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[#2762] Not expand ByteBuffer[] in ChannelOutboundBuffer

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Motivation:

At the moment we expand the ByteBuffer[] when we have more then 1024 ByteBuffer to write and replace the stored instance in its FastThreadLocal. This is not needed and may even harm performance on linux as IOV_MAX is 1024 and so this may cause the JVM to do an array copy.

Modifications:

Just exit the nioBuffers() method if we can not fit more ByteBuffer in the array. This way we will pick them up on the next call.

Result:

Remove uncessary array copy and simplify the code.
This commit is contained in:
Norman Maurer 2014-08-13 11:55:06 +02:00
parent 4059c9f354
commit 3db0128db9
1 changed files with 6 additions and 21 deletions
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27
transport/src/main/java/io/netty/channel/ChannelOutboundBuffer.java
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@ -46,6 +46,10 @@ public final class ChannelOutboundBuffer {
private static final FastThreadLocal<ByteBuffer[]> NIO_BUFFERS = new FastThreadLocal<ByteBuffer[]>() {
@Override
protected ByteBuffer[] initialValue() throws Exception {
// Use 1024 as this is the IOV_MAX value on linux. If you sue a bigger one the JDK may do some array
// copy which we should not trigger.
//
// See 'man 2 writev' for more informations.
return new ByteBuffer[1024];
}
};
@ -355,8 +359,8 @@ public final class ChannelOutboundBuffer {
int count = buf.nioBufferCount();
int neededSpace = nioBufferCount + count;
if (neededSpace > nioBuffers.length) {
nioBuffers = expandNioBufferArray(nioBuffers, neededSpace, nioBufferCount);
NIO_BUFFERS.set(threadLocalMap, nioBuffers);
// We have not enough space left in the array to add the ByteBuffers so break here.
break;
}
if (count == 1) {
ByteBuffer nioBuf = buf.internalNioBuffer(readerIndex, readableBytes);
@ -385,25 +389,6 @@ public final class ChannelOutboundBuffer {
return nioBufferCount;
}
private static ByteBuffer[] expandNioBufferArray(ByteBuffer[] array, int neededSpace, int size) {
int newCapacity = array.length;
do {
// double capacity until it is big enough
// See https://github.com/netty/netty/issues/1890
newCapacity <<= 1;
if (newCapacity < 0) {
throw new IllegalStateException();
}
} while (neededSpace > newCapacity);
ByteBuffer[] newArray = new ByteBuffer[newCapacity];
System.arraycopy(array, 0, newArray, 0, size);
return newArray;
}
/**
* Returns the number of {@link ByteBuffer} that can be written out of the {@link ByteBuffer} array that was
* obtained via {@link #nioBuffers()}. This method <strong>MUST</strong> be called after {@link #nioBuffers()}