This class defines a thread synchronisation object. More...

#include <semaphor.h>

Inheritance diagram for PSemaphore:

Collaboration diagram for PSemaphore:

Public Member Functions
Construction
	PSemaphore (unsigned initial=0, unsigned maximum=UINT_MAX)
	Create a new semaphore with maximum count and initial value specified. More...

	PSemaphore (const PString &name, unsigned initial=0, unsigned maximum=UINT_MAX)
	Create a new system global semaphore with maximum count and initial value specified. More...

	PSemaphore (const PSemaphore &sem)
	Create a new semaphore with the same initial and maximum values as the original. More...

	~PSemaphore ()
	Destroy the semaphore. More...

Operations
virtual void	Wait ()
	If the semaphore count is > 0, decrement the semaphore and return. More...

virtual PBoolean	Wait (const PTimeInterval &timeout)
	If the semaphore count is > 0, decrement the semaphore and return. More...

virtual void	Signal ()
	If there are waiting (blocked) threads then unblock the first one that was blocked. More...

virtual void	Reset (unsigned initial=0, unsigned maximum=UINT_MAX)
	Reset the semaphore to the specified inital and maximum values. More...

unsigned	GetInitial () const
	Get the initial value semaphore was creted with. More...

unsigned	GetMaximum () const
	Get the initial value semaphore was creted with. More...

Public Member Functions inherited from PSync
	PSync ()

virtual bool	InstrumentedWait (const PTimeInterval &timeout, const PDebugLocation &)
	As for Wait() but with location of call for instrumentation. Mostly used internally. More...

virtual void	InstrumentedSignal (const PDebugLocation &)
	As for Signal() but with location of call for instrumentation. Mostly used internally. More...

Public Member Functions inherited from PObject
__inline unsigned	GetTraceContextIdentifier () const
	Get PTRACE context identifier. More...

__inline void	SetTraceContextIdentifier (unsigned id)

__inline void	SetTraceContextIdentifier (const PObject &obj)

__inline void	SetTraceContextIdentifier (const PObject *obj)

__inline void	CopyTraceContextIdentifier (PObject &obj) const

__inline void	CopyTraceContextIdentifier (PObject *obj) const

virtual	~PObject ()

__inline const char *	GetClass () const

__inline bool	IsClass (const char *name) const

__inline const PObject *	PTraceObjectInstance () const

virtual PObject *	Clone () const
	Create a copy of the class on the heap. More...

template<class CLS >
CLS *	CloneAs () const
	As for Clone() but converts to specified type. More...

virtual PINDEX	HashFunction () const
	This function yields a hash value required by the `PDictionary` class. More...

virtual Comparison	Compare (const PObject &obj) const
	Compare the two objects and return their relative rank. More...

virtual Comparison	CompareObjectMemoryDirect (const PObject &obj) const
	Determine the byte wise comparison of two objects. More...

bool	operator== (const PObject &obj) const
	Compare the two objects. More...

bool	operator!= (const PObject &obj) const
	Compare the two objects. More...

bool	operator< (const PObject &obj) const
	Compare the two objects. More...

bool	operator> (const PObject &obj) const
	Compare the two objects. More...

bool	operator<= (const PObject &obj) const
	Compare the two objects. More...

bool	operator>= (const PObject &obj) const
	Compare the two objects. More...

virtual void	PrintOn (ostream &strm) const
	Output the contents of the object to the stream. More...

virtual void	ReadFrom (istream &strm)
	Input the contents of the object from the stream. More...

Protected Member Functions
	PQUEUE (ThreadQueue, PThread)

Protected Member Functions inherited from PObject
	PObject ()
	Constructor for PObject, made protected so cannot ever create one on its own. More...

Protected Attributes
PString	m_name

unsigned	m_maximum

unsigned	m_initial

ThreadQueue	waitQueue

Protected Attributes inherited from PObject
unsigned	m_traceContextIdentifier

Additional Inherited Members
Public Types inherited from PObject
enum	Comparison { LessThan = -1, EqualTo = 0, GreaterThan = 1 }
	Result of the comparison operation performed by the `Compare()` function. More...

Static Public Member Functions inherited from PObject
static __inline void	CopyTraceContextIdentifier (PObject &to, const PObject &from)

static __inline void	CopyTraceContextIdentifier (PObject &to, const PObject *from)

static __inline void	CopyTraceContextIdentifier (PObject *to, const PObject &from)

static __inline void	CopyTraceContextIdentifier (PObject to, const PObject from)

static __inline const char *	Class ()

static __inline const PObject *	PTraceObjectInstance (const char *)

static __inline const PObject *	PTraceObjectInstance (const PObject *obj)

template<typename T >
static Comparison	Compare2 (T v1, T v2)
	Compare two types, returning Comparison type. More...

static Comparison	InternalCompareObjectMemoryDirect (const PObject obj1, const PObject obj2, PINDEX size)
	Internal function caled from CompareObjectMemoryDirect() More...

Detailed Description

This class defines a thread synchronisation object.

This is in the form of a integer semaphore. The semaphore has a count and a maximum value. The various combinations of count and usage of the Wait() and Signal() functions determine the type of synchronisation mechanism to be employed.

The Wait() operation is that if the semaphore count is > 0, decrement the semaphore and return. If it is = 0 then wait (block).

The Signal() operation is that if there are waiting threads then unblock the first one that was blocked. If no waiting threads and the count is less than the maximum then increment the semaphore.

The most common is to create a mutual exclusion zone. A mutex is where a piece of code or data cannot be accessed by more than one thread at a time. To prevent this the PSemaphore is used in the following manner:


      PSemaphore mutex(1, 1);  // Maximum value of 1 and initial value of 1.

...

      mutex.Wait();

      ... critical section - only one thread at a time here.

      mutex.Signal();

...

The first thread will pass through the Wait() function, a second thread will block on that function until the first calls the Signal() function, releasing the second thread.

Constructor & Destructor Documentation

PSemaphore::PSemaphore	(	unsigned	initial = `0`,
		unsigned	maximum = `UINT_MAX`
	)

inline

Create a new semaphore with maximum count and initial value specified.

If the initial value is larger than the maximum value then is is set to the maximum value.

Parameters

initial	Initial value for semaphore count.
maximum	Maximum value for semaphore count.

References Reset().

PSemaphore::PSemaphore	(	const PString &	name,
		unsigned	initial = `0`,
		unsigned	maximum = `UINT_MAX`
	)

inline

Create a new system global semaphore with maximum count and initial value specified.

If the initial value is larger than the maximum value then is is set to the maximum value.

Parameters

initial	Initial value for semaphore count.
maximum	Maximum value for semaphore count.

References Reset().

PSemaphore::PSemaphore ( const PSemaphore & sem )

inline

Create a new semaphore with the same initial and maximum values as the original.

References m_initial, m_maximum, and Reset().

PSemaphore::~PSemaphore ( )

Destroy the semaphore.

This will assert if there are still waiting threads on the semaphore.

Member Function Documentation

unsigned PSemaphore::GetInitial ( ) const

inline

Get the initial value semaphore was creted with.

References m_initial.

unsigned PSemaphore::GetMaximum ( ) const

inline

Get the initial value semaphore was creted with.

References m_maximum.

PSemaphore::PQUEUE	(	ThreadQueue	,
		PThread
	)

protected

virtual void PSemaphore::Reset	(	unsigned	initial = `0`,
		unsigned	maximum = `UINT_MAX`
	)

virtual

Reset the semaphore to the specified inital and maximum values.

Note that the behaviour is undetermined if something is waiting on the semaphire when this is called.

Parameters

initial	Initial value for semaphore count.
maximum	Maximum value for semaphore count.

Referenced by PSemaphore().

virtual void PSemaphore::Signal ( )

virtual

If there are waiting (blocked) threads then unblock the first one that was blocked.

If no waiting threads and the count is less than the maximum then increment the semaphore.

Implements PSync.

Referenced by PSyncQueue< PQueuedThreadPool::QueuedWorkerThread::QueuedWork >::Close(), PSyncQueue< PQueuedThreadPool::QueuedWorkerThread::QueuedWork >::Drain(), and PSyncQueue< PQueuedThreadPool::QueuedWorkerThread::QueuedWork >::Enqueue().

virtual void PSemaphore::Wait ( )

virtual

If the semaphore count is > 0, decrement the semaphore and return.

If if is = 0 then wait (block).

Implements PSync.

Referenced by PSyncQueue< PQueuedThreadPool::QueuedWorkerThread::QueuedWork >::Dequeue(), and PSyncQueue< PQueuedThreadPool::QueuedWorkerThread::QueuedWork >::Restart().

virtual PBoolean PSemaphore::Wait ( const PTimeInterval & timeout )

virtual

If the semaphore count is > 0, decrement the semaphore and return.

If if is = 0 then wait (block) for the specified amount of time.

Returns: true if semaphore was signalled, false if timed out.

Implements PSync.

Member Data Documentation

unsigned PSemaphore::m_initial

protected

Referenced by GetInitial(), and PSemaphore().

unsigned PSemaphore::m_maximum

protected

Referenced by GetMaximum(), and PSemaphore().

PString PSemaphore::m_name

protected

ThreadQueue PSemaphore::waitQueue

protected

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

semaphor.h

Public Member Functions

Protected Member Functions

Protected Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation