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25 
26 package sun.nio.fs;
27 
28 import java.nio.file.*;
29 import java.util.*;
30 
31 /**
32  * Base implementation class for watch keys.
33  */
34 
35 abstract class AbstractWatchKey implements WatchKey {
36 
37     /**
38      * Maximum size of event list (in the future this may be tunable)
39      */
40     static final int MAX_EVENT_LIST_SIZE    = 512;
41 
42     /**
43      * Special event to signal overflow
44      */
45     static final Event<Object> OVERFLOW_EVENT =
46         new Event<Object>(StandardWatchEventKinds.OVERFLOW, null);
47 
48     /**
49      * Possible key states
50      */
51     private static enum State { READY, SIGNALLED };
52 
53     // reference to watcher
54     private final AbstractWatchService watcher;
55 
56     // reference to the original directory
57     private final Path dir;
58 
59     // key state
60     private State state;
61 
62     // pending events
63     private List<WatchEvent<?>> events;
64 
65     // maps a context to the last event for the context (iff the last queued
66     // event for the context is an ENTRY_MODIFY event).
67     private Map<Object,WatchEvent<?>> lastModifyEvents;
68 
AbstractWatchKey(Path dir, AbstractWatchService watcher)69     protected AbstractWatchKey(Path dir, AbstractWatchService watcher) {
70         this.watcher = watcher;
71         this.dir = dir;
72         this.state = State.READY;
73         this.events = new ArrayList<WatchEvent<?>>();
74         this.lastModifyEvents = new HashMap<Object,WatchEvent<?>>();
75     }
76 
watcher()77     final AbstractWatchService watcher() {
78         return watcher;
79     }
80 
81     /**
82      * Return the original watchable (Path)
83      */
84     @Override
watchable()85     public Path watchable() {
86         return dir;
87     }
88 
89     /**
90      * Enqueues this key to the watch service
91      */
signal()92     final void signal() {
93         synchronized (this) {
94             if (state == State.READY) {
95                 state = State.SIGNALLED;
96                 watcher.enqueueKey(this);
97             }
98         }
99     }
100 
101     /**
102      * Adds the event to this key and signals it.
103      */
104     @SuppressWarnings("unchecked")
signalEvent(WatchEvent.Kind<?> kind, Object context)105     final void signalEvent(WatchEvent.Kind<?> kind, Object context) {
106         boolean isModify = (kind == StandardWatchEventKinds.ENTRY_MODIFY);
107         synchronized (this) {
108             int size = events.size();
109             if (size > 0) {
110                 // if the previous event is an OVERFLOW event or this is a
111                 // repeated event then we simply increment the counter
112                 WatchEvent<?> prev = events.get(size-1);
113                 if ((prev.kind() == StandardWatchEventKinds.OVERFLOW) ||
114                     ((kind == prev.kind() &&
115                      Objects.equals(context, prev.context()))))
116                 {
117                     ((Event<?>)prev).increment();
118                     return;
119                 }
120 
121                 // if this is a modify event and the last entry for the context
122                 // is a modify event then we simply increment the count
123                 if (!lastModifyEvents.isEmpty()) {
124                     if (isModify) {
125                         WatchEvent<?> ev = lastModifyEvents.get(context);
126                         if (ev != null) {
127                             assert ev.kind() == StandardWatchEventKinds.ENTRY_MODIFY;
128                             ((Event<?>)ev).increment();
129                             return;
130                         }
131                     } else {
132                         // not a modify event so remove from the map as the
133                         // last event will no longer be a modify event.
134                         lastModifyEvents.remove(context);
135                     }
136                 }
137 
138                 // if the list has reached the limit then drop pending events
139                 // and queue an OVERFLOW event
140                 if (size >= MAX_EVENT_LIST_SIZE) {
141                     kind = StandardWatchEventKinds.OVERFLOW;
142                     isModify = false;
143                     context = null;
144                 }
145             }
146 
147             // non-repeated event
148             Event<Object> ev =
149                 new Event<Object>((WatchEvent.Kind<Object>)kind, context);
150             if (isModify) {
151                 lastModifyEvents.put(context, ev);
152             } else if (kind == StandardWatchEventKinds.OVERFLOW) {
153                 // drop all pending events
154                 events.clear();
155                 lastModifyEvents.clear();
156             }
157             events.add(ev);
158             signal();
159         }
160     }
161 
162     @Override
pollEvents()163     public final List<WatchEvent<?>> pollEvents() {
164         synchronized (this) {
165             List<WatchEvent<?>> result = events;
166             events = new ArrayList<WatchEvent<?>>();
167             lastModifyEvents.clear();
168             return result;
169         }
170     }
171 
172     @Override
reset()173     public final boolean reset() {
174         synchronized (this) {
175             if (state == State.SIGNALLED && isValid()) {
176                 if (events.isEmpty()) {
177                     state = State.READY;
178                 } else {
179                     // pending events so re-queue key
180                     watcher.enqueueKey(this);
181                 }
182             }
183             return isValid();
184         }
185     }
186 
187     /**
188      * WatchEvent implementation
189      */
190     private static class Event<T> implements WatchEvent<T> {
191         private final WatchEvent.Kind<T> kind;
192         private final T context;
193 
194         // synchronize on watch key to access/increment count
195         private int count;
196 
Event(WatchEvent.Kind<T> type, T context)197         Event(WatchEvent.Kind<T> type, T context) {
198             this.kind = type;
199             this.context = context;
200             this.count = 1;
201         }
202 
203         @Override
kind()204         public WatchEvent.Kind<T> kind() {
205             return kind;
206         }
207 
208         @Override
context()209         public T context() {
210             return context;
211         }
212 
213         @Override
count()214         public int count() {
215             return count;
216         }
217 
218         // for repeated events
increment()219         void increment() {
220             count++;
221         }
222     }
223 }
224