libjava/gnu/classpath/VMStackWalker.java

   1 /* VMStackWalker.java -- Reference implementation of VM hooks for stack access
   2    Copyright (C) 2005, 2006 Free Software Foundation
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38 package gnu.classpath;
  39
  40 import gnu.gcj.RawData;
  41
  42 /**
  43  * This class provides access to the classes on the Java stack
  44  * for reflection and security purposes.
  45  *
  46  * <p>
  47  * This class is only available to privileged code (i.e., code loaded
  48  * by the bootstrap loader).
  49  *
  50  * @author John Keiser
  51  * @author Eric Blake <ebb9@email.byu.edu>
  52  * @author Archie Cobbs
  53  * @author Andrew Haley <aph@redhat.com>
  54  * @author Gary Benson <gbenson@redhat.com>
  55  */
  56 public final class VMStackWalker
  57 {
  58   /**
  59    * Get a list of all the classes currently executing methods on the
  60    * Java stack. <code>getClassContext()[0]</code> is the class associated
  61    * with the currently executing method, i.e., the method that called
  62    * <code>VMStackWalker.getClassContext()</code> (possibly through
  63    * reflection). So you may need to pop off these stack frames from
  64    * the top of the stack:
  65    * <ul>
  66    * <li><code>VMStackWalker.getClassContext()</code>
  67    * <li><code>Method.invoke()</code>
  68    * </ul>
  69    *
  70    * @return an array of the declaring classes of each stack frame
  71    */
  72   public static native Class[] getClassContext();
  73
  74   /**
  75    * Get the class associated with the method invoking the method
  76    * invoking this method, or <code>null</code> if the stack is not
  77    * that deep (e.g., invoked via JNI invocation API). This method
  78    * is an optimization for the expression <code>getClassContext()[1]</code>
  79    * and should return the same result.
  80    *
  81    * <p>
  82    * When compiling to native code gcj translates calls to this
  83    * method into calls to <code>getCallingClass(addr)</code>, with
  84    * <code>addr</code> being the address of the method calling this
  85    * method. <code>getCallingClass(addr)</code> does not unwind the
  86    * stack, so is therefore more efficient.
  87    */
  88   public static native Class getCallingClass();
  89
  90   /**
  91    * Get the class associated with the method invoking the method
  92    * invoking this method, or <code>null</code> if the stack is not
  93    * that deep (e.g., invoked via JNI invocation API).
  94    *
  95    * @param addr The address of the method invoking this method.
  96    */
  97   private static native Class getCallingClass(RawData addr);
  98
  99   /**
 100    * Get the class loader associated with the Class returned by
 101    * <code>getCallingClass()</code>, or <code>null</code> if no such class
 102    * exists or it is the boot loader. This method is an optimization for the
 103    * expression <code>VMStackWalker.getClassLoader(getClassContext()[1])</code>
 104    * and should return the same result.
 105    *
 106    * <p>
 107    * When compiling to native code gcj translates calls to this
 108    * method into calls to <code>getCallingClassLoader(addr)</code>,
 109    * with <code>addr</code> being the address of the method calling
 110    * this method. <code>getCallingClassLoader(addr)</code> does not
 111    * unwind the stack, so is therefore more efficient.
 112    */
 113   public static native ClassLoader getCallingClassLoader();
 114
 115   /**
 116    * Get the class loader associated with the Class returned by
 117    * <code>getCallingClass()</code>, or <code>null</code> if no
 118    * such class exists or it is the boot loader.
 119    *
 120    * @param addr The address of the method invoking this method.
 121    */
 122   private static native ClassLoader getCallingClassLoader(RawData addr);
 123
 124   /**
 125    * Retrieve the class's ClassLoader, or <code>null</code> if loaded
 126    * by the bootstrap loader. I.e., this should return the same thing
 127    * as {@link java.lang.VMClass#getClassLoader}. This duplicate version
 128    * is here to work around access permissions.
 129    */
 130   public static native ClassLoader getClassLoader(Class cl);
 131
 132   /**
 133    * Walk up the stack and return the first non-null class loader.
 134    * If there aren't any non-null class loaders on the stack, return null.
 135    */
 136   public static native ClassLoader firstNonNullClassLoader();
 137 }
 138