An idea on multithreading implementation

[Kee Nethery]

My two cents on how Livecode could implement this is to mimic the get URL and URLstatus functionality paired with functions. For example:

This is a simple pseudo-code example of calling a threaded function 7 times and then waiting until all 7 threads are complete:

on domythreads
   global lat,long,countryName
   put myThreadFunction(1,lat[1],long[1]) into countryName[1]
   put myThreadFunction(2,lat[2],long[2]) into countryName[2]
   put myThreadFunction(3,lat[3],long[3]) into countryName[3]
   put myThreadFunction(4,lat[4],long[4]) into countryName[4]
   put myThreadFunction(5,lat[5],long[5]) into countryName[5]
   put myThreadFunction(6,lat[6],long[6]) into countryName[6]
   put myThreadFunction(7,lat[7],long[7]) into countryName[7]

   repeat until threadStatus(1) = "complete" \
      and threadStatus(2) = "complete" \
      and threadStatus(3) = "complete" \
      and threadStatus(4) = "complete" \
      and threadStatus(5) = "complete" \
      and threadStatus(6) = "complete" \
      and threadStatus(7) = "complete" 
     wait 1 second
   end repeat
end domythreads

This is what I envision the generic thread call looks like, similar to a function except it has a unique ID and it cannot use globals or data in the stack. Everything it is going to use has to be passed into it as a parameter. 

thread myThreadFunction requiredThreadIdParameter, optionalThreadParameter1, optionalThreadParameter2, etc.
  set threadStatus = "started" -- allow the thread to communicate while it is working
  do stuff
  call functions in the stack that do not have globals nor use data stored in the stack
  send to commands to objects in the stack that do not have globals nor use data stored in the stack
  no reads or writes from any field or button data stored in the stack 
  set threadStatus = "almost done"
  OK to get or write stuff from/to external things like URLs or serial ports or files
  package up a result
  return allTheResults
  -- after the return the status goes to "complete"
end thread

The way I see it, thread is like a function. You give it a unique ID (requiredThreadIdParameter) and then call it with the parameters you want it to have. What would happen next is Livecode would execute the scripts using the scripts in the stacks that are marked as thread safe using the data provided as parameters. 

The other part to this is the threadStatus function. In the above example the code just looks for the status to be complete but since the thread can set threadStatus, the main program can watch it's progress.

I guess my final thread request would be a way to kill a thread that has gone rogue. For example, perhaps a function like killThread(requiredThreadIdParameter)

As I see it, each function or command (or thread) in a script would get a marker declaring it thread safe or not. A thread could only call thread safe code. If the code had a global in it, not thread safe. if the code looked in a field, not thread safe.

Anyway that's my two cents on multithreading if I ruled the Livecode world. Seems like it would be easy enough to implement in the existing code base but still quite powerful.

I do something similar to this with URLs. A stack running as a HTTP server / cgi gets hit and it doles out a bunch of URL requests to various other servers. All those servers work in parallel and when they are done and the urlStatus for each request is "cached", I grab the results and return a summary to the client.

Kee Nethery
not holding my breath.