Added in API level 1

Summary: Protected Ctors | Methods | Inherited Methods

ReentrantReadWriteLock.ReadLock

public static class ReentrantReadWriteLock.ReadLock
extends Object implements Lock, Serializable

java.lang.Object
↳	java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock

---

The lock returned by method ReentrantReadWriteLock#readLock.

Summary

Protected constructors
ReadLock(ReentrantReadWriteLock lock) Constructor for use by subclasses.

Public methods
void	lock() Acquires the read lock.
void	lockInterruptibly() Acquires the read lock unless the current thread is interrupted.
Condition	newCondition() Throws UnsupportedOperationException because ReadLocks do not support conditions.
String	toString() Returns a string identifying this lock, as well as its lock state.
boolean	tryLock() Acquires the read lock only if the write lock is not held by another thread at the time of invocation.
boolean	tryLock(long timeout, TimeUnit unit) Acquires the read lock if the write lock is not held by another thread within the given waiting time and the current thread has not been interrupted.
void	unlock() Attempts to release this lock.

Inherited methods
From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait(long timeoutMillis, int nanos) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait(long timeoutMillis) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait() Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
From interface java.util.concurrent.locks.Lock abstract void lock() Acquires the lock. abstract void lockInterruptibly() Acquires the lock unless the current thread is interrupted. abstract Condition newCondition() Returns a new Condition instance that is bound to this Lock instance. abstract boolean tryLock() Acquires the lock only if it is free at the time of invocation. abstract boolean tryLock(long time, TimeUnit unit) Acquires the lock if it is free within the given waiting time and the current thread has not been interrupted. abstract void unlock() Releases the lock.

Protected constructors

ReadLock

Added in API level 1

protected ReadLock (ReentrantReadWriteLock lock)

Constructor for use by subclasses.

Parameters
lock	ReentrantReadWriteLock: the outer lock object

Throws
NullPointerException	if the lock is null

Public methods

lock

Added in API level 1

public void lock ()

Acquires the read lock.

Acquires the read lock if the write lock is not held by another thread and returns immediately.

If the write lock is held by another thread then the current thread becomes disabled for thread scheduling purposes and lies dormant until the read lock has been acquired.

lockInterruptibly

Added in API level 1

public void lockInterruptibly ()

Acquires the read lock unless the current thread is interrupted.

Acquires the read lock if the write lock is not held by another thread and returns immediately.

If the write lock is held by another thread then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of two things happens:

• The read lock is acquired by the current thread; or
• Some other thread interrupts the current thread.

If the current thread:

• has its interrupted status set on entry to this method; or
• is interrupted while acquiring the read lock,

then InterruptedException is thrown and the current thread's interrupted status is cleared.

In this implementation, as this method is an explicit interruption point, preference is given to responding to the interrupt over normal or reentrant acquisition of the lock.

Throws
InterruptedException	if the current thread is interrupted

newCondition

Added in API level 1

public Condition newCondition ()

Throws UnsupportedOperationException because ReadLocks do not support conditions.

Returns
Condition	A new Condition instance for this Lock instance

Throws
UnsupportedOperationException	always

toString

Added in API level 1

public String toString ()

Returns a string identifying this lock, as well as its lock state. The state, in brackets, includes the String "Read locks =" followed by the number of held read locks.

Returns
String	a string identifying this lock, as well as its lock state

tryLock

Added in API level 1

public boolean tryLock ()

Acquires the read lock only if the write lock is not held by another thread at the time of invocation.

Acquires the read lock if the write lock is not held by another thread and returns immediately with the value true. Even when this lock has been set to use a fair ordering policy, a call to tryLock() will immediately acquire the read lock if it is available, whether or not other threads are currently waiting for the read lock. This "barging" behavior can be useful in certain circumstances, even though it breaks fairness. If you want to honor the fairness setting for this lock, then use tryLock(0, TimeUnit.SECONDS) which is almost equivalent (it also detects interruption).

If the write lock is held by another thread then this method will return immediately with the value false.

Returns
boolean	true if the read lock was acquired

tryLock

Added in API level 1

public boolean tryLock (long timeout, 
                TimeUnit unit)

Acquires the read lock if the write lock is not held by another thread within the given waiting time and the current thread has not been interrupted.

Acquires the read lock if the write lock is not held by another thread and returns immediately with the value true. If this lock has been set to use a fair ordering policy then an available lock will not be acquired if any other threads are waiting for the lock. This is in contrast to the tryLock() method. If you want a timed tryLock that does permit barging on a fair lock then combine the timed and un-timed forms together:

 if (lock.tryLock() ||
     lock.tryLock(timeout, unit)) {
   ...
 }

If the write lock is held by another thread then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of three things happens:

• The read lock is acquired by the current thread; or
• Some other thread interrupts the current thread; or
• The specified waiting time elapses.

If the read lock is acquired then the value true is returned.

If the current thread:

• has its interrupted status set on entry to this method; or
• is interrupted while acquiring the read lock,

then InterruptedException is thrown and the current thread's interrupted status is cleared.

If the specified waiting time elapses then the value false is returned. If the time is less than or equal to zero, the method will not wait at all.

In this implementation, as this method is an explicit interruption point, preference is given to responding to the interrupt over normal or reentrant acquisition of the lock, and over reporting the elapse of the waiting time.

Parameters
timeout	long: the time to wait for the read lock
unit	TimeUnit: the time unit of the timeout argument

Returns
boolean	true if the read lock was acquired

Throws
InterruptedException	if the current thread is interrupted
NullPointerException	if the time unit is null

unlock

Added in API level 1

public void unlock ()

Attempts to release this lock.

If the number of readers is now zero then the lock is made available for write lock attempts. If the current thread does not hold this lock then IllegalMonitorStateException is thrown.

Throws
IllegalMonitorStateException	if the current thread does not hold this lock