问题
I am building a UDP-based application that receives and sends multiple packets.
I could build a new DatagramPacket for each send, or I recycle one instance for the life of my application.
- Are there any advantages to reusing a
DatagramPacket? (e.g. memory-allocation) - Are there any potential problems? (e.g. thread-safety)
回答1:
It looks like you can't. I just tried sending the same DatagramPacket twice and I get the following behavior:
- The packet is sent only once
- Netty logs the warning below
So, instead of reusing the DatagramPacket, you can reuse the arguments you pass to the DatagramPacket constructor, mainly the buffer.
2018-10-18 09:29:11.103 WARN 5468 --- [nioEventLoopGroup-2-1] i.n.c.AbstractChannelHandlerContext : Failed to mark a promise as failure because it has failed already: DefaultChannelPromise@748a9b0e(failure: java.lang.IndexOutOfBoundsException: srcIndex: 0), unnotified cause: java.lang.IndexOutOfBoundsException: srcIndex: 0 at io.netty.buffer.UnsafeByteBufUtil.setBytes(UnsafeByteBufUtil.java:519) at io.netty.buffer.PooledUnsafeDirectByteBuf.setBytes(PooledUnsafeDirectByteBuf.java:260) at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:1080) at io.netty.channel.nio.AbstractNioChannel.newDirectBuffer(AbstractNioChannel.java:481) at io.netty.channel.socket.nio.NioDatagramChannel.filterOutboundMessage(NioDatagramChannel.java:308) at io.netty.channel.AbstractChannel$AbstractUnsafe.write(AbstractChannel.java:877) at io.netty.channel.DefaultChannelPipeline$HeadContext.write(DefaultChannelPipeline.java:1391) at io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:738) at io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:730) at io.netty.channel.AbstractChannelHandlerContext.access$1900(AbstractChannelHandlerContext.java:38) at io.netty.channel.AbstractChannelHandlerContext$AbstractWriteTask.write(AbstractChannelHandlerContext.java:1081) at io.netty.channel.AbstractChannelHandlerContext$WriteAndFlushTask.write(AbstractChannelHandlerContext.java:1128) at io.netty.channel.AbstractChannelHandlerContext$AbstractWriteTask.run(AbstractChannelHandlerContext.java:1070) at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163) at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:404) at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:446) at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884) at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) at java.lang.Thread.run(Thread.java:748)
io.netty.util.IllegalReferenceCountException: refCnt: 0, decrement: 1 at io.netty.buffer.AbstractReferenceCountedByteBuf.release0(AbstractReferenceCountedByteBuf.java:100) ~[netty-buffer-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.buffer.AbstractReferenceCountedByteBuf.release(AbstractReferenceCountedByteBuf.java:84) ~[netty-buffer-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.util.ReferenceCountUtil.release(ReferenceCountUtil.java:88) ~[netty-common-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.channel.DefaultAddressedEnvelope.release(DefaultAddressedEnvelope.java:101) ~[netty-transport-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.util.ReferenceCountUtil.release(ReferenceCountUtil.java:88) ~[netty-common-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.channel.AbstractChannel$AbstractUnsafe.write(AbstractChannel.java:884) ~[netty-transport-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.channel.DefaultChannelPipeline$HeadContext.write(DefaultChannelPipeline.java:1391) ~[netty-transport-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:738) [netty-transport-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:730) [netty-transport-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.channel.AbstractChannelHandlerContext.access$1900(AbstractChannelHandlerContext.java:38) [netty-transport-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.channel.AbstractChannelHandlerContext$AbstractWriteTask.write(AbstractChannelHandlerContext.java:1081) [netty-transport-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.channel.AbstractChannelHandlerContext$WriteAndFlushTask.write(AbstractChannelHandlerContext.java:1128) [netty-transport-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.channel.AbstractChannelHandlerContext$AbstractWriteTask.run(AbstractChannelHandlerContext.java:1070) [netty-transport-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163) [netty-common-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:404) [netty-common-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:446) [netty-transport-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884) [netty-common-4.1.29.Final.jar!/:4.1.29.Final] at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) [netty-common-4.1.29.Final.jar!/:4.1.29.Final] at java.lang.Thread.run(Thread.java:748) [na:1.8.0_181]
来源：https://stackoverflow.com/questions/33109579/should-i-reuse-datagrampacket