[Plplot-devel] --with-pthreads: Use pthreads with the xwin driver!

[Joao C. <jc...@fe...>]

Hi,

The xwin driver has been plagued for ages with a severe problem: whenever=
 the=20
user program goes to lengthly calculations, without doing any calls to=20
PLplot, the plot window couldn't be refreshed if obscured by other window=
s.=20
Nor resized.

You can quickly watch this behavior if you insert a getchar() statement j=
ust=20
before plend() in x01c.c. The getchar() call simulates the user program d=
oing=20
other jobs and not calling any plplot API. If you now obscure the plot wi=
ndow=20
you will see that it is not redrawn (of course).

This behaviour is most inconvenient for interactive languages like Octave=
 or=20
python, where the same behaviour is observed while the user is typing=20
commands at the prompt.

The obvious solution would be to write a xwin server or daemon, like the =
tk=20
driver plserver, but that means a lot of work. Instead, I have implemente=
d,=20
and cvs commit, a threaded xwin driver. It updates and resizes the plot=20
window, if needed.

This feature is disabled by default at configure time.

For most compiled programs, it can be safely turned on, even if the host=20
program is not threads aware.
For already build programs that somehow use PLplot, usually loading it as=
 an=20
extension, as Octave or python or tk does, things are a bit complicated, =
as=20
those programs must themself be linked with the pthread library, even if =
not=20
thread aware!

For example, in my system Octave is build by default without being linked=
 with=20
pthreads, because Octave is not threads aware. To use the new threads ena=
bled=20
xwin driver, I have to *relink* (only) octave with -lpthread, and after t=
hat=20
all goes well.

Python, by contrary, is already linked with the pthreads library, so noth=
ing=20
special needs to be done -- the threads enabled xwin driver works without=
 a=20
problem with python.

This is the reason why --with-pthreads=3Dno by default, and should not be=
 turned=20
on.
But users must know that this feature is available and why it is turned o=
ff,=20
so they can turn it on if that is the appropriate action for them.

Enjoy,
Joao