# ReentrantReadWriteLock.ReadLock

public static class **ReentrantReadWriteLock.ReadLock** extends [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)  
implements [Lock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Lock.html) [Serializable](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/Serializable.html) The lock returned by method `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.html#readLock()`.

### Protected Constructor Summary

|---|---|
|   | [ReadLock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.ReadLock.html#ReadLock(java.util.concurrent.locks.ReentrantReadWriteLock))([ReentrantReadWriteLock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.html) lock) Constructor for use by subclasses. |

### Public Method Summary

|---|---|
| void | [lock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.ReadLock.html#lock())() Acquires the read lock. |
| void | [lockInterruptibly](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.ReadLock.html#lockInterruptibly())() Acquires the read lock unless the current thread is {@linkplain Thread#interrupt interrupted}. |
| [Condition](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Condition.html) | [newCondition](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.ReadLock.html#newCondition())() Throws `UnsupportedOperationException` because `ReadLocks` do not support conditions. |
| [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.ReadLock.html#toString())() Returns a string identifying this lock, as well as its lock state. |
| boolean | [tryLock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.ReadLock.html#tryLock())() Acquires the read lock only if the write lock is not held by another thread at the time of invocation. |
| boolean | [tryLock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.ReadLock.html#tryLock(long,%20java.util.concurrent.TimeUnit))(long timeout, [TimeUnit](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/TimeUnit.html) 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 {@linkplain Thread#interrupt interrupted}. |
| void | [unlock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.ReadLock.html#unlock())() Attempts to release this lock. |

### Inherited Method Summary

From class [java.lang.Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)

|---|---|
| [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#clone())() Creates and returns a copy of this `Object`. |
| boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) obj) Compares this instance with the specified object and indicates if they are equal. |
| void | [finalize](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#finalize())() Invoked when the garbage collector has detected that this instance is no longer reachable. |
| final [Class](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> | [getClass](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#getClass())() Returns the unique instance of `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html` that represents this object's class. |
| int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#hashCode())() Returns an integer hash code for this object. |
| final void | [notify](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#notify())() Causes a thread which is waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up. |
| final void | [notifyAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#notifyAll())() Causes all threads which are waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up. |
| [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#toString())() Returns a string containing a concise, human-readable description of this object. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long,%20int))(long timeout, int nanos) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long))(long timeout) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait())() Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object. |

From interface [java.util.concurrent.locks.Lock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Lock.html)

|---|---|
| abstract void | [lock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Lock.html#lock())() Acquires the lock. |
| abstract void | [lockInterruptibly](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Lock.html#lockInterruptibly())() Acquires the lock unless the current thread is {@linkplain Thread#interrupt interrupted}. |
| abstract [Condition](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Condition.html) | [newCondition](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Lock.html#newCondition())() Returns a new `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Condition.html` instance that is bound to this `Lock` instance. |
| abstract boolean | [tryLock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Lock.html#tryLock())() Acquires the lock only if it is free at the time of invocation. |
| abstract boolean | [tryLock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Lock.html#tryLock(long,%20java.util.concurrent.TimeUnit))(long time, [TimeUnit](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/TimeUnit.html) unit) Acquires the lock if it is free within the given waiting time and the current thread has not been {@linkplain Thread#interrupt interrupted}. |
| abstract void | [unlock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Lock.html#unlock())() Releases the lock. |

## Protected Constructors

#### protected
**ReadLock**
([ReentrantReadWriteLock](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.html) lock)

Constructor for use by subclasses.

##### Parameters

| lock | the outer lock object |
|---|---|

##### Throws

| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the lock is null |
|---|---|

## Public Methods

#### 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.

#### public void
**lockInterruptibly**
()

Acquires the read lock unless the current thread is
{@linkplain Thread#interrupt 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 {@linkplain Thread#interrupt interrupts} the current thread.

If the current thread:

- has its interrupted status set on entry to this method; or
- is {@linkplain Thread#interrupt interrupted} while acquiring the read lock,

then `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/InterruptedException.html` 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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/InterruptedException.html) | if the current thread is interrupted |
|---|---|

#### public [Condition](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Condition.html)
**newCondition**
()

Throws `UnsupportedOperationException` because
`ReadLocks` do not support conditions.

##### Returns

- A new `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/Condition.html` instance for this `Lock` instance

##### Throws

| [UnsupportedOperationException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/UnsupportedOperationException.html) | always |
|---|---|

#### public [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html)
**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

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

#### 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 `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.ReadLock.html#tryLock(long,%20java.util.concurrent.TimeUnit)` 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](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/TimeUnit.html) 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 {@linkplain Thread#interrupt
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 `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/concurrent/locks/ReentrantReadWriteLock.ReadLock.html#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 {@linkplain Thread#interrupt 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 {@linkplain Thread#interrupt interrupted} while acquiring the read lock,

then `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/InterruptedException.html` 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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/InterruptedException.html) | if the current thread is interrupted |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the time unit is null |
|---|---|

#### 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 `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalMonitorStateException.html` is thrown.

##### Throws

| [IllegalMonitorStateException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalMonitorStateException.html) | if the current thread does not hold this lock |
|---|---|