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	core.sync.rwmutex
The read/write mutex module provides a primitive for maintaining shared read
 access and mutually exclusive write access.
License: 
Authors: 
Sean Kelly
Source core/sync/rwmutex.d
- classReadWriteMutex;
- This class represents a mutex that allows any number of readers to enter, but when a writer enters, all other readers and writers are blocked.Please note that this mutex is not recursive and is intended to guard access to data only. Also, no deadlock checking is in place because doing so would require dynamic memory allocation, which would reduce performance by an unacceptable amount. As a result, any attempt to recursively acquire this mutex may well deadlock the caller, particularly if a write lock is acquired while holding a read lock, or vice-versa. In practice, this should not be an issue however, because it is uncommon to call deeply into unknown code while holding a lock that simply protects data.Examples:import core.atomic, core.thread, core.sync.semaphore; static void runTest(ReadWriteMutex.Policy policy) { scope mutex = new ReadWriteMutex(policy); scope rdSemA = new Semaphore, rdSemB = new Semaphore, wrSemA = new Semaphore, wrSemB = new Semaphore; shared size_t numReaders, numWriters; void readerFn() { synchronized (mutex.reader) { atomicOp!"+="(numReaders, 1); rdSemA.notify(); rdSemB.wait(); atomicOp!"-="(numReaders, 1); } } void writerFn() { synchronized (mutex.writer) { atomicOp!"+="(numWriters, 1); wrSemA.notify(); wrSemB.wait(); atomicOp!"-="(numWriters, 1); } } void waitQueued(size_t queuedReaders, size_t queuedWriters) { for (;;) { synchronized (mutex.m_commonMutex) { if (mutex.m_numQueuedReaders == queuedReaders && mutex.m_numQueuedWriters == queuedWriters) break; } Thread.yield(); } } scope group = new ThreadGroup; // 2 simultaneous readers group.create(&readerFn); group.create(&readerFn); rdSemA.wait(); rdSemA.wait(); assert(numReaders == 2); rdSemB.notify(); rdSemB.notify(); group.joinAll(); assert(numReaders == 0); foreach (t; group) group.remove(t); // 1 writer at a time group.create(&writerFn); group.create(&writerFn); wrSemA.wait(); assert(!wrSemA.tryWait()); assert(numWriters == 1); wrSemB.notify(); wrSemA.wait(); assert(numWriters == 1); wrSemB.notify(); group.joinAll(); assert(numWriters == 0); foreach (t; group) group.remove(t); // reader and writer are mutually exclusive group.create(&readerFn); rdSemA.wait(); group.create(&writerFn); waitQueued(0, 1); assert(!wrSemA.tryWait()); assert(numReaders == 1 && numWriters == 0); rdSemB.notify(); wrSemA.wait(); assert(numReaders == 0 && numWriters == 1); wrSemB.notify(); group.joinAll(); assert(numReaders == 0 && numWriters == 0); foreach (t; group) group.remove(t); // writer and reader are mutually exclusive group.create(&writerFn); wrSemA.wait(); group.create(&readerFn); waitQueued(1, 0); assert(!rdSemA.tryWait()); assert(numReaders == 0 && numWriters == 1); wrSemB.notify(); rdSemA.wait(); assert(numReaders == 1 && numWriters == 0); rdSemB.notify(); group.joinAll(); assert(numReaders == 0 && numWriters == 0); foreach (t; group) group.remove(t); // policy determines whether queued reader or writers progress first group.create(&writerFn); wrSemA.wait(); group.create(&readerFn); group.create(&writerFn); waitQueued(1, 1); assert(numReaders == 0 && numWriters == 1); wrSemB.notify(); if (policy == ReadWriteMutex.Policy.PREFER_READERS) { rdSemA.wait(); assert(numReaders == 1 && numWriters == 0); rdSemB.notify(); wrSemA.wait(); assert(numReaders == 0 && numWriters == 1); wrSemB.notify(); } else if (policy == ReadWriteMutex.Policy.PREFER_WRITERS) { wrSemA.wait(); assert(numReaders == 0 && numWriters == 1); wrSemB.notify(); rdSemA.wait(); assert(numReaders == 1 && numWriters == 0); rdSemB.notify(); } group.joinAll(); assert(numReaders == 0 && numWriters == 0); foreach (t; group) group.remove(t); } runTest(ReadWriteMutex.Policy.PREFER_READERS); runTest(ReadWriteMutex.Policy.PREFER_WRITERS); - enumPolicy: int;
- Defines the policy used by this mutex. Currently, two policies are defined.The first will queue writers until no readers hold the mutex, then pass the writers through one at a time. If a reader acquires the mutex while there are still writers queued, the reader will take precedence. The second will queue readers if there are any writers queued. Writers are passed through one at a time, and once there are no writers present, all queued readers will be alerted. Future policies may offer a more even balance between reader and writer precedence.- PREFER_READERS
- Readers get preference. This may starve writers.
- PREFER_WRITERS
- Writers get preference. This may starve readers.
 
- nothrow @safe this(Policypolicy= Policy.PREFER_WRITERS);
 nothrow @safe this(Policypolicy= Policy.PREFER_WRITERS) shared;
- Initializes a read/write mutex object with the supplied policy.Parameters:Policy policyThe policy to use. Throws:SyncError on error.
- nothrow @property @safe Policypolicy();
 nothrow @property @safe Policypolicy() shared;
- Gets the policy used by this mutex.Returns:The policy used by this mutex.
- nothrow @property @safe Readerreader();
 nothrow @property @safe shared(Reader)reader() shared;
- Gets an object representing the reader lock for the associated mutex.Returns:A reader sub-mutex.
- nothrow @property @safe Writerwriter();
 nothrow @property @safe shared(Writer)writer() shared;
- Gets an object representing the writer lock for the associated mutex.Returns:A writer sub-mutex.
- classReader: object.Object.Monitor;
- This class can be considered a mutex in its own right, and is used to negotiate a read lock for the enclosing mutex.- nothrow @trusted this(this Q)()
 if (is(Q == Reader) || is(Q == shared(Reader)));
- Initializes a read/write mutex reader proxy object.
- @trusted voidlock();
 @trusted voidlock() shared;
- Acquires a read lock on the enclosing mutex.
- @trusted voidunlock();
 @trusted voidunlock() shared;
- Releases a read lock on the enclosing mutex.
- @trusted booltryLock();
 @trusted booltryLock() shared;
- Attempts to acquire a read lock on the enclosing mutex. If one can be obtained without blocking, the lock is acquired and true is returned. If not, the lock is not acquired and false is returned.Returns:true if the lock was acquired and false if not.
- @trusted booltryLock(Durationtimeout);
 @trusted booltryLock(Durationtimeout) shared;
- Attempts to acquire a read lock on the enclosing mutex. If one can be obtained without blocking, the lock is acquired and true is returned. If not, the function blocks until either the lock can be obtained or the time elapsed exceeds timeout, returning true if the lock was acquired and false if the function timed out.Parameters:Duration timeoutmaximum amount of time to wait for the lock Returns:true if the lock was acquired and false if not.
 
- classWriter: object.Object.Monitor;
- This class can be considered a mutex in its own right, and is used to negotiate a write lock for the enclosing mutex.- nothrow @trusted this(this Q)()
 if (is(Q == Writer) || is(Q == shared(Writer)));
- Initializes a read/write mutex writer proxy object.
- @trusted voidlock();
 @trusted voidlock() shared;
- Acquires a write lock on the enclosing mutex.
- @trusted voidunlock();
 @trusted voidunlock() shared;
- Releases a write lock on the enclosing mutex.
- @trusted booltryLock();
 @trusted booltryLock() shared;
- Attempts to acquire a write lock on the enclosing mutex. If one can be obtained without blocking, the lock is acquired and true is returned. If not, the lock is not acquired and false is returned.Returns:true if the lock was acquired and false if not.
- @trusted booltryLock(Durationtimeout);
 @trusted booltryLock(Durationtimeout) shared;
- Attempts to acquire a write lock on the enclosing mutex. If one can be obtained without blocking, the lock is acquired and true is returned. If not, the function blocks until either the lock can be obtained or the time elapsed exceeds timeout, returning true if the lock was acquired and false if the function timed out.Parameters:Duration timeoutmaximum amount of time to wait for the lock Returns:true if the lock was acquired and false if not.
 
 
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