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diff --git a/libjava/classpath/external/jsr166/java/util/concurrent/Semaphore.java b/libjava/classpath/external/jsr166/java/util/concurrent/Semaphore.java
new file mode 100644
index 000000000..105236439
--- /dev/null
+++ b/libjava/classpath/external/jsr166/java/util/concurrent/Semaphore.java
@@ -0,0 +1,681 @@
+/*
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent;
+import java.util.*;
+import java.util.concurrent.locks.*;
+import java.util.concurrent.atomic.*;
+
+/**
+ * A counting semaphore.  Conceptually, a semaphore maintains a set of
+ * permits.  Each {@link #acquire} blocks if necessary until a permit is
+ * available, and then takes it.  Each {@link #release} adds a permit,
+ * potentially releasing a blocking acquirer.
+ * However, no actual permit objects are used; the {@code Semaphore} just
+ * keeps a count of the number available and acts accordingly.
+ *
+ * <p>Semaphores are often used to restrict the number of threads than can
+ * access some (physical or logical) resource. For example, here is
+ * a class that uses a semaphore to control access to a pool of items:
+ * <pre>
+ * class Pool {
+ *   private static final int MAX_AVAILABLE = 100;
+ *   private final Semaphore available = new Semaphore(MAX_AVAILABLE, true);
+ *
+ *   public Object getItem() throws InterruptedException {
+ *     available.acquire();
+ *     return getNextAvailableItem();
+ *   }
+ *
+ *   public void putItem(Object x) {
+ *     if (markAsUnused(x))
+ *       available.release();
+ *   }
+ *
+ *   // Not a particularly efficient data structure; just for demo
+ *
+ *   protected Object[] items = ... whatever kinds of items being managed
+ *   protected boolean[] used = new boolean[MAX_AVAILABLE];
+ *
+ *   protected synchronized Object getNextAvailableItem() {
+ *     for (int i = 0; i < MAX_AVAILABLE; ++i) {
+ *       if (!used[i]) {
+ *          used[i] = true;
+ *          return items[i];
+ *       }
+ *     }
+ *     return null; // not reached
+ *   }
+ *
+ *   protected synchronized boolean markAsUnused(Object item) {
+ *     for (int i = 0; i < MAX_AVAILABLE; ++i) {
+ *       if (item == items[i]) {
+ *          if (used[i]) {
+ *            used[i] = false;
+ *            return true;
+ *          } else
+ *            return false;
+ *       }
+ *     }
+ *     return false;
+ *   }
+ *
+ * }
+ * </pre>
+ *
+ * <p>Before obtaining an item each thread must acquire a permit from
+ * the semaphore, guaranteeing that an item is available for use. When
+ * the thread has finished with the item it is returned back to the
+ * pool and a permit is returned to the semaphore, allowing another
+ * thread to acquire that item.  Note that no synchronization lock is
+ * held when {@link #acquire} is called as that would prevent an item
+ * from being returned to the pool.  The semaphore encapsulates the
+ * synchronization needed to restrict access to the pool, separately
+ * from any synchronization needed to maintain the consistency of the
+ * pool itself.
+ *
+ * <p>A semaphore initialized to one, and which is used such that it
+ * only has at most one permit available, can serve as a mutual
+ * exclusion lock.  This is more commonly known as a <em>binary
+ * semaphore</em>, because it only has two states: one permit
+ * available, or zero permits available.  When used in this way, the
+ * binary semaphore has the property (unlike many {@link Lock}
+ * implementations), that the &quot;lock&quot; can be released by a
+ * thread other than the owner (as semaphores have no notion of
+ * ownership).  This can be useful in some specialized contexts, such
+ * as deadlock recovery.
+ *
+ * <p> The constructor for this class optionally accepts a
+ * <em>fairness</em> parameter. When set false, this class makes no
+ * guarantees about the order in which threads acquire permits. In
+ * particular, <em>barging</em> is permitted, that is, a thread
+ * invoking {@link #acquire} can be allocated a permit ahead of a
+ * thread that has been waiting - logically the new thread places itself at
+ * the head of the queue of waiting threads. When fairness is set true, the
+ * semaphore guarantees that threads invoking any of the {@link
+ * #acquire() acquire} methods are selected to obtain permits in the order in
+ * which their invocation of those methods was processed
+ * (first-in-first-out; FIFO). Note that FIFO ordering necessarily
+ * applies to specific internal points of execution within these
+ * methods.  So, it is possible for one thread to invoke
+ * {@code acquire} before another, but reach the ordering point after
+ * the other, and similarly upon return from the method.
+ * Also note that the untimed {@link #tryAcquire() tryAcquire} methods do not
+ * honor the fairness setting, but will take any permits that are
+ * available.
+ *
+ * <p>Generally, semaphores used to control resource access should be
+ * initialized as fair, to ensure that no thread is starved out from
+ * accessing a resource. When using semaphores for other kinds of
+ * synchronization control, the throughput advantages of non-fair
+ * ordering often outweigh fairness considerations.
+ *
+ * <p>This class also provides convenience methods to {@link
+ * #acquire(int) acquire} and {@link #release(int) release} multiple
+ * permits at a time.  Beware of the increased risk of indefinite
+ * postponement when these methods are used without fairness set true.
+ *
+ * <p>Memory consistency effects: Actions in a thread prior to calling
+ * a "release" method such as {@code release()}
+ * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
+ * actions following a successful "acquire" method such as {@code acquire()}
+ * in another thread.
+ *
+ * @since 1.5
+ * @author Doug Lea
+ *
+ */
+
+public class Semaphore implements java.io.Serializable {
+    private static final long serialVersionUID = -3222578661600680210L;
+    /** All mechanics via AbstractQueuedSynchronizer subclass */
+    private final Sync sync;
+
+    /**
+     * Synchronization implementation for semaphore.  Uses AQS state
+     * to represent permits. Subclassed into fair and nonfair
+     * versions.
+     */
+    abstract static class Sync extends AbstractQueuedSynchronizer {
+        private static final long serialVersionUID = 1192457210091910933L;
+
+        Sync(int permits) {
+            setState(permits);
+        }
+
+        final int getPermits() {
+            return getState();
+        }
+
+        final int nonfairTryAcquireShared(int acquires) {
+            for (;;) {
+                int available = getState();
+                int remaining = available - acquires;
+                if (remaining < 0 ||
+                    compareAndSetState(available, remaining))
+                    return remaining;
+            }
+        }
+
+        protected final boolean tryReleaseShared(int releases) {
+            for (;;) {
+                int p = getState();
+                if (compareAndSetState(p, p + releases))
+                    return true;
+            }
+        }
+
+        final void reducePermits(int reductions) {
+            for (;;) {
+                int current = getState();
+                int next = current - reductions;
+                if (compareAndSetState(current, next))
+                    return;
+            }
+        }
+
+        final int drainPermits() {
+            for (;;) {
+                int current = getState();
+                if (current == 0 || compareAndSetState(current, 0))
+                    return current;
+            }
+        }
+    }
+
+    /**
+     * NonFair version
+     */
+    final static class NonfairSync extends Sync {
+        private static final long serialVersionUID = -2694183684443567898L;
+
+        NonfairSync(int permits) {
+            super(permits);
+        }
+
+        protected int tryAcquireShared(int acquires) {
+            return nonfairTryAcquireShared(acquires);
+        }
+    }
+
+    /**
+     * Fair version
+     */
+    final static class FairSync extends Sync {
+        private static final long serialVersionUID = 2014338818796000944L;
+
+        FairSync(int permits) {
+            super(permits);
+        }
+
+        protected int tryAcquireShared(int acquires) {
+            Thread current = Thread.currentThread();
+            for (;;) {
+                Thread first = getFirstQueuedThread();
+                if (first != null && first != current)
+                    return -1;
+                int available = getState();
+                int remaining = available - acquires;
+                if (remaining < 0 ||
+                    compareAndSetState(available, remaining))
+                    return remaining;
+            }
+        }
+    }
+
+    /**
+     * Creates a {@code Semaphore} with the given number of
+     * permits and nonfair fairness setting.
+     *
+     * @param permits the initial number of permits available.
+     *        This value may be negative, in which case releases
+     *        must occur before any acquires will be granted.
+     */
+    public Semaphore(int permits) {
+        sync = new NonfairSync(permits);
+    }
+
+    /**
+     * Creates a {@code Semaphore} with the given number of
+     * permits and the given fairness setting.
+     *
+     * @param permits the initial number of permits available.
+     *        This value may be negative, in which case releases
+     *        must occur before any acquires will be granted.
+     * @param fair {@code true} if this semaphore will guarantee
+     *        first-in first-out granting of permits under contention,
+     *        else {@code false}
+     */
+    public Semaphore(int permits, boolean fair) {
+        sync = (fair)? new FairSync(permits) : new NonfairSync(permits);
+    }
+
+    /**
+     * Acquires a permit from this semaphore, blocking until one is
+     * available, or the thread is {@linkplain Thread#interrupt interrupted}.
+     *
+     * <p>Acquires a permit, if one is available and returns immediately,
+     * reducing the number of available permits by one.
+     *
+     * <p>If no permit is available then the current thread becomes
+     * disabled for thread scheduling purposes and lies dormant until
+     * one of two things happens:
+     * <ul>
+     * <li>Some other thread invokes the {@link #release} method for this
+     * semaphore and the current thread is next to be assigned a permit; or
+     * <li>Some other thread {@linkplain Thread#interrupt interrupts}
+     * the current thread.
+     * </ul>
+     *
+     * <p>If the current thread:
+     * <ul>
+     * <li>has its interrupted status set on entry to this method; or
+     * <li>is {@linkplain Thread#interrupt interrupted} while waiting
+     * for a permit,
+     * </ul>
+     * then {@link InterruptedException} is thrown and the current thread's
+     * interrupted status is cleared.
+     *
+     * @throws InterruptedException if the current thread is interrupted
+     */
+    public void acquire() throws InterruptedException {
+        sync.acquireSharedInterruptibly(1);
+    }
+
+    /**
+     * Acquires a permit from this semaphore, blocking until one is
+     * available.
+     *
+     * <p>Acquires a permit, if one is available and returns immediately,
+     * reducing the number of available permits by one.
+     *
+     * <p>If no permit is available then the current thread becomes
+     * disabled for thread scheduling purposes and lies dormant until
+     * some other thread invokes the {@link #release} method for this
+     * semaphore and the current thread is next to be assigned a permit.
+     *
+     * <p>If the current thread is {@linkplain Thread#interrupt interrupted}
+     * while waiting for a permit then it will continue to wait, but the
+     * time at which the thread is assigned a permit may change compared to
+     * the time it would have received the permit had no interruption
+     * occurred.  When the thread does return from this method its interrupt
+     * status will be set.
+     */
+    public void acquireUninterruptibly() {
+        sync.acquireShared(1);
+    }
+
+    /**
+     * Acquires a permit from this semaphore, only if one is available at the
+     * time of invocation.
+     *
+     * <p>Acquires a permit, if one is available and returns immediately,
+     * with the value {@code true},
+     * reducing the number of available permits by one.
+     *
+     * <p>If no permit is available then this method will return
+     * immediately with the value {@code false}.
+     *
+     * <p>Even when this semaphore has been set to use a
+     * fair ordering policy, a call to {@code tryAcquire()} <em>will</em>
+     * immediately acquire a permit if one is available, whether or not
+     * other threads are currently waiting.
+     * This &quot;barging&quot; behavior can be useful in certain
+     * circumstances, even though it breaks fairness. If you want to honor
+     * the fairness setting, then use
+     * {@link #tryAcquire(long, TimeUnit) tryAcquire(0, TimeUnit.SECONDS) }
+     * which is almost equivalent (it also detects interruption).
+     *
+     * @return {@code true} if a permit was acquired and {@code false}
+     *         otherwise
+     */
+    public boolean tryAcquire() {
+        return sync.nonfairTryAcquireShared(1) >= 0;
+    }
+
+    /**
+     * Acquires a permit from this semaphore, if one becomes available
+     * within the given waiting time and the current thread has not
+     * been {@linkplain Thread#interrupt interrupted}.
+     *
+     * <p>Acquires a permit, if one is available and returns immediately,
+     * with the value {@code true},
+     * reducing the number of available permits by one.
+     *
+     * <p>If no permit is available then the current thread becomes
+     * disabled for thread scheduling purposes and lies dormant until
+     * one of three things happens:
+     * <ul>
+     * <li>Some other thread invokes the {@link #release} method for this
+     * semaphore and the current thread is next to be assigned a permit; or
+     * <li>Some other thread {@linkplain Thread#interrupt interrupts}
+     * the current thread; or
+     * <li>The specified waiting time elapses.
+     * </ul>
+     *
+     * <p>If a permit is acquired then the value {@code true} is returned.
+     *
+     * <p>If the current thread:
+     * <ul>
+     * <li>has its interrupted status set on entry to this method; or
+     * <li>is {@linkplain Thread#interrupt interrupted} while waiting
+     * to acquire a permit,
+     * </ul>
+     * then {@link InterruptedException} is thrown and the current thread's
+     * interrupted status is cleared.
+     *
+     * <p>If the specified waiting time elapses then the value {@code false}
+     * is returned.  If the time is less than or equal to zero, the method
+     * will not wait at all.
+     *
+     * @param timeout the maximum time to wait for a permit
+     * @param unit the time unit of the {@code timeout} argument
+     * @return {@code true} if a permit was acquired and {@code false}
+     *         if the waiting time elapsed before a permit was acquired
+     * @throws InterruptedException if the current thread is interrupted
+     */
+    public boolean tryAcquire(long timeout, TimeUnit unit)
+        throws InterruptedException {
+        return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
+    }
+
+    /**
+     * Releases a permit, returning it to the semaphore.
+     *
+     * <p>Releases a permit, increasing the number of available permits by
+     * one.  If any threads are trying to acquire a permit, then one is
+     * selected and given the permit that was just released.  That thread
+     * is (re)enabled for thread scheduling purposes.
+     *
+     * <p>There is no requirement that a thread that releases a permit must
+     * have acquired that permit by calling {@link #acquire}.
+     * Correct usage of a semaphore is established by programming convention
+     * in the application.
+     */
+    public void release() {
+        sync.releaseShared(1);
+    }
+
+    /**
+     * Acquires the given number of permits from this semaphore,
+     * blocking until all are available,
+     * or the thread is {@linkplain Thread#interrupt interrupted}.
+     *
+     * <p>Acquires the given number of permits, if they are available,
+     * and returns immediately, reducing the number of available permits
+     * by the given amount.
+     *
+     * <p>If insufficient permits are available then the current thread becomes
+     * disabled for thread scheduling purposes and lies dormant until
+     * one of two things happens:
+     * <ul>
+     * <li>Some other thread invokes one of the {@link #release() release}
+     * methods for this semaphore, the current thread is next to be assigned
+     * permits and the number of available permits satisfies this request; or
+     * <li>Some other thread {@linkplain Thread#interrupt interrupts}
+     * the current thread.
+     * </ul>
+     *
+     * <p>If the current thread:
+     * <ul>
+     * <li>has its interrupted status set on entry to this method; or
+     * <li>is {@linkplain Thread#interrupt interrupted} while waiting
+     * for a permit,
+     * </ul>
+     * then {@link InterruptedException} is thrown and the current thread's
+     * interrupted status is cleared.
+     * Any permits that were to be assigned to this thread are instead
+     * assigned to other threads trying to acquire permits, as if
+     * permits had been made available by a call to {@link #release()}.
+     *
+     * @param permits the number of permits to acquire
+     * @throws InterruptedException if the current thread is interrupted
+     * @throws IllegalArgumentException if {@code permits} is negative
+     */
+    public void acquire(int permits) throws InterruptedException {
+        if (permits < 0) throw new IllegalArgumentException();
+        sync.acquireSharedInterruptibly(permits);
+    }
+
+    /**
+     * Acquires the given number of permits from this semaphore,
+     * blocking until all are available.
+     *
+     * <p>Acquires the given number of permits, if they are available,
+     * and returns immediately, reducing the number of available permits
+     * by the given amount.
+     *
+     * <p>If insufficient permits are available then the current thread becomes
+     * disabled for thread scheduling purposes and lies dormant until
+     * some other thread invokes one of the {@link #release() release}
+     * methods for this semaphore, the current thread is next to be assigned
+     * permits and the number of available permits satisfies this request.
+     *
+     * <p>If the current thread is {@linkplain Thread#interrupt interrupted}
+     * while waiting for permits then it will continue to wait and its
+     * position in the queue is not affected.  When the thread does return
+     * from this method its interrupt status will be set.
+     *
+     * @param permits the number of permits to acquire
+     * @throws IllegalArgumentException if {@code permits} is negative
+     *
+     */
+    public void acquireUninterruptibly(int permits) {
+        if (permits < 0) throw new IllegalArgumentException();
+        sync.acquireShared(permits);
+    }
+
+    /**
+     * Acquires the given number of permits from this semaphore, only
+     * if all are available at the time of invocation.
+     *
+     * <p>Acquires the given number of permits, if they are available, and
+     * returns immediately, with the value {@code true},
+     * reducing the number of available permits by the given amount.
+     *
+     * <p>If insufficient permits are available then this method will return
+     * immediately with the value {@code false} and the number of available
+     * permits is unchanged.
+     *
+     * <p>Even when this semaphore has been set to use a fair ordering
+     * policy, a call to {@code tryAcquire} <em>will</em>
+     * immediately acquire a permit if one is available, whether or
+     * not other threads are currently waiting.  This
+     * &quot;barging&quot; behavior can be useful in certain
+     * circumstances, even though it breaks fairness. If you want to
+     * honor the fairness setting, then use {@link #tryAcquire(int,
+     * long, TimeUnit) tryAcquire(permits, 0, TimeUnit.SECONDS) }
+     * which is almost equivalent (it also detects interruption).
+     *
+     * @param permits the number of permits to acquire
+     * @return {@code true} if the permits were acquired and
+     *         {@code false} otherwise
+     * @throws IllegalArgumentException if {@code permits} is negative
+     */
+    public boolean tryAcquire(int permits) {
+        if (permits < 0) throw new IllegalArgumentException();
+        return sync.nonfairTryAcquireShared(permits) >= 0;
+    }
+
+    /**
+     * Acquires the given number of permits from this semaphore, if all
+     * become available within the given waiting time and the current
+     * thread has not been {@linkplain Thread#interrupt interrupted}.
+     *
+     * <p>Acquires the given number of permits, if they are available and
+     * returns immediately, with the value {@code true},
+     * reducing the number of available permits by the given amount.
+     *
+     * <p>If insufficient permits are available then
+     * the current thread becomes disabled for thread scheduling
+     * purposes and lies dormant until one of three things happens:
+     * <ul>
+     * <li>Some other thread invokes one of the {@link #release() release}
+     * methods for this semaphore, the current thread is next to be assigned
+     * permits and the number of available permits satisfies this request; or
+     * <li>Some other thread {@linkplain Thread#interrupt interrupts}
+     * the current thread; or
+     * <li>The specified waiting time elapses.
+     * </ul>
+     *
+     * <p>If the permits are acquired then the value {@code true} is returned.
+     *
+     * <p>If the current thread:
+     * <ul>
+     * <li>has its interrupted status set on entry to this method; or
+     * <li>is {@linkplain Thread#interrupt interrupted} while waiting
+     * to acquire the permits,
+     * </ul>
+     * then {@link InterruptedException} is thrown and the current thread's
+     * interrupted status is cleared.
+     * Any permits that were to be assigned to this thread, are instead
+     * assigned to other threads trying to acquire permits, as if
+     * the permits had been made available by a call to {@link #release()}.
+     *
+     * <p>If the specified waiting time elapses then the value {@code false}
+     * is returned.  If the time is less than or equal to zero, the method
+     * will not wait at all.  Any permits that were to be assigned to this
+     * thread, are instead assigned to other threads trying to acquire
+     * permits, as if the permits had been made available by a call to
+     * {@link #release()}.
+     *
+     * @param permits the number of permits to acquire
+     * @param timeout the maximum time to wait for the permits
+     * @param unit the time unit of the {@code timeout} argument
+     * @return {@code true} if all permits were acquired and {@code false}
+     *         if the waiting time elapsed before all permits were acquired
+     * @throws InterruptedException if the current thread is interrupted
+     * @throws IllegalArgumentException if {@code permits} is negative
+     */
+    public boolean tryAcquire(int permits, long timeout, TimeUnit unit)
+        throws InterruptedException {
+        if (permits < 0) throw new IllegalArgumentException();
+        return sync.tryAcquireSharedNanos(permits, unit.toNanos(timeout));
+    }
+
+    /**
+     * Releases the given number of permits, returning them to the semaphore.
+     *
+     * <p>Releases the given number of permits, increasing the number of
+     * available permits by that amount.
+     * If any threads are trying to acquire permits, then one
+     * is selected and given the permits that were just released.
+     * If the number of available permits satisfies that thread's request
+     * then that thread is (re)enabled for thread scheduling purposes;
+     * otherwise the thread will wait until sufficient permits are available.
+     * If there are still permits available
+     * after this thread's request has been satisfied, then those permits
+     * are assigned in turn to other threads trying to acquire permits.
+     *
+     * <p>There is no requirement that a thread that releases a permit must
+     * have acquired that permit by calling {@link Semaphore#acquire acquire}.
+     * Correct usage of a semaphore is established by programming convention
+     * in the application.
+     *
+     * @param permits the number of permits to release
+     * @throws IllegalArgumentException if {@code permits} is negative
+     */
+    public void release(int permits) {
+        if (permits < 0) throw new IllegalArgumentException();
+        sync.releaseShared(permits);
+    }
+
+    /**
+     * Returns the current number of permits available in this semaphore.
+     *
+     * <p>This method is typically used for debugging and testing purposes.
+     *
+     * @return the number of permits available in this semaphore
+     */
+    public int availablePermits() {
+        return sync.getPermits();
+    }
+
+    /**
+     * Acquires and returns all permits that are immediately available.
+     *
+     * @return the number of permits acquired
+     */
+    public int drainPermits() {
+        return sync.drainPermits();
+    }
+
+    /**
+     * Shrinks the number of available permits by the indicated
+     * reduction. This method can be useful in subclasses that use
+     * semaphores to track resources that become unavailable. This
+     * method differs from {@code acquire} in that it does not block
+     * waiting for permits to become available.
+     *
+     * @param reduction the number of permits to remove
+     * @throws IllegalArgumentException if {@code reduction} is negative
+     */
+    protected void reducePermits(int reduction) {
+        if (reduction < 0) throw new IllegalArgumentException();
+        sync.reducePermits(reduction);
+    }
+
+    /**
+     * Returns {@code true} if this semaphore has fairness set true.
+     *
+     * @return {@code true} if this semaphore has fairness set true
+     */
+    public boolean isFair() {
+        return sync instanceof FairSync;
+    }
+
+    /**
+     * Queries whether any threads are waiting to acquire. Note that
+     * because cancellations may occur at any time, a {@code true}
+     * return does not guarantee that any other thread will ever
+     * acquire.  This method is designed primarily for use in
+     * monitoring of the system state.
+     *
+     * @return {@code true} if there may be other threads waiting to
+     *         acquire the lock
+     */
+    public final boolean hasQueuedThreads() {
+        return sync.hasQueuedThreads();
+    }
+
+    /**
+     * Returns an estimate of the number of threads waiting to acquire.
+     * The value is only an estimate because the number of threads may
+     * change dynamically while this method traverses internal data
+     * structures.  This method is designed for use in monitoring of the
+     * system state, not for synchronization control.
+     *
+     * @return the estimated number of threads waiting for this lock
+     */
+    public final int getQueueLength() {
+        return sync.getQueueLength();
+    }
+
+    /**
+     * Returns a collection containing threads that may be waiting to acquire.
+     * Because the actual set of threads may change dynamically while
+     * constructing this result, the returned collection is only a best-effort
+     * estimate.  The elements of the returned collection are in no particular
+     * order.  This method is designed to facilitate construction of
+     * subclasses that provide more extensive monitoring facilities.
+     *
+     * @return the collection of threads
+     */
+    protected Collection<Thread> getQueuedThreads() {
+        return sync.getQueuedThreads();
+    }
+
+    /**
+     * Returns a string identifying this semaphore, as well as its state.
+     * The state, in brackets, includes the String {@code "Permits ="}
+     * followed by the number of permits.
+     *
+     * @return a string identifying this semaphore, as well as its state
+     */
+    public String toString() {
+        return super.toString() + "[Permits = " + sync.getPermits() + "]";
+    }
+}