heapMemory, thisPos, len); // temp buffer -> other UNSAFE.copyMemory(tempBuffer, BYTE_ARRAY_BASE_OFFSET, seg2.heapMemory, otherPos, len); return; } else if (this.address > this.addressLimit) { throw new IllegalStateException("this memory segment has been freed."); } else if (seg2.address > seg2.addressLimit) { throw new IllegalStateException("other memory segment has been freed."); } } // index is in fact invalid throw new IndexOutOfBoundsException( String.format("offset1=%d, offset2=%d, len=%d, bufferSize=%d, address1=%d, address2=%d", offset1, offset2, len, tempBuffer.length, this.address, seg2.address)); }}复制代码 - MemorySegment有点类似java.nio.ByteBuffer；它有一个byte[]类型的heapMemory属性；它有两个构造器，带有byte[]类型参数的构造器会将byte[]赋给heapMemory，不带byte[]类型参数的构造器则heapMemory为null；isOffHeap方法则用于判断当前的memory segment是heap还是off-heap，它根据heapMemory是否为null来判断，如果为null则是off-heap；另外提供了compare、swapBytes、copyTo方法；还显示提供了BigEndian及LittleEndian的get、put方法
- BigEndian的相关方法有：get/putCharBigEndian、get/putShortBigEndian、get/putIntBigEndian、get/putLongBigEndian、get/putFloatBigEndian、get/putDoubleBigEndian；LittleEndian的相关方法有：get/putCharLittleEndian、get/putShortLittleEndian、get/putIntLittleEndian、get/putLongLittleEndian、get/putFloatLittleEndian、get/putDoubleLittleEndian
- MemorySegment定义了free、wrap、get、put、getBoolean、putBoolean抽象方法，要求子类去实现；MemorySegment有两个子类，分别是HeapMemorySegment、HybridMemorySegment
HeapMemorySegment
flink-release-1.7.2/flink-core/src/main/java/org/apache/flink/core/memory/HeapMemorySegment.java
@SuppressWarnings("unused")@Internalpublic final class HeapMemorySegment extends MemorySegment { private byte[] memory; HeapMemorySegment(byte[] memory) { this(memory, null); } HeapMemorySegment(byte[] memory, Object owner) { super(Objects.requireNonNull(memory), owner); this.memory = memory; } // ------------------------------------------------------------------------- // MemorySegment operations // ------------------------------------------------------------------------- @Override public void free() { super.free(); this.memory = null; } @Override public ByteBuffer wrap(int offset, int length) { try { return ByteBuffer.wrap(this.memory, offset, length); } catch (NullPointerException e) { throw new IllegalStateException("segment has been freed"); } } public byte[] getArray() { return this.heapMemory; } // ------------------------------------------------------------------------ // Random Access get() and put() methods // ------------------------------------------------------------------------ @Override public final byte get(int index) { return this.memory[index]; } @Override public final void put(int index, byte b) { this.memory[index] = b; } @Override public final void get(int index, byte[] dst) { get(index, dst, 0, dst.length); } @Override public final void put(int index, byte[] src) { put(index, src, 0, src.length); } @Override public final void get(int index, byte[] dst, int offset, int length) { // system arraycopy does the boundary checks anyways, no need to check extra System.arraycopy(this.memory, index, dst, offset, length); } @Override public final void put(int index, byte[] src, int offset, int length) { // system arraycopy does the boundary checks anyways, no need to check extra System.arraycopy(src, offset, this.memory, index, length); } @Override public final boolean getBoolean(int index) { return this.memory[index] != 0; } @Override public final void putBoolean(int index, boolean value) { this.memory[index] = (byte) (value ? 1 : 0); } // ------------------------------------------------------------------------- // Bulk Read and Write Methods // ------------------------------------------------------------------------- @Override public final void get(DataOutput out, int offset, int length) throws IOException { out.write(this.memory, offset, length); } @Override public final void put(DataInput in, int offset, int length) throws IOException { in.readFully(this.memory, offset, length); } @Override public final void get(int offset, ByteBuffer target, int numBytes) { // ByteBuffer performs the boundary checks target.put(this.memory, offset, numBytes); } @Override public final void put(int offset, ByteBuffer source, int numBytes) { // ByteBuffer performs the boundary checks source.get(this.memory, offset, numBytes); } // ------------------------------------------------------------------------- // Factoring // ------------------------------------------------------------------------- /** * A memory segment factory that produces heap memory segments. Note that this factory does not * support to allocate off-heap memory. */ public static final class HeapMemorySegmentFactory { public HeapMemorySegment wrap(byte[] memory) { return new HeapMemorySegment(memory); } public HeapMemorySegment allocateUnpooledSegment(int size, Object owner) { return new HeapMemorySegment(new byte[size], owner); } public HeapMemorySegment wrapPooledHeapMemory(byte[] memory, Object owner) { return new HeapMemorySegment(memory, owner); } /** * Prevent external instantiation. */ HeapMemorySegmentFactory() {} } public static final HeapMemorySegmentFactory FACTORY = new HeapMemorySegmentFactory();}复制代码 - HeapMemorySegment继承了MemorySegment，它有一个byte[]的memory属性，free操作会将memory设置为null，wrap方法使用的是memory属性；它的构造器要求传入的memory不能为null，然后赋给父类的heapMemory属性及自己定义的memory属性(
引用)；它还定义了HeapMemorySegmentFactory，提供了wrap、allocateUnpooledSegment、wrapPooledHeapMemory方法
HybridMemorySegment
flink-release-1.7.2/flink-core/src/main/java/org/apache/flink/core/memory/HybridMemorySegment.java
@Internalpublic final class HybridMemorySegment extends MemorySegment { /** * The direct byte buffer that allocated the off-heap memory. This memory segment holds a * reference to that buffer, so as long as this memory segment lives, the memory will not be * released. */ private final ByteBuffer offHeapBuffer; /** * Creates a new memory segment that represents the memory backing the given direct byte buffer. * Note that the given ByteBuffer must be direct {@link java.nio.ByteBuffer#allocateDirect(int)}, * otherwise this method with throw an IllegalArgumentException. * * The owner referenced by this memory segment is null. * * @param buffer The byte buffer whose memory is represented by this memory segment. * @throws IllegalArgumentException Thrown, if the given ByteBuffer is not direct. */ HybridMemorySegment(ByteBuffer buffer) { this(buffer, null); } /** * Creates a new memory segment that represents the memory backing the given direct byte buffer. * Note that the given ByteBuffer must be direct {@link java.nio.ByteBuffer#allocateDirect(int)}, * otherwise this method with throw an IllegalArgumentException. * *
The memory segment references the given owner. * * @param buffer The byte buffer whose memory is represented by this memory segment. * @param owner The owner references by this memory segment. * @throws IllegalArgumentException Thrown, if the given ByteBuffer is not direct. */ HybridMemorySegment(ByteBuffer buffer, Object owner) { super(checkBufferAndGetAddress(buffer), buffer.capacity(), owner); this.offHeapBuffer = buffer; } /** * Creates a new memory segment that represents the memory of the byte array. * *
The owner referenced by this memory segment is null. * * @param buffer The byte array whose memory is represented by this memory segment. */ HybridMemorySegment(byte[] buffer) { this(buffer, null); } /** * Creates a new memory segment that represents the memory of the byte array. * *
The memory segment references the given owner. * * @param buffer The byte array whose memory is represented by this memory segment. * @param owner The owner references by this memory segment. */ HybridMemorySegment(byte[] buffer, Object owner) { super(buffer, owner); this.offHeapBuffer = null; } // ------------------------------------------------------------------------- // MemorySegment operations // ------------------------------------------------------------------------- /** * Gets the buffer that owns the memory of this memory segment. * * @return The byte buffer that owns the memory of this memory segment. */ public ByteBuffer getOffHeapBuffer() { if (offHeapBuffer != null) { return offHeapBuffer; } else { throw new IllegalStateException("Memory segment does not represent off heap memory"); } } @Override public ByteBuffer wrap(int offset, int length) { if (address <= addressLimit) { if (heapMemory != null) { return ByteBuffer.wrap(heapMemory, offset, length); } else { try { ByteBuffer wrapper = offHeapBuffer.duplicate(); wrapper.limit(offset + length); wrapper.position(offset); return wrapper; } catch (IllegalArgumentException e) { throw new IndexOutOfBoundsException(); } } } else { throw new IllegalStateException("segment has been freed"); } } // ------------------------------------------------------------------------ // Random Access get() and put() methods // ------------------------------------------------------------------------ @Override public final byte get(int index) { final long pos = address + index; if (index >= 0 && pos < addressLimit) { return UNSAFE.getByte(heapMemory, pos); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { // index is in fact invalid throw new IndexOutOfBoundsException(); } } @Override public final void put(int index, byte b) { final long pos = address + index; if (index >= 0 && pos < addressLimit) { UNSAFE.putByte(heapMemory, pos, b); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { // index is in fact invalid throw new IndexOutOfBoundsException(); } } @Override public final void get(int index, byte[] dst) { get(index, dst, 0, dst.length); } @Override public final void put(int index, byte[] src) { put(index, src, 0, src.length); } @Override public final void get(int index, byte[] dst, int offset, int length) { // check the byte array offset and length and the status if ((offset | length | (offset + length) | (dst.length - (offset + length))) < 0) { throw new IndexOutOfBoundsException(); } final long pos = address + index; if (index >= 0 && pos <= addressLimit - length) { final long arrayAddress = BYTE_ARRAY_BASE_OFFSET + offset; UNSAFE.copyMemory(heapMemory, pos, dst, arrayAddress, length); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { // index is in fact invalid throw new IndexOutOfBoundsException(); } } @Override public final void put(int index, byte[] src, int offset, int length) { // check the byte array offset and length if ((offset | length | (offset + length) | (src.length - (offset + length))) < 0) { throw new IndexOutOfBoundsException(); } final long pos = address + index; if (index >= 0 && pos <= addressLimit - length) { final long arrayAddress = BYTE_ARRAY_BASE_OFFSET + offset; UNSAFE.copyMemory(src, arrayAddress, heapMemory, pos, length); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { // index is in fact invalid throw new IndexOutOfBoundsException(); } } @Override public final boolean getBoolean(int index) { return get(index) != 0; } @Override public final void putBoolean(int index, boolean value) { put(index, (byte) (value ? 1 : 0)); } // ------------------------------------------------------------------------- // Bulk Read and Write Methods // ------------------------------------------------------------------------- @Override public final void get(DataOutput out, int offset, int length) throws IOException { if (address <= addressLimit) { if (heapMemory != null) { out.write(heapMemory, offset, length); } else { while (length >= 8) { out.writeLong(getLongBigEndian(offset)); offset += 8; length -= 8; } while (length > 0) { out.writeByte(get(offset)); offset++; length--; } } } else { throw new IllegalStateException("segment has been freed"); } } @Override public final void put(DataInput in, int offset, int length) throws IOException { if (address <= addressLimit) { if (heapMemory != null) { in.readFully(heapMemory, offset, length); } else { while (length >= 8) { putLongBigEndian(offset, in.readLong()); offset += 8; length -= 8; } while (length > 0) { put(offset, in.readByte()); offset++; length--; } } } else { throw new IllegalStateException("segment has been freed"); } } @Override public final void get(int offset, ByteBuffer target, int numBytes) { // check the byte array offset and length if ((offset | numBytes | (offset + numBytes)) < 0) { throw new IndexOutOfBoundsException(); } final int targetOffset = target.position(); final int remaining = target.remaining(); if (remaining < numBytes) { throw new BufferOverflowException(); } if (target.isDirect()) { if (target.isReadOnly()) { throw new ReadOnlyBufferException(); } // copy to the target memory directly final long targetPointer = getAddress(target) + targetOffset; final long sourcePointer = address + offset; if (sourcePointer <= addressLimit - numBytes) { UNSAFE.copyMemory(heapMemory, sourcePointer, null, targetPointer, numBytes); target.position(targetOffset + numBytes); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { throw new IndexOutOfBoundsException(); } } else if (target.hasArray()) { // move directly into the byte array get(offset, target.array(), targetOffset + target.arrayOffset(), numBytes); // this must be after the get() call to ensue that the byte buffer is not // modified in case the call fails target.position(targetOffset + numBytes); } else { // neither heap buffer nor direct buffer while (target.hasRemaining()) { target.put(get(offset++)); } } } @Override public final void put(int offset, ByteBuffer source, int numBytes) { // check the byte array offset and length if ((offset | numBytes | (offset + numBytes)) < 0) { throw new IndexOutOfBoundsException(); } final int sourceOffset = source.position(); final int remaining = source.remaining(); if (remaining < numBytes) { throw new BufferUnderflowException(); } if (source.isDirect()) { // copy to the target memory directly final long sourcePointer = getAddress(source) + sourceOffset; final long targetPointer = address + offset; if (targetPointer <= addressLimit - numBytes) { UNSAFE.copyMemory(null, sourcePointer, heapMemory, targetPointer, numBytes); source.position(sourceOffset + numBytes); } else if (address > addressLimit) { throw new IllegalStateException("segment has been freed"); } else { throw new IndexOutOfBoundsException(); } } else if (source.hasArray()) { // move directly into the byte array put(offset, source.array(), sourceOffset + source.arrayOffset(), numBytes); // this must be after the get() call to ensue that the byte buffer is not // modified in case the call fails source.position(sourceOffset + numBytes); } else { // neither heap buffer nor direct buffer while (source.hasRemaining()) { put(offset++, source.get()); } } } //......}复制代码
- HybridMemorySegment继承了MemorySegment，它有一个ByteBuffer类型的offHeapBuffer属性，由于父类本身已经有一个byte[]类型的heapMemory属性了，因而HybridMemorySegment管理的memory可以是on-heap的(
使用带有byte[]类型参数的构造器)也可以是off-heap的(使用带有ByteBuffer类型参数的构造器)；wrap方法会判断，如果heapMemory不为null，则使用heapMemory，否则使用offHeapBuffer
小结
- MemorySegment有点类似java.nio.ByteBuffer；它有一个byte[]类型的heapMemory属性；它有两个构造器，带有byte[]类型参数的构造器会将byte[]赋给heapMemory，不带byte[]类型参数的构造器则heapMemory为null；isOffHeap方法则用于判断当前的memory segment是heap还是off-heap，它根据heapMemory是否为null来判断，如果为null则是off-heap；另外提供了compare、swapBytes、copyTo方法；还显示提供了BigEndian及LittleEndian的get、put方法；MemorySegment定义了free、wrap、get、put、getBoolean、putBoolean抽象方法，要求子类去实现；MemorySegment有两个子类，分别是HeapMemorySegment、HybridMemorySegment
- HeapMemorySegment继承了MemorySegment，它有一个byte[]的memory属性，free操作会将memory设置为null，wrap方法使用的是memory属性；它的构造器要求传入的memory不能为null，然后赋给父类的heapMemory属性及自己定义的memory属性(
引用)；它还定义了HeapMemorySegmentFactory，提供了wrap、allocateUnpooledSegment、wrapPooledHeapMemory方法 - HybridMemorySegment继承了MemorySegment，它有一个ByteBuffer类型的offHeapBuffer属性，由于父类本身已经有一个byte[]类型的heapMemory属性了，因而HybridMemorySegment管理的memory可以是on-heap的(
使用带有byte[]类型参数的构造器)也可以是off-heap的(使用带有ByteBuffer类型参数的构造器)；wrap方法会判断，如果heapMemory不为null，则使用heapMemory，否则使用offHeapBuffer