GPK is an addon library to permit thread-safe access to GTK. It is used
in conjunction with POSIX threads and GTK 0.99.1 and higher.
Motivation
- GPK was developed as a solution for a GTK-based application
I am writing for measuring web server
performance. By its nature, the application is heavily
threaded and individual threads need to make "real time"
updates to the GUI as it progresses.
After looking at many approaches,
I finally settled on one. GPK is the result of the effort to
implement this one design and make it reusable
by the GTK community.
A more complete discussion of the benefits and pitfalls of
threads is available on the
GTK and Pthreads page.
The Problem
- Developing multithreaded GUI applications for X-Windows can
be a real challenge. Most X-Windows development toolkits, such as
Motif 2.0, Athena, GTK, OpenLook and others are not thread-safe. In
addition, the supporting X libraries themselves may not
thread-safe.
Each of these libraries are examples of event loop programming,
where much of the state of the application is maintained in
library's data structures. But one of the principle structural
advantages
of threaded programs is the ability to maintain transitional
state information directly within the state of each of the threads.
This contrast means that integrating threads with event-driven
libraries can be difficult. The bottom line: multiple
threads cannot always work simultaneously with X-Windows based
libraries and toolkits.
A Solution
- One solution to this problem is to dedicate a single thread
to maintaining the GUI and have other threads send it requests.
Because this thread is doing work on behalf of another, it
is called a proxy thread.
Keeping the event-loop libraries confined to a single proxy thread,
and performing long running operations in separate threads
provides both a safe and more responsive solution.
GPK or the General Proxy Kit (for lack of better name) is
a library that turns the main GTK event loop thread into
a server thread that listens for requests from other threads.
The GPK Architecture page details
the design of the GPK proxy system.
How Do I Use It?
- Using the library is straightforward:
- Have the thread that will run int the gtk_main() event loop
call gpk_init() prior to entering the loop.
- Use any gpk_ call from the library from any thread
(including the GTK main thread) to perform any GUI
operation provided. Callbacks (running of course in the
GTK event loop thread) can also call GPK routines safely.
GPK will detect that the request is a proxy to itself and
will execute the command on the spot.
- To aid in understanding the usage of GPK, a
Using GPK page is provided. A
sample application called PerfMon
is included.
- With the help of users, GPK will hopefully be expanded over
time to include more of the
full function of GTK. Today it provides access to
commonly used collections of functions.
Where Do I Get It?
- GPK can be downloaded from the
GPK Download page.
Acknowlegdements
- GPK makes use of modified versions of existing code. Much thanks
needs to be given to the authors of these codes. They are:
- Ron Winacott for his
Thread Extension Library that includes a thread proxy
implementation.
- Tom Bech for
GCK (General Convenience Kit) library.
- Steve Klieman, Devang Shah and Bart Smaalders for their
implementations of thread-safe queues and linked lists from
their book "Programming with Threads".
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