java.util.concurrent.locks

## Class AbstractQueuedLongSynchronizer

- java.lang.Object
- - java.util.concurrent.locks.AbstractOwnableSynchronizer
  - - java.util.concurrent.locks.AbstractQueuedLongSynchronizer

- All Implemented Interfaces:
    Serializable

      public abstract class AbstractQueuedLongSynchronizer
      extends AbstractOwnableSynchronizer
      implements Serializable

  A version of `AbstractQueuedSynchronizer` in which synchronization state is maintained as a `long`. This class has exactly the same structure, properties, and methods as `AbstractQueuedSynchronizer` with the exception that all state-related parameters and results are defined as `long` rather than `int`. This class may be useful when creating synchronizers such as multilevel locks and barriers that require 64 bits of state.

  See `AbstractQueuedSynchronizer` for usage notes and examples.

  Since:
    1.6
  Author:
    Doug Lea
  See Also:
    Serialized Form

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `class` | `AbstractQueuedLongSynchronizer.ConditionObject` Condition implementation for a `AbstractQueuedLongSynchronizer` serving as the basis of a `Lock` implementation.

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `AbstractQueuedLongSynchronizer()` Creates a new `AbstractQueuedLongSynchronizer` instance with initial synchronization state of zero.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `acquire(long arg)` Acquires in exclusive mode, ignoring interrupts.
    `void` | `acquireInterruptibly(long arg)` Acquires in exclusive mode, aborting if interrupted.
    `void` | `acquireShared(long arg)` Acquires in shared mode, ignoring interrupts.
    `void` | `acquireSharedInterruptibly(long arg)` Acquires in shared mode, aborting if interrupted.
    `protected boolean` | `compareAndSetState(long expect, long update)` Atomically sets synchronization state to the given updated value if the current state value equals the expected value.
    `Collection<Thread>` | `getExclusiveQueuedThreads()` Returns a collection containing threads that may be waiting to acquire in exclusive mode.
    `Thread` | `getFirstQueuedThread()` Returns the first (longest-waiting) thread in the queue, or `null` if no threads are currently queued.
    `Collection<Thread>` | `getQueuedThreads()` Returns a collection containing threads that may be waiting to acquire.
    `int` | `getQueueLength()` Returns an estimate of the number of threads waiting to acquire.
    `Collection<Thread>` | `getSharedQueuedThreads()` Returns a collection containing threads that may be waiting to acquire in shared mode.
    `protected long` | `getState()` Returns the current value of synchronization state.
    `Collection<Thread>` | `getWaitingThreads(AbstractQueuedLongSynchronizer.ConditionObject condition)` Returns a collection containing those threads that may be waiting on the given condition associated with this synchronizer.
    `int` | `getWaitQueueLength(AbstractQueuedLongSynchronizer.ConditionObject condition)` Returns an estimate of the number of threads waiting on the given condition associated with this synchronizer.
    `boolean` | `hasContended()` Queries whether any threads have ever contended to acquire this synchronizer; that is if an acquire method has ever blocked.
    `boolean` | `hasQueuedPredecessors()` Queries whether any threads have been waiting to acquire longer than the current thread.
    `boolean` | `hasQueuedThreads()` Queries whether any threads are waiting to acquire.
    `boolean` | `hasWaiters(AbstractQueuedLongSynchronizer.ConditionObject condition)` Queries whether any threads are waiting on the given condition associated with this synchronizer.
    `protected boolean` | `isHeldExclusively()` Returns `true` if synchronization is held exclusively with respect to the current (calling) thread.
    `boolean` | `isQueued(Thread thread)` Returns true if the given thread is currently queued.
    `boolean` | `owns(AbstractQueuedLongSynchronizer.ConditionObject condition)` Queries whether the given ConditionObject uses this synchronizer as its lock.
    `boolean` | `release(long arg)` Releases in exclusive mode.
    `boolean` | `releaseShared(long arg)` Releases in shared mode.
    `protected void` | `setState(long newState)` Sets the value of synchronization state.
    `String` | `toString()` Returns a string identifying this synchronizer, as well as its state.
    `protected boolean` | `tryAcquire(long arg)` Attempts to acquire in exclusive mode.
    `boolean` | `tryAcquireNanos(long arg, long nanosTimeout)` Attempts to acquire in exclusive mode, aborting if interrupted, and failing if the given timeout elapses.
    `protected long` | `tryAcquireShared(long arg)` Attempts to acquire in shared mode.
    `boolean` | `tryAcquireSharedNanos(long arg, long nanosTimeout)` Attempts to acquire in shared mode, aborting if interrupted, and failing if the given timeout elapses.
    `protected boolean` | `tryRelease(long arg)` Attempts to set the state to reflect a release in exclusive mode.
    `protected boolean` | `tryReleaseShared(long arg)` Attempts to set the state to reflect a release in shared mode.

    - ### Methods inherited from class java.util.concurrent.locks.AbstractOwnableSynchronizer

      `getExclusiveOwnerThread, setExclusiveOwnerThread`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### AbstractQueuedLongSynchronizer

          protected AbstractQueuedLongSynchronizer()

      Creates a new `AbstractQueuedLongSynchronizer` instance with initial synchronization state of zero.

  - ### Method Detail

    - #### getState

          protected final long getState()

      Returns the current value of synchronization state. This operation has memory semantics of a `volatile` read.
      Returns:
        current state value

    - #### setState

          protected final void setState(long newState)

      Sets the value of synchronization state. This operation has memory semantics of a `volatile` write.
      Parameters:
        `newState` - the new state value

    - #### compareAndSetState

          protected final boolean compareAndSetState(long expect,
                                                     long update)

      Atomically sets synchronization state to the given updated value if the current state value equals the expected value. This operation has memory semantics of a `volatile` read and write.
      Parameters:
        `expect` - the expected value
        `update` - the new value
      Returns:
        true if successful. False return indicates that the actual value was not equal to the expected value.

    - #### tryAcquire

          protected boolean tryAcquire(long arg)

      Attempts to acquire in exclusive mode. This method should query if the state of the object permits it to be acquired in the exclusive mode, and if so to acquire it.

      This method is always invoked by the thread performing acquire. If this method reports failure, the acquire method may queue the thread, if it is not already queued, until it is signalled by a release from some other thread. This can be used to implement method `Lock.tryLock()`.

      The default implementation throws `UnsupportedOperationException`.

      Parameters:
        `arg` - the acquire argument. This value is always the one passed to an acquire method, or is the value saved on entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like.
      Returns:
        `true` if successful. Upon success, this object has been acquired.
      Throws:
        `IllegalMonitorStateException` - if acquiring would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly.
        `UnsupportedOperationException` - if exclusive mode is not supported

    - #### tryRelease

          protected boolean tryRelease(long arg)

      Attempts to set the state to reflect a release in exclusive mode.

      This method is always invoked by the thread performing release.

      The default implementation throws `UnsupportedOperationException`.

      Parameters:
        `arg` - the release argument. This value is always the one passed to a release method, or the current state value upon entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like.
      Returns:
        `true` if this object is now in a fully released state, so that any waiting threads may attempt to acquire; and `false` otherwise.
      Throws:
        `IllegalMonitorStateException` - if releasing would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly.
        `UnsupportedOperationException` - if exclusive mode is not supported

    - #### tryAcquireShared

          protected long tryAcquireShared(long arg)

      Attempts to acquire in shared mode. This method should query if the state of the object permits it to be acquired in the shared mode, and if so to acquire it.

      This method is always invoked by the thread performing acquire. If this method reports failure, the acquire method may queue the thread, if it is not already queued, until it is signalled by a release from some other thread.

      The default implementation throws `UnsupportedOperationException`.

      Parameters:
        `arg` - the acquire argument. This value is always the one passed to an acquire method, or is the value saved on entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like.
      Returns:
        a negative value on failure; zero if acquisition in shared mode succeeded but no subsequent shared-mode acquire can succeed; and a positive value if acquisition in shared mode succeeded and subsequent shared-mode acquires might also succeed, in which case a subsequent waiting thread must check availability. (Support for three different return values enables this method to be used in contexts where acquires only sometimes act exclusively.) Upon success, this object has been acquired.
      Throws:
        `IllegalMonitorStateException` - if acquiring would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly.
        `UnsupportedOperationException` - if shared mode is not supported

    - #### tryReleaseShared

          protected boolean tryReleaseShared(long arg)

      Attempts to set the state to reflect a release in shared mode.

      This method is always invoked by the thread performing release.

      The default implementation throws `UnsupportedOperationException`.

      Parameters:
        `arg` - the release argument. This value is always the one passed to a release method, or the current state value upon entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like.
      Returns:
        `true` if this release of shared mode may permit a waiting acquire (shared or exclusive) to succeed; and `false` otherwise
      Throws:
        `IllegalMonitorStateException` - if releasing would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly.
        `UnsupportedOperationException` - if shared mode is not supported

    - #### isHeldExclusively

          protected boolean isHeldExclusively()

      Returns `true` if synchronization is held exclusively with respect to the current (calling) thread. This method is invoked upon each call to a non-waiting `AbstractQueuedLongSynchronizer.ConditionObject` method. (Waiting methods instead invoke `release(long)`.)

      The default implementation throws `UnsupportedOperationException`. This method is invoked internally only within `AbstractQueuedLongSynchronizer.ConditionObject` methods, so need not be defined if conditions are not used.

      Returns:
        `true` if synchronization is held exclusively; `false` otherwise
      Throws:
        `UnsupportedOperationException` - if conditions are not supported

    - #### acquire

          public final void acquire(long arg)

      Acquires in exclusive mode, ignoring interrupts. Implemented by invoking at least once `tryAcquire(long)`, returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking `tryAcquire(long)` until success. This method can be used to implement method `Lock.lock()`.
      Parameters:
        `arg` - the acquire argument. This value is conveyed to `tryAcquire(long)` but is otherwise uninterpreted and can represent anything you like.

    - #### acquireInterruptibly

          public final void acquireInterruptibly(long arg)
                                          throws InterruptedException

      Acquires in exclusive mode, aborting if interrupted. Implemented by first checking interrupt status, then invoking at least once `tryAcquire(long)`, returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking `tryAcquire(long)` until success or the thread is interrupted. This method can be used to implement method `Lock.lockInterruptibly()`.
      Parameters:
        `arg` - the acquire argument. This value is conveyed to `tryAcquire(long)` but is otherwise uninterpreted and can represent anything you like.
      Throws:
        `InterruptedException` - if the current thread is interrupted

    - #### tryAcquireNanos

          public final boolean tryAcquireNanos(long arg,
                                               long nanosTimeout)
                                        throws InterruptedException

      Attempts to acquire in exclusive mode, aborting if interrupted, and failing if the given timeout elapses. Implemented by first checking interrupt status, then invoking at least once `tryAcquire(long)`, returning on success. Otherwise, the thread is queued, possibly repeatedly blocking and unblocking, invoking `tryAcquire(long)` until success or the thread is interrupted or the timeout elapses. This method can be used to implement method `Lock.tryLock(long, TimeUnit)`.
      Parameters:
        `arg` - the acquire argument. This value is conveyed to `tryAcquire(long)` but is otherwise uninterpreted and can represent anything you like.
        `nanosTimeout` - the maximum number of nanoseconds to wait
      Returns:
        `true` if acquired; `false` if timed out
      Throws:
        `InterruptedException` - if the current thread is interrupted

    - #### release

          public final boolean release(long arg)

      Releases in exclusive mode. Implemented by unblocking one or more threads if `tryRelease(long)` returns true. This method can be used to implement method `Lock.unlock()`.
      Parameters:
        `arg` - the release argument. This value is conveyed to `tryRelease(long)` but is otherwise uninterpreted and can represent anything you like.
      Returns:
        the value returned from `tryRelease(long)`

    - #### acquireShared

          public final void acquireShared(long arg)

      Acquires in shared mode, ignoring interrupts. Implemented by first invoking at least once `tryAcquireShared(long)`, returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking `tryAcquireShared(long)` until success.
      Parameters:
        `arg` - the acquire argument. This value is conveyed to `tryAcquireShared(long)` but is otherwise uninterpreted and can represent anything you like.

    - #### acquireSharedInterruptibly

          public final void acquireSharedInterruptibly(long arg)
                                                throws InterruptedException

      Acquires in shared mode, aborting if interrupted. Implemented by first checking interrupt status, then invoking at least once `tryAcquireShared(long)`, returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking `tryAcquireShared(long)` until success or the thread is interrupted.
      Parameters:
        `arg` - the acquire argument This value is conveyed to `tryAcquireShared(long)` but is otherwise uninterpreted and can represent anything you like.
      Throws:
        `InterruptedException` - if the current thread is interrupted

    - #### tryAcquireSharedNanos

          public final boolean tryAcquireSharedNanos(long arg,
                                                     long nanosTimeout)
                                              throws InterruptedException

      Attempts to acquire in shared mode, aborting if interrupted, and failing if the given timeout elapses. Implemented by first checking interrupt status, then invoking at least once `tryAcquireShared(long)`, returning on success. Otherwise, the thread is queued, possibly repeatedly blocking and unblocking, invoking `tryAcquireShared(long)` until success or the thread is interrupted or the timeout elapses.
      Parameters:
        `arg` - the acquire argument. This value is conveyed to `tryAcquireShared(long)` but is otherwise uninterpreted and can represent anything you like.
        `nanosTimeout` - the maximum number of nanoseconds to wait
      Returns:
        `true` if acquired; `false` if timed out
      Throws:
        `InterruptedException` - if the current thread is interrupted

    - #### releaseShared

          public final boolean releaseShared(long arg)

      Releases in shared mode. Implemented by unblocking one or more threads if `tryReleaseShared(long)` returns true.
      Parameters:
        `arg` - the release argument. This value is conveyed to `tryReleaseShared(long)` but is otherwise uninterpreted and can represent anything you like.
      Returns:
        the value returned from `tryReleaseShared(long)`

    - #### hasQueuedThreads

          public final boolean hasQueuedThreads()

      Queries whether any threads are waiting to acquire. Note that because cancellations due to interrupts and timeouts may occur at any time, a `true` return does not guarantee that any other thread will ever acquire.

      In this implementation, this operation returns in constant time.

      Returns:
        `true` if there may be other threads waiting to acquire

    - #### hasContended

          public final boolean hasContended()

      Queries whether any threads have ever contended to acquire this synchronizer; that is if an acquire method has ever blocked.

      In this implementation, this operation returns in constant time.

      Returns:
        `true` if there has ever been contention

    - #### getFirstQueuedThread

          public final Thread getFirstQueuedThread()

      Returns the first (longest-waiting) thread in the queue, or `null` if no threads are currently queued.

      In this implementation, this operation normally returns in constant time, but may iterate upon contention if other threads are concurrently modifying the queue.

      Returns:
        the first (longest-waiting) thread in the queue, or `null` if no threads are currently queued

    - #### isQueued

          public final boolean isQueued(Thread thread)

      Returns true if the given thread is currently queued.

      This implementation traverses the queue to determine presence of the given thread.

      Parameters:
        `thread` - the thread
      Returns:
        `true` if the given thread is on the queue
      Throws:
        `NullPointerException` - if the thread is null

    - #### hasQueuedPredecessors

          public final boolean hasQueuedPredecessors()

      Queries whether any threads have been waiting to acquire longer than the current thread.

      An invocation of this method is equivalent to (but may be more efficient than):

           getFirstQueuedThread() != Thread.currentThread() &&
           hasQueuedThreads()

      Note that because cancellations due to interrupts and timeouts may occur at any time, a `true` return does not guarantee that some other thread will acquire before the current thread. Likewise, it is possible for another thread to win a race to enqueue after this method has returned `false`, due to the queue being empty.

      This method is designed to be used by a fair synchronizer to avoid barging. Such a synchronizer's `tryAcquire(long)` method should return `false`, and its `tryAcquireShared(long)` method should return a negative value, if this method returns `true` (unless this is a reentrant acquire). For example, the `tryAcquire` method for a fair, reentrant, exclusive mode synchronizer might look like this:

           protected boolean tryAcquire(int arg) {
             if (isHeldExclusively()) {
               // A reentrant acquire; increment hold count
               return true;
             } else if (hasQueuedPredecessors()) {
               return false;
             } else {
               // try to acquire normally
             }
           }

      Returns:
        `true` if there is a queued thread preceding the current thread, and `false` if the current thread is at the head of the queue or the queue is empty
      Since:
        1.7

    - #### getQueueLength

          public final int getQueueLength()

      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 system state, not for synchronization control.
      Returns:
        the estimated number of threads waiting to acquire

    - #### getQueuedThreads

          public final Collection<Thread> getQueuedThreads()

      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.
      Returns:
        the collection of threads

    - #### getExclusiveQueuedThreads

          public final Collection<Thread> getExclusiveQueuedThreads()

      Returns a collection containing threads that may be waiting to acquire in exclusive mode. This has the same properties as `getQueuedThreads()` except that it only returns those threads waiting due to an exclusive acquire.
      Returns:
        the collection of threads

    - #### getSharedQueuedThreads

          public final Collection<Thread> getSharedQueuedThreads()

      Returns a collection containing threads that may be waiting to acquire in shared mode. This has the same properties as `getQueuedThreads()` except that it only returns those threads waiting due to a shared acquire.
      Returns:
        the collection of threads

    - #### toString

          public String toString()

      Returns a string identifying this synchronizer, as well as its state. The state, in brackets, includes the String `"State ="` followed by the current value of `getState()`, and either `"nonempty"` or `"empty"` depending on whether the queue is empty.
      Overrides:
        `toString` in class `Object`
      Returns:
        a string identifying this synchronizer, as well as its state

    - #### owns

          public final boolean owns(AbstractQueuedLongSynchronizer.ConditionObject condition)

      Queries whether the given ConditionObject uses this synchronizer as its lock.
      Parameters:
        `condition` - the condition
      Returns:
        `true` if owned
      Throws:
        `NullPointerException` - if the condition is null

    - #### hasWaiters

          public final boolean hasWaiters(AbstractQueuedLongSynchronizer.ConditionObject condition)

      Queries whether any threads are waiting on the given condition associated with this synchronizer. Note that because timeouts and interrupts may occur at any time, a `true` return does not guarantee that a future `signal` will awaken any threads. This method is designed primarily for use in monitoring of the system state.
      Parameters:
        `condition` - the condition
      Returns:
        `true` if there are any waiting threads
      Throws:
        `IllegalMonitorStateException` - if exclusive synchronization is not held
        `IllegalArgumentException` - if the given condition is not associated with this synchronizer
        `NullPointerException` - if the condition is null

    - #### getWaitQueueLength

          public final int getWaitQueueLength(AbstractQueuedLongSynchronizer.ConditionObject condition)

      Returns an estimate of the number of threads waiting on the given condition associated with this synchronizer. Note that because timeouts and interrupts may occur at any time, the estimate serves only as an upper bound on the actual number of waiters. This method is designed for use in monitoring of the system state, not for synchronization control.
      Parameters:
        `condition` - the condition
      Returns:
        the estimated number of waiting threads
      Throws:
        `IllegalMonitorStateException` - if exclusive synchronization is not held
        `IllegalArgumentException` - if the given condition is not associated with this synchronizer
        `NullPointerException` - if the condition is null

    - #### getWaitingThreads

          public final Collection<Thread> getWaitingThreads(AbstractQueuedLongSynchronizer.ConditionObject condition)

      Returns a collection containing those threads that may be waiting on the given condition associated with this synchronizer. 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.
      Parameters:
        `condition` - the condition
      Returns:
        the collection of threads
      Throws:
        `IllegalMonitorStateException` - if exclusive synchronization is not held
        `IllegalArgumentException` - if the given condition is not associated with this synchronizer
        `NullPointerException` - if the condition is null

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