Task reentrance

quarz · March 29, 2022 at 1:00 AM

Hello.

I have just started programming on AS.

For example I want to create wrapper subroutines for PRINT instruction to add some additional info to log output:

Code

.PROGRAM LOG.pc (.$msg)
    PRINT $TIME + ": " + .$msg
.END

then I call it from two background programs:

Code

.PROGRAM main.pc ()
  WHILE TRUE DO
    IF TASK (1002) <> 1 THEN
      PCEXECUTE 2:program1.pc
    END
    
    IF TASK (1003) <> 1 THEN
      PCEXECUTE 3:program2.pc
    END
    
    TWAIT 5.0
  END  
.END

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each program1.pc and program2.pc calls LOG.pc in infinite loops:

Code

.PROGRAM program1.pc ()
  WHILE TRUE DO
    CALL LOG.pc ("program1")
    TWAIT 0.5
  END
.END

.PROGRAM program2.pc ()
  WHILE TRUE DO
    CALL LOG.pc ("program2")
    TWAIT 0.5
  END
.END

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When I start main.pc I got an error: (P1014) Cannot execute because program already in use. No = 1002.

But why? LOG.pc does not use any global variables

quarz · March 29, 2022 at 1:05 AM

For the same reason I cannot call example subroutine TcpOpenSrv.pc from two background tasks simultaneously.

Is this really a limitation of AS system or am I wrong?

**kwakisaki** · March 29, 2022 at 2:37 AM

It seems logical to me that this error occurs.

How can the same program be called at the same time by a different program.

When calling a subroutine you are placing it in the execution stack, so therefore it will be in use.

I am pretty sure no 'caching' or 'prefetching' occurs with PC Programs as there are no motion instructions allowed.

PC programs executed (including calls) are asynchronous.

Personally with a simple print instruction like that, replace the call, with the print command and it'll more than likely work fine, but as you are waiting 0.5s per cycle, I would expect you to probably see more than one consecutive print instruction for each program.

ie

Time + program1

Time + program2

Not too sure what your intentions are with this?

quarz · March 29, 2022 at 10:52 AM

Yes, I found it in AS manual.

It's a pity that it is impossible to move common parts of code to subroutines and call them independently

**kwakisaki** · March 29, 2022 at 11:20 AM

Quote from quarz

It's a pity that it is impossible to move common parts of code to subroutines and call them independently

Yes, you can by using the parse parameter feature in step 0 as you're doing.

What you can't do is simultaneously call the same program.

Variables/values which are parsed in, get grabbed and stored locally at the start of execution.

What you are doing fails at the start because they are starting together and stops one of the PC tasks.

With your auto restart routine every 5 secs, then starts it back up and as long as it starts it back up when the other task is not using the subroutine, it'll run as they are executing at different times now.

An alternative (haven't tried it, something for you to try).

PCSCAN instruction.

You can set the PC Scan time using this, so logically thinking, you should be able to introduce an offset between the PC Tasks......not sure whether this would be reliable enough, but worth a shot

Task reentrance

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