Global Variable Safety with Multi-tasking

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  • Posted by cp Aug 13, 2012
  • 1624 views

What technique (if any) do I need to use to ensure safety when using global variables with real-time tasks?

For example two real-time tasks need to access a global sequence. Task A will read from configuration file every few minutes and may update (add or remove) some elements in the global sequence. Task B will loop thru the elements in the global sequence performing some operations.

If task B yields to task A and task A changes the number of elements in the sequence, when execution returns to task B that could cause a problem with the "for" loop count?

Do I need to ensure that task B only yields after the for loop is complete to be safe? something like: 

procedure task_B() 
while 1 
for i = 1 to length(seqGlobal) do 
 DoSomeStuff(seqGlobal[i]) 
end for 
task_yield() 
end while 
end procedure

Or are their other options which will allow yield more often within the for loop?

thanks, Casey

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