Semaphore Class Reference

A counting semaphore – a synchronization primitive that allows multiple processes to coordinate access to a shared resource. More...

#include <Semaphore.h++>

Inheritance diagram for Semaphore:

Collaboration diagram for Semaphore:

Public Member Functions
	Semaphore (const String &name, uint_t value=1, const Permissions &perm=Permissions::USER_READ_WRITE)
	Construct a new Semaphore with the given name, initial value, and permissions. More...
	~Semaphore ()
	Destructor. More...
void	init ()
	Initialize the semaphore. More...
bool	wait ()
	Wait on the semaphore. More...
void	lock ()
	Equivalent to wait(). More...
bool	tryWait ()
	Try to wait on the semaphore, returning immediately if it couldn't be acquired. More...
bool	signal ()
	Signal the semaphore. More...
void	unlock ()
	Equivalent to signal(). More...
int	getValue () const
	Get the current value of the semaphore. More...
String	getName () const
	Get the name of the semaphore. More...

Detailed Description

A counting semaphore – a synchronization primitive that allows multiple processes to coordinate access to a shared resource.

A Semaphore has an initial value, which represents the quantity of some shared resource. When a process acquires the semaphore, this value is decremented, and when it releases the semaphore, the value is incremented.

A Semaphore must be initialized before it can be used, via a call to the init() method.

Author

Mark Lindner

Constructor & Destructor Documentation

Semaphore()

Semaphore	(	const String &	name,
		uint_t	value = 1,
		const Permissions &	perm = Permissions::USER_READ_WRITE
	)

Construct a new Semaphore with the given name, initial value, and permissions.

Parameters

name	The name of the semaphore. On POSIX systems, the name must consist of at most 14 alphanumeric characters and may not contain slashes.
value	The initial value of the semaphore. Must be at least 1.
perm	The permissions with which to create the semaphore, if it does not yet exist.

~Semaphore()

~Semaphore

(

)

Destructor.

Destroys the underlying semaphore object, if no other processes have a reference to it.

Member Function Documentation

getName()

String getName ( ) const

inline

Get the name of the semaphore.

getValue()

int getValue

(

)

const

Get the current value of the semaphore.

init()

void init

(

)

Initialize the semaphore.

If the underlying semaphore object did not yet exist, it is created.

Exceptions

SystemException

If the operation fails.

lock()

void lock ( )

inlinevirtual

Equivalent to wait().

Implements Lock.

signal()

bool signal

(

)

Signal the semaphore.

Increments the semaphore's value by 1. The semaphore must have previously been acquired.

Returns

true if the semaphore was released, false otherwise.

tryWait()

bool tryWait

(

)

Try to wait on the semaphore, returning immediately if it couldn't be acquired.

Returns

true if the semaphore was acquired, false otherwise.

unlock()

void unlock ( )

inlinevirtual

Equivalent to signal().

Implements Lock.

wait()

bool wait

(

)

Wait on the semaphore.

If the semaphore's value is greater than 0, it's value is decremented and the method returns. Otherwise, the method blocks until the value becomes greater than 0.

Returns

true if the semaphore was acquired, false if an error occurred.

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

• Semaphore.h++
• Semaphore.c++