itk::Semaphore Class Reference

The semaphore class is used to synchronize execution between threads. More...

#include <itkSemaphore.h>

Inheritance diagram for itk::Semaphore:

[legend]Collaboration diagram for itk::Semaphore:

[legend]List of all members.

Public Types
typedef Semaphore	Self
typedef LightObject	Superclass
typedef SmartPointer< Self >	Pointer
typedef SmartPointer< const Self >	ConstPointer
Public Member Functions
virtual const char *	GetClassName () const
void	Initialize (unsigned int value)
void	Up ()
void	Down ()
void	Remove ()
Static Public Member Functions
Pointer	New ()
Protected Member Functions
	Semaphore ()
	~Semaphore ()

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Detailed Description

The semaphore class is used to synchronize execution between threads.

Semaphore objects maintain a counter value that can be incremented and decremented by atomic calls to Up() and Down(). Semaphores are commonly used to manage the use of a limited pool of system resources among several threads. If Down() is called when the value of the semaphore is zero, the calling thread will block until the semaphore value goes above zero again. When a blocked thread is released, it decrements the Semaphore counter before continuing to execute.

The Up() and Down() operations are standard as defined by E.W. Dijkstra. The Initialize( num ) operation creates the system semaphore object with an initial counter value of num. Initialize must be called before the Semaphore can be used. The Remove() method destroys the system semaphore object. It is not necessary to call Remove() unless you want to re-Initialize() the object.

This class supports 3 types of semaphores on Unix systems, POSIX semaphores, IPC semaphores, and IRIX semaphores from the SGI Sproc library. On Windows systems, POSIX semaphores and WIN32 thread library semaphores are supported.

Definition at line 112 of file itkSemaphore.h.

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Member Typedef Documentation

typedef SmartPointer<const Self> itk::Semaphore::ConstPointer

Reimplemented from itk::LightObject. Definition at line 119 of file itkSemaphore.h.

typedef SmartPointer<Self> itk::Semaphore::Pointer

Reimplemented from itk::LightObject. Definition at line 118 of file itkSemaphore.h.

typedef Semaphore itk::Semaphore::Self

Standard class typedefs. Reimplemented from itk::LightObject. Definition at line 116 of file itkSemaphore.h.

typedef LightObject itk::Semaphore::Superclass

Definition at line 117 of file itkSemaphore.h.

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Constructor & Destructor Documentation

itk::Semaphore::Semaphore (   )  [protected]

itk::Semaphore::~Semaphore (   )  [protected]

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Member Function Documentation

void itk::Semaphore::Down (   )

Decrement the semaphore count. If the count is zero, this thread will be blocked until another thread calls the up() method. The order in which threads will be unblocked is not defined, but implementors should give preference to those threads that have waited the longest.

virtual const char* itk::Semaphore::GetClassName (   )  const [virtual]

Run-time type information (and related methods).

void itk::Semaphore::Initialize (  unsigned int  value  )

Initialize the semaphore with a count of value.

Pointer itk::Semaphore::New (   )  [static]

Method for creation through the object factory. Reimplemented from itk::LightObject.

void itk::Semaphore::Remove (   )

Remove the semaphore from the system.

void itk::Semaphore::Up (   )

Increment the semaphore count, unblocking up to one thread that may be blocked in the down() method.

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The documentation for this class was generated from the following file:

• itkSemaphore.h

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