Inheritance diagram for ReentrantReadWriteLock:
This class has the following properties:
This class does not impose a reader or writer preference ordering for lock access. However, it does support an optional fairness policy. When constructed as fair, threads contend for entry using an approximately arrival-order policy. When the write lock is released either the longest-waiting single writer will be assigned the write lock, or if there is a reader waiting longer than any writer, the set of readers will be assigned the read lock. When constructed as non-fair, the order of entry to the lock need not be in arrival order. In either case, if readers are active and a writer enters the lock then no subsequent readers will be granted the read lock until after that writer has acquired and released the write lock.
This lock allows both readers and writers to reacquire read or write locks in the style of a ReentrantLock. Readers are not allowed until all write locks held by the writing thread have been released.
Additionally, a writer can acquire the read lock - but not vice-versa. Among other applications, reentrancy can be useful when write locks are held during calls or callbacks to methods that perform reads under read locks. If a reader tries to acquire the write lock it will never succeed.
Reentrancy also allows downgrading from the write lock to a read lock, by acquiring the write lock, then the read lock and then releasing the write lock. However, upgrading from a read lock to the write lock, is not possible.
The write lock provides a Condition implementation that behaves in the same way, with respect to the write lock, as the Condition implementation provided by ReentrantLock.newCondition does for ReentrantLock. This Condition can, of course, only be used with the write lock.
The read lock does not support a Condition and readLock().newCondition()
throws UnsupportedOperationException
.
This class supports methods to determine whether locks are held or contended. These methods are designed for monitoring system state, not for synchronization control.
Sample usages. Here is a code sketch showing how to exploit reentrancy to perform lock downgrading after updating a cache (exception handling is elided for simplicity):
class CachedData { Object data; bool cacheValid; ReentrantReadWriteLock rwl; this() { rwl = new ReentrantReadWriteLock(); } void processCachedData() { rwl.readLock().lock(); if (!cacheValid) { // upgrade lock manually rwl.readLock().unlock(); // must unlock first to obtain writelock rwl.writeLock().lock(); if (!cacheValid) { // recheck data = ... cacheValid = true; } // downgrade lock rwl.readLock().lock(); // reacquire read without giving up write lock rwl.writeLock().unlock(); // unlock write, still hold read } use(data); rwl.readLock().unlock(); } }
ReentrantReadWriteLocks can be used to improve concurrency in some uses of some kinds of collections. This is typically worthwhile only when the collections are expected to be large, accessed by more reader threads than writer threads, and entail operations with overhead that outweighs synchronization overhead.
A reentrant write lock intrinsically defines an owner and can only be released by the thread that acquired it. In contrast, in this implementation, the read lock has no concept of ownership, and there is no requirement that the thread releasing a read lock is the same as the one that acquired it. However, this property is not guaranteed to hold in future implementations of this class.
This lock supports a maximum of 65536 recursive write locks and 65536 read locks. Attempts to exceed these limits result in Error throws from locking methods.
Definition at line 194 of file ReadWriteLock.d.
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Creates a new
Definition at line 208 of file ReadWriteLock.d. References readerLock, sync, and writerLock. |
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Returns the lock used for writing.
Reimplemented from ReadWriteLock. Definition at line 217 of file ReadWriteLock.d. References writerLock. |
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Returns the lock used for reading.
Reimplemented from ReadWriteLock. Definition at line 218 of file ReadWriteLock.d. References readerLock. |
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Returns the number of shared holds represented in count Definition at line 232 of file ReadWriteLock.d. References SHARED_SHIFT. Referenced by ReentrantReadWriteLock::Sync::getReadLockCount(), and toString(). |
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Returns the number of exclusive holds represented in count Definition at line 234 of file ReadWriteLock.d. References EXCLUSIVE_MASK. Referenced by ReentrantReadWriteLock::Sync::getOwner(), ReentrantReadWriteLock::Sync::getWriteHoldCount(), ReentrantReadWriteLock::Sync::isHeldExclusively(), ReentrantReadWriteLock::Sync::isWriteLocked(), ReentrantReadWriteLock::Sync::nonfairTryAcquire(), ReentrantReadWriteLock::Sync::nonfairTryAcquireShared(), toString(), ReentrantReadWriteLock::FairSync::tryAcquire(), ReentrantReadWriteLock::FairSync::tryAcquireShared(), and ReentrantReadWriteLock::Sync::tryRelease(). |
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Returns true if this lock has fairness set true.
Definition at line 709 of file ReadWriteLock.d. References sync. |
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Returns the thread that currently owns the exclusive lock, or
Definition at line 722 of file ReadWriteLock.d. References ReentrantReadWriteLock::Sync::getOwner(), and sync. |
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Queries the number of read locks held for this lock. This method is designed for use in monitoring system state, not for synchronization control.
Definition at line 732 of file ReadWriteLock.d. References ReentrantReadWriteLock::Sync::getReadLockCount(), and sync. |
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Queries if the write lock is held by any thread. This method is designed for use in monitoring system state, not for synchronization control.
Definition at line 743 of file ReadWriteLock.d. References ReentrantReadWriteLock::Sync::isWriteLocked(), and sync. |
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Queries if the write lock is held by the current thread.
Definition at line 752 of file ReadWriteLock.d. References ReentrantReadWriteLock::Sync::isHeldExclusively(), and sync. |
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Queries the number of reentrant write holds on this lock by the current thread. A writer thread has a hold on a lock for each lock action that is not matched by an unlock action.
Definition at line 764 of file ReadWriteLock.d. References ReentrantReadWriteLock::Sync::getWriteHoldCount(), and sync. |
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Returns a collection containing threads that may be waiting to acquire the write lock. Because the actual set of threads may change dynamically while constructing this result, the returned collection is only a best-effort estimate. The elements of the returned collection are in no particular order. This method is designed to facilitate construction of subclasses that provide more extensive lock monitoring facilities.
Definition at line 778 of file ReadWriteLock.d. References sync. |
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Returns a collection containing threads that may be waiting to acquire the read lock. Because the actual set of threads may change dynamically while constructing this result, the returned collection is only a best-effort estimate. The elements of the returned collection are in no particular order. This method is designed to facilitate construction of subclasses that provide more extensive lock monitoring facilities.
Definition at line 792 of file ReadWriteLock.d. References sync. |
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Queries whether any threads are waiting to acquire. Note that because cancellations may occur at any time, a
Definition at line 806 of file ReadWriteLock.d. References AbstractLock::hasQueuedThreads(), and sync. |
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Queries whether the given thread is waiting to acquire this lock. Note that because cancellations may occur at any time, a
Definition at line 820 of file ReadWriteLock.d. |
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Returns an estimate of the number of threads waiting to acquire. The value is only an estimate because the number of threads may change dynamically while this method traverses internal data structures. This method is designed for use in monitoring of the system state, not for synchronization control.
Definition at line 833 of file ReadWriteLock.d. References sync. |
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Returns a collection containing threads that may be waiting to acquire. Because the actual set of threads may change dynamically while constructing this result, the returned collection is only a best-effort estimate. The elements of the returned collection are in no particular order. This method is designed to facilitate construction of subclasses that provide more extensive monitoring facilities.
Definition at line 847 of file ReadWriteLock.d. References sync. |
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Queries whether any threads are waiting on the given condition associated with the write lock. Note that because timeouts and interrupts may occur at any time, a
Definition at line 861 of file ReadWriteLock.d. References sync. |
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Returns an estimate of the number of threads waiting on the given condition associated with the write lock. Note that because timeouts and interrupts may occur at any time, the estimate serves only as an upper bound on the actual number of waiters. This method is designed for use in monitoring of the system state, not for synchronization control.
Definition at line 878 of file ReadWriteLock.d. References sync. |
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Returns a collection containing those threads that may be waiting on the given condition associated with the write lock. Because the actual set of threads may change dynamically while constructing this result, the returned collection is only a best-effort estimate. The elements of the returned collection are in no particular order. This method is designed to facilitate construction of subclasses that provide more extensive condition monitoring facilities.
Definition at line 897 of file ReadWriteLock.d. References sync. |
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Returns a string identifying this lock, as well as its lock state. The state, in brackets, includes the String "Write locks =" follwed by the number of reentrantly held write locks, and the String "Read locks =" followed by the number of held read locks.
Definition at line 912 of file ReadWriteLock.d. References exclusiveCount(), ReentrantReadWriteLock::Sync::getCount(), sharedCount(), and sync. |
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Definition at line 196 of file ReadWriteLock.d. Referenced by readLock(), and this(). |
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Definition at line 198 of file ReadWriteLock.d. Referenced by this(), and writeLock(). |
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Definition at line 200 of file ReadWriteLock.d. Referenced by getOwner(), getQueuedReaderThreads(), getQueuedThreads(), getQueuedWriterThreads(), getQueueLength(), getReadLockCount(), getWaitingThreads(), getWaitQueueLength(), getWriteHoldCount(), hasQueuedThread(), hasQueuedThreads(), hasWaiters(), isFair(), isWriteLocked(), isWriteLockedByCurrentThread(), this(), and toString(). |
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Definition at line 227 of file ReadWriteLock.d. Referenced by sharedCount(). |
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Definition at line 228 of file ReadWriteLock.d. |
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Definition at line 229 of file ReadWriteLock.d. Referenced by exclusiveCount(). |