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       QSemaphore - Robust integer semaphore


       All the functions in this class are thread-safe when Qt is built with thread support.</p>

       #include <qsemaphore.h>

   Public Members
       QSemaphore ( int maxcount )
       virtual ~QSemaphore ()
       int available () const
       int total () const
       int operator++ ( int )
       int operator-- ( int )
       int operator+= ( int n )
       int operator-= ( int n )
       bool tryAccess ( int n )


       The QSemaphore class provides a robust integer semaphore.

       A QSemaphore can be used to serialize thread execution, in a similar way to a QMutex. A
       semaphore differs from a mutex, in that a semaphore can be accessed by more than one
       thread at a time.

       For example, suppose we have an application that stores data in a large tree structure.
       The application creates 10 threads (commonly called a thread pool) to perform searches on
       the tree. When the application searches the tree for some piece of data, it uses one
       thread per base node to do the searching. A semaphore could be used to make sure that two
       threads don't try to search the same branch of the tree at the same time.

       A non-computing example of a semaphore would be dining at a restuarant. A semaphore is
       initialized to have a maximum count equal to the number of chairs in the restuarant. As
       people arrive, they want a seat. As seats are filled, the semaphore is accessed, once per
       person. As people leave, the access is released, allowing more people to enter. If a party
       of 10 people want to be seated, but there are only 9 seats, those 10 people will wait, but
       a party of 4 people would be seated (taking the available seats to 5, making the party of
       10 people wait longer).

       When a semaphore is created it is given a number which is the maximum number of concurrent
       accesses it will permit. Accesses to the sempahore are gained using operator++() or
       operator+=(), and released with operator--() or operator-=(). The number of accesses
       allowed is retrieved with available(), and the total number with total(). Note that the
       incrementing functions will block if there aren't enough available accesses. Use
       tryAccess() if you want to acquire accesses without blocking.

       See also Environment Classes and Threading.


QSemaphore::QSemaphore ( int maxcount )

       Creates a new semaphore. The semaphore can be concurrently accessed at most maxcount

QSemaphore::~QSemaphore () [virtual]

       Destroys the semaphore.

       Warning: If you destroy a semaphore that has accesses in use the resultant behavior is

int QSemaphore::available () const

       Returns the number of accesses currently available to the semaphore.

int QSemaphore::operator++ ( int )

       Postfix ++ operator.

       Try to get access to the semaphore. If available() == 0, this call will block until it can
       get access, i.e. until available() > 0.

int QSemaphore::operator+= ( int n )

       Try to get access to the semaphore. If available() < n, this call will block until it can
       get all the accesses it wants, i.e. until available() >= n.

int QSemaphore::operator-- ( int )

       Postfix -- operator.

       Release access of the semaphore. This wakes all threads waiting for access to the

int QSemaphore::operator-= ( int n )

       Release n accesses to the semaphore.

int QSemaphore::total () const

       Returns the total number of accesses to the semaphore.

bool QSemaphore::tryAccess ( int n )

       Try to get access to the semaphore. If available() < n, this function will return FALSE
       immediately. If available() >= n, this function will take n accesses and return TRUE. This
       function does not block.



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