Shutdown


1   /*
2    * @(#)Shutdown.java    1.11 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package java.lang;
9   
10  import java.util.HashSet  ;
11  import java.util.Iterator  ;
12  
13  
14  /**
15   * Package-private utility class containing data structures and logic
16   * governing the virtual-machine shutdown sequence.
17   *
18   * @author   Mark Reinhold
19   * @version  1.11, 03/12/19
20   * @since    1.3
21   */
22  
23  class Shutdown {
24  
25      /* Wrapper class for registered hooks, to ensure that hook identity is
26       * object identity rather than .equals identity
27       */
28      private static class WrappedHook {
29  
30      private Thread   hook;
31  
32      WrappedHook(Thread   t) {
33          hook = t;
34      }
35  
36      public int hashCode() {
37          return System.identityHashCode(hook);
38      }
39  
40      public boolean equals(Object   o) {
41          if (!(o instanceof WrappedHook)) return false;
42          return (((WrappedHook)o).hook == hook);
43      }
44  
45      }
46  
47  
48      /* Shutdown state */
49      private static final int RUNNING = 0;
50      private static final int HOOKS = 1;
51      private static final int FINALIZERS = 2;
52      private static int state = RUNNING;
53  
54      /* Should we run all finalizers upon exit? */
55      private static boolean runFinalizersOnExit = false;
56  
57      /* The set of registered, wrapped hooks, or null if there aren't any */
58      private static HashSet   hooks = null;
59  
60      /* The preceding static fields are protected by this lock */
61      private static class Lock { };
62      private static Object   lock = new Lock();
63  
64      /* Lock object for the native halt method */
65      private static Object   haltLock = new Lock();
66  
67      /* Invoked by Runtime.runFinalizersOnExit */
68      static void setRunFinalizersOnExit(boolean run) {
69      synchronized (lock) {
70          runFinalizersOnExit = run;
71      }
72      }
73  
74  
75      /* Add a new shutdown hook.  Checks the shutdown state and the hook itself,
76       * but does not do any security checks.
77       */
78      static void add(Thread   hook) {
79      synchronized (lock) {
80          if (state > RUNNING)
81          throw new IllegalStateException  ("Shutdown in progress");
82          if (hook.isAlive())
83          throw new IllegalArgumentException  ("Hook already running");
84          if (hooks == null) {
85          hooks = new HashSet  (11);
86          hooks.add(new WrappedHook(hook));
87          Terminator.setup();
88          } else {
89          WrappedHook wh = new WrappedHook(hook);
90          if (hooks.contains(wh))
91              throw new IllegalArgumentException  ("Hook previously registered");
92          hooks.add(wh);
93          }
94      }
95      }
96  
97  
98      /* Remove a previously-registered hook.  Like the add method, this method
99       * does not do any security checks.
100      */
101     static boolean remove(Thread   hook) {
102     synchronized (lock) {
103         if (state > RUNNING)
104         throw new IllegalStateException  ("Shutdown in progress");
105         if (hook == null) throw new NullPointerException  ();
106         if (hooks == null) {
107         return false;
108         } else {
109         boolean rv = hooks.remove(new WrappedHook(hook));
110         if (rv && hooks.isEmpty()) {
111             hooks = null;
112             Terminator.teardown();
113         }
114         return rv;
115         }
116     }
117     }
118 
119 
120     /* Run all registered shutdown hooks
121      */
122     private static void runHooks() {
123     /* We needn't bother acquiring the lock just to read the hooks field,
124      * since the hooks can't be modified once shutdown is in progress
125      */
126     if (hooks == null) return;
127     for (Iterator   i = hooks.iterator(); i.hasNext();) {
128         ((WrappedHook)(i.next())).hook.start();
129     }
130     for (Iterator   i = hooks.iterator(); i.hasNext();) {
131         try {
132         ((WrappedHook)(i.next())).hook.join();
133         } catch (InterruptedException   x) {
134         continue;
135         }
136     }
137     }
138 
139     /* The halt method is synchronized on the halt lock
140      * to avoid corruption of the delete-on-shutdown file list.
141      * It invokes the true native halt method.
142      */
143     static void halt(int status) {
144         synchronized (haltLock) {
145             halt0(status);
146         }
147     }
148 
149     static native void halt0(int status);
150 
151     /* Wormhole for invoking java.lang.ref.Finalizer.runAllFinalizers */
152     private static native void runAllFinalizers();
153 
154 
155     /* The actual shutdown sequence is defined here.
156      *
157      * If it weren't for runFinalizersOnExit, this would be simple -- we'd just
158      * run the hooks and then halt.  Instead we need to keep track of whether
159      * we're running hooks or finalizers.  In the latter case a finalizer could
160      * invoke exit(1) to cause immediate termination, while in the former case
161      * any further invocations of exit(n), for any n, simply stall.  Note that
162      * if on-exit finalizers are enabled they're run iff the shutdown is
163      * initiated by an exit(0); they're never run on exit(n) for n != 0 or in
164      * response to SIGINT, SIGTERM, etc.
165      */
166     private static void sequence() {
167     synchronized (lock) {
168         /* Guard against the possibility of a daemon thread invoking exit
169          * after DestroyJavaVM initiates the shutdown sequence
170          */
171         if (state != HOOKS) return;
172     }
173     runHooks();
174     boolean rfoe;
175     synchronized (lock) {
176         state = FINALIZERS;
177         rfoe = runFinalizersOnExit;
178     }
179     if (rfoe) runAllFinalizers();
180     }
181 
182 
183     /* Invoked by Runtime.exit, which does all the security checks.
184      * Also invoked by handlers for system-provided termination events,
185      * which should pass a nonzero status code.
186      */
187     static void exit(int status) {
188     boolean runMoreFinalizers = false;
189     synchronized (lock) {
190         if (status != 0) runFinalizersOnExit = false;
191         switch (state) {
192         case RUNNING:   /* Initiate shutdown */
193         state = HOOKS;
194         break;
195         case HOOKS:     /* Stall and halt */
196         break;
197         case FINALIZERS:
198         if (status != 0) {
199             /* Halt immediately on nonzero status */
200             halt(status);
201         } else {
202             /* Compatibility with old behavior:
203              * Run more finalizers and then halt
204              */
205             runMoreFinalizers = runFinalizersOnExit;
206         }
207         break;
208         }
209     }
210     if (runMoreFinalizers) {
211         runAllFinalizers();
212         halt(status);
213     }
214     synchronized (Shutdown  .class) {
215         /* Synchronize on the class object, causing any other thread
216              * that attempts to initiate shutdown to stall indefinitely
217          */
218         sequence();
219         halt(status);
220     }
221     }
222 
223 
224     /* Invoked by the JNI DestroyJavaVM procedure when the last non-daemon
225      * thread has finished.  Unlike the exit method, this method does not
226      * actually halt the VM.
227      */
228     static void shutdown() {
229     synchronized (lock) {
230         switch (state) {
231         case RUNNING:   /* Initiate shutdown */
232         state = HOOKS;
233         break;
234         case HOOKS:     /* Stall and then return */
235         case FINALIZERS:
236         break;
237         }
238     }
239     synchronized (Shutdown  .class) {
240         sequence();
241     }
242     }
243 
244 }
245
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