This class makes it possible to write asynchronous socket-based code in Qt. Using synchronous socket operations blocks the program, which is clearly not acceptable for an event-driven GUI program.
.PP
Once you have opened a non-blocking socket (whether for TCP, UDP, a UNIX-domain socket, or any other protocol family your operating system supports), you can create a socket notifier to monitor the socket. Then you connect the activated() signal to the slot you want to be called when a socket event occurs.
For example, if you need to monitor both reads and writes for the same socket you must create two socket notifiers.
.PP
For read notifiers it makes little sense to connect the activated() signal to more than one slot because the data can be read from the socket only once.
.PP
Also observe that if you do not read all the available data when the read notifier fires, it fires again and again.
.PP
For write notifiers, immediately disable the notifier after the activated() signal has been received and you have sent the data to be written on the socket. When you have more data to be written, enable it again to get a new activated() signal. The exception is if the socket data writing operation (send() or equivalent) fails with a "would block" error, which means that some buffer is full and you must wait before sending more data. In that case you do not need to disable and re-enable the write notifier; it will fire again as soon as the system allows more data to be sent.
.PP
The behavior of a write notifier that is left in enabled state after having emitting the first activated() signal (and no "would block" error has occurred) is undefined. Depending on the operating system, it may fire on every pass of the event loop or not at all.
Socket action is detected in the main event loop of Qt. The X11 version of TQt has a single UNIX select() call that incorporates all socket notifiers and the X socket.
Enables the notifier if \fIenable\fR is TRUE or disables it if \fIenable\fR is FALSE.
.PP
The notifier is enabled by default.
.PP
If the notifier is enabled, it emits the activated() signal whenever a socket event corresponding to its type occurs. If it is disabled, it ignores socket events (the same effect as not creating the socket notifier).
.PP
Write notifiers should normally be disabled immediately after the activated() signal has been emitted; see discussion of write notifiers in the class description above.
