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Multiple coroutines in parallel use
Threading and Coroutines. example from a Well House Consultants training course
More on Threading and Coroutines. [link]

This example is described in the following article(s):
   • Lua examples - coroutines, error handling, objects, etc - [link]

Source code: ff2.lua Module: U114

This program resulted from a request for a demonstration described as

"We want to load in a series of [images] and output them at intervals
of one second, updating the play list if more images get added to the
directory from which images are loaded ..."

The solution shown uses several coroutines all active at the same time;
the first co-routine checks to see if any new image files have appeared,
and if they have it loads them into memory and updates the play list.
The second co-routine remembers how far through the cycle it is and
outputs the next image. Both routines need to remember the previous
state they were left in, so simple function calls are going to be
inadequate unless you rely on global variables.


-- Sleeping in Lua - no built in method, and delay loops that
-- keep checking the clock are going to burn c.p.u. cycles, so ...

sleep_awhile = function (period)
        os.execute("sleep "..period)

load_images = function()
        -- see if any new files have appeared
        -- if they HAVE, read them into cache buffer
        while true do
                nnew = 0
                phandle = io.popen("ls -1","r")
                imnames = {}
                        while true do
                        lyne = phandle:read()
                        if lyne == nil then break end
                        imnames[#imnames+1] = lyne
                        if image_list[lyne] == nil then
                                fh = io.open(lyne,"r")
                                image_list[lyne] = fh:read("*all")
                                nnew = nnew + 1
                -- temporary return - pass back count of extras loaded
                print ("AGAIN ...")

show_images = function()
        -- Pass back NEXT image in sequence
        count = 0
        while true do
                count = count + 1
                current = 1 + math.floor(count % #imnames)
                print (current, imnames[current])

-- ======= Main code =============

image_list = {}
zonked = 0
tap = coroutine.create(load_images)
plughole = coroutine.create(show_images)

while zonked == 0 do
        itdidit,newcount = coroutine.resume(tap)
        print (newcount)
        itdidit = coroutine.resume(plughole)

--[[ ========== Sample Output ================

[trainee@easterton nats]$ lua ff2.lua
2 anim_o1.lua
3 bpm
4 clever


Learn about this subject
This module and example are covered on the following public courses:
 * Learning to program in Lua
 * Lua Programming
 * Lua Programming
Also available on on site courses for larger groups

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Other Examples
This example comes from our "Threading and Coroutines." training module. You'll find a description of the topic and some other closely related examples on the "Threading and Coroutines." module index page.

Full description of the source code
You can learn more about this example on the training courses listed on this page, on which you'll be given a full set of training notes.

Many other training modules are available for download (for limited use) from our download centre under an Open Training Notes License.

Other resources
• Our Solutions centre provides a number of longer technical articles.
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Web site author
This web site is written and maintained by Well House Consultants.

Purpose of this website
This is a sample program, class demonstration or answer from a training course. It's main purpose is to provide an after-course service to customers who have attended our public private or on site courses, but the examples are made generally available under conditions described below.

Conditions of use
Past attendees on our training courses are welcome to use individual examples in the course of their programming, but must check the examples they use to ensure that they are suitable for their job. Remember that some of our examples show you how not to do things - check in your notes. Well House Consultants take no responsibility for the suitability of these example programs to customer's needs.

This program is copyright Well House Consultants Ltd. You are forbidden from using it for running your own training courses without our prior written permission. See our page on courseware provision for more details.

Any of our images within this code may NOT be reused on a public URL without our prior permission. For Bona Fide personal use, we will often grant you permission provided that you provide a link back. Commercial use on a website will incur a license fee for each image used - details on request.

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