org.atlasapi.util

Class GroupLock<T>

java.lang.Object

org.atlasapi.util.GroupLock<T>

Type Parameters:

T - - the type on which the lock acts.

public final class GroupLock<T>
extends Object

Lock multiple values simultaneously. This intended for use for controlling access by a number of threads to a number of resources, identified by values of type T.

This is not re-entrant: if the same thread attempts to lock the same value(s) twice it will block until interrupted.

Method Summary

Methods

Modifier and Type	Method and Description
static <U> GroupLock<U>	fromComparator(Comparator<? super U> comparator) Creates a new lock which uses the ordering of the provided comparator to determine the order in which locks on the value are acquired.
void	lock(Set<T> ids) Acquires locks on a number of ids progressively, in order specified by this locks ordering.
void	lock(T id) Lock the provided id so no other thread may lock it.
static <C extends Comparable<? super C>> GroupLock<C>	natural() Creates a new lock which uses the natural ordering of the value type to determine the order in which locks on the value are acquired.
boolean	tryLock(Set<T> ids) Attempt to lock all the ids.
boolean	tryLock(T id) Attempt to lock id, if it is not already locked.
void	unlock(Set<T> ids) Release locks on all the ids, if any were held.
void	unlock(T id) Release the lock held on id.

Methods inherited from class java.lang.Object

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

Method Detail

natural

public static final <C extends Comparable<? super C>> GroupLock<C> natural()

Creates a new lock which uses the natural ordering of the value type to determine the order in which locks on the value are acquired.

Returns:

a new GroupLock

fromComparator

public static final <U> GroupLock<U> fromComparator(Comparator<? super U> comparator)

Creates a new lock which uses the ordering of the provided comparator to determine the order in which locks on the value are acquired.

Returns:

a new GroupLock

lock

public void lock(T id)
          throws InterruptedException

Lock the provided id so no other thread may lock it. If the id is already locked then this thread blocks until awoken.

Whether or not this value has already been locked is determined by equality.

Parameters:

id - - the value on which to lock.

Throws:

InterruptedException - thread was interrupted whilst waiting for the lock.

unlock

public void unlock(T id)

Release the lock held on id. Any threads also attempting to lock this value will be awoken.

If the value is not locked then this call has no effect.

Parameters:

id - - the id to unlock

Throws:

InterruptedException

tryLock

public boolean tryLock(T id)
                throws InterruptedException

Attempt to lock id, if it is not already locked.

Parameters:

id - - the value to attempt to lock

Returns:

true if the value was successfully locked, false otherwise.

Throws:

InterruptedException - thread was interrupted whilst waiting for the lock.

lock

public void lock(Set<T> ids)
          throws InterruptedException

Acquires locks on a number of ids progressively, in order specified by this locks ordering.

E.g. if lock(Arrays.asList("A","B","C")) is called by Thread 1 whilst "C" is already locked by Thread 2 then Thread 1 blocks, holding locks on "A" and "B", until it can lock "C".

Parameters:

ids - - the values to lock

Throws:

InterruptedException - thread was interrupted whilst waiting for the lock.

unlock

public void unlock(Set<T> ids)

Release locks on all the ids, if any were held.

Parameters:

ids - = the values to unlock

tryLock

public boolean tryLock(Set<T> ids)
                throws InterruptedException

Attempt to lock all the ids. If not all can be locked then none are.

Parameters:

ids - - the values to attempt to lock

Returns:

true if all ids were locked, false otherwise.

Throws:

InterruptedException - thread was interrupted whilst waiting for the lock.