Without knowing much about Tie::File, it seems that you either don't know or have forgot about the concept of prototyping.
Whe you define a sub in Perl, you do it by writing 
sub NAME {
   CODE
}

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There is another option though, which is prototyping. This means that you can provide the compiler with additional information to facilitate the calls to your subroutine. this prototyping is done with the following syntax 
sub NAME (PROTOTYPES) {
   CODE
}

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Note the additional parens. When PROTOTYPES is the empty string, i.e. when you just provide parens, the compiler will always call your function in a void context and the @_ array will be empty.
You get the first few error messages, because the compiler "knows" that the sub is prototyped but it doesn't know the prototype yet, I don't know about the last few error messages.
In any case, changing your function declaration to 
sub update_threads() {

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should at least eliminate the first few error messages.

P.S.: Which part of your code has what line number?

In reply to Re: Tie::File strangeness with unshift by CombatSquirrel
in thread Tie::File strangeness with unshift by u914

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