java.net.SocketException: Too many open files问题分析及解决方案

xiaoxiao2021-03-28 25

Java web应用在执行一段时间之后出现了这么个问题

[java] view plain copy java.net.SocketException: Too many open files at java.net.PlainSocketImpl.socketAccept(Native Method) at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:384) at java.net.ServerSocket.implAccept(ServerSocket.java:453) at java.net.ServerSocket.accept(ServerSocket.java:421) at org.apache.tomcat.util.net.DefaultServerSocketFactory.acceptSocket(DefaultServerSocketFactory.java:60) at org.apache.tomcat.util.net.JIoEndpoint$Acceptor.run(JIoEndpoint.java:216)

用ulimit -a看看Linux打开文件限制

[java] view plain copy [admin@test ~]# ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 360448 max locked memory (kbytes, -l) 32 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 10240 cpu time (seconds, -t) unlimited max user processes (-u) 360448 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited

[java] view plain copy 用lsof -p [进程ID] 可以看到某ID的打开文件状况。进程ID可能用 ps -ef|grep java列出

[java] view plain copy [admin@test ~]# lsof -p 1940 COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME java 1940 admin cwd DIR 0,68 4096 385090717 /admin/apache-tomcat-7.0.39/bin java 1940 admin rtd DIR 0,68 4096 384141801 / java 1940 admin txt REG 0,68 47308 385122308 /admin/jdk1.6.0_13/jre/bin/java java 1940 admin mem REG 202,3 385122339 /admin/jdk1.6.0_13/jre/lib/i386/client/libjvm.so (path dev=0,68) java 1940 admin mem REG 202,3 385122308 /admin/jdk1.6.0_13/jre/bin/java (path dev=0,68) java 1940 admin mem REG 202,3 385122425 /admin/jdk1.6.0_13/jre/lib/i386/client/classes.jsa (path dev=0,68) java 1940 admin mem REG 202,3 385122426 /admin/jdk1.6.0_13/jre/lib/charsets.jar (path dev=0,68) java 1940 admin mem REG 202,3 384959153 /lib/libresolv-2.12.so (path dev=0,68) java 1940 admin mem REG 202,3 384959143 /lib/libnss_dns-2.12.so (path dev=0,68) java 1940 admin mem REG 202,3 385122355 /admin/jdk1.6.0_13/jre/lib/i386/libnio.so (path dev=0,68) java 1940 admin mem REG 202,3 385122354 /admin/jdk1.6.0_13/jre/lib/i386/libnet.so (path dev=0,68) java 1940 admin mem REG 202,3 385122325 /admin/jdk1.6.0_13/jre/lib/ext/sunjce_provider.jar (path dev=0,68) java 1940 admin mem REG 202,3 385122326 /admin/jdk1.6.0_13/jre/lib/ext/sunpkcs11.jar (path dev=0,68) java 1940 admin mem REG 202,3 385122392 /admin/jdk1.6.0_13/jre/lib/jce.jar (path dev=0,68) java 1940 admin mem REG 202,3 385122405 /admin/jdk1.6.0_13/jre/lib/resources.jar (path dev=0,68) java 1940 admin mem REG 202,3 385122391 /admin/jdk1.6.0_13/jre/lib/jsse.jar (path dev=0,68) java 1940 admin mem REG 202,3 385090820 /admin/apache-tomcat-7.0.39/lib/tomcat-dbcp.jar (path dev=0,68) java 1940 admin mem REG 202,3 385090824 /admin/apache-tomcat-7.0.39/lib/tomcat-jdbc.jar (path dev=0,68) java 1940 admin mem REG 202,3 385090821 /admin/apache-tomcat-7.0.39/lib/tomcat-i18n-es.jar (path dev=0,68) java 1940 admin mem REG 202,3 385090816 /admin/apache-tomcat-7.0.39/lib/jsp-api.jar (path dev=0,68) java 1940 admin mem REG 202,3 385090817 /admin/apache-tomcat-7.0.39/lib/servlet-api.jar (path dev=0,68) java 1940 admin mem REG 202,3 385090813 /admin/apache-tomcat-7.0.39/lib/el-api.jar (path dev=0,68)

通过以上命令，我们可以看到open files 的最大数为1024 那么我们可以通过一下命令修改该参数的最大值 2. ulimit -n 4096 [root@test security]# ulimit -n 4096 [root@test security]# ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited file size (blocks, -f) unlimited max locked memory (kbytes, -l) unlimited max memory size (kbytes, -m) unlimited open files (-n) 4096 pipe size (512 bytes, -p) 8 stack size (kbytes, -s) 8192 cpu time (seconds, -t) unlimited max user processes (-u) 7168 virtual memory (kbytes, -v) unlimited

这样我们就修改了系统在同一时间打开文件资源的最大数，基本解决以上问题。

以上部分是查找网络上的解决方法。设置了之后段时间内有作用。

后来仔细想来，问题还是要从根本上解决，于是把以前的代码由认真地看了一遍。终于找到了，罪魁祸首。

在读取文件时，有一些使用的BufferedReader 没有关闭。导致文件一直处于打开状态。造成资源的严重浪费。

修改之后的简单代码如下：

public void test(){ BufferedReader reader = null ; try { reader = 读取文件; String line = "" ; while ( ( ine = reader.readLine()) != null ){ 其他操作 } } catch (IOException e){ System.out.println(e); } finally { if (reader != null ){ try { reader.close(); } catch (IOException e) { e.printStackTrace(); } } } }

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因为Socket没有释放,以致文件句柄用完了.如果用HttpClient去调用的, HttpClient本身存在这个问题, 解决方式就是加个httpHeader, 使用HttpClient如下: Java代码 client = new HttpClient(); client.getParams().setBooleanParameter("http.protocol.expect-continue", false); HttpMethod httpMethod = ...; httpMethod.addRequestHeader("Connection", "close"); client.executeMethod(httpMethod); [java] view plain copy client = new HttpClient(); client.getParams().setBooleanParameter("http.protocol.expect-continue", false); HttpMethod httpMethod = ...; httpMethod.addRequestHeader("Connection", "close"); client.executeMethod(httpMethod); , 其它的API应该也可以加这两个值. 用unlimit放大操作系统最大打开文件数的确可以短时间解决 Too many open files的现象，但这不是本质原因。本质原因肯定能够是你的程序中没有及时close掉文件（在linux/unix中Socket也是文件）。否则只有在上千的绝对同时并发时，才可能出现Too many open files错误。

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