1 package org.apache.bcel.generic;
2
3 /* ====================================================================
4 * The Apache Software License, Version 1.1
5 *
6 * Copyright (c) 2001 The Apache Software Foundation. All rights
7 * reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 *
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 *
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in
18 * the documentation and/or other materials provided with the
19 * distribution.
20 *
21 * 3. The end-user documentation included with the redistribution,
22 * if any, must include the following acknowledgment:
23 * "This product includes software developed by the
24 * Apache Software Foundation (http://www.apache.org/)."
25 * Alternately, this acknowledgment may appear in the software itself,
26 * if and wherever such third-party acknowledgments normally appear.
27 *
28 * 4. The names "Apache" and "Apache Software Foundation" and
29 * "Apache BCEL" must not be used to endorse or promote products
30 * derived from this software without prior written permission. For
31 * written permission, please contact apache@apache.org.
32 *
33 * 5. Products derived from this software may not be called "Apache",
34 * "Apache BCEL", nor may "Apache" appear in their name, without
35 * prior written permission of the Apache Software Foundation.
36 *
37 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
38 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
39 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
40 * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
41 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
42 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
43 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
44 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
45 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
46 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
47 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
48 * SUCH DAMAGE.
49 * ====================================================================
50 *
51 * This software consists of voluntary contributions made by many
52 * individuals on behalf of the Apache Software Foundation. For more
53 * information on the Apache Software Foundation, please see
54 * <http://www.apache.org/>.
55 */
56
57 import org.apache.bcel.classfile.Utility;
58 import java.util.HashSet;
59 import java.util.Collection;
60 import java.util.HashMap;
61
62 /***
63 * Instances of this class give users a handle to the instructions contained in
64 * an InstructionList. Instruction objects may be used more than once within a
65 * list, this is useful because it saves memory and may be much faster.
66 *
67 * Within an InstructionList an InstructionHandle object is wrapped
68 * around all instructions, i.e., it implements a cell in a
69 * doubly-linked list. From the outside only the next and the
70 * previous instruction (handle) are accessible. One
71 * can traverse the list via an Enumeration returned by
72 * InstructionList.elements().
73 *
74 * @version $Id: InstructionHandle.java,v 1.1.1.1 2001/10/29 20:00:19 jvanzyl Exp $
75 * @author <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
76 * @see Instruction
77 * @see BranchHandle
78 * @see InstructionList
79 */
80 public class InstructionHandle implements java.io.Serializable {
81 InstructionHandle next, prev; // Will be set from the outside
82 Instruction instruction;
83 protected int i_position = -1; // byte code offset of instruction
84 private HashSet targeters;
85 private HashMap attributes;
86
87 public final InstructionHandle getNext() { return next; }
88 public final InstructionHandle getPrev() { return prev; }
89 public final Instruction getInstruction() { return instruction; }
90
91 /***
92 * Replace current instruction contained in this handle.
93 * Old instruction is disposed using Instruction.dispose().
94 */
95 public void setInstruction(Instruction i) { // Overridden in BranchHandle
96 if(i == null)
97 throw new ClassGenException("Assigning null to handle");
98
99 if((this.getClass() != BranchHandle.class) && (i instanceof BranchInstruction))
100 throw new ClassGenException("Assigning branch instruction " + i + " to plain handle");
101
102 if(instruction != null)
103 instruction.dispose();
104
105 instruction = i;
106 }
107
108 /***
109 * Temporarily swap the current instruction, without disturbing
110 * anything. Meant to be used by a debugger, implementing
111 * breakpoints. Current instruction is returned.
112 */
113 public Instruction swapInstruction(Instruction i) {
114 Instruction oldInstruction = instruction;
115 instruction = i;
116 return oldInstruction;
117 }
118
119 /*private*/ protected InstructionHandle(Instruction i) {
120 setInstruction(i);
121 }
122
123 private static InstructionHandle ih_list = null; // List of reusable handles
124
125 /*** Factory method.
126 */
127 static final InstructionHandle getInstructionHandle(Instruction i) {
128 if(ih_list == null)
129 return new InstructionHandle(i);
130 else {
131 InstructionHandle ih = ih_list;
132 ih_list = ih.next;
133
134 ih.setInstruction(i);
135
136 return ih;
137 }
138 }
139
140 /***
141 * Called by InstructionList.setPositions when setting the position for every
142 * instruction. In the presence of variable length instructions `setPositions()'
143 * performs multiple passes over the instruction list to calculate the
144 * correct (byte) positions and offsets by calling this function.
145 *
146 * @param offset additional offset caused by preceding (variable length) instructions
147 * @param max_offset the maximum offset that may be caused by these instructions
148 * @return additional offset caused by possible change of this instruction's length
149 */
150 protected int updatePosition(int offset, int max_offset) {
151 i_position += offset;
152 return 0;
153 }
154
155 /*** @return the position, i.e., the byte code offset of the contained
156 * instruction. This is accurate only after
157 * InstructionList.setPositions() has been called.
158 */
159 public int getPosition() { return i_position; }
160
161 /*** Set the position, i.e., the byte code offset of the contained
162 * instruction.
163 */
164 void setPosition(int pos) { i_position = pos; }
165
166 /*** Overridden in BranchHandle
167 */
168 protected void addHandle() {
169 next = ih_list;
170 ih_list = this;
171 }
172
173 /***
174 * Delete contents, i.e., remove user access and make handle reusable.
175 */
176 void dispose() {
177 next = prev = null;
178 instruction.dispose();
179 instruction = null;
180 i_position = -1;
181 attributes = null;
182 removeAllTargeters();
183 addHandle();
184 }
185
186 /*** Remove all targeters, if any.
187 */
188 public void removeAllTargeters() {
189 if(targeters != null)
190 targeters.clear();
191 }
192
193 /***
194 * Denote this handle isn't referenced anymore by t.
195 */
196 public void removeTargeter(InstructionTargeter t) {
197 targeters.remove(t);
198 }
199
200 /***
201 * Denote this handle is being referenced by t.
202 */
203 public void addTargeter(InstructionTargeter t) {
204 if(targeters == null)
205 targeters = new HashSet();
206
207 //if(!targeters.contains(t))
208 targeters.add(t);
209 }
210
211 public boolean hasTargeters() {
212 return (targeters != null) && (targeters.size() > 0);
213 }
214
215 /***
216 * @return null, if there are no targeters
217 */
218 public InstructionTargeter[] getTargeters() {
219 if(!hasTargeters())
220 return null;
221
222 InstructionTargeter[] t = new InstructionTargeter[targeters.size()];
223 targeters.toArray(t);
224 return t;
225 }
226
227 /*** @return a (verbose) string representation of the contained instruction.
228 */
229 public String toString(boolean verbose) {
230 return Utility.format(i_position, 4, false, ' ') + ": " + instruction.toString(verbose);
231 }
232
233 /*** @return a string representation of the contained instruction.
234 */
235 public String toString() {
236 return toString(true);
237 }
238
239 /*** Add an attribute to an instruction handle.
240 *
241 * @param key the key object to store/retrieve the attribute
242 * @param attr the attribute to associate with this handle
243 */
244 public void addAttribute(Object key, Object attr) {
245 if(attributes == null)
246 attributes = new HashMap(3);
247
248 attributes.put(key, attr);
249 }
250
251 /*** Delete an attribute of an instruction handle.
252 *
253 * @param key the key object to retrieve the attribute
254 */
255 public void removeAttribute(Object key) {
256 if(attributes != null)
257 attributes.remove(key);
258 }
259
260 /*** Get attribute of an instruction handle.
261 *
262 * @param key the key object to store/retrieve the attribute
263 */
264 public Object getAttribute(Object key) {
265 if(attributes != null)
266 return attributes.get(key);
267
268 return null;
269 }
270
271 /*** @return all attributes associated with this handle
272 */
273 public Collection getAttributes() {
274 return attributes.values();
275 }
276
277 /*** Convenience method, simply calls accept() on the contained instruction.
278 *
279 * @param v Visitor object
280 */
281 public void accept(Visitor v) {
282 instruction.accept(v);
283 }
284 }
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