Tomcat的NIO 连接器中oomParachute的作用

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NIO oomParachute的作用

在Server启动的时候，启动NIO连接器，此时判断oomParachute的配置是否大于0，由于默认为 1024 * 1024，
因此在执行NioEndpoint.bind时，
bind() {
...
if (oomParachute>0) reclaimParachute(true);
...
}

    protected boolean reclaimParachute(boolean force) {
        if ( oomParachuteData != null ) return true;
        if ( oomParachute > 0 && ( force || (Runtime.getRuntime().freeMemory() > (oomParachute*2))) )
            oomParachuteData = new byte[oomParachute];  
        return oomParachuteData != null;
    }
上面oomParachute > 0 并且  force传入值为true,因此，此处会创建 oomParachuteData，值为1M的byte数组
注意：是每个connector都会创建一个，


[2014-04-16 16:01:18] [WARNING] [System.out] [java.lang.OutOfMemoryError: Java heap space]
[2014-04-16 16:01:19] [WARNING] [System.out] [Exception in thread "RMI TCP Connection(idle)" ]
[2014-04-16 16:01:19] [WARNING] [System.out] [java.lang.OutOfMemoryError: Java heap space]
[2014-04-16 16:01:19] [WARNING] [System.out] [Exception in thread "RMI TCP Connection(idle)" ]
[2014-04-16 16:01:19] [WARNING] [System.out] [java.lang.OutOfMemoryError: Java heap space]
[2014-04-16 16:02:54] [SEVERE] [web-container] []
java.lang.OutOfMemoryError: Java heap space
        at com.tongweb.web.webutil.util.buf.ByteChunk.allocate(ByteChunk.java:168)
        at com.tongweb.web.webutil.util.buf.ByteChunk.<init>(ByteChunk.java:130)
        at com.tongweb.web.oro.http11.filters.BufferedInputFilter.<init>(BufferedInputFilter.java:43
)
        at com.tongweb.web.oro.http11.AbstractHttp11Processor.initializeFilters(AbstractHttp11Proces
sor.java:698)
        at com.tongweb.web.oro.http11.Http11NioProcessor.<init>(Http11NioProcessor.java:76)
        at com.tongweb.web.oro.http11.ThorHttp11NioProcessor.<init>(ThorHttp11NioProcessor.java:14)
        at com.tongweb.web.oro.http11.ThorHttp11NioProtocol$ThorHttp11ConnectionHandler.createProces
sor(ThorHttp11NioProtocol.java:27)
        at com.tongweb.web.oro.http11.ThorHttp11NioProtocol$ThorHttp11ConnectionHandler.createProces
sor(ThorHttp11NioProtocol.java:17)
        at com.tongweb.web.oro.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.j
ava:569)
        at com.tongweb.web.webutil.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1653)
        at com.tongweb.web.webutil.util.threads.TWThreadPoolExecutor.runWorker(TWThreadPoolExecutor.
java:1165)
        at com.tongweb.web.webutil.util.threads.TWThreadPoolExecutor$Worker.run(TWThreadPoolExecutor
.java:622)
        at java.lang.Thread.run(Thread.java:662)
[2014-04-16 16:03:05] [SEVERE] [web-container] []
java.lang.OutOfMemoryError: Java heap space
[2014-04-16 16:05:34] [SEVERE] [web-container] []
java.lang.OutOfMemoryError: Java heap space
[2014-04-16 16:05:56] [SEVERE] [web-container] [SEVERE:Memory usage is low, parachute is non existen
t, your system may start failing.]
[2014-04-16 16:06:10] [SEVERE] [web-container] [SEVERE:Memory usage is low, parachute is non existen
t, your system may start failing.]
[2014-04-16 16:06:20] [SEVERE] [web-container] [SEVERE:Memory usage is low, parachute is non existen
t, your system may start failing.]
[2014-04-16 16:06:22] [SEVERE] [web-container] []
java.lang.OutOfMemoryError: Java heap space
[2014-04-16 16:06:26] [SEVERE] [web-container] [SEVERE:Memory usage is low, parachute is non existen
t, your system may start failing.]
[2014-04-16 16:06:30] [SEVERE] [web-container] [SEVERE:Memory usage is low, parachute is non existen
t, your system may start failing.]
[2014-04-16 16:06:31] [SEVERE] [web-container] []
java.lang.OutOfMemoryError: Java heap space
[2014-04-16 16:06:36] [SEVERE] [web-container] [SEVERE:Memory usage is low, parachute is non existen
t, your system may start failing.]
[2014-04-16 16:06:40] [SEVERE] [web-container] [SEVERE:Memory usage is low, parachute is non existen
t, your system may start failing.]
[2014-04-16 16:06:46] [SEVERE] [web-container] [SEVERE:Memory usage is low, parachute is non existen
t, your system may start failing.]

目前可以模拟相应的场景，在OOM产生时，该内存块会被置为null进行释放，此时请求不能再处理，但应用服务器并没有马上挂掉，后台仍然在不停的打印SEVERE:Memory usage is low, parachute is non existent, your system may start failing.


catch (OutOfMemoryError oom) {
                    try {
                        oomParachuteData = null;
                        releaseCaches();
                        log.error("", oom);
                    }catch ( Throwable oomt ) {
                        try {
                            System.err.println(oomParachuteMsg);
                            oomt.printStackTrace();
                        }catch (Throwable letsHopeWeDontGetHere){
                            ExceptionUtils.handleThrowable(letsHopeWeDontGetHere);
                        }
                    }
                }


    protected void releaseCaches() {
        this.keyCache.clear();
        this.nioChannels.clear();
        this.processorCache.clear();
        if ( handler != null ) handler.recycle();

    }






模拟该问题使用NIO通道产生OOM从而使用该参数生效。每个通道在启动时都会根据参数包含这样一个parachute块，默认大小是1M的byte数组，发现OOM产生时，该数组会被设为null，同时清理一些组件的缓存
    protected void releaseCaches() {
        this.keyCache.clear();
        this.nioChannels.clear();
        this.processorCache.clear();
        if ( handler != null ) handler.recycle();

    }
之后该通道的请求不会被响应，其它通道仍能正常工作。



    protected boolean reclaimParachute(boolean force) {
        if ( oomParachuteData != null ) return true;
        if ( oomParachute > 0 && ( force || (Runtime.getRuntime().freeMemory() > (oomParachute*2))) )
            oomParachuteData = new byte[oomParachute];
        return oomParachuteData != null;
    }