Multitasking question
I am worried by the following scenario, which is bound to happen more and
more as using of tasks will spread.
lib1.e has a routine r1 which accesses a local variable v1. For instance, r1
may be recursive and v1 holds intermediate results. It does not use threads.
It calls a routine r2 in a third party lib2.e
Currently, lib2.e doesn't use threads, and everything works as expected.
lib2.e gets upgraded so that r2() now has a task_yield() statement in it.
The task switch that will occur then may well cause a thread to execute r1()
again using a new value for v1. Code in lib1.e then randomly crashes as,
when it resumes, r1() does not find consistent values in v1. Or worse yet,
it may not crash but produce unexpected results.
I think there is a real need for some mechanism to preserve local
(filewide) variables in a multitasking environement, even cooperative, as
the example above shows.
Several possibilities can be explored:
1/ introduce a new "thread" prefix for variables. It will instruct the
interpreter to define multiple instances of the variable, one for each
thread that ever accesses it. An error should be raised if "thread" is used
with a routine, global variable or private variable.
2/ Diminish the necessity of local variables by introducing symbols shared
between routines. You might then have:
integer n
function f1()
-- some code here
end function
function f2()
-- some more code here
end function
share n r1,r2
The last line would instruct the interpreter to treat n as a private
variable common to r1 and r2, and no longer as a local symbol.
"share n r1" then would be equivalent to "share n between all active
instances of r1", in other words, would define a static variable.
If allowed for global symbols, this would allow routines to exchange
information without polluting the unnamed namespace, which would greatly
help Eu being more modular.
CChris
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