| 1 | package org.dcache.cells; |
| 2 | |
| 3 | import java.util.Collection; |
| 4 | import java.util.Map; |
| 5 | import java.util.HashMap; |
| 6 | import java.util.ArrayList; |
| 7 | import java.util.concurrent.CopyOnWriteArrayList; |
| 8 | |
| 9 | import java.lang.reflect.Method; |
| 10 | import java.lang.reflect.Constructor; |
| 11 | import java.lang.reflect.Field; |
| 12 | import java.lang.reflect.InvocationTargetException; |
| 13 | |
| 14 | import dmg.cells.nucleus.CellMessage; |
| 15 | |
| 16 | import org.dcache.util.ReflectionUtils; |
| 17 | |
| 18 | /** |
| 19 | * Helper class for message dispatching. Used internally in |
| 20 | * CellMessageDispatcher; |
| 21 | */ |
| 22 | abstract class Receiver |
| 23 | { |
| 24 | final protected Object _object; |
| 25 | final protected Method _method; |
| 26 | |
| 27 | public Receiver(Object object, Method method) |
| 28 | { |
| 29 | _object = object; |
| 30 | _method = method; |
| 31 | } |
| 32 | |
| 33 | abstract public Object deliver(CellMessage envelope, Object message) |
| 34 | throws IllegalAccessException, InvocationTargetException; |
| 35 | |
| 36 | public String toString() |
| 37 | { |
| 38 | return String.format("Object: %1$s; Method: %2$s", _object, _method); |
| 39 | } |
| 40 | } |
| 41 | |
| 42 | class ShortReceiver extends Receiver |
| 43 | { |
| 44 | public ShortReceiver(Object object, Method method) |
| 45 | { |
| 46 | super(object, method); |
| 47 | } |
| 48 | |
| 49 | public Object deliver(CellMessage envelope, Object message) |
| 50 | throws IllegalAccessException, InvocationTargetException |
| 51 | { |
| 52 | return _method.invoke(_object, message); |
| 53 | } |
| 54 | } |
| 55 | |
| 56 | |
| 57 | class LongReceiver extends Receiver |
| 58 | { |
| 59 | public LongReceiver(Object object, Method method) |
| 60 | { |
| 61 | super(object, method); |
| 62 | } |
| 63 | |
| 64 | public Object deliver(CellMessage envelope, Object message) |
| 65 | throws IllegalAccessException, InvocationTargetException |
| 66 | { |
| 67 | return _method.invoke(_object, envelope, message); |
| 68 | } |
| 69 | } |
| 70 | |
| 71 | |
| 72 | /** |
| 73 | * Automatic dispatch of dCache messages to message handlers. |
| 74 | */ |
| 75 | public class CellMessageDispatcher |
| 76 | { |
| 77 | /** Cached message handlers for fast dispatch. */ |
| 78 | private final Map<Class,Collection<Receiver>> _receivers = |
| 79 | new HashMap<Class,Collection<Receiver>>(); |
| 80 | |
| 81 | /** Name of receiver methods. */ |
| 82 | private final String _receiverName; |
| 83 | |
| 84 | /** |
| 85 | * Registered message listeners. |
| 86 | * |
| 87 | * @see addMessageListener |
| 88 | */ |
| 89 | private final Collection<Object> _messageListeners = |
| 90 | new CopyOnWriteArrayList<Object>(); |
| 91 | |
| 92 | public CellMessageDispatcher(String receiverName) |
| 93 | { |
| 94 | _receiverName = receiverName; |
| 95 | } |
| 96 | |
| 97 | /** |
| 98 | * Returns true if <code>c</code> has a method suitable for |
| 99 | * message delivery. |
| 100 | */ |
| 101 | private boolean hasListener(Class c) |
| 102 | { |
| 103 | for (Method m : c.getMethods()) { |
| 104 | if (m.getName().equals(_receiverName)) { |
| 105 | return true; |
| 106 | } |
| 107 | } |
| 108 | return false; |
| 109 | } |
| 110 | |
| 111 | /** |
| 112 | * Adds a listener for dCache messages. |
| 113 | * |
| 114 | * The object is scanned for public methods with the signature |
| 115 | * <code>name(Object message)</code> or <code>name(CellMessage |
| 116 | * envelope, Object message)</code>, where <code>name</code> is |
| 117 | * the receiver name, <code>envelope</code> is the envelope |
| 118 | * containing the message. |
| 119 | * |
| 120 | * After registration, all cell messages with a message object |
| 121 | * matching the type of the argument will be send to object. |
| 122 | * |
| 123 | * Message dispatching is performed in the <code>call</code> |
| 124 | * method. If that method is overridden in derivatives, the |
| 125 | * derivative must make sure that <code>call</code> is still |
| 126 | * called. |
| 127 | */ |
| 128 | public void addMessageListener(Object o) |
| 129 | { |
| 130 | Class c = o.getClass(); |
| 131 | if (hasListener(c)) { |
| 132 | synchronized (_receivers) { |
| 133 | if (_messageListeners.add(o)) { |
| 134 | _receivers.clear(); |
| 135 | } |
| 136 | } |
| 137 | } |
| 138 | } |
| 139 | |
| 140 | /** |
| 141 | * Removes a listener previously added with addMessageListener. |
| 142 | */ |
| 143 | public void removeMessageListener(Object o) |
| 144 | { |
| 145 | synchronized (_receivers) { |
| 146 | if (_messageListeners.remove(o)) { |
| 147 | _receivers.clear(); |
| 148 | } |
| 149 | } |
| 150 | } |
| 151 | |
| 152 | /** |
| 153 | * Returns the message types that can be reveived by an object of |
| 154 | * the given class. |
| 155 | */ |
| 156 | public Collection<Class> getMessageTypes(Object o) |
| 157 | { |
| 158 | Class c = o.getClass(); |
| 159 | Collection<Class> types = new ArrayList(); |
| 160 | |
| 161 | for (Method method : c.getMethods()) { |
| 162 | if (method.getName().equals(_receiverName)) { |
| 163 | Class[] parameterTypes = method.getParameterTypes(); |
| 164 | switch (parameterTypes.length) { |
| 165 | case 1: |
| 166 | types.add(parameterTypes[0]); |
| 167 | break; |
| 168 | case 2: |
| 169 | if (CellMessage.class.isAssignableFrom(parameterTypes[0])) { |
| 170 | types.add(parameterTypes[1]); |
| 171 | } |
| 172 | break; |
| 173 | } |
| 174 | } |
| 175 | } |
| 176 | return types; |
| 177 | } |
| 178 | |
| 179 | /** |
| 180 | * Finds the objects and methods, in other words the receivers, of |
| 181 | * messages of a given type. |
| 182 | * |
| 183 | * FIXME: This is still not quite the right thing: if you have |
| 184 | * messageArrived(CellMessage, X) and messageArrived(Y) and Y is |
| 185 | * more specific than X, then you would expect the latter to be |
| 186 | * called for message Y. This is not yet the case. |
| 187 | */ |
| 188 | private Collection<Receiver> findReceivers(Class c) |
| 189 | { |
| 190 | synchronized (_receivers) { |
| 191 | Collection<Receiver> receivers = new ArrayList<Receiver>(); |
| 192 | for (Object listener : _messageListeners) { |
| 193 | Method m = ReflectionUtils.resolve(listener.getClass(), |
| 194 | _receiverName, |
| 195 | CellMessage.class, c); |
| 196 | if (m != null) { |
| 197 | receivers.add(new LongReceiver(listener, m)); |
| 198 | continue; |
| 199 | } |
| 200 | |
| 201 | m = ReflectionUtils.resolve(listener.getClass(), |
| 202 | _receiverName, |
| 203 | c); |
| 204 | if (m != null) { |
| 205 | receivers.add(new ShortReceiver(listener, m)); |
| 206 | } |
| 207 | } |
| 208 | return receivers; |
| 209 | } |
| 210 | } |
| 211 | |
| 212 | private String multipleRepliesError(Collection<Receiver> receivers, Object message) |
| 213 | { |
| 214 | return String.format("Processing of message [%s] of type %s failed: Multiple replies were generated by %s.", message, message.getClass().getName(), receivers); |
| 215 | } |
| 216 | |
| 217 | /** |
| 218 | * Delivers messages to registered message listeners. The return |
| 219 | * value is determined by the following rules (in order): |
| 220 | * |
| 221 | * 1. If any message listener throws an unchecked exception other |
| 222 | * than IllegalArgumentException or IllegalStateException, that |
| 223 | * exception is rethrown. |
| 224 | * |
| 225 | * 2. If more than one message listener returns a non-null value |
| 226 | * or throws a checked exception, IllegalArgumentException or |
| 227 | * IllegalStateException, then a RuntimeException is thrown |
| 228 | * reporting that multiple replies have been generated. This is |
| 229 | * a coding error. |
| 230 | * |
| 231 | * 3. If one message listener returns a non null value then that |
| 232 | * value is returned. If one message listener throws a checked |
| 233 | * exception, IllegalArgumentException or |
| 234 | * IllegalStateException, then that exception is returned. |
| 235 | * |
| 236 | * 4. Otherwise null is returned. |
| 237 | */ |
| 238 | public Object call(CellMessage envelope) |
| 239 | { |
| 240 | Object message = envelope.getMessageObject(); |
| 241 | Class c = message.getClass(); |
| 242 | Collection<Receiver> receivers; |
| 243 | |
| 244 | synchronized (_receivers) { |
| 245 | receivers = _receivers.get(c); |
| 246 | if (receivers == null) { |
| 247 | receivers = findReceivers(c); |
| 248 | _receivers.put(c, receivers); |
| 249 | } |
| 250 | } |
| 251 | |
| 252 | Object result = null; |
| 253 | for (Receiver receiver : receivers) { |
| 254 | try { |
| 255 | Object obj = receiver.deliver(envelope, message); |
| 256 | if (obj != null && result != null) { |
| 257 | throw new RuntimeException(multipleRepliesError(receivers, message)); |
| 258 | } |
| 259 | result = obj; |
| 260 | } catch (IllegalAccessException e) { |
| 261 | throw new RuntimeException("Cannot process message due to access error", e); |
| 262 | } catch (InvocationTargetException e) { |
| 263 | Throwable cause = e.getCause(); |
| 264 | if (cause instanceof IllegalArgumentException || |
| 265 | cause instanceof IllegalStateException) { |
| 266 | /* We recognize these two unchecked exceptions as |
| 267 | * something special and report back to the |
| 268 | * client. |
| 269 | */ |
| 270 | } else if (cause instanceof RuntimeException) { |
| 271 | throw (RuntimeException)cause; |
| 272 | } else if (cause instanceof Error) { |
| 273 | throw (Error)cause; |
| 274 | } |
| 275 | |
| 276 | if (result != null) { |
| 277 | throw new RuntimeException(multipleRepliesError(receivers, message)); |
| 278 | } |
| 279 | result = cause; |
| 280 | } |
| 281 | } |
| 282 | |
| 283 | return result; |
| 284 | } |
| 285 | } |