Threads and Procedures

[vwidmer]

Sorry, if this is a.. its right there in the manual question, but threads drive me crazy, so hope someone can help me explain a little.

If I have a program like

Code: Select all

Procedure doSOMETHING(DATA$)
	***code to dosomething**
	ProcedureReturn DATA$
EndProcedure[

Procedure getURL(URL$)
	***code to get url**
	ProcedureReturn doSOMETHING(DATA$)
EndProcedure[

Procedure YourProcedure(*Value)
Repeat
	getURL(Value)
	Delay(1000)    
  ForEver
EndProcedure

  CreateThread(@YourProcedure(), "SOMEURL")
  CreateThread(@YourProcedure(), "SOMEOTHERURL")

I know the above code is incomplete.

My problem is that it sometimes seems one of the threads will overwrite the other when its running one of the procedures. How can I stop that from happening, but still allow them to run independently and not have to wait?

Hope someone understands what I am asking, and I didn't overcomplicate it.

Thanks

[jacdelad]

Hi vwidmer,
I don't know if I get the task right and your example has a lot of errors. Try this:

Code: Select all

Procedure.s doSOMETHING(Data$)
  ;***code To dosomething**
  ProcedureReturn Data$
EndProcedure

Procedure.s getURL(URL$)
  ;***code To get url**
  ProcedureReturn doSOMETHING(URL$)
EndProcedure

Procedure YourProcedure(*Value)
  Repeat
    Debug getURL(PeekS(*Value))
    Delay(1000)    
  ForEver
EndProcedure

CreateThread(@YourProcedure(), @"SOMEURL")
CreateThread(@YourProcedure(), @"SOMEOTHERURL")
Repeat
  Delay(1)
ForEver

- Don't give a string as a parameter to a thread-procedure, use the address of the string.
- "YourProcedure" receives "*Value", but utilizes "Value", which is a different variable. You can prevent this by using "EnableExplicit". The same applies to the "getURL"-function: one variable "URL$" (which contains the string) and one "DATA$" (which is empty).
- "getURL" needs to peek (see point one on this list).
- Procedures that return strings must be declared as "Procedure.s".
- You don't wait at the end, so the program is terminated. I added a simple forever-loop, so please don't compile it into a program and abort it via IDE.

Is this helpful?

[STARGÅTE]

Some additionals from my side:
If a threaded procedure should run independently, all resources have to pass as a real copy to the thread (procedure).
This means, also variable strings have to be copied, instead of just using @String, if the Thread wants to read this string and at the same time the main program changes this string after starting the thread.
For example (main program)

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CreateThread(@AnyProcedure(), UTF8(MyString))

and the Thread:

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Procedure AnyProcedure(*StringPointer)
  LocalString = PeekS(*StringPointer, -1, #PB_UTF8)
  FreeMemory(*StringPointer)

[Olli]

I am absolutely agree with stargate. A common data block must be shared between several threads. We can also imagine the threads are as any bus. The time is explicite, with several period scales.

Code: Select all

Structure townCenter
   *TheTimes
   flashInfos.s{256}
   *TrainHours
   *busHours
EndStructure

Procedure myAction(*this.townCenter)
   With *this
      If \TheTimes ; whatever
         ; ...
      EndIf  ; whatever
   EndWith
EndProcedure

[vwidmer]

Sorry, I think my question got confusing. I am not having problem passing the thread procedure.

My question is on the "doSOMETHING" and "getURL" procedures.

I will try again an example

so once the threads are running.

They call getURL procedure

if I have in that procedure

like 2

Code: Select all

Debug URL$
Debug URL$

Most of the time they will be the same, but occasionally, I get it showing one from each procedure.
Like the getURL procedure is being run together with the 2 threads rather than running independently.

So I am expecting or thinking it works something like this:

- - - - - - - - / getURL --- doSOMETHING
Thread1 /
Thread2 \
- - - - - - - - \ getURL --- doSOMETHING


But It seems like its sometimes doing like

Thread1 \
- - - - -- - - > getURL --- doSOMETHING
Thread2 /

[juergenkulow]

Threaded
Please send a running example.

[vwidmer]

I seen this example in the help already.

I am asking if procedures called from multiple threads overlap and how to prevent it allowing all the threads to run.

[skywalk]

You need to slow down and run the most basic threaded examples from mk-soft, infratec, TI-994A and others.
My suggestion is focus on Semaphores. Mutexes are limited in scope.
Of course your threads will run independently but with Semaphores, you can control their behavior with the granularity of your code.
SignalSemaphore() / WaitSemaphore().

[mk-soft]

1. Use always compiler option thread-safe.
2. Do never change GUI objects from thread (crash)
3. Exiting Threads before end program.
4. Use not KillThread for exiting thread (Only if thread hangs)

Examples: Mini Thread Control

[AZJIO]

2. Do never change GUI objects from thread (crash)

Linux = crash
Windows = not crash

And how then to change the status bar during data processing?

[jacdelad]

Post a custom event into the main loop.

[AZJIO]

Post a custom event into the main loop.

Does not work

Works if the event has ended. If you have a long processing time and during the process you need to display information to the user at what stage the process is, then only the last line will enter the status line, perhaps all the rest will be in the queue and will be inserted in the last microsecond. That is, the user cannot monitor the process, for example, "files are being scanned", then "MD5 calculation", then "MD5 comparison", then "Finish". Instead, nothing will be output, and it will output "Done" at the end.

[jacdelad]

Erm...a quick example would be helpful. I post events over events in my threads and it works fine. Also this is the ways it shall be done.

[AZJIO]

Try the program: "Search duplicates" https://www.purebasic.fr/english/viewtopic.php?t=79382
Use source: "Search_duplicates (Linux) En.pb"
In the "Compare" procedure, uncomment the lines "StatusBarText(#StatusBar, ...".

Perform a search, it is not necessary to do a delete, you will simply get a list of duplicates without changing anything in your file system, but at the same time, see if you get a status bar output for intermediate steps. Another option made using thread (Search_duplicates +Thread (Windows) En.pb) outputs as expected. There is nothing special, sequential actions, they do not interfere with the output in any way, they are simply executed under one button press event and there will be no output until the event ends.

[jacdelad]

Hm, ok, I only use Windows. I thought using PostMessage would be inteded to be used with every platform...