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Semaphore Class Reference

#include <Semaphore.h>

Inheritance diagram for Semaphore:

List of all members.

Public Methods
	Semaphore (int count=1, unsigned int maxCount=1) throw (Synchronization_Exception)
virtual	~Semaphore () throw ()
	Destroy the Semaphore.
void	wait () throw (Synchronization_Exception)
bool	tryWait (unsigned long) throw (Synchronization_Exception)
void	post () throw (Synchronization_Exception)
virtual int	count () throw ()
virtual bool	tryAcquire (unsigned long timeout) throw (Synchronization_Exception)
virtual void	acquire () throw (Synchronization_Exception)
virtual void	release () throw (Synchronization_Exception)

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Detailed Description

Author:

Eric Crahen <crahen@cse.buffalo.edu>

Date:

<2002-06-02T08:11:14-0400>

Version:

2.2.1

A Semaphore is an ownerless Lockable object. Its probably best described as a set of 'permits'. A Semaphore is initlized with an intial count and a maximum count, these would correspond to the number of 'permits' currently available and the number of' permits' in total.

acquire()ing the Semaphore means taking a permit, but if there are none (the count is 0) the Semaphore will block the calling thread.

release()ing the Semaphore means returning a permit, unblocking a thread waiting for one.

A Semaphore with an initial value of 1 and maximum value of 1 will act as a Mutex.

Scheduling

Threads blocked on a Semaphore are resumed in FIFO order.

Error Checking

An attempt to increase a Semaphore beyond its maximum value will result in an InvalidOp_Exception.

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Constructor & Destructor Documentation

Semaphore (  int    count = 1, unsigned int    maxCount = 1 )  throw (Synchronization_Exception)

Create a new Semaphore. Parameters: count  - initial count maxCount  - upper bound Exceptions: Synchronization_Exception  thrown if the Semaphore could not be created

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Member Function Documentation

virtual void acquire (    )  throw (Synchronization_Exception) [virtual]

Decrement the count, blocking that calling thread if the count becomes 0 or less than 0. The calling thread will remain blocked until the count is raised above 0 or if an exception is thrown. Exceptions: Interrupted_Exception  thrown when the calling thread is interupt()ed. A thread may be interrupted at any time, prematurely ending any wait. Synchronization_Exception  thrown if there is some other error. See also: Lockable::acquire() Implements Lockable.

virtual int count (    )  throw () [virtual]

Get the current count of the semaphore. This value may change immediately after this function returns to the calling thread. Returns: int - count

void post (    )  throw (Synchronization_Exception)

Increment the count. See also: release() - provided to reflect the traditional Semaphore semantics

virtual void release (    )  throw (Synchronization_Exception) [virtual]

Increment the count, unblocking one thread if count is posative. Exceptions: InvalidOp_Exception  thrown if this operation would increase the count beyond the maximum Synchronization_Exception  thrown if there is some other error. See also: Lockable::release() Implements Lockable.

virtual bool tryAcquire (  unsigned long    timeout )  throw (Synchronization_Exception) [virtual]

Decrement the count, blocking that calling thread if the count becomes 0 or less than 0. The calling thread will remain blocked until the count is raised above 0, an exception is thrown or the given amount of time expires. Parameters: timeout  - maximum amount of time (milliseconds) this method could block Returns: bool true if the Semaphore was acquire()ed before the timeout expired, otherwise false Exceptions: Interrupted_Exception  thrown when the calling thread is interupt()ed. A thread may be interrupted at any time, prematurely ending any wait. Synchronization_Exception  thrown if there is some other error. See also: Lockable::tryAcquire(unsigned long) Implements Lockable.

bool tryWait (  unsigned    long )  throw (Synchronization_Exception)

Decrement the count. See also: tryAcquire() - provided to reflect the traditional Semaphore semantics

void wait (    )  throw (Synchronization_Exception)

Decrement the count. See also: acquire() - provided to reflect the traditional Semaphore semantics

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

• Semaphore.h

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