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3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4    *
5    * This code is free software; you can redistribute it and/or modify it
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7    * published by the Free Software Foundation.  Oracle designates this
8    * particular file as subject to the "Classpath" exception as provided
9    * by Oracle in the LICENSE file that accompanied this code.
10   *
11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
16   *
17   * You should have received a copy of the GNU General Public License version
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19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20   *
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24   */
25  
26  package java.lang;
27  
28  
29  /**
30   * Package-private utility class containing data structures and logic
31   * governing the virtual-machine shutdown sequence.
32   *
33   * @author   Mark Reinhold
34   * @since    1.3
35   */
36  
37  class Shutdown {
38  
39      /* Shutdown state */
40      private static final int RUNNING = 0;
41      private static final int HOOKS = 1;
42      private static final int FINALIZERS = 2;
43      private static int state = RUNNING;
44  
45      /* Should we run all finalizers upon exit? */
46      private static boolean runFinalizersOnExit = false;
47  
48      // The system shutdown hooks are registered with a predefined slot.
49      // The list of shutdown hooks is as follows:
50      // (0) Console restore hook
51      // (1) Application hooks
52      // (2) DeleteOnExit hook
53      private static final int MAX_SYSTEM_HOOKS = 10;
54      private static final Runnable[] hooks = new Runnable[MAX_SYSTEM_HOOKS];
55  
56      // the index of the currently running shutdown hook to the hooks array
57      private static int currentRunningHook = 0;
58  
59      /* The preceding static fields are protected by this lock */
60      private static class Lock { };
61      private static Object lock = new Lock();
62  
63      /* Lock object for the native halt method */
64      private static Object haltLock = new Lock();
65  
66      /* Invoked by Runtime.runFinalizersOnExit */
67      static void setRunFinalizersOnExit(boolean run) {
68          synchronized (lock) {
69              runFinalizersOnExit = run;
70          }
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       * The registerShutdownInProgress parameter should be false except
79       * registering the DeleteOnExitHook since the first file may
80       * be added to the delete on exit list by the application shutdown
81       * hooks.
82       *
83       * @params slot  the slot in the shutdown hook array, whose element
84       *               will be invoked in order during shutdown
85       * @params registerShutdownInProgress true to allow the hook
86       *               to be registered even if the shutdown is in progress.
87       * @params hook  the hook to be registered
88       *
89       * @throw IllegalStateException
90       *        if registerShutdownInProgress is false and shutdown is in progress; or
91       *        if registerShutdownInProgress is true and the shutdown process
92       *           already passes the given slot
93       */
94      static void add(int slot, boolean registerShutdownInProgress, Runnable hook) {
95          synchronized (lock) {
96              if (hooks[slot] != null)
97                  throw new InternalError("Shutdown hook at slot " + slot + " already registered");
98  
99              if (!registerShutdownInProgress) {
100                 if (state > RUNNING)
101                     throw new IllegalStateException("Shutdown in progress");
102             } else {
103                 if (state > HOOKS || (state == HOOKS && slot <= currentRunningHook))
104                     throw new IllegalStateException("Shutdown in progress");
105             }
106 
107             hooks[slot] = hook;
108         }
109     }
110 
111     /* Run all registered shutdown hooks
112      */
113     private static void runHooks() {
114         for (int i=0; i < MAX_SYSTEM_HOOKS; i++) {
115             try {
116                 Runnable hook;
117                 synchronized (lock) {
118                     // acquire the lock to make sure the hook registered during
119                     // shutdown is visible here.
120                     currentRunningHook = i;
121                     hook = hooks[i];
122                 }
123                 if (hook != null) hook.run();
124             } catch(Throwable t) {
125                 if (t instanceof ThreadDeath) {
126                     ThreadDeath td = (ThreadDeath)t;
127                     throw td;
128                 }
129             }
130         }
131     }
132 
133     /* The halt method is synchronized on the halt lock
134      * to avoid corruption of the delete-on-shutdown file list.
135      * It invokes the true native halt method.
136      */
137     static void halt(int status) {
138         synchronized (haltLock) {
139             halt0(status);
140         }
141     }
142 
143     static native void halt0(int status);
144 
145     /* Wormhole for invoking java.lang.ref.Finalizer.runAllFinalizers */
146     private static native void runAllFinalizers();
147 
148 
149     /* The actual shutdown sequence is defined here.
150      *
151      * If it weren't for runFinalizersOnExit, this would be simple -- we'd just
152      * run the hooks and then halt.  Instead we need to keep track of whether
153      * we're running hooks or finalizers.  In the latter case a finalizer could
154      * invoke exit(1) to cause immediate termination, while in the former case
155      * any further invocations of exit(n), for any n, simply stall.  Note that
156      * if on-exit finalizers are enabled they're run iff the shutdown is
157      * initiated by an exit(0); they're never run on exit(n) for n != 0 or in
158      * response to SIGINT, SIGTERM, etc.
159      */
160     private static void sequence() {
161         synchronized (lock) {
162             /* Guard against the possibility of a daemon thread invoking exit
163              * after DestroyJavaVM initiates the shutdown sequence
164              */
165             if (state != HOOKS) return;
166         }
167         runHooks();
168         boolean rfoe;
169         synchronized (lock) {
170             state = FINALIZERS;
171             rfoe = runFinalizersOnExit;
172         }
173         if (rfoe) runAllFinalizers();
174     }
175 
176 
177     /* Invoked by Runtime.exit, which does all the security checks.
178      * Also invoked by handlers for system-provided termination events,
179      * which should pass a nonzero status code.
180      */
181     static void exit(int status) {
182         boolean runMoreFinalizers = false;
183         synchronized (lock) {
184             if (status != 0) runFinalizersOnExit = false;
185             switch (state) {
186             case RUNNING:       /* Initiate shutdown */
187                 state = HOOKS;
188                 break;
189             case HOOKS:         /* Stall and halt */
190                 break;
191             case FINALIZERS:
192                 if (status != 0) {
193                     /* Halt immediately on nonzero status */
194                     halt(status);
195                 } else {
196                     /* Compatibility with old behavior:
197                      * Run more finalizers and then halt
198                      */
199                     runMoreFinalizers = runFinalizersOnExit;
200                 }
201                 break;
202             }
203         }
204         if (runMoreFinalizers) {
205             runAllFinalizers();
206             halt(status);
207         }
208         synchronized (Shutdown.class) {
209             /* Synchronize on the class object, causing any other thread
210              * that attempts to initiate shutdown to stall indefinitely
211              */
212             sequence();
213             halt(status);
214         }
215     }
216 
217 
218     /* Invoked by the JNI DestroyJavaVM procedure when the last non-daemon
219      * thread has finished.  Unlike the exit method, this method does not
220      * actually halt the VM.
221      */
222     static void shutdown() {
223         synchronized (lock) {
224             switch (state) {
225             case RUNNING:       /* Initiate shutdown */
226                 state = HOOKS;
227                 break;
228             case HOOKS:         /* Stall and then return */
229             case FINALIZERS:
230                 break;
231             }
232         }
233         synchronized (Shutdown.class) {
234             sequence();
235         }
236     }
237 
238 }