/interpreter/tags/at2-build270707/src/edu/vub/at/objects/natives/NATCallframe.java

  1/**
  2 * AmbientTalk/2 Project
  3 * NATCallframe.java created on Jul 28, 2006 at 11:26:17 AM
  4 * (c) Programming Technology Lab, 2006 - 2007
  5 * Authors: Tom Van Cutsem & Stijn Mostinckx
  6 * 
  7 * Permission is hereby granted, free of charge, to any person
  8 * obtaining a copy of this software and associated documentation
  9 * files (the "Software"), to deal in the Software without
 10 * restriction, including without limitation the rights to use,
 11 * copy, modify, merge, publish, distribute, sublicense, and/or
 12 * sell copies of the Software, and to permit persons to whom the
 13 * Software is furnished to do so, subject to the following
 14 * conditions:
 15 *
 16 * The above copyright notice and this permission notice shall be
 17 * included in all copies or substantial portions of the Software.
 18 *
 19 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 20 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 21 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 22 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 23 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 24 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 25 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 26 * OTHER DEALINGS IN THE SOFTWARE.
 27 */
 28package edu.vub.at.objects.natives;
 29
 30import edu.vub.at.exceptions.InterpreterException;
 31import edu.vub.at.exceptions.XDuplicateSlot;
 32import edu.vub.at.exceptions.XIllegalOperation;
 33import edu.vub.at.exceptions.XSelectorNotFound;
 34import edu.vub.at.exceptions.XUndefinedSlot;
 35import edu.vub.at.objects.ATBoolean;
 36import edu.vub.at.objects.ATField;
 37import edu.vub.at.objects.ATMethod;
 38import edu.vub.at.objects.ATNil;
 39import edu.vub.at.objects.ATObject;
 40import edu.vub.at.objects.ATTable;
 41import edu.vub.at.objects.grammar.ATSymbol;
 42
 43import java.util.Iterator;
 44import java.util.LinkedList;
 45import java.util.Vector;
 46
 47/**
 48 * NATCallframe is a native implementation of a callframe. A callframe differs from
 49 * an ordinary object in the following regards:
 50 * - it has no dynamic parent
 51 * - it treats method definition as the addition of a closure to its variables.
 52 * - it cannot be extended nor cloned
 53 * 
 54 * Callframes can be regarded as 'field-only' objects. Fields are implemented as follows:
 55 *  - native fields are implemented efficiently using a 'map': the map datastructure maps
 56 *    selectors to indices into a state vector, such that field names can be shared efficiently
 57 *    across clones.
 58 *  - custom fields are collected in a linked list. Their lookup and assignment is slower,
 59 *    and when an object is cloned, the custom field objects are re-instantiated.
 60 *    The new clone is passed as the sole argument to 'new'.
 61 * 
 62 * @author tvcutsem
 63 * @author smostinc
 64 */
 65public class NATCallframe extends NATByRef implements ATObject {
 66	
 67	protected FieldMap 		variableMap_;
 68	protected final Vector	stateVector_;
 69	
 70    /**
 71     * The lexical parent 'scope' of this call frame/object.
 72     * A lexical scope should never travel along with an object when it is serialized,
 73     * hence it is declared transient. Serializable isolate objects will have to reset
 74     * this field upon deserialization.
 75     */
 76	protected transient ATObject lexicalParent_;
 77	
 78	protected LinkedList customFields_;
 79	
 80	/**
 81	 * Default constructor: creates a new call frame with a given scope pointer.
 82	 */
 83	public NATCallframe(ATObject lexicalParent) {
 84		variableMap_   = new FieldMap();
 85		stateVector_   = new Vector();
 86		lexicalParent_ = lexicalParent;
 87		customFields_ = null;
 88	}
 89	
 90	/**
 91	 * Used internally for cloning a callframe/object.
 92	 */
 93	protected NATCallframe(FieldMap varMap, Vector stateVector, ATObject lexicalParent, LinkedList customFields) {
 94		variableMap_ = varMap;
 95		stateVector_ = stateVector;
 96		lexicalParent_ = lexicalParent;
 97		customFields_ = customFields;
 98	}
 99	
100	/* ------------------------------------------
101	 * -- Slot accessing and mutating protocol --
102	 * ------------------------------------------ */
103
104	/**
105	 * A field can be added to either a call frame or an object.
106	 * In both cases, it is checked whether the field does not already exist.
107	 * If it does not, a new field is created and its value set to the given initial value.
108	 * @throws InterpreterException 
109	 */
110	public ATNil meta_defineField(ATSymbol name, ATObject value) throws InterpreterException {
111		if (this.hasLocalField(name)) {
112			// field already exists...
113			throw new XDuplicateSlot(name);			
114		} else {
115			boolean fieldAdded = variableMap_.put(name);
116			if (!fieldAdded) {
117				throw new RuntimeException("Assertion failed: field not added to map while not duplicate");
118			}
119			// field now defined, add its value to the state vector
120			stateVector_.add(value);
121		}
122		return OBJNil._INSTANCE_;
123	}
124
125	/* ------------------------------------
126	 * -- Extension and cloning protocol --
127	 * ------------------------------------ */
128
129	public ATObject meta_clone() throws InterpreterException {
130		throw new XIllegalOperation("Cannot clone a call frame, clone its owning object instead.");
131	}
132
133	public ATObject meta_newInstance(ATTable initargs) throws InterpreterException {
134		throw new XIllegalOperation("Cannot create a new instance of a call frame, new its owning object instead.");
135	}
136
137	/* ---------------------------------
138	 * -- Structural Access Protocol  --
139	 * --------------------------------- */
140	
141	public ATNil meta_addField(ATField field) throws InterpreterException {
142		// when adding a native field, revert to the more optimized implementation using the map
143		if (field.isNativeField()) {
144			return this.meta_defineField(field.base_name(), field.base_readField());
145		}
146		
147		ATSymbol name = field.base_name();
148		if (this.hasLocalField(name)) {
149			// field already exists...
150			throw new XDuplicateSlot(name);			
151		} else {
152			// add a clone of the field initialized with its new host
153			field = field.base_new(new ATObject[] { this }).asField();
154			
155			// add the field to the list of custom fields, which is created lazily
156			if (customFields_ == null) {
157				customFields_ = new LinkedList();
158			}
159			// append the custom field object
160			customFields_.add(field);
161		}
162		return OBJNil._INSTANCE_;
163	}
164	
165	public ATNil meta_addMethod(ATMethod method) throws InterpreterException {
166		throw new XIllegalOperation("Cannot add method "+
167								   method.base_name().base_text().asNativeText().javaValue +
168				                    " to a call frame. Add it as a closure field instead.");
169	}
170	
171	public ATField meta_grabField(ATSymbol selector) throws InterpreterException {
172		if (this.hasLocalNativeField(selector)) {
173			return new NATField(selector, this);
174		} else {
175			ATField fld = this.getLocalCustomField(selector);
176			if (fld != null) {
177				return fld;
178			} else {
179				throw new XUndefinedSlot("field grabbed", selector.toString());
180			}
181		}
182	}
183
184	public ATMethod meta_grabMethod(ATSymbol selector) throws InterpreterException {
185		throw new XSelectorNotFound(selector, this);
186	}
187
188	public ATTable meta_listFields() throws InterpreterException {
189		ATObject[] nativeFields = new ATObject[stateVector_.size()];
190		ATSymbol[] fieldNames = variableMap_.listFields();
191		// native fields first
192		for (int i = 0; i < fieldNames.length; i++) {
193			nativeFields[i] = new NATField(fieldNames[i], this);
194		}
195		if (customFields_ == null) {
196			// no custom fields
197			return NATTable.atValue(nativeFields);
198		} else {
199			ATObject[] customFields = (ATObject[]) customFields_.toArray(new ATObject[customFields_.size()]);
200			return NATTable.atValue(NATTable.collate(nativeFields, customFields));
201		}
202	}
203
204	public ATTable meta_listMethods() throws InterpreterException {
205		return NATTable.EMPTY;
206	}
207	
208	public NATText meta_print() throws InterpreterException {
209		return NATText.atValue("<callframe>");
210	}
211	
212	/* ---------------------
213	 * -- Mirror Fields   --
214	 * --------------------- */
215	
216	/**
217	 * Auxiliary method to dynamically select the 'super' field from this object.
218	 * Note that this method is part of the base-level interface to an object.
219	 * 
220	 * Also note that this method performs the behaviour equivalent to evaluating
221	 * 'super' and not 'self.super', which could lead to infinite loops.
222	 */
223	public ATObject base_super() throws InterpreterException {
224		return this.impl_call(NATObject._SUPER_NAME_, NATTable.EMPTY);
225	};
226	
227	public ATObject impl_lexicalParent() throws InterpreterException {
228		return lexicalParent_;
229	}
230
231	/* --------------------------
232	 * -- Conversion Protocol  --
233	 * -------------------------- */
234	
235	public boolean isCallFrame() {
236		return true;
237	}
238	
239	public ATBoolean meta_isCloneOf(ATObject original) throws InterpreterException {
240		if(	(original instanceof NATCallframe) &
241			! (original instanceof NATObject)) {
242			FieldMap originalVariables = ((NATCallframe)original).variableMap_;
243			
244			return NATBoolean.atValue(
245					variableMap_.isDerivedFrom(originalVariables));
246		} else {
247			return NATBoolean._FALSE_;
248		}
249	}
250
251	public ATBoolean meta_isRelatedTo(ATObject object) throws InterpreterException {
252		return super.meta_isRelatedTo(object);
253	}
254	
255    /* -----------------------------
256     * -- Object Passing protocol --
257     * ----------------------------- */
258	
259	// protected methods, only to be used by NATCallframe and NATObject
260
261	protected boolean hasLocalField(ATSymbol selector) throws InterpreterException {
262		return hasLocalNativeField(selector) || hasLocalCustomField(selector);
263	}
264	
265	protected boolean hasLocalNativeField(ATSymbol selector) {
266		return variableMap_.get(selector) != -1;
267	}
268	
269	protected boolean hasLocalCustomField(ATSymbol selector) throws InterpreterException {
270		if (customFields_ == null) {
271			return false;
272		} else {
273			Iterator it = customFields_.iterator();
274			while (it.hasNext()) {
275				ATField field = (ATField) it.next();
276				if (field.base_name().equals(selector)) {
277					return true;
278				}
279			}
280			return false;
281		}
282	}
283	
284	/**
285	 * Reads out the value of either a native or a custom field.
286	 * @throws XSelectorNotFound if no native or custom field with the given name exists locally.
287	 */
288	protected ATObject getLocalField(ATSymbol selector) throws InterpreterException {
289		int index = variableMap_.get(selector);
290		if(index != -1) {
291			return (ATObject) (stateVector_.get(index));
292		} else {
293			ATField fld = getLocalCustomField(selector);
294			if (fld != null) {
295				return fld.base_readField();
296			} else {
297				throw new XSelectorNotFound(selector, this);
298			}
299		}
300	}
301	
302	/**
303	 * @return a custom field matching the given selector or null if such a field does not exist
304	 */
305	protected ATField getLocalCustomField(ATSymbol selector) throws InterpreterException {
306		if (customFields_ == null) {
307			return null;
308		} else {
309			Iterator it = customFields_.iterator();
310			while (it.hasNext()) {
311				ATField field = (ATField) it.next();
312				if (field.base_name().equals(selector)) {
313					return field;
314				}
315			}
316			return null;
317		}
318	}
319	
320	/**
321	 * Set a given field if it exists.
322	 */
323	protected void setLocalField(ATSymbol selector, ATObject value) throws InterpreterException {
324		int index = variableMap_.get(selector);
325		if(index != -1) {
326			// field exists, modify the state vector
327			stateVector_.set(index, value);
328			// ok
329		} else {
330			ATField fld = getLocalCustomField(selector);
331			if (fld != null) {
332				fld.base_writeField(value);
333				// ok
334			} else {
335				// fail
336				throw new XSelectorNotFound(selector, this);
337			}
338		}
339	}
340
341	/**
342	 * A call frame has no methods.
343	 */
344	protected boolean hasLocalMethod(ATSymbol atSelector) throws InterpreterException {
345        return false;
346	}
347	
348	/**
349	 * A call frame has no methods.
350	 */
351	protected ATMethod getLocalMethod(ATSymbol selector) throws InterpreterException {
352		throw new XSelectorNotFound(selector, this);
353	}
354
355	
356}