1 /***************************************************************************** 2 * Licensed to the Apache Software Foundation (ASF) under one * 3 * or more contributor license agreements. See the NOTICE file * 4 * distributed with this work for additional information * 5 * regarding copyright ownership. The ASF licenses this file * 6 * to you under the Apache License, Version 2.0 (the * 7 * "License"); you may not use this file except in compliance * 8 * with the License. You may obtain a copy of the License at * 9 * * 10 * http://www.apache.org/licenses/LICENSE-2.0 * 11 * * 12 * Unless required by applicable law or agreed to in writing, * 13 * software distributed under the License is distributed on an * 14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * 15 * KIND, either express or implied. See the License for the * 16 * specific language governing permissions and limitations * 17 * under the License. * 18 * * 19 * This file is part of the BeanShell Java Scripting distribution. * 20 * Documentation and updates may be found at http://www.beanshell.org/ * 21 * Patrick Niemeyer (pat@pat.net) * 22 * Author of Learning Java, O'Reilly & Associates * 23 * * 24 *****************************************************************************/ 25 26 package bsh; 27 28 import java.io.Serializable; 29 import java.util.Stack; 30 import java.util.EmptyStackException; 31 32 /** 33 A stack of NameSpaces representing the call path. 34 Each method invocation, for example, pushes a new NameSpace onto the stack. 35 The top of the stack is always the current namespace of evaluation. 36 <p> 37 38 This is used to support the this.caller magic reference and to print 39 script "stack traces" when evaluation errors occur. 40 <p> 41 42 Note: How can this be thread safe, you might ask? Wouldn't a thread 43 executing various beanshell methods be mutating the callstack? Don't we 44 need one CallStack per Thread in the interpreter? The answer is that we do. 45 Any java.lang.Thread enters our script via an external (hard) Java 46 reference via a This type interface, e.g. the Runnable interface 47 implemented by This or an arbitrary interface implemented by XThis. 48 In that case the This invokeMethod() method (called by any interface that 49 it exposes) creates a new CallStack for each external call. 50 <p> 51 */ 52 public final class CallStack implements Serializable { 53 54 private static final long serialVersionUID = 0L; 55 56 private final Stack<NameSpace> stack = new Stack<NameSpace>(); 57 58 CallStack()59 public CallStack() { } 60 CallStack( NameSpace namespace )61 public CallStack( NameSpace namespace ) { 62 push( namespace ); 63 } 64 clear()65 public void clear() { 66 stack.removeAllElements(); 67 } 68 push( NameSpace ns )69 public void push( NameSpace ns ) { 70 stack.push( ns ); 71 } 72 top()73 public NameSpace top() { 74 return stack.peek(); 75 } 76 77 /** 78 zero based. 79 */ get(int depth)80 public NameSpace get(int depth) { 81 int size = stack.size(); 82 if ( depth >= size ) 83 return NameSpace.JAVACODE; 84 else 85 return stack.get(size-1-depth); 86 } 87 88 /** 89 This is kind of crazy, but used by the setNameSpace command. 90 zero based. 91 */ set(int depth, NameSpace ns)92 public void set(int depth, NameSpace ns) { 93 stack.set( stack.size()-1-depth, ns ); 94 } 95 pop()96 public NameSpace pop() { 97 try { 98 return stack.pop(); 99 } catch(EmptyStackException e) { 100 throw new InterpreterError("pop on empty CallStack"); 101 } 102 } 103 104 /** 105 Swap in the value as the new top of the stack and return the old 106 value. 107 */ swap( NameSpace newTop )108 public NameSpace swap( NameSpace newTop ) { 109 int last = stack.size() - 1; 110 NameSpace oldTop = stack.get(last); 111 stack.set( last, newTop ); 112 return oldTop; 113 } 114 depth()115 public int depth() { 116 return stack.size(); 117 } 118 /* 119 public NameSpace [] toArray() { 120 NameSpace [] nsa = new NameSpace [ depth() ]; 121 stack.copyInto( nsa ); 122 return nsa; 123 } 124 */ toString()125 public String toString() { 126 StringBuilder sb = new StringBuilder(); 127 sb.append("CallStack:\n"); 128 for( int i=stack.size()-1; i>=0; i-- ) 129 sb.append("\t"+stack.get(i)+"\n"); 130 131 return sb.toString(); 132 } 133 134 /** 135 Occasionally we need to freeze the callstack for error reporting 136 purposes, etc. 137 */ copy()138 public CallStack copy() { 139 CallStack cs = new CallStack(); 140 cs.stack.addAll(this.stack); 141 return cs; 142 } 143 } 144