I was wondering the rule on MULTI-THREADING when trying to make something THREAD SAFE.
I Have multiple threads running, and I MADE EACH have its OWN set of VARIABLES - so there isn't VARIABLE Stomping from other THREADS.
The routines I CALL USUALLY have a few variables they use to keep track of counters or stuff that is only VALID during the life of the Call.
My Problem is sometimes THESE Variables that are local to the sub routines are getting stomped in longer routines (That perhaps are getting task switched).
My Question: Do I NEED to write THREAD SAFE ROUTINES in a manner so they do NOT have any local variables?
Example Pseudo Code - Hoping Someone can verify or deny I understand this right.
-------------------
Type JThread= Class(TTHREAD)
MyOwnVariable: Ansistring;
MyOwnInteger: Integer;
Procedure MyRoutine(var p_MyOwnVariable: ansistring);
Procedure EXECUTE; override;
End;
Procedure JThread.EXECUTETHREAD;
Begin
Repeat
MyRoutine(MyOwnVariable);
Until 1=2;
End;
Var MYTHREAD1: JTHREAD;
Var MYTHREAD2: JTHREAD;
Procedure MyRoutine(var p_MyOwnVariable: ansistring);
Var i: integer;
Begin
For i=0 to 100 do begin
Write('AM I SAFE TO USE i?'+
'DURING LIFE OF this '+
'routine while other '+
'threads use same routine?'+
inttostr(i));
end;
// CHANGE Thread Class Vari Sample via reference
p_MyOwnVariable:='Hi Mom';
end;
begin
MYTHREAD1:=JTHREAD.Create;
MYTHREAD1.EXECUTETHREAD;
MYTHREAD2:=JTHREAD.Create;
MYTHREAD2.EXECUTETHREAD;
Repeat until 1=2;
End.The Question is the local variable "i" safe all the time? Does it get its own stack space? Or does it get stomped by multiple threads because its only allocated in memory one time but multiple threads are calling the routine "My Routine"
My experience has led me to the impression that local variables are allocated on the stack. If they are, does each thread own its own stack space? Do local variables get allocated on the THREAD's Stack? Or the main program's?
Are AnsiStrings managed intelligently in threaded applications? Meaning - do they have the same rules as other variables concerning multi-threaded applications or does the memory counters or "reference counts" to chunk of mem get hosed?
Thanx for any and all responses!
Jason P Sage