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JMockit is a Java toolkit for developer (unit/integration) testing. It contains mocking APIs and other tools, supporting both JUnit and TestNG. The mocking APIs allow all kinds of Java code, without testability restrictions, to be tested in isolation from selected dependencies.
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/*
 * Copyright 2005 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */
package sun.tools.attach;

import java.io.*;
import java.util.*;

import com.sun.tools.attach.*;
import com.sun.tools.attach.spi.*;

public final class WindowsVirtualMachine extends HotSpotVirtualMachine
{
   // The enqueue code stub (copied into each target VM).
   private static final byte[] stub;

   private volatile long hProcess;     // handle to the process

   public WindowsVirtualMachine(AttachProvider provider, String id) throws IOException
   {
      super(provider, id);
      int pid = Integer.parseInt(id);
      hProcess = openProcess(pid);
   }

   @Override
   public void detach() throws IOException
   {
      synchronized (this) {
         if (hProcess != -1) {
            closeProcess(hProcess);
            hProcess = -1;
         }
      }
   }

   @Override
   InputStream execute(String cmd, Object... args) throws AgentLoadException, IOException
   {
      assert args.length <= 3;        // includes null

      // create a pipe using a random name
      int r = new Random().nextInt();
      String pipeName = "\\\\.\\pipe\\javatool" + r;
      long hPipe = createPipe(pipeName);

      // check if we are detached - in theory it's possible that detach is invoked
      // after this check but before we enqueue the command.
      if (hProcess == -1) {
         closePipe(hPipe);
         throw new IOException("Detached from target VM");
      }

      try {
         // enqueue the command to the process
         enqueue(hProcess, stub, cmd, pipeName, args);

         // wait for command to complete - process will connect with the
         // completion status
         connectPipe(hPipe);

         // create an input stream for the pipe
         PipedInputStream is = new PipedInputStream(hPipe);

         // read completion status
         int status = readInt(is);

         if (status != 0) {
            // special case the load command so that the right exception is thrown
            if ("load".equals(cmd)) {
               throw new AgentLoadException("Failed to load agent library");
            }
            else {
               throw new IOException("Command failed in target VM");
            }
         }

         // return the input stream
         return is;
      }
      catch (IOException ioe) {
         closePipe(hPipe);
         throw ioe;
      }
   }

   // An InputStream based on a pipe to the target VM
   private final class PipedInputStream extends InputStream
   {
      private long hPipe;

      PipedInputStream(long hPipe)
      {
         this.hPipe = hPipe;
      }

      @Override
      public synchronized int read() throws IOException
      {
         byte[] b = new byte[1];
         int n = read(b, 0, 1);

         if (n == 1) {
            return b[0] & 0xff;
         }
         else {
            return -1;
         }
      }

      @Override
      public synchronized int read(byte[] bs, int off, int len) throws IOException
      {
         if (off < 0 || off > bs.length || len < 0 || off + len > bs.length || off + len < 0) {
            throw new IndexOutOfBoundsException();
         }
         else if (len == 0) {
            return 0;
         }

         return readPipe(hPipe, bs, off, len);
      }

      @Override
      public void close() throws IOException
      {
         if (hPipe != -1) {
            closePipe(hPipe);
            hPipe = -1;
         }
      }
   }

   //-- native methods

   static native void init();
   static native byte[] generateStub();
   static native long openProcess(int pid) throws IOException;
   static native void closeProcess(long hProcess) throws IOException;
   static native long createPipe(String name) throws IOException;
   static native void closePipe(long hPipe) throws IOException;
   static native void connectPipe(long hPipe) throws IOException;
   static native int readPipe(long hPipe, byte[] buf, int off, int bufLen) throws IOException;
   static native void enqueue(
      long hProcess, byte[] stub, String cmd, String pipeName, Object... args) throws IOException;

   static {
      System.loadLibrary("attach");
      init();                                 // native initialization
      stub = generateStub();                  // generate stub to copy into target process
   }
}