Type: System.Threading.ReaderWriterLock

System.Threading.ReaderWriterLock Class

Assembly: Mscorlib.dll
Namespace: System.Threading

Summary: Defines the lock that implements single-writer and multiple-reader semantics.

C# Syntax:


        public sealed class ReaderWriterLock

Remarks

ReaderWriterLock supports the following features:

Use in large numbers, for activities such as per object synchronization.
Timeouts. This is a valuable feature to detect deadlocks.
Caching of events. This allows the events to be moved from the least contentious regions to the most contentious regions. The number of events needed by ReaderWriterLock is bounded by the number of threads in the process.
Nested locks by readers and writers.
Spin counts for avoiding context switches on multiprocessor machines.
Upgrades and downgrades of writer locks. Upgrading to a writer lock returns argument that indicates intermediate writes, while downgrading from a writer lock restores the state of the lock.
Methods to release the lock so the thread can call application code. ReaderWriterLock.RestoreLock restores the lock state and indicates intermediate writes.
Recovery from most common failures, such as creation of events. The lock maintains consistent internal state and remains usable.

Timeout is in milliseconds. The following table shows the possible timeout values.

Value	Description
-1	Infinite.
0	No timeout.
>0	The number of milliseconds to wait.

Negative numbers are interpreted as unsigned, with the exception of -1, which has special meaning.

See also:

System.Threading Namespace

System.Threading.ReaderWriterLock Member List:

Public Constructors

ctor #1

Default constructor. This constructor is called by derived class constructors to initialize state in this type.
Initializes a new instance of the ReaderWriterLock class.

Public Properties

IsReaderLockHeld	Read-only Gets a value indicating whether the current thread holds the reader lock.
IsWriterLockHeld	Read-only Gets a value indicating whether the current thread holds the writer lock.
WriterSeqNum	Read-only Gets the current sequence number.

Public Methods

AcquireReaderLock	Overloaded: `AcquireReaderLock(int millisecondsTimeout)` Acquires reader lock, using an Int32 value for the timeout.
AcquireReaderLock	Overloaded: `AcquireReaderLock(TimeSpan timeout)` Acquires the reader lock, using a TimeSpan value for the timeout.
AcquireWriterLock	Overloaded: `AcquireWriterLock(int millisecondsTimeout)` Acquires the writer lock, using an Int32 value for the timeout.
AcquireWriterLock	Overloaded: `AcquireWriterLock(TimeSpan timeout)` Acquires the writer lock, using a TimeSpan value for the timeout.
AnyWritersSince	Indicates whether intermediate writes have occurred since the sequence number was obtained.
DowngradeFromWriterLock	Restores the lock status of the thread to when it calls ReaderWriterLock.UpgradeToWriterLock.
Equals (inherited from System.Object)	See base class member description: System.Object.Equals Derived from System.Object, the primary base class for all objects.
GetHashCode (inherited from System.Object)	See base class member description: System.Object.GetHashCode Derived from System.Object, the primary base class for all objects.
GetType (inherited from System.Object)	See base class member description: System.Object.GetType Derived from System.Object, the primary base class for all objects.
ReleaseLock	Releases the lock, regardless of the number of times the thread acquired the lock.
ReleaseReaderLock	Releases the reader lock.
ReleaseWriterLock	Releases the writer lock.
RestoreLock	Restores the lock status of the thread to what it was before calling ReaderWriterLock.ReleaseLock.
ToString (inherited from System.Object)	See base class member description: System.Object.ToString Derived from System.Object, the primary base class for all objects.
UpgradeToWriterLock	Overloaded: `UpgradeToWriterLock(int millisecondsTimeout)` Upgrades the reader thread to a writer, using an Int32 value for the timeout.
UpgradeToWriterLock	Overloaded: `UpgradeToWriterLock(TimeSpan timeout)` Upgrades the reader thread to a writer, using a TimeSpan value for the timeout.

Protected Methods

Finalize (inherited from System.Object)	See base class member description: System.Object.Finalize Derived from System.Object, the primary base class for all objects.
MemberwiseClone (inherited from System.Object)	See base class member description: System.Object.MemberwiseClone Derived from System.Object, the primary base class for all objects.

Hierarchy:

System.Object

System.Threading.ReaderWriterLock

System.Threading.ReaderWriterLock Member Details

ctor #1

Summary: Initializes a new instance of the ReaderWriterLock class.

Default constructor. This constructor is called by derived class constructors to initialize state in this type.

C# Syntax:


            public ReaderWriterLock();

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Property: IsReaderLockHeld (read-only)

Summary: Gets a value indicating whether the current thread holds the reader lock.

C# Syntax:


            public bool IsReaderLockHeld {get;}

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Property: IsWriterLockHeld (read-only)

Summary: Gets a value indicating whether the current thread holds the writer lock.

C# Syntax:


            public bool IsWriterLockHeld {get;}

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Property: WriterSeqNum (read-only)

Summary: Gets the current sequence number.

C# Syntax:


            public int WriterSeqNum {get;}

Remarks

The caller should be a reader or writer to get meaningful results.

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Overloaded Method: AcquireReaderLock(
int millisecondsTimeout
)

Summary: Acquires reader lock, using an Int32 value for the timeout.

C# Syntax:


            public void AcquireReaderLock(
   int millisecondsTimeout
);

Parameters:

millisecondsTimeout

The timeout in milliseconds.

Remarks

ReaderWriterLock.AcquireReaderLock supports nested reader locks. The thread blocks if a different thread has the writer lock.

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Overloaded Method: AcquireReaderLock(
TimeSpan timeout
)

Summary: Acquires the reader lock, using a TimeSpan value for the timeout.

C# Syntax:


            public void AcquireReaderLock(
   TimeSpan timeout
);

Parameters:

timeout

A TimeSpan specifying the timeout period.

Remarks

ReaderWriterLock.AcquireReaderLock supports nested reader locks. The thread blocks if a different thread has the writer lock.

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Overloaded Method: AcquireWriterLock(
int millisecondsTimeout
)

Summary: Acquires the writer lock, using an Int32 value for the timeout.

C# Syntax:


            public void AcquireWriterLock(
   int millisecondsTimeout
);

Parameters:

millisecondsTimeout

The timeout in milliseconds.

Remarks

ReaderWriterLock.AcquireWriterLock supports nested writer locks. The thread blocks if a different thread has the reader lock, and deadlocks if it has the reader lock. Use ReaderWriterLock.UpgradeToWriterLock if you are not sure that the thread has the reader lock. This will upgrade the reader thread to a writer.

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Overloaded Method: AcquireWriterLock(
TimeSpan timeout
)

Summary: Acquires the writer lock, using a TimeSpan value for the timeout.

C# Syntax:


            public void AcquireWriterLock(
   TimeSpan timeout
);

Parameters:

timeout

The TimeSpan specifying the timeout period.

Remarks

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Method: AnyWritersSince(
int seqNum
)

Summary: Indicates whether intermediate writes have occurred since the sequence number was obtained.

C# Syntax:


            public bool AnyWritersSince(
   int seqNum
);

Parameters:

seqNum

The sequence number.

Return Value:: true if intermediate writes have occurred since the sequence number was obtained; otherwise, false.

Remarks

The caller should be a reader or writer to get meaningful results.

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Method: DowngradeFromWriterLock(
ref LockCookie lockCookie
)

Summary: Restores the lock status of the thread to when it calls ReaderWriterLock.UpgradeToWriterLock.

C# Syntax:


            public void DowngradeFromWriterLock(
   ref LockCookie lockCookie
);

Parameters:

lockCookie

The LockCookie.

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Method: Equals(
object obj
)

Inherited
See base class member description: System.Object.Equals

C# Syntax:


            public virtual bool Equals(
   object obj
);

For more information on members inherited from System.Object click on the link above.

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Method: Finalize()

Inherited
See base class member description: System.Object.Finalize

C# Syntax:


            ~ReaderWriterLock();

For more information on members inherited from System.Object click on the link above.

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Method: GetHashCode()

Inherited
See base class member description: System.Object.GetHashCode

C# Syntax:


            public virtual int GetHashCode();

For more information on members inherited from System.Object click on the link above.

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Method: GetType()

Inherited
See base class member description: System.Object.GetType

C# Syntax:


            public Type GetType();

For more information on members inherited from System.Object click on the link above.

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Method: MemberwiseClone()

Inherited
See base class member description: System.Object.MemberwiseClone

C# Syntax:


            protected object MemberwiseClone();

For more information on members inherited from System.Object click on the link above.

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Method: ReleaseLock()

Summary: Releases the lock, regardless of the number of times the thread acquired the lock.

C# Syntax:


            public LockCookie ReleaseLock();

Return Value:: A LockCookie value representing the released lock.

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Method: ReleaseReaderLock()

Summary: Releases the reader lock.

C# Syntax:


            public void ReleaseReaderLock();

Remarks

If the current thread is holding the writer lock, calling ReaderWriterLock.ReleaseReaderLock releases the writer lock as well as the reader lock.

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Method: ReleaseWriterLock()

Summary: Releases the writer lock.

C# Syntax:


            public void ReleaseWriterLock();

Remarks

ReaderWriterLock.ReleaseWriterLock removes the thread as a writer if this is not a nested call to release the lock. If the current thread is holding the reader lock, calling ReaderWriterLock.ReleaseWriterLock throws an ApplicationException.

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Method: RestoreLock(
ref LockCookie lockCookie
)

Summary: Restores the lock status of the thread to what it was before calling ReaderWriterLock.ReleaseLock.

C# Syntax:


            public void RestoreLock(
   ref LockCookie lockCookie
);

Parameters:

lockCookie

The LockCookie.

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Method: ToString()

Inherited
See base class member description: System.Object.ToString

C# Syntax:


            public virtual string ToString();

For more information on members inherited from System.Object click on the link above.

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Overloaded Method: UpgradeToWriterLock(
int millisecondsTimeout
)

Summary: Upgrades the reader thread to a writer, using an Int32 value for the timeout.

C# Syntax:


            public LockCookie UpgradeToWriterLock(
   int millisecondsTimeout
);

Parameters:

millisecondsTimeout

The timeout in milliseconds.

Return Value:: A LockCookie value.

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Overloaded Method: UpgradeToWriterLock(
TimeSpan timeout
)

Summary: Upgrades the reader thread to a writer, using a TimeSpan value for the timeout.

C# Syntax:


            public LockCookie UpgradeToWriterLock(
   TimeSpan timeout
);

Parameters:

timeout

The TimeSpan specifying the timeout period.

Return Value:: A LockCookie value.