21.10.2013 14:45, Rainer Gerhards:
yeah, mmsequence works, and it does so because it kind of atomically
increments the global count saves this value to the message variable.
If I had already implemented that (planned) function, you could do the
same thing in scripting via
set $$!msgctr = atomic_inc($$/zz); and use $$!msgcntr for the rest of
the checks.
Yes, but this function does not look as a general solution, as it would
be. It is just a sequence generator, and even mmsequence is better for
this purpose. By the way, is it possible to read and set local/global
variables from the module?
(Also, I could dream of dynamic loadable functions - just like modules,
which can execute in message context.)
The so-called "SIMD" engine is very counter-intuitive, particulary when
it's syntax replicates conventional shell. (It is not SIMD, in reality,
because it iterates every line instead of executing in parallel.) It is
transparent for local variables and messages, but it is disastrous for
global variables. Everytime anyone will do complex computations with
global variables, he will be surprised with unexpected results. And, for
complex I mean computation which consist of more than one line of
script, which is like anyone does in every scripting language. Worse
yet, it will work for tests under low load, where batch=1, but will fail
at production. Those implications need to be noted in BIG RED LETTERS
everywhere to prevent user's confusion.
But global variables are still useful for some kind of things. Like,
say, changing rsyslog's behaviour without reload. And, to some extent,
for rough counters; but I honestly cannot contrive any valid application
for that.
Consistent look is good, while global variable remains constant. It
becomes worse when a user thinks that similarily looking entities will
behave alike.
To work around known limitations, I would suggest something like
enclosing group of statements into a block, which is either executed
atomically or supports locking for global variables. Something like this:
Atomic {
set $/var1 = $/var1 + 1;
if $/var1 > 10000 and $/var2 == "waiting" then {
set $/var2 = "overload";
}
}
Or
Do (lock="$/var1 $/var2") {
set $/var1 = $/var1 + 1;
if $/var1 > 10000 and $/var2 == "waiting" then
set $/var2 = "overload";
}
Just thoughts.
--
Pavel Levshin
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