Added in API level 1

AbstractQueuedSynchronizer

abstract class AbstractQueuedSynchronizer : AbstractOwnableSynchronizer, Serializable

kotlin.Any
↳	java.util.concurrent.locks.AbstractOwnableSynchronizer
	↳	java.util.concurrent.locks.AbstractQueuedSynchronizer

Provides a framework for implementing blocking locks and related synchronizers (semaphores, events, etc) that rely on first-in-first-out (FIFO) wait queues. This class is designed to be a useful basis for most kinds of synchronizers that rely on a single atomic int value to represent state. Subclasses must define the protected methods that change this state, and which define what that state means in terms of this object being acquired or released. Given these, the other methods in this class carry out all queuing and blocking mechanics. Subclasses can maintain other state fields, but only the atomically updated int value manipulated using methods getState, setState and compareAndSetState is tracked with respect to synchronization.

Subclasses should be defined as non-public internal helper classes that are used to implement the synchronization properties of their enclosing class. Class AbstractQueuedSynchronizer does not implement any synchronization interface. Instead it defines methods such as acquireInterruptibly that can be invoked as appropriate by concrete locks and related synchronizers to implement their public methods.

This class supports either or both a default exclusive mode and a shared mode. When acquired in exclusive mode, attempted acquires by other threads cannot succeed. Shared mode acquires by multiple threads may (but need not) succeed. This class does not "understand" these differences except in the mechanical sense that when a shared mode acquire succeeds, the next waiting thread (if one exists) must also determine whether it can acquire as well. Threads waiting in the different modes share the same FIFO queue. Usually, implementation subclasses support only one of these modes, but both can come into play for example in a ReadWriteLock. Subclasses that support only exclusive or only shared modes need not define the methods supporting the unused mode.

This class defines a nested ConditionObject class that can be used as a Condition implementation by subclasses supporting exclusive mode for which method isHeldExclusively reports whether synchronization is exclusively held with respect to the current thread, method release invoked with the current getState value fully releases this object, and acquire, given this saved state value, eventually restores this object to its previous acquired state. No AbstractQueuedSynchronizer method otherwise creates such a condition, so if this constraint cannot be met, do not use it. The behavior of ConditionObject depends of course on the semantics of its synchronizer implementation.

This class provides inspection, instrumentation, and monitoring methods for the internal queue, as well as similar methods for condition objects. These can be exported as desired into classes using an AbstractQueuedSynchronizer for their synchronization mechanics.

Serialization of this class stores only the underlying atomic integer maintaining state, so deserialized objects have empty thread queues. Typical subclasses requiring serializability will define a readObject method that restores this to a known initial state upon deserialization.

Usage

To use this class as the basis of a synchronizer, redefine the following methods, as applicable, by inspecting and/or modifying the synchronization state using getState, setState and/or compareAndSetState:

• tryAcquire
• tryRelease
• tryAcquireShared
• tryReleaseShared
• isHeldExclusively

Each of these methods by default throws UnsupportedOperationException. Implementations of these methods must be internally thread-safe, and should in general be short and not block. Defining these methods is the only supported means of using this class. All other methods are declared final because they cannot be independently varied.

You may also find the inherited methods from AbstractOwnableSynchronizer useful to keep track of the thread owning an exclusive synchronizer. You are encouraged to use them -- this enables monitoring and diagnostic tools to assist users in determining which threads hold locks.

Even though this class is based on an internal FIFO queue, it does not automatically enforce FIFO acquisition policies. The core of exclusive synchronization takes the form:

<em>Acquire:</em>while (!tryAcquire(arg)) {
         <em>enqueue thread if it is not already queued</em>;
         <em>possibly block current thread</em>;
      }
 
  <em>Release:</em>if (tryRelease(arg))
         <em>unblock the first queued thread</em>;
  

(Shared mode is similar but may involve cascading signals.)

Because checks in acquire are invoked before enqueuing, a newly acquiring thread may barge ahead of others that are blocked and queued. However, you can, if desired, define tryAcquire and/or tryAcquireShared to disable barging by internally invoking one or more of the inspection methods, thereby providing a fair FIFO acquisition order. In particular, most fair synchronizers can define tryAcquire to return false if hasQueuedPredecessors (a method specifically designed to be used by fair synchronizers) returns true. Other variations are possible.

Throughput and scalability are generally highest for the default barging (also known as greedy, renouncement, and convoy-avoidance) strategy. While this is not guaranteed to be fair or starvation-free, earlier queued threads are allowed to recontend before later queued threads, and each recontention has an unbiased chance to succeed against incoming threads. Also, while acquires do not "spin" in the usual sense, they may perform multiple invocations of tryAcquire interspersed with other computations before blocking. This gives most of the benefits of spins when exclusive synchronization is only briefly held, without most of the liabilities when it isn't. If so desired, you can augment this by preceding calls to acquire methods with "fast-path" checks, possibly prechecking hasContended and/or hasQueuedThreads to only do so if the synchronizer is likely not to be contended.

This class provides an efficient and scalable basis for synchronization in part by specializing its range of use to synchronizers that can rely on int state, acquire, and release parameters, and an internal FIFO wait queue. When this does not suffice, you can build synchronizers from a lower level using atomic classes, your own custom java.util.Queue classes, and LockSupport blocking support.

Usage Examples

Here is a non-reentrant mutual exclusion lock class that uses the value zero to represent the unlocked state, and one to represent the locked state. While a non-reentrant lock does not strictly require recording of the current owner thread, this class does so anyway to make usage easier to monitor. It also supports conditions and exposes some instrumentation methods:

<code>class Mutex implements Lock, java.io.Serializable {
 
    // Our internal helper class
    private static class Sync extends AbstractQueuedSynchronizer {
      // Acquires the lock if state is zero
      public boolean tryAcquire(int acquires) {
        assert acquires == 1; // Otherwise unused
        if (compareAndSetState(0, 1)) {
          setExclusiveOwnerThread(Thread.currentThread());
          return true;
        }
        return false;
      }
 
      // Releases the lock by setting state to zero
      protected boolean tryRelease(int releases) {
        assert releases == 1; // Otherwise unused
        if (!isHeldExclusively())
          throw new IllegalMonitorStateException();
        setExclusiveOwnerThread(null);
        setState(0);
        return true;
      }
 
      // Reports whether in locked state
      public boolean isLocked() {
        return getState() != 0;
      }
 
      public boolean isHeldExclusively() {
        // a data race, but safe due to out-of-thin-air guarantees
        return getExclusiveOwnerThread() == Thread.currentThread();
      }
 
      // Provides a Condition
      public Condition newCondition() {
        return new ConditionObject();
      }
 
      // Deserializes properly
      private void readObject(ObjectInputStream s)
          throws IOException, ClassNotFoundException {
        s.defaultReadObject();
        setState(0); // reset to unlocked state
      }
    }
 
    // The sync object does all the hard work. We just forward to it.
    private final Sync sync = new Sync();
 
    public void lock()              { sync.acquire(1); }
    public boolean tryLock()        { return sync.tryAcquire(1); }
    public void unlock()            { sync.release(1); }
    public Condition newCondition() { return sync.newCondition(); }
    public boolean isLocked()       { return sync.isLocked(); }
    public boolean isHeldByCurrentThread() {
      return sync.isHeldExclusively();
    }
    public boolean hasQueuedThreads() {
      return sync.hasQueuedThreads();
    }
    public void lockInterruptibly() throws InterruptedException {
      sync.acquireInterruptibly(1);
    }
    public boolean tryLock(long timeout, TimeUnit unit)
        throws InterruptedException {
      return sync.tryAcquireNanos(1, unit.toNanos(timeout));
    }
  }</code>

Here is a latch class that is like a CountDownLatch except that it only requires a single signal to fire. Because a latch is non-exclusive, it uses the shared acquire and release methods.

<code>class BooleanLatch {
 
    private static class Sync extends AbstractQueuedSynchronizer {
      boolean isSignalled() { return getState() != 0; }
 
      protected int tryAcquireShared(int ignore) {
        return isSignalled() ? 1 : -1;
      }
 
      protected boolean tryReleaseShared(int ignore) {
        setState(1);
        return true;
      }
    }
 
    private final Sync sync = new Sync();
    public boolean isSignalled() { return sync.isSignalled(); }
    public void signal()         { sync.releaseShared(1); }
    public void await() throws InterruptedException {
      sync.acquireSharedInterruptibly(1);
    }
  }</code>

Summary

Nested classes
open	ConditionObject Condition implementation for a AbstractQueuedSynchronizer serving as the basis of a Lock implementation.

Protected constructors
AbstractQueuedSynchronizer() Creates a new AbstractQueuedSynchronizer instance with initial synchronization state of zero.

Public methods
Unit	acquire(arg: Int) Acquires in exclusive mode, ignoring interrupts.
Unit	acquireInterruptibly(arg: Int) Acquires in exclusive mode, aborting if interrupted.
Unit	acquireShared(arg: Int) Acquires in shared mode, ignoring interrupts.
Unit	acquireSharedInterruptibly(arg: Int) Acquires in shared mode, aborting if interrupted.
MutableCollection<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.
Int	getQueueLength() Returns an estimate of the number of threads waiting to acquire.
MutableCollection<Thread!>!	getQueuedThreads() Returns a collection containing threads that may be waiting to acquire.
MutableCollection<Thread!>!	getSharedQueuedThreads() Returns a collection containing threads that may be waiting to acquire in shared mode.
Int	getWaitQueueLength(condition: AbstractQueuedSynchronizer.ConditionObject!) Returns an estimate of the number of threads waiting on the given condition associated with this synchronizer.
MutableCollection<Thread!>!	getWaitingThreads(condition: AbstractQueuedSynchronizer.ConditionObject!) Returns a collection containing those threads that may be 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(condition: AbstractQueuedSynchronizer.ConditionObject!) Queries whether any threads are waiting on the given condition associated with this synchronizer.
Boolean	isQueued(thread: Thread!) Returns true if the given thread is currently queued.
Boolean	owns(condition: AbstractQueuedSynchronizer.ConditionObject!) Queries whether the given ConditionObject uses this synchronizer as its lock.
Boolean	release(arg: Int) Releases in exclusive mode.
Boolean	releaseShared(arg: Int) Releases in shared mode.
open String	toString() Returns a string identifying this synchronizer, as well as its state.
Boolean	tryAcquireNanos(arg: Int, nanosTimeout: Long) Attempts to acquire in exclusive mode, aborting if interrupted, and failing if the given timeout elapses.
Boolean	tryAcquireSharedNanos(arg: Int, nanosTimeout: Long) Attempts to acquire in shared mode, aborting if interrupted, and failing if the given timeout elapses.

Protected methods
Boolean	compareAndSetState(expect: Int, update: Int) Atomically sets synchronization state to the given updated value if the current state value equals the expected value.
Int	getState() Returns the current value of synchronization state.
open Boolean	isHeldExclusively() Returns true if synchronization is held exclusively with respect to the current (calling) thread.
Unit	setState(newState: Int) Sets the value of synchronization state.
open Boolean	tryAcquire(arg: Int) Attempts to acquire in exclusive mode.
open Int	tryAcquireShared(arg: Int) Attempts to acquire in shared mode.
open Boolean	tryRelease(arg: Int) Attempts to set the state to reflect a release in exclusive mode.
open Boolean	tryReleaseShared(arg: Int) Attempts to set the state to reflect a release in shared mode.

Inherited functions

From class AbstractOwnableSynchronizer Thread! getExclusiveOwnerThread() Returns the thread last set by setExclusiveOwnerThread, or null if never set. This method does not otherwise impose any synchronization or volatile field accesses. Unit setExclusiveOwnerThread(thread: Thread!) Sets the thread that currently owns exclusive access. A null argument indicates that no thread owns access. This method does not otherwise impose any synchronization or volatile field accesses.

Protected constructors

AbstractQueuedSynchronizer

Added in API level 1

protected AbstractQueuedSynchronizer()

Creates a new AbstractQueuedSynchronizer instance with initial synchronization state of zero.

Public methods

acquire

Added in API level 1

fun acquire(arg: Int): Unit

Acquires in exclusive mode, ignoring interrupts. Implemented by invoking at least once tryAcquire, returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquire until success. This method can be used to implement method Lock.lock.

Parameters
arg	Int: the acquire argument. This value is conveyed to tryAcquire but is otherwise uninterpreted and can represent anything you like.

acquireInterruptibly

Added in API level 1

fun acquireInterruptibly(arg: Int): Unit

Acquires in exclusive mode, aborting if interrupted. Implemented by first checking interrupt status, then invoking at least once tryAcquire, returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquire until success or the thread is interrupted. This method can be used to implement method Lock.lockInterruptibly.

Parameters
arg	Int: the acquire argument. This value is conveyed to tryAcquire but is otherwise uninterpreted and can represent anything you like.

Exceptions
java.lang.InterruptedException	if the current thread is interrupted

acquireShared

Added in API level 1

fun acquireShared(arg: Int): Unit

Acquires in shared mode, ignoring interrupts. Implemented by first invoking at least once tryAcquireShared, returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquireShared until success.

Parameters
arg	Int: the acquire argument. This value is conveyed to tryAcquireShared but is otherwise uninterpreted and can represent anything you like.

acquireSharedInterruptibly

Added in API level 1

fun acquireSharedInterruptibly(arg: Int): Unit

Acquires in shared mode, aborting if interrupted. Implemented by first checking interrupt status, then invoking at least once tryAcquireShared, returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquireShared until success or the thread is interrupted.

Parameters
arg	Int: the acquire argument. This value is conveyed to tryAcquireShared but is otherwise uninterpreted and can represent anything you like.

Exceptions
java.lang.InterruptedException	if the current thread is interrupted

getExclusiveQueuedThreads

Added in API level 1

fun getExclusiveQueuedThreads(): MutableCollection<Thread!>!

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.

Return
MutableCollection<Thread!>!	the collection of threads

getFirstQueuedThread

Added in API level 1

fun getFirstQueuedThread(): Thread!

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.

Return
Thread!	the first (longest-waiting) thread in the queue, or null if no threads are currently queued

getQueueLength

Added in API level 1

fun getQueueLength(): Int

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.

Return
Int	the estimated number of threads waiting to acquire

getQueuedThreads

Added in API level 1

fun getQueuedThreads(): MutableCollection<Thread!>!

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
MutableCollection<Thread!>!	the collection of threads

getSharedQueuedThreads

Added in API level 1

fun getSharedQueuedThreads(): MutableCollection<Thread!>!

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.

Return
MutableCollection<Thread!>!	the collection of threads

getWaitQueueLength

Added in API level 1

fun getWaitQueueLength(condition: AbstractQueuedSynchronizer.ConditionObject!): Int

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 system state, not for synchronization control.

Parameters
condition	AbstractQueuedSynchronizer.ConditionObject!: the condition

Return
Int	the estimated number of waiting threads

Exceptions
java.lang.IllegalMonitorStateException	if exclusive synchronization is not held
java.lang.IllegalArgumentException	if the given condition is not associated with this synchronizer
java.lang.NullPointerException	if the condition is null

getWaitingThreads

Added in API level 1

fun getWaitingThreads(condition: AbstractQueuedSynchronizer.ConditionObject!): MutableCollection<Thread!>!

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	AbstractQueuedSynchronizer.ConditionObject!: the condition

Return
MutableCollection<Thread!>!	the collection of threads

Exceptions
java.lang.IllegalMonitorStateException	if exclusive synchronization is not held
java.lang.IllegalArgumentException	if the given condition is not associated with this synchronizer
java.lang.NullPointerException	if the condition is null

hasContended

Added in API level 1

fun hasContended(): Boolean

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.

Return
Boolean	true if there has ever been contention

hasQueuedPredecessors

Added in API level 21

fun hasQueuedPredecessors(): Boolean

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):

<code>getFirstQueuedThread() != Thread.currentThread()
    &amp;&amp; hasQueuedThreads()</code>

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 method should return false, and its tryAcquireShared 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:

<code>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
    }
  }</code>

Return
Boolean	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

hasQueuedThreads

Added in API level 1

fun hasQueuedThreads(): Boolean

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.

Return
Boolean	true if there may be other threads waiting to acquire

hasWaiters

Added in API level 1

fun hasWaiters(condition: AbstractQueuedSynchronizer.ConditionObject!): Boolean

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	AbstractQueuedSynchronizer.ConditionObject!: the condition

Return
Boolean	true if there are any waiting threads

Exceptions
java.lang.IllegalMonitorStateException	if exclusive synchronization is not held
java.lang.IllegalArgumentException	if the given condition is not associated with this synchronizer
java.lang.NullPointerException	if the condition is null

isQueued

Added in API level 1

fun isQueued(thread: Thread!): Boolean

Returns true if the given thread is currently queued.

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

Parameters
thread	Thread!: the thread

Return
Boolean	true if the given thread is on the queue

Exceptions
java.lang.NullPointerException	if the thread is null

owns

Added in API level 1

fun owns(condition: AbstractQueuedSynchronizer.ConditionObject!): Boolean

Queries whether the given ConditionObject uses this synchronizer as its lock.

Parameters
condition	AbstractQueuedSynchronizer.ConditionObject!: the condition

Return
Boolean	true if owned

Exceptions
java.lang.NullPointerException	if the condition is null

release

Added in API level 1

fun release(arg: Int): Boolean

Releases in exclusive mode. Implemented by unblocking one or more threads if tryRelease returns true. This method can be used to implement method Lock.unlock.

Parameters
arg	Int: the release argument. This value is conveyed to tryRelease but is otherwise uninterpreted and can represent anything you like.

Return
Boolean	the value returned from tryRelease

releaseShared

Added in API level 1

fun releaseShared(arg: Int): Boolean

Releases in shared mode. Implemented by unblocking one or more threads if tryReleaseShared returns true.

Parameters
arg	Int: the release argument. This value is conveyed to tryReleaseShared but is otherwise uninterpreted and can represent anything you like.

Return
Boolean	the value returned from tryReleaseShared

toString

Added in API level 1

open fun toString(): String

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.

Return
String	a string identifying this synchronizer, as well as its state

tryAcquireNanos

Added in API level 1

fun tryAcquireNanos(
    arg: Int, 
    nanosTimeout: Long
): Boolean

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, returning on success. Otherwise, the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquire 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	Int: the acquire argument. This value is conveyed to tryAcquire but is otherwise uninterpreted and can represent anything you like.
nanosTimeout	Long: the maximum number of nanoseconds to wait

Return
Boolean	true if acquired; false if timed out

Exceptions
java.lang.InterruptedException	if the current thread is interrupted

tryAcquireSharedNanos

Added in API level 1

fun tryAcquireSharedNanos(
    arg: Int, 
    nanosTimeout: Long
): Boolean

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, returning on success. Otherwise, the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquireShared until success or the thread is interrupted or the timeout elapses.

Parameters
arg	Int: the acquire argument. This value is conveyed to tryAcquireShared but is otherwise uninterpreted and can represent anything you like.
nanosTimeout	Long: the maximum number of nanoseconds to wait

Return
Boolean	true if acquired; false if timed out

Exceptions
java.lang.InterruptedException	if the current thread is interrupted

Protected methods

compareAndSetState

Added in API level 1

protected fun compareAndSetState(
    expect: Int, 
    update: Int
): Boolean

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	Int: the expected value
update	Int: the new value

Return
Boolean	true if successful. False return indicates that the actual value was not equal to the expected value.

getState

Added in API level 1

protected fun getState(): Int

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

Return
Int	current state value

isHeldExclusively

Added in API level 1

protected open fun isHeldExclusively(): Boolean

Returns true if synchronization is held exclusively with respect to the current (calling) thread. This method is invoked upon each call to a ConditionObject method.

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

Return
Boolean	true if synchronization is held exclusively; false otherwise

Exceptions
java.lang.UnsupportedOperationException	if conditions are not supported

setState

Added in API level 1

protected fun setState(newState: Int): Unit

Sets the value of synchronization state. This operation has memory semantics of a volatile write.

Parameters
newState	Int: the new state value

tryAcquire

Added in API level 1

protected open fun tryAcquire(arg: Int): Boolean

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	Int: 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.

Return
Boolean	true if successful. Upon success, this object has been acquired.

Exceptions
java.lang.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.
java.lang.UnsupportedOperationException	if exclusive mode is not supported

tryAcquireShared

Added in API level 1

protected open fun tryAcquireShared(arg: Int): Int

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	Int: 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.

Return

Int

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.

Exceptions
java.lang.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.
java.lang.UnsupportedOperationException	if shared mode is not supported

tryRelease

Added in API level 1

protected open fun tryRelease(arg: Int): Boolean

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	Int: 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.

Return
Boolean	true if this object is now in a fully released state, so that any waiting threads may attempt to acquire; and false otherwise.

Exceptions
java.lang.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.
java.lang.UnsupportedOperationException	if exclusive mode is not supported

tryReleaseShared

Added in API level 1

protected open fun tryReleaseShared(arg: Int): Boolean

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	Int: 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.

Return
Boolean	true if this release of shared mode may permit a waiting acquire (shared or exclusive) to succeed; and false otherwise

Exceptions
java.lang.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.
java.lang.UnsupportedOperationException	if shared mode is not supported