ReadLock

open class ReadLock : Lock, Serializable

ReadLock

protected ReadLock(lock: ReentrantReadWriteLock!)

Constructor for use by subclasses.

Parameters
lock	ReentrantReadWriteLock!: the outer lock object

Exceptions
java.lang.NullPointerException	if the lock is null

lock

open fun lock(): Unit

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

open fun lockInterruptibly(): Unit

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.

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

newCondition

open fun newCondition(): Condition!

Throws UnsupportedOperationException because ReadLocks do not support conditions.

Return
Condition!	A new Condition instance for this Lock instance

Exceptions
java.lang.UnsupportedOperationException	always

toString

open fun toString(): String

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.

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

tryLock

open fun tryLock(): Boolean

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.

Return
Boolean	true if the read lock was acquired

tryLock

open fun tryLock(
    timeout: Long, 
    unit: TimeUnit!
): Boolean

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:

<code>if (lock.tryLock() ||
      lock.tryLock(timeout, unit)) {
    ...
  }</code>

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
time	the maximum time to wait for the lock
unit	TimeUnit!: the time unit of the timeout argument
timeout	Long: the time to wait for the read lock

Return
Boolean	true if the read lock was acquired

Exceptions
java.lang.InterruptedException	if the current thread is interrupted
java.lang.NullPointerException	if the time unit is null

unlock

open fun unlock(): Unit

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.

Exceptions
java.lang.IllegalMonitorStateException	if the current thread does not hold this lock