public static class

ReentrantReadWriteLock.ReadLock

extends Object
implements Serializable Lock
java.lang.Object
   ↳ java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock

Class Overview

The lock returned by method readLock().

Summary

Protected Constructors
ReentrantReadWriteLock.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.
[Expand]
Inherited Methods
From class java.lang.Object
From interface java.util.concurrent.locks.Lock

Protected Constructors

protected ReentrantReadWriteLock.ReadLock (ReentrantReadWriteLock lock)

Since: API Level 1

Constructor for use by subclasses

Parameters
lock the outer lock object
Throws
NullPointerException if the lock is null

Public Methods

public void lock ()

Since: API Level 1

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.

public void lockInterruptibly ()

Since: API Level 1

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

public Condition newCondition ()

Since: API Level 1

Throws UnsupportedOperationException because ReadLocks do not support conditions.

Returns
  • A new Condition instance for this Lock instance
Throws
UnsupportedOperationException always

public String toString ()

Since: API Level 1

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
  • a string identifying this lock, as well as its lock state

public boolean tryLock ()

Since: API Level 1

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
  • true if the read lock was acquired

public boolean tryLock (long timeout, TimeUnit unit)

Since: API Level 1

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 the time to wait for the read lock
unit the time unit of the timeout argument
Returns
  • true if the read lock was acquired
Throws
InterruptedException if the current thread is interrupted
NullPointerException if the time unit is null

public void unlock ()

Since: API Level 1

Attempts to release this lock.

If the number of readers is now zero then the lock is made available for write lock attempts.