java - 什么是 weblogic.socket.Muxer？

Question

你们中有人了解 weblogic.socket.Muxer 在 WebLogic 8.1 中的用途吗？

我经常在线程转储中看到与此类似的堆栈跟踪:

"ExecuteThread: '0' for queue: 'weblogic.socket.Muxer'" id=20 idx=0x68 tid=26709 prio=5 alive, in native, blocked, daemon
    -- Blocked trying to get lock: java/lang/String@0x2b673d373c50[fat lock]
    at jrockit/vm/Threads.waitForUnblockSignal()V(Native Method)
    at jrockit/vm/Locks.fatLockBlockOrSpin(Locks.java:1675)[optimized]
    at jrockit/vm/Locks.lockFat(Locks.java:1776)[optimized]
    at jrockit/vm/Locks.monitorEnterSecondStageHard(Locks.java:1312)[optimized]
    at jrockit/vm/Locks.monitorEnterSecondStage(Locks.java:1259)[optimized]
    at jrockit/vm/Locks.monitorEnter(Locks.java:2439)[optimized]
    at weblogic/socket/EPollSocketMuxer.processSockets(EPollSocketMuxer.java:153)
    at weblogic/socket/SocketReaderRequest.run(SocketReaderRequest.java:29)
    at weblogic/socket/SocketReaderRequest.execute(SocketReaderRequest.java:42)
    at weblogic/kernel/ExecuteThread.execute(ExecuteThread.java:145)
    at weblogic/kernel/ExecuteThread.run(ExecuteThread.java:117)
    at jrockit/vm/RNI.c2java(JJJJJ)V(Native Method)
    -- end of trace

这并不是我有任何问题，只是想了解一下:

1) 它在做什么？
2) 它会影响任何性能吗？

Answer 1

来自文档(http://download.oracle.com/docs/cd/E13222_01/wls/docs100/perform/WLSTuning.html#wp1152246):

WebLogic Server uses software modules called muxers to read incoming requests on the server and incoming responses on the client. These muxers are of two primary types: the Java muxer or native muxer.

A Java muxer has the following characteristics:

• Uses pure Java to read data from sockets.
• It is also the only muxer available for RMI clients.
• Blocks on reads until there is data to be read from a socket. This behavior does not scale well when there are a large number of sockets and/or when data arrives infrequently at sockets. This is typically not an issue for clients, but it can create a huge bottleneck for a server.

Native muxers use platform-specific native binaries to read data from sockets. The majority of all platforms provide some mechanism to poll a socket for data. For example, Unix systems use the poll system and the Windows architecture uses completion ports. Native provide superior scalability because they implement a non-blocking thread model. When a native muxer is used, the server creates a fixed number of threads dedicated to reading incoming requests. BEA recommends using the default setting of selected for the Enable Native IO parameter which allows the server automatically selects the appropriate muxer for the server to use.

If the Enable Native IO parameter is not selected, the server instance exclusively uses the Java muxer. This maybe acceptable if there are a small number of clients and the rate at which requests arrive at the server is fairly high. Under these conditions, the Java muxer performs as well as a native muxer and eliminate Java Native Interface (JNI) overhead. Unlike native muxers, the number of threads used to read requests is not fixed and is tunable for Java muxers by configuring the Percent Socket Readers parameter setting in the Administration Console. See Changing the Number of Available Socket Readers. Ideally, you should configure this parameter so the number of threads roughly equals the number of remote concurrently connected clients up to 50% of the total thread pool size. Each thread waits for a fixed amount of time for data to become available at a socket. If no data arrives, the thread moves to the next socket.

那么，出于这些原因，使用 native 混合器显然更好。

在这里，看起来您使用的是默认的 native 多路复用器 (weblogic.socket.EPollSocketMuxer)，而不是 Java 多路复用器 (weblogic.socket.SocketMuxer)。