Package io.netty.buffer
package io.netty.buffer
Abstraction of a byte buffer - the fundamental data structure
to represent a low-level binary and text message.
Netty uses its own buffer API instead of NIO
ByteBuffer
to
represent a sequence of bytes. This approach has significant advantage over
using ByteBuffer
. Netty's new buffer type,
ByteBuf
, has been designed from ground
up to address the problems of ByteBuffer
and to meet the
daily needs of network application developers. To list a few cool features:
- You can define your buffer type if necessary.
- Transparent zero copy is achieved by built-in composite buffer type.
- A dynamic buffer type is provided out-of-the-box, whose capacity is
expanded on demand, just like
StringBuffer
. - There's no need to call the
flip()
method anymore. - It is often faster than
ByteBuffer
.
Extensibility
ByteBuf
has rich set of operations
optimized for rapid protocol implementation. For example,
ByteBuf
provides various operations
for accessing unsigned values and strings and searching for certain byte
sequence in a buffer. You can also extend or wrap existing buffer type
to add convenient accessors. The custom buffer type still implements
ByteBuf
interface rather than
introducing an incompatible type.
Transparent Zero Copy
To lift up the performance of a network application to the extreme, you need to reduce the number of memory copy operation. You might have a set of buffers that could be sliced and combined to compose a whole message. Netty provides a composite buffer which allows you to create a new buffer from the arbitrary number of existing buffers with no memory copy. For example, a message could be composed of two parts; header and body. In a modularized application, the two parts could be produced by different modules and assembled later when the message is sent out.+--------+----------+ | header | body | +--------+----------+If
ByteBuffer
were used, you would have to create a new big
buffer and copy the two parts into the new buffer. Alternatively, you can
perform a gathering write operation in NIO, but it restricts you to represent
the composite of buffers as an array of ByteBuffer
s rather
than a single buffer, breaking the abstraction and introducing complicated
state management. Moreover, it's of no use if you are not going to read or
write from an NIO channel.
// The composite type is incompatible with the component type. ByteBuffer[] message = new ByteBuffer[] { header, body };By contrast,
ByteBuf
does not have such
caveats because it is fully extensible and has a built-in composite buffer
type.
// The composite type is compatible with the component type.ByteBuf
message =Unpooled
.wrappedBuffer(header, body); // Therefore, you can even create a composite by mixing a composite and an // ordinary buffer.ByteBuf
messageWithFooter =Unpooled
.wrappedBuffer(message, footer); // Because the composite is still aByteBuf
, you can access its content // easily, and the accessor method will behave just like it's a single buffer // even if the region you want to access spans over multiple components. The // unsigned integer being read here is located across body and footer. messageWithFooter.getUnsignedInt( messageWithFooter.readableBytes() - footer.readableBytes() - 1);
Automatic Capacity Extension
Many protocols define variable length messages, which means there's no way to determine the length of a message until you construct the message or it is difficult and inconvenient to calculate the length precisely. It is just like when you build aString
. You often estimate the length
of the resulting string and let StringBuffer
expand itself
on demand.
// A new dynamic buffer is created. Internally, the actual buffer is created // lazily to avoid potentially wasted memory space.ByteBuf
b =Unpooled
.buffer(4); // When the first write attempt is made, the internal buffer is created with // the specified initial capacity (4). b.writeByte('1'); b.writeByte('2'); b.writeByte('3'); b.writeByte('4'); // When the number of written bytes exceeds the initial capacity (4), the // internal buffer is reallocated automatically with a larger capacity. b.writeByte('5');
Better Performance
Most frequently used buffer implementation ofByteBuf
is a very thin wrapper of a
byte array (i.e. byte[]
). Unlike ByteBuffer
, it has
no complicated boundary check and index compensation, and therefore it is
easier for a JVM to optimize the buffer access. More complicated buffer
implementation is used only for sliced or composite buffers, and it performs
as well as ByteBuffer
.-
ClassDescriptionA skeletal implementation of a buffer.Skeletal
ByteBufAllocator
implementation to extend.Deprecated.Do not use.Abstract base class for derivedByteBuf
implementations.Abstract base class forByteBuf
implementations that count references.SpecialSwappedByteBuf
forByteBuf
s that is using unsafe.An auto-tuning poolingByteBufAllocator
, that follows an anti-generational hypothesis.An auto-tuning pooling allocator, that follows an anti-generational hypothesis.The strategy for howAdaptivePoolingAllocator
should allocate chunk buffers.A random and sequential accessible sequence of zero or more bytes (octets).Implementations are responsible to allocate buffers.An interface that can be implemented by any object that know how to turn itself into aByteBuf
.A packet which is send or receive.AnInputStream
which reads data from aByteBuf
.AnOutputStream
which writes data to aByteBuf
.Deprecated.UseByteProcessor
.A collection of utility methods that is related with handlingByteBuf
, such as the generation of hex dump and swapping an integer's byte order.A virtual buffer which shows multiple buffers as a single merged buffer.Default implementation of aByteBufHolder
that holds it's data in aByteBuf
.Deprecated.Do not use.An emptyByteBuf
whose capacity and maximum capacity are all0
.Utility class for heap buffers.Internal primitive priority queue, used byPoolChunk
.Internal primitive map implementation that is specifically optimised for the runs availability map use case inPoolChunk
.PoolArena<T>Expose metrics for an arena.PoolChunk<T>Description of algorithm for PageRun/PoolSubpage allocation from PoolChunk Notation: The following terms are important to understand the code > page - a page is the smallest unit of memory chunk that can be allocated > run - a run is a collection of pages > chunk - a chunk is a collection of runs > in this code chunkSize = maxPages * pageSize To begin we allocate a byte array of size = chunkSize Whenever a ByteBuf of given size needs to be created we search for the first position in the byte array that has enough empty space to accommodate the requested size and return a (long) handle that encodes this offset information, (this memory segment is then marked as reserved so it is always used by exactly one ByteBuf and no more) For simplicity all sizes are normalized according toinvalid @link
{@link PoolArena#sizeClass#size2SizeIdx(int)
Metrics for a list of chunks.Metrics for a chunk.Exposed metric forPooledByteBufAllocator
.PoolSubpage<T>Metrics for a sub-page.Acts a Thread cache for allocations.Cache used for buffers which are backed by NORMAL size.Cache used for buffers which are backed by TINY or SMALL size.Deprecated.Do not use.Read-only ByteBuf which wraps a read-only ByteBuffer.Read-only ByteBuf which wraps a read-only direct ByteBuffer and use unsafe for best performance.SizeClasses requirespageShifts
to be defined prior to inclusion, and it in turn defines:Expose metrics for an SizeClasses.Deprecated.Do not use.Deprecated.use the Little Endian accessors, e.g.Creates a newByteBuf
by allocating new space or by wrapping or copying existing byte arrays, byte buffers and a string.SimplisticByteBufAllocator
implementation that does not pool anything.A NIOByteBuffer
based buffer.DuplicatedByteBuf
implementation that can do optimizations because it knows the duplicated buffer is of typeAbstractByteBuf
.Big endian Java heap buffer implementation.A specialAbstractUnpooledSlicedByteBuf
that can make optimizations because it knows the sliced buffer is of typeAbstractByteBuf
.A NIOByteBuffer
based buffer.Big endian Java heap buffer implementation.AByteBuf
implementation that wraps another buffer to prevent a user from increasing or decreasing the wrapped buffer's reference count.All operations get and set asByteOrder.BIG_ENDIAN
.SpecialSwappedByteBuf
forByteBuf
s that use unsafe to access the byte array.Wraps anotherByteBuf
.