Re: confusion about message passing between the tasks

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

compguy45@gmail.com writes:
> In those directories all example are graphics example. Which directory
> is one that creates N tasks?

The directories 1..5 all contain different versions of the same
graphical program.

Version 1: no tasks.

Version 2: N tasks, race condition when multiple tasks want to draw
using a shared graphics context.

Version 3: race condition solved by placing the graphics context in a
protected object. But the problem now, with 10_000 tasks, is excessive
virtual memory consumption (8 MiB of stack per task), which luckily does
not translate into physical memory usage, at least on Linux.

Version 4: Introduce a task queue.  Now the number of tasks is
independent on the number of rectangles.  But there is still a problem;
a deadlock exists when one task A finds that there remains a rectangle
in the queue but another task B gets to dequeue it first.  Then A tries
to dequeue the last rectangle but waits forever as the queue is now
empty.  As a consequence the master task waits forever for A to
complete.

Version 5: deadlock solved by a select statement.

-- 
Ludovic Brenta.