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tim |
1.1 |
/* |
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dl |
1.2 |
* Written by Doug Lea with assistance from members of JCP JSR-166 |
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dl |
1.23 |
* Expert Group and released to the public domain, as explained at |
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jsr166 |
1.59 |
* http://creativecommons.org/publicdomain/zero/1.0/ |
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tim |
1.1 |
*/ |
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package java.util.concurrent; |
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jsr166 |
1.108 |
|
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dl |
1.115 |
import java.lang.invoke.MethodHandles; |
10 |
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import java.lang.invoke.VarHandle; |
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dl |
1.62 |
import java.util.concurrent.locks.LockSupport; |
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dl |
1.13 |
|
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tim |
1.1 |
/** |
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dl |
1.8 |
* A cancellable asynchronous computation. This class provides a base |
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* implementation of {@link Future}, with methods to start and cancel |
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* a computation, query to see if the computation is complete, and |
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dl |
1.4 |
* retrieve the result of the computation. The result can only be |
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jsr166 |
1.64 |
* retrieved when the computation has completed; the {@code get} |
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* methods will block if the computation has not yet completed. Once |
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dl |
1.8 |
* the computation has completed, the computation cannot be restarted |
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jsr166 |
1.64 |
* or cancelled (unless the computation is invoked using |
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* {@link #runAndReset}). |
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tim |
1.1 |
* |
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jsr166 |
1.64 |
* <p>A {@code FutureTask} can be used to wrap a {@link Callable} or |
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* {@link Runnable} object. Because {@code FutureTask} implements |
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* {@code Runnable}, a {@code FutureTask} can be submitted to an |
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* {@link Executor} for execution. |
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tim |
1.1 |
* |
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dl |
1.14 |
* <p>In addition to serving as a standalone class, this class provides |
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jsr166 |
1.64 |
* {@code protected} functionality that may be useful when creating |
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dl |
1.14 |
* customized task classes. |
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* |
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tim |
1.1 |
* @since 1.5 |
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dl |
1.4 |
* @author Doug Lea |
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jsr166 |
1.64 |
* @param <V> The result type returned by this FutureTask's {@code get} methods |
36 |
tim |
1.1 |
*/ |
37 |
peierls |
1.39 |
public class FutureTask<V> implements RunnableFuture<V> { |
38 |
dl |
1.62 |
/* |
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* Revision notes: This differs from previous versions of this |
40 |
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* class that relied on AbstractQueuedSynchronizer, mainly to |
41 |
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* avoid surprising users about retaining interrupt status during |
42 |
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* cancellation races. Sync control in the current design relies |
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* on a "state" field updated via CAS to track completion, along |
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* with a simple Treiber stack to hold waiting threads. |
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*/ |
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/** |
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jsr166 |
1.73 |
* The run state of this task, initially NEW. The run state |
49 |
dl |
1.78 |
* transitions to a terminal state only in methods set, |
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* setException, and cancel. During completion, state may take on |
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* transient values of COMPLETING (while outcome is being set) or |
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* INTERRUPTING (only while interrupting the runner to satisfy a |
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* cancel(true)). Transitions from these intermediate to final |
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* states use cheaper ordered/lazy writes because values are unique |
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* and cannot be further modified. |
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jsr166 |
1.69 |
* |
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* Possible state transitions: |
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jsr166 |
1.73 |
* NEW -> COMPLETING -> NORMAL |
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* NEW -> COMPLETING -> EXCEPTIONAL |
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* NEW -> CANCELLED |
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* NEW -> INTERRUPTING -> INTERRUPTED |
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dl |
1.62 |
*/ |
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private volatile int state; |
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jsr166 |
1.73 |
private static final int NEW = 0; |
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jsr166 |
1.70 |
private static final int COMPLETING = 1; |
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private static final int NORMAL = 2; |
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private static final int EXCEPTIONAL = 3; |
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private static final int CANCELLED = 4; |
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private static final int INTERRUPTING = 5; |
70 |
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private static final int INTERRUPTED = 6; |
71 |
dl |
1.62 |
|
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dl |
1.78 |
/** The underlying callable; nulled out after running */ |
73 |
dl |
1.77 |
private Callable<V> callable; |
74 |
dl |
1.62 |
/** The result to return or exception to throw from get() */ |
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private Object outcome; // non-volatile, protected by state reads/writes |
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/** The thread running the callable; CASed during run() */ |
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private volatile Thread runner; |
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/** Treiber stack of waiting threads */ |
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private volatile WaitNode waiters; |
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/** |
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jsr166 |
1.64 |
* Returns result or throws exception for completed task. |
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* |
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dl |
1.62 |
* @param s completed state value |
85 |
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*/ |
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jsr166 |
1.98 |
@SuppressWarnings("unchecked") |
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dl |
1.62 |
private V report(int s) throws ExecutionException { |
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Object x = outcome; |
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jsr166 |
1.98 |
if (s == NORMAL) |
90 |
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return (V)x; |
91 |
jsr166 |
1.69 |
if (s >= CANCELLED) |
92 |
dl |
1.62 |
throw new CancellationException(); |
93 |
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throw new ExecutionException((Throwable)x); |
94 |
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} |
95 |
dl |
1.11 |
|
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tim |
1.1 |
/** |
97 |
jsr166 |
1.64 |
* Creates a {@code FutureTask} that will, upon running, execute the |
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* given {@code Callable}. |
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tim |
1.1 |
* |
100 |
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* @param callable the callable task |
101 |
jsr166 |
1.79 |
* @throws NullPointerException if the callable is null |
102 |
tim |
1.1 |
*/ |
103 |
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public FutureTask(Callable<V> callable) { |
104 |
dl |
1.9 |
if (callable == null) |
105 |
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throw new NullPointerException(); |
106 |
dl |
1.62 |
this.callable = callable; |
107 |
jsr166 |
1.85 |
this.state = NEW; // ensure visibility of callable |
108 |
tim |
1.1 |
} |
109 |
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110 |
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/** |
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jsr166 |
1.64 |
* Creates a {@code FutureTask} that will, upon running, execute the |
112 |
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* given {@code Runnable}, and arrange that {@code get} will return the |
113 |
tim |
1.1 |
* given result on successful completion. |
114 |
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* |
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jsr166 |
1.54 |
* @param runnable the runnable task |
116 |
tim |
1.1 |
* @param result the result to return on successful completion. If |
117 |
dl |
1.9 |
* you don't need a particular result, consider using |
118 |
dl |
1.16 |
* constructions of the form: |
119 |
jsr166 |
1.58 |
* {@code Future<?> f = new FutureTask<Void>(runnable, null)} |
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jsr166 |
1.79 |
* @throws NullPointerException if the runnable is null |
121 |
tim |
1.1 |
*/ |
122 |
dl |
1.15 |
public FutureTask(Runnable runnable, V result) { |
123 |
dl |
1.62 |
this.callable = Executors.callable(runnable, result); |
124 |
jsr166 |
1.85 |
this.state = NEW; // ensure visibility of callable |
125 |
dl |
1.20 |
} |
126 |
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127 |
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public boolean isCancelled() { |
128 |
jsr166 |
1.69 |
return state >= CANCELLED; |
129 |
dl |
1.20 |
} |
130 |
jsr166 |
1.35 |
|
131 |
dl |
1.20 |
public boolean isDone() { |
132 |
jsr166 |
1.73 |
return state != NEW; |
133 |
dl |
1.13 |
} |
134 |
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135 |
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public boolean cancel(boolean mayInterruptIfRunning) { |
136 |
dl |
1.115 |
if (!(state == NEW && STATE.compareAndSet |
137 |
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(this, NEW, mayInterruptIfRunning ? INTERRUPTING : CANCELLED))) |
138 |
dl |
1.78 |
return false; |
139 |
jsr166 |
1.102 |
try { // in case call to interrupt throws exception |
140 |
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if (mayInterruptIfRunning) { |
141 |
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try { |
142 |
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Thread t = runner; |
143 |
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if (t != null) |
144 |
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t.interrupt(); |
145 |
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} finally { // final state |
146 |
dl |
1.115 |
STATE.setRelease(this, INTERRUPTED); |
147 |
jsr166 |
1.102 |
} |
148 |
dl |
1.100 |
} |
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jsr166 |
1.102 |
} finally { |
150 |
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finishCompletion(); |
151 |
dl |
1.78 |
} |
152 |
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return true; |
153 |
dl |
1.13 |
} |
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jsr166 |
1.35 |
|
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jsr166 |
1.43 |
/** |
156 |
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* @throws CancellationException {@inheritDoc} |
157 |
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*/ |
158 |
dl |
1.2 |
public V get() throws InterruptedException, ExecutionException { |
159 |
jsr166 |
1.64 |
int s = state; |
160 |
jsr166 |
1.91 |
if (s <= COMPLETING) |
161 |
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s = awaitDone(false, 0L); |
162 |
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return report(s); |
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tim |
1.1 |
} |
164 |
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jsr166 |
1.43 |
/** |
166 |
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* @throws CancellationException {@inheritDoc} |
167 |
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*/ |
168 |
dl |
1.2 |
public V get(long timeout, TimeUnit unit) |
169 |
tim |
1.1 |
throws InterruptedException, ExecutionException, TimeoutException { |
170 |
jsr166 |
1.82 |
if (unit == null) |
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throw new NullPointerException(); |
172 |
jsr166 |
1.64 |
int s = state; |
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if (s <= COMPLETING && |
174 |
jsr166 |
1.82 |
(s = awaitDone(true, unit.toNanos(timeout))) <= COMPLETING) |
175 |
dl |
1.62 |
throw new TimeoutException(); |
176 |
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return report(s); |
177 |
tim |
1.1 |
} |
178 |
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dl |
1.121 |
@Override |
180 |
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public V resultNow() { |
181 |
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switch (state()) { // Future.State |
182 |
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case SUCCESS: |
183 |
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@SuppressWarnings("unchecked") |
184 |
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V result = (V) outcome; |
185 |
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return result; |
186 |
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case FAILED: |
187 |
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throw new IllegalStateException("Task completed with exception"); |
188 |
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case CANCELLED: |
189 |
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throw new IllegalStateException("Task was cancelled"); |
190 |
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default: |
191 |
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throw new IllegalStateException("Task has not completed"); |
192 |
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} |
193 |
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} |
194 |
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195 |
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@Override |
196 |
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public Throwable exceptionNow() { |
197 |
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switch (state()) { // Future.State |
198 |
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case SUCCESS: |
199 |
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throw new IllegalStateException("Task completed with a result"); |
200 |
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case FAILED: |
201 |
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Object x = outcome; |
202 |
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return (Throwable) x; |
203 |
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case CANCELLED: |
204 |
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throw new IllegalStateException("Task was cancelled"); |
205 |
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default: |
206 |
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throw new IllegalStateException("Task has not completed"); |
207 |
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} |
208 |
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} |
209 |
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210 |
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@Override |
211 |
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public State state() { |
212 |
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int s = state; |
213 |
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while (s == COMPLETING) { |
214 |
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// waiting for transition to NORMAL or EXCEPTIONAL |
215 |
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Thread.yield(); |
216 |
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s = state; |
217 |
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} |
218 |
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switch (s) { |
219 |
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case NORMAL: |
220 |
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return State.SUCCESS; |
221 |
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case EXCEPTIONAL: |
222 |
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return State.FAILED; |
223 |
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case CANCELLED: |
224 |
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case INTERRUPTING: |
225 |
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case INTERRUPTED: |
226 |
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return State.CANCELLED; |
227 |
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default: |
228 |
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return State.RUNNING; |
229 |
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} |
230 |
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} |
231 |
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tim |
1.1 |
/** |
233 |
dl |
1.20 |
* Protected method invoked when this task transitions to state |
234 |
jsr166 |
1.64 |
* {@code isDone} (whether normally or via cancellation). The |
235 |
dl |
1.20 |
* default implementation does nothing. Subclasses may override |
236 |
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* this method to invoke completion callbacks or perform |
237 |
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* bookkeeping. Note that you can query status inside the |
238 |
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* implementation of this method to determine whether this task |
239 |
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* has been cancelled. |
240 |
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*/ |
241 |
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protected void done() { } |
242 |
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243 |
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/** |
244 |
jsr166 |
1.64 |
* Sets the result of this future to the given value unless |
245 |
dl |
1.29 |
* this future has already been set or has been cancelled. |
246 |
jsr166 |
1.64 |
* |
247 |
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* <p>This method is invoked internally by the {@link #run} method |
248 |
dl |
1.40 |
* upon successful completion of the computation. |
249 |
jsr166 |
1.64 |
* |
250 |
tim |
1.1 |
* @param v the value |
251 |
jsr166 |
1.35 |
*/ |
252 |
dl |
1.2 |
protected void set(V v) { |
253 |
dl |
1.115 |
if (STATE.compareAndSet(this, NEW, COMPLETING)) { |
254 |
dl |
1.78 |
outcome = v; |
255 |
dl |
1.115 |
STATE.setRelease(this, NORMAL); // final state |
256 |
dl |
1.78 |
finishCompletion(); |
257 |
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} |
258 |
tim |
1.1 |
} |
259 |
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260 |
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/** |
261 |
jsr166 |
1.64 |
* Causes this future to report an {@link ExecutionException} |
262 |
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* with the given throwable as its cause, unless this future has |
263 |
dl |
1.24 |
* already been set or has been cancelled. |
264 |
jsr166 |
1.64 |
* |
265 |
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* <p>This method is invoked internally by the {@link #run} method |
266 |
dl |
1.40 |
* upon failure of the computation. |
267 |
jsr166 |
1.64 |
* |
268 |
jsr166 |
1.41 |
* @param t the cause of failure |
269 |
jsr166 |
1.35 |
*/ |
270 |
dl |
1.2 |
protected void setException(Throwable t) { |
271 |
dl |
1.115 |
if (STATE.compareAndSet(this, NEW, COMPLETING)) { |
272 |
dl |
1.78 |
outcome = t; |
273 |
dl |
1.115 |
STATE.setRelease(this, EXCEPTIONAL); // final state |
274 |
dl |
1.78 |
finishCompletion(); |
275 |
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} |
276 |
tim |
1.1 |
} |
277 |
jsr166 |
1.35 |
|
278 |
dl |
1.24 |
public void run() { |
279 |
jsr166 |
1.87 |
if (state != NEW || |
280 |
dl |
1.115 |
!RUNNER.compareAndSet(this, null, Thread.currentThread())) |
281 |
jsr166 |
1.87 |
return; |
282 |
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try { |
283 |
dl |
1.77 |
Callable<V> c = callable; |
284 |
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if (c != null && state == NEW) { |
285 |
jsr166 |
1.87 |
V result; |
286 |
jsr166 |
1.92 |
boolean ran; |
287 |
dl |
1.77 |
try { |
288 |
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result = c.call(); |
289 |
jsr166 |
1.92 |
ran = true; |
290 |
dl |
1.77 |
} catch (Throwable ex) { |
291 |
jsr166 |
1.92 |
result = null; |
292 |
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ran = false; |
293 |
dl |
1.77 |
setException(ex); |
294 |
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} |
295 |
jsr166 |
1.92 |
if (ran) |
296 |
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set(result); |
297 |
dl |
1.62 |
} |
298 |
jsr166 |
1.87 |
} finally { |
299 |
jsr166 |
1.93 |
// runner must be non-null until state is settled to |
300 |
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// prevent concurrent calls to run() |
301 |
jsr166 |
1.68 |
runner = null; |
302 |
jsr166 |
1.93 |
// state must be re-read after nulling runner to prevent |
303 |
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// leaked interrupts |
304 |
jsr166 |
1.86 |
int s = state; |
305 |
|
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if (s >= INTERRUPTING) |
306 |
|
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handlePossibleCancellationInterrupt(s); |
307 |
dl |
1.62 |
} |
308 |
dl |
1.24 |
} |
309 |
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|
310 |
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/** |
311 |
dl |
1.30 |
* Executes the computation without setting its result, and then |
312 |
jsr166 |
1.64 |
* resets this future to initial state, failing to do so if the |
313 |
dl |
1.24 |
* computation encounters an exception or is cancelled. This is |
314 |
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* designed for use with tasks that intrinsically execute more |
315 |
|
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* than once. |
316 |
jsr166 |
1.64 |
* |
317 |
jsr166 |
1.103 |
* @return {@code true} if successfully run and reset |
318 |
dl |
1.24 |
*/ |
319 |
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protected boolean runAndReset() { |
320 |
jsr166 |
1.87 |
if (state != NEW || |
321 |
dl |
1.115 |
!RUNNER.compareAndSet(this, null, Thread.currentThread())) |
322 |
jsr166 |
1.87 |
return false; |
323 |
jsr166 |
1.92 |
boolean ran = false; |
324 |
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int s = state; |
325 |
jsr166 |
1.87 |
try { |
326 |
dl |
1.77 |
Callable<V> c = callable; |
327 |
jsr166 |
1.92 |
if (c != null && s == NEW) { |
328 |
dl |
1.77 |
try { |
329 |
|
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c.call(); // don't set result |
330 |
jsr166 |
1.92 |
ran = true; |
331 |
dl |
1.77 |
} catch (Throwable ex) { |
332 |
|
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setException(ex); |
333 |
|
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} |
334 |
jsr166 |
1.68 |
} |
335 |
jsr166 |
1.87 |
} finally { |
336 |
jsr166 |
1.93 |
// runner must be non-null until state is settled to |
337 |
|
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// prevent concurrent calls to run() |
338 |
jsr166 |
1.68 |
runner = null; |
339 |
jsr166 |
1.93 |
// state must be re-read after nulling runner to prevent |
340 |
|
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// leaked interrupts |
341 |
jsr166 |
1.92 |
s = state; |
342 |
jsr166 |
1.87 |
if (s >= INTERRUPTING) |
343 |
|
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handlePossibleCancellationInterrupt(s); |
344 |
dl |
1.62 |
} |
345 |
jsr166 |
1.92 |
return ran && s == NEW; |
346 |
dl |
1.14 |
} |
347 |
dl |
1.3 |
|
348 |
dl |
1.14 |
/** |
349 |
jsr166 |
1.95 |
* Ensures that any interrupt from a possible cancel(true) is only |
350 |
|
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* delivered to a task while in run or runAndReset. |
351 |
jsr166 |
1.86 |
*/ |
352 |
|
|
private void handlePossibleCancellationInterrupt(int s) { |
353 |
|
|
// It is possible for our interrupter to stall before getting a |
354 |
|
|
// chance to interrupt us. Let's spin-wait patiently. |
355 |
jsr166 |
1.96 |
if (s == INTERRUPTING) |
356 |
|
|
while (state == INTERRUPTING) |
357 |
jsr166 |
1.86 |
Thread.yield(); // wait out pending interrupt |
358 |
jsr166 |
1.96 |
|
359 |
jsr166 |
1.89 |
// assert state == INTERRUPTED; |
360 |
jsr166 |
1.94 |
|
361 |
jsr166 |
1.95 |
// We want to clear any interrupt we may have received from |
362 |
|
|
// cancel(true). However, it is permissible to use interrupts |
363 |
|
|
// as an independent mechanism for a task to communicate with |
364 |
|
|
// its caller, and there is no way to clear only the |
365 |
|
|
// cancellation interrupt. |
366 |
|
|
// |
367 |
|
|
// Thread.interrupted(); |
368 |
jsr166 |
1.86 |
} |
369 |
|
|
|
370 |
|
|
/** |
371 |
dl |
1.62 |
* Simple linked list nodes to record waiting threads in a Treiber |
372 |
jsr166 |
1.64 |
* stack. See other classes such as Phaser and SynchronousQueue |
373 |
dl |
1.62 |
* for more detailed explanation. |
374 |
dl |
1.20 |
*/ |
375 |
dl |
1.62 |
static final class WaitNode { |
376 |
|
|
volatile Thread thread; |
377 |
dl |
1.76 |
volatile WaitNode next; |
378 |
|
|
WaitNode() { thread = Thread.currentThread(); } |
379 |
dl |
1.62 |
} |
380 |
dl |
1.42 |
|
381 |
dl |
1.62 |
/** |
382 |
jsr166 |
1.85 |
* Removes and signals all waiting threads, invokes done(), and |
383 |
|
|
* nulls out callable. |
384 |
dl |
1.62 |
*/ |
385 |
dl |
1.78 |
private void finishCompletion() { |
386 |
jsr166 |
1.90 |
// assert state > COMPLETING; |
387 |
jsr166 |
1.81 |
for (WaitNode q; (q = waiters) != null;) { |
388 |
jsr166 |
1.118 |
if (WAITERS.weakCompareAndSet(this, q, null)) { |
389 |
dl |
1.62 |
for (;;) { |
390 |
|
|
Thread t = q.thread; |
391 |
|
|
if (t != null) { |
392 |
|
|
q.thread = null; |
393 |
|
|
LockSupport.unpark(t); |
394 |
|
|
} |
395 |
|
|
WaitNode next = q.next; |
396 |
|
|
if (next == null) |
397 |
dl |
1.78 |
break; |
398 |
dl |
1.62 |
q.next = null; // unlink to help gc |
399 |
|
|
q = next; |
400 |
|
|
} |
401 |
dl |
1.78 |
break; |
402 |
dl |
1.62 |
} |
403 |
dl |
1.24 |
} |
404 |
jsr166 |
1.85 |
|
405 |
dl |
1.78 |
done(); |
406 |
jsr166 |
1.85 |
|
407 |
|
|
callable = null; // to reduce footprint |
408 |
dl |
1.62 |
} |
409 |
dl |
1.24 |
|
410 |
dl |
1.62 |
/** |
411 |
jsr166 |
1.64 |
* Awaits completion or aborts on interrupt or timeout. |
412 |
|
|
* |
413 |
dl |
1.62 |
* @param timed true if use timed waits |
414 |
jsr166 |
1.64 |
* @param nanos time to wait, if timed |
415 |
jsr166 |
1.105 |
* @return state upon completion or at timeout |
416 |
dl |
1.62 |
*/ |
417 |
|
|
private int awaitDone(boolean timed, long nanos) |
418 |
|
|
throws InterruptedException { |
419 |
jsr166 |
1.106 |
// The code below is very delicate, to achieve these goals: |
420 |
|
|
// - call nanoTime exactly once for each call to park |
421 |
jsr166 |
1.113 |
// - if nanos <= 0L, return promptly without allocation or nanoTime |
422 |
jsr166 |
1.106 |
// - if nanos == Long.MIN_VALUE, don't underflow |
423 |
|
|
// - if nanos == Long.MAX_VALUE, and nanoTime is non-monotonic |
424 |
|
|
// and we suffer a spurious wakeup, we will do no worse than |
425 |
|
|
// to park-spin for a while |
426 |
|
|
long startTime = 0L; // Special value 0L means not yet parked |
427 |
dl |
1.62 |
WaitNode q = null; |
428 |
|
|
boolean queued = false; |
429 |
jsr166 |
1.64 |
for (;;) { |
430 |
|
|
int s = state; |
431 |
|
|
if (s > COMPLETING) { |
432 |
dl |
1.62 |
if (q != null) |
433 |
|
|
q.thread = null; |
434 |
|
|
return s; |
435 |
|
|
} |
436 |
jsr166 |
1.111 |
else if (s == COMPLETING) |
437 |
|
|
// We may have already promised (via isDone) that we are done |
438 |
|
|
// so never return empty-handed or throw InterruptedException |
439 |
dl |
1.97 |
Thread.yield(); |
440 |
jsr166 |
1.111 |
else if (Thread.interrupted()) { |
441 |
|
|
removeWaiter(q); |
442 |
|
|
throw new InterruptedException(); |
443 |
|
|
} |
444 |
jsr166 |
1.106 |
else if (q == null) { |
445 |
|
|
if (timed && nanos <= 0L) |
446 |
|
|
return s; |
447 |
dl |
1.62 |
q = new WaitNode(); |
448 |
jsr166 |
1.106 |
} |
449 |
dl |
1.62 |
else if (!queued) |
450 |
jsr166 |
1.118 |
queued = WAITERS.weakCompareAndSet(this, q.next = waiters, q); |
451 |
dl |
1.62 |
else if (timed) { |
452 |
jsr166 |
1.106 |
final long parkNanos; |
453 |
|
|
if (startTime == 0L) { // first time |
454 |
|
|
startTime = System.nanoTime(); |
455 |
|
|
if (startTime == 0L) |
456 |
|
|
startTime = 1L; |
457 |
|
|
parkNanos = nanos; |
458 |
|
|
} else { |
459 |
|
|
long elapsed = System.nanoTime() - startTime; |
460 |
|
|
if (elapsed >= nanos) { |
461 |
|
|
removeWaiter(q); |
462 |
|
|
return state; |
463 |
|
|
} |
464 |
|
|
parkNanos = nanos - elapsed; |
465 |
dl |
1.50 |
} |
466 |
jsr166 |
1.107 |
// nanoTime may be slow; recheck before parking |
467 |
|
|
if (state < COMPLETING) |
468 |
|
|
LockSupport.parkNanos(this, parkNanos); |
469 |
dl |
1.50 |
} |
470 |
dl |
1.62 |
else |
471 |
|
|
LockSupport.park(this); |
472 |
dl |
1.24 |
} |
473 |
dl |
1.62 |
} |
474 |
dl |
1.24 |
|
475 |
dl |
1.62 |
/** |
476 |
jsr166 |
1.64 |
* Tries to unlink a timed-out or interrupted wait node to avoid |
477 |
|
|
* accumulating garbage. Internal nodes are simply unspliced |
478 |
dl |
1.62 |
* without CAS since it is harmless if they are traversed anyway |
479 |
jsr166 |
1.81 |
* by releasers. To avoid effects of unsplicing from already |
480 |
|
|
* removed nodes, the list is retraversed in case of an apparent |
481 |
|
|
* race. This is slow when there are a lot of nodes, but we don't |
482 |
|
|
* expect lists to be long enough to outweigh higher-overhead |
483 |
|
|
* schemes. |
484 |
dl |
1.62 |
*/ |
485 |
|
|
private void removeWaiter(WaitNode node) { |
486 |
|
|
if (node != null) { |
487 |
|
|
node.thread = null; |
488 |
jsr166 |
1.81 |
retry: |
489 |
|
|
for (;;) { // restart on removeWaiter race |
490 |
|
|
for (WaitNode pred = null, q = waiters, s; q != null; q = s) { |
491 |
|
|
s = q.next; |
492 |
|
|
if (q.thread != null) |
493 |
|
|
pred = q; |
494 |
|
|
else if (pred != null) { |
495 |
|
|
pred.next = s; |
496 |
|
|
if (pred.thread == null) // check for race |
497 |
|
|
continue retry; |
498 |
|
|
} |
499 |
dl |
1.115 |
else if (!WAITERS.compareAndSet(this, q, s)) |
500 |
jsr166 |
1.81 |
continue retry; |
501 |
jsr166 |
1.55 |
} |
502 |
jsr166 |
1.81 |
break; |
503 |
jsr166 |
1.56 |
} |
504 |
dl |
1.14 |
} |
505 |
dl |
1.62 |
} |
506 |
dl |
1.14 |
|
507 |
jsr166 |
1.119 |
/** |
508 |
|
|
* Returns a string representation of this FutureTask. |
509 |
|
|
* |
510 |
|
|
* @implSpec |
511 |
|
|
* The default implementation returns a string identifying this |
512 |
|
|
* FutureTask, as well as its completion state. The state, in |
513 |
|
|
* brackets, contains one of the strings {@code "Completed Normally"}, |
514 |
|
|
* {@code "Completed Exceptionally"}, {@code "Cancelled"}, or {@code |
515 |
|
|
* "Not completed"}. |
516 |
|
|
* |
517 |
|
|
* @return a string representation of this FutureTask |
518 |
|
|
*/ |
519 |
|
|
public String toString() { |
520 |
|
|
final String status; |
521 |
|
|
switch (state) { |
522 |
|
|
case NORMAL: |
523 |
|
|
status = "[Completed normally]"; |
524 |
|
|
break; |
525 |
|
|
case EXCEPTIONAL: |
526 |
|
|
status = "[Completed exceptionally: " + outcome + "]"; |
527 |
|
|
break; |
528 |
|
|
case CANCELLED: |
529 |
|
|
case INTERRUPTING: |
530 |
|
|
case INTERRUPTED: |
531 |
|
|
status = "[Cancelled]"; |
532 |
|
|
break; |
533 |
|
|
default: |
534 |
|
|
final Callable<?> callable = this.callable; |
535 |
|
|
status = (callable == null) |
536 |
|
|
? "[Not completed]" |
537 |
|
|
: "[Not completed, task = " + callable + "]"; |
538 |
|
|
} |
539 |
|
|
return super.toString() + status; |
540 |
|
|
} |
541 |
|
|
|
542 |
dl |
1.115 |
// VarHandle mechanics |
543 |
|
|
private static final VarHandle STATE; |
544 |
|
|
private static final VarHandle RUNNER; |
545 |
|
|
private static final VarHandle WAITERS; |
546 |
dl |
1.62 |
static { |
547 |
|
|
try { |
548 |
dl |
1.115 |
MethodHandles.Lookup l = MethodHandles.lookup(); |
549 |
|
|
STATE = l.findVarHandle(FutureTask.class, "state", int.class); |
550 |
|
|
RUNNER = l.findVarHandle(FutureTask.class, "runner", Thread.class); |
551 |
|
|
WAITERS = l.findVarHandle(FutureTask.class, "waiters", WaitNode.class); |
552 |
jsr166 |
1.109 |
} catch (ReflectiveOperationException e) { |
553 |
jsr166 |
1.120 |
throw new ExceptionInInitializerError(e); |
554 |
dl |
1.14 |
} |
555 |
jsr166 |
1.116 |
|
556 |
jsr166 |
1.112 |
// Reduce the risk of rare disastrous classloading in first call to |
557 |
|
|
// LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773 |
558 |
|
|
Class<?> ensureLoaded = LockSupport.class; |
559 |
dl |
1.15 |
} |
560 |
dl |
1.62 |
|
561 |
dl |
1.15 |
} |