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jsr166 |
1.1 |
/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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jsr166 |
1.46 |
* http://creativecommons.org/publicdomain/zero/1.0/ |
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jsr166 |
1.1 |
*/ |
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package java.util.concurrent; |
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dl |
1.60 |
import java.security.AccessControlContext; |
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import java.security.ProtectionDomain; |
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jsr166 |
1.1 |
/** |
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jsr166 |
1.40 |
* A thread managed by a {@link ForkJoinPool}, which executes |
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* {@link ForkJoinTask}s. |
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* This class is subclassable solely for the sake of adding |
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* functionality -- there are no overridable methods dealing with |
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* scheduling or execution. However, you can override initialization |
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* and termination methods surrounding the main task processing loop. |
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* If you do create such a subclass, you will also need to supply a |
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jsr166 |
1.57 |
* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to |
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* {@linkplain ForkJoinPool#ForkJoinPool use it} in a {@code ForkJoinPool}. |
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1.1 |
* |
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* @since 1.7 |
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* @author Doug Lea |
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*/ |
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public class ForkJoinWorkerThread extends Thread { |
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/* |
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* ForkJoinWorkerThreads are managed by ForkJoinPools and perform |
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1.52 |
* ForkJoinTasks. For explanation, see the internal documentation |
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* of class ForkJoinPool. |
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1.55 |
* |
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* This class just maintains links to its pool and WorkQueue. The |
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* pool field is set immediately upon construction, but the |
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* workQueue field is not set until a call to registerWorker |
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* completes. This leads to a visibility race, that is tolerated |
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* by requiring that the workQueue field is only accessed by the |
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* owning thread. |
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1.60 |
* |
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* Support for (non-public) subclass InnocuousForkJoinWorkerThread |
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1.62 |
* requires that we break quite a lot of encapsulation (via Unsafe) |
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1.60 |
* both here and in the subclass to access and set Thread fields. |
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1.1 |
*/ |
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1.52 |
final ForkJoinPool pool; // the pool this thread works in |
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1.56 |
final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics |
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|
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/** |
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1.1 |
* Creates a ForkJoinWorkerThread operating in the given pool. |
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* |
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* @param pool the pool this thread works in |
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* @throws NullPointerException if pool is null |
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*/ |
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protected ForkJoinWorkerThread(ForkJoinPool pool) { |
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// Use a placeholder until a useful name can be set in registerWorker |
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super("aForkJoinWorkerThread"); |
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this.pool = pool; |
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this.workQueue = pool.registerWorker(this); |
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1.14 |
} |
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jsr166 |
1.1 |
/** |
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1.60 |
* Version for InnocuousForkJoinWorkerThread |
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*/ |
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ForkJoinWorkerThread(ForkJoinPool pool, ThreadGroup threadGroup, |
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AccessControlContext acc) { |
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super(threadGroup, null, "aForkJoinWorkerThread"); |
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U.putOrderedObject(this, INHERITEDACCESSCONTROLCONTEXT, acc); |
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eraseThreadLocals(); // clear before registering |
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this.pool = pool; |
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this.workQueue = pool.registerWorker(this); |
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} |
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/** |
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jsr166 |
1.1 |
* Returns the pool hosting this thread. |
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* |
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* @return the pool |
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*/ |
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public ForkJoinPool getPool() { |
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return pool; |
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} |
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/** |
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1.59 |
* Returns the unique index number of this thread in its pool. |
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* The returned value ranges from zero to the maximum number of |
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* threads (minus one) that may exist in the pool, and does not |
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* change during the lifetime of the thread. This method may be |
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* useful for applications that track status or collect results |
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* per-worker-thread rather than per-task. |
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1.1 |
* |
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* @return the index number |
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*/ |
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public int getPoolIndex() { |
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1.58 |
return workQueue.poolIndex >>> 1; // ignore odd/even tag bit |
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1.45 |
} |
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jsr166 |
1.1 |
/** |
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1.14 |
* Initializes internal state after construction but before |
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* processing any tasks. If you override this method, you must |
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jsr166 |
1.39 |
* invoke {@code super.onStart()} at the beginning of the method. |
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1.14 |
* Initialization requires care: Most fields must have legal |
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* default values, to ensure that attempted accesses from other |
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* threads work correctly even before this thread starts |
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* processing tasks. |
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jsr166 |
1.1 |
*/ |
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1.14 |
protected void onStart() { |
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} |
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1.1 |
|
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/** |
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1.14 |
* Performs cleanup associated with termination of this worker |
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* thread. If you override this method, you must invoke |
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* {@code super.onTermination} at the end of the overridden method. |
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jsr166 |
1.4 |
* |
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1.14 |
* @param exception the exception causing this thread to abort due |
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* to an unrecoverable error, or {@code null} if completed normally |
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jsr166 |
1.1 |
*/ |
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1.14 |
protected void onTermination(Throwable exception) { |
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jsr166 |
1.1 |
} |
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/** |
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* This method is required to be public, but should never be |
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* called explicitly. It performs the main run loop to execute |
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jsr166 |
1.40 |
* {@link ForkJoinTask}s. |
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jsr166 |
1.1 |
*/ |
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public void run() { |
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dl |
1.60 |
if (workQueue.array == null) { // only run once |
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Throwable exception = null; |
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1.52 |
try { |
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1.60 |
onStart(); |
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pool.runWorker(workQueue); |
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1.52 |
} catch (Throwable ex) { |
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1.60 |
exception = ex; |
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1.52 |
} finally { |
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1.60 |
try { |
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onTermination(exception); |
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} catch (Throwable ex) { |
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if (exception == null) |
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exception = ex; |
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} finally { |
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pool.deregisterWorker(this, exception); |
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} |
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} |
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} |
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} |
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/** |
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jsr166 |
1.63 |
* Erases ThreadLocals by nulling out Thread maps. |
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dl |
1.60 |
*/ |
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final void eraseThreadLocals() { |
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U.putObject(this, THREADLOCALS, null); |
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U.putObject(this, INHERITABLETHREADLOCALS, null); |
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} |
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/** |
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* Non-public hook method for InnocuousForkJoinWorkerThread |
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*/ |
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void afterTopLevelExec() { |
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} |
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// Set up to allow setting thread fields in constructor |
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private static final sun.misc.Unsafe U; |
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private static final long THREADLOCALS; |
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private static final long INHERITABLETHREADLOCALS; |
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private static final long INHERITEDACCESSCONTROLCONTEXT; |
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static { |
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try { |
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U = sun.misc.Unsafe.getUnsafe(); |
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Class<?> tk = Thread.class; |
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THREADLOCALS = U.objectFieldOffset |
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(tk.getDeclaredField("threadLocals")); |
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INHERITABLETHREADLOCALS = U.objectFieldOffset |
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(tk.getDeclaredField("inheritableThreadLocals")); |
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INHERITEDACCESSCONTROLCONTEXT = U.objectFieldOffset |
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(tk.getDeclaredField("inheritedAccessControlContext")); |
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} catch (Exception e) { |
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throw new Error(e); |
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} |
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} |
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/** |
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* A worker thread that has no permissions, is not a member of any |
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* user-defined ThreadGroup, and erases all ThreadLocals after |
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* running each top-level task. |
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*/ |
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static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread { |
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/** The ThreadGroup for all InnocuousForkJoinWorkerThreads */ |
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private static final ThreadGroup innocuousThreadGroup = |
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createThreadGroup(); |
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/** An AccessControlContext supporting no privileges */ |
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private static final AccessControlContext INNOCUOUS_ACC = |
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new AccessControlContext( |
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new ProtectionDomain[] { |
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new ProtectionDomain(null, null) |
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}); |
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InnocuousForkJoinWorkerThread(ForkJoinPool pool) { |
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super(pool, innocuousThreadGroup, INNOCUOUS_ACC); |
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} |
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@Override // to erase ThreadLocals |
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void afterTopLevelExec() { |
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eraseThreadLocals(); |
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} |
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@Override // to always report system loader |
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public ClassLoader getContextClassLoader() { |
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return ClassLoader.getSystemClassLoader(); |
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} |
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@Override // to silently fail |
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public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { } |
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@Override // paranoically |
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public void setContextClassLoader(ClassLoader cl) { |
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throw new SecurityException("setContextClassLoader"); |
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} |
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/** |
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* Returns a new group with the system ThreadGroup (the |
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jsr166 |
1.62 |
* topmost, parent-less group) as parent. Uses Unsafe to |
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jsr166 |
1.64 |
* traverse Thread.group and ThreadGroup.parent fields. |
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dl |
1.60 |
*/ |
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private static ThreadGroup createThreadGroup() { |
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try { |
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sun.misc.Unsafe u = sun.misc.Unsafe.getUnsafe(); |
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Class<?> tk = Thread.class; |
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Class<?> gk = ThreadGroup.class; |
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long tg = u.objectFieldOffset(tk.getDeclaredField("group")); |
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long gp = u.objectFieldOffset(gk.getDeclaredField("parent")); |
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ThreadGroup group = (ThreadGroup) |
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u.getObject(Thread.currentThread(), tg); |
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while (group != null) { |
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ThreadGroup parent = (ThreadGroup)u.getObject(group, gp); |
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if (parent == null) |
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return new ThreadGroup(group, |
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"InnocuousForkJoinWorkerThreadGroup"); |
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group = parent; |
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} |
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} catch (Exception e) { |
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throw new Error(e); |
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dl |
1.45 |
} |
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dl |
1.60 |
// fall through if null as cannot-happen safeguard |
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throw new Error("Cannot create ThreadGroup"); |
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dl |
1.45 |
} |
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jsr166 |
1.1 |
} |
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dl |
1.60 |
|
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jsr166 |
1.1 |
} |