MappedByteBuffer强制释放后读取引发jvm crash

 

这几天使用MappedByteBuffer对系统进行了实现，在压测过程中发现启动多个group订阅时服务端会发生jvm crash ，排查后找到了原因，记录一下。

 

部分信息如下：

#

# A fatal error has been detected by the Java Runtime Environment:

#

#  EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x01b8d4d7, pid=10236, tid=8452

#

# JRE version: 6.0_18-b02

# Java VM: Java HotSpot(TM) Client VM (16.0-b09 mixed mode, sharing windows-x86 )

# Problematic frame:

# J  java.nio.DirectByteBuffer.get(I)B

#

# An error report file with more information is saved as:

# D:\workspace_new\metamorphosis\metamorphosis-server\hs_err_pid10236.log

#

# If you would like to submit a bug report, please visit:

#   http://java.sun.com/webapps/bugreport/crash.jsp

#

 

原因是在MappedByteBuffer释放后再对它进行读操作的话就会引发这个crash，在并发情况下很容易正在释放时另一个线程正开始读取，于是crash就发生了。下面这个测试代码可以重现：

 

@Test

public void unmapAndRead()throws Exception {

  File file =new File("unmapAndRead.txt");

  FileChannel fileChannel =new RandomAccessFile(file,"rw").getChannel();

  MappedByteBuffer buf = fileChannel.map(MapMode.READ_WRITE, 0, 4096);

  buf.putInt(5);

  buf.force();

  this.unmap(buf);

  buf.get(2);//Crash occur

}

 

void unmap(finalMappedByteBuffer mappedByteBuffer) {

  try {

    if (mappedByteBuffer ==null) {

    return;

  }

  mappedByteBuffer.force();

  AccessController.doPrivileged(new PrivilegedAction<Object>() {

  @Override

  public Object run() {

    try {

       Method getCleanerMethod =      mappedByteBuffer.getClass().getMethod("cleaner",new Class[0]);

       getCleanerMethod.setAccessible(true);

       sun.misc.Cleaner cleaner =

       (sun.misc.Cleaner)getCleanerMethod.invoke(mappedByteBuffer,new Object[0]);

       cleaner.clean();

    }

    catch (Exception e) {

       e.printStackTrace();

    }

    return null;

   }

  });

 

 }

catch (Exception e) {

   e.printStackTrace();

}

}