source: trunk/src/qt3support/tools/q3semaphore.cpp@ 318

Last change on this file since 318 was 2, checked in by Dmitry A. Kuminov, 16 years ago

Initially imported qt-all-opensource-src-4.5.1 from Trolltech.
File size: 6.8 KB
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41
42#include "q3semaphore.h"
43
44#include "qmutex.h"
45#include "qwaitcondition.h"
46
47QT_BEGIN_NAMESPACE
48
49/*!
50 \class Q3Semaphore
51 \threadsafe
52 \brief The Q3Semaphore class provides a robust integer semaphore.
53
54 \compat
55
56 A Q3Semaphore can be used to serialize thread execution, in a
57 similar way to a QMutex. A semaphore differs from a mutex, in
58 that a semaphore can be accessed by more than one thread at a
59 time.
60
61 For example, suppose we have an application that stores data in a
62 large tree structure. The application creates 10 threads
63 (commonly called a thread pool) to perform searches on the tree.
64 When the application searches the tree for some piece of data, it
65 uses one thread per base node to do the searching. A semaphore
66 could be used to make sure that two threads don't try to search
67 the same branch of the tree at the same time.
68
69 A non-computing example of a semaphore would be dining at a
70 restaurant. A semaphore is initialized to have a maximum count
71 equal to the number of chairs in the restaurant. As people
72 arrive, they want a seat. As seats are filled, the semaphore is
73 accessed, once per person. As people leave, the access is
74 released, allowing more people to enter. If a party of 10 people
75 want to be seated, but there are only 9 seats, those 10 people
76 will wait, but a party of 4 people would be seated (taking the
77 available seats to 5, making the party of 10 people wait longer).