- All Implemented Interfaces:
Serializable
,Lock
- Enclosing class:
- ReentrantReadWriteLock
public static class ReentrantReadWriteLock.ReadLock extends Object implements Lock, Serializable
ReentrantReadWriteLock.readLock()
.- See Also:
- Serialized Form
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Constructor Summary
ModifierConstructorDescriptionprotected
ReadLock(ReentrantReadWriteLock lock)
Constructor for use by subclasses. -
Method Summary
Modifier and TypeMethodDescriptionvoid
lock()
Acquires the read lock.void
Acquires the read lock unless the current thread is interrupted.ThrowsUnsupportedOperationException
becauseReadLocks
do not support conditions.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
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.
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Constructor Details
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ReadLock
Constructor for use by subclasses.- Parameters:
lock
- the outer lock object- Throws:
NullPointerException
- if the lock is null
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Method Details
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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.
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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,
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
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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 totryLock()
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 usetryLock(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
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tryLock
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 thetryLock()
method. If you want a timedtryLock
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 lockunit
- the time unit of the timeout argument- Returns:
true
if the read lock was acquired- Throws:
InterruptedException
- if the current thread is interruptedNullPointerException
- if the time unit is null
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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
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newCondition
ThrowsUnsupportedOperationException
becauseReadLocks
do not support conditions.- Specified by:
newCondition
in interfaceLock
- Returns:
- A new
Condition
instance for thisLock
instance - Throws:
UnsupportedOperationException
- always
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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.
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