Class ReentrantReadWriteLock.ReadLock
- java.lang.Object
-
- java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock
- All Implemented Interfaces:
-
Serializable
,Lock
- Enclosing class:
- ReentrantReadWriteLock
public static class ReentrantReadWriteLock.ReadLock extends Object implements Lock, Serializable
The lock returned by method ReadWriteLock.readLock()
.
- See Also:
- Serialized Form
Constructor Summary
Modifier | Constructor | Description |
---|---|---|
protected | ReadLock(ReentrantReadWriteLock lock) | Constructor for use by subclasses. |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
void | lock() | Acquires the read lock. |
void | lockInterruptibly() | Acquires the read lock unless the current thread is interrupted. |
Condition | newCondition() | Throws |
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. |
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Constructor Detail
ReadLock
protected ReadLock(ReentrantReadWriteLock lock)
Constructor for use by subclasses.
- Parameters:
-
lock
- the outer lock object - Throws:
-
NullPointerException
- if the lock is null
Method Detail
lock
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
public void lockInterruptibly() throws InterruptedException
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,
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.
- Specified by:
-
lockInterruptibly
in interfaceLock
- Throws:
-
InterruptedException
- if the current thread is interrupted
tryLock
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
.
tryLock
public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException
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,
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.
- Specified by:
-
tryLock
in interfaceLock
- 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
unlock
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.
- Specified by:
-
unlock
in interfaceLock
- Throws:
-
IllegalMonitorStateException
- if the current thread does not hold this lock
newCondition
public Condition newCondition()
Throws UnsupportedOperationException
because ReadLocks
do not support conditions.
- Specified by:
-
newCondition
in interfaceLock
- Returns:
- A new
Condition
instance for thisLock
instance - Throws:
-
UnsupportedOperationException
- always
toString
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.