What's the difference between spawn and call?

[Maurdekye 10]

Both commands seem to do exactly the same thing, and I'm not sure why there are two separate ones.

[sxp2high 22]

spawn creates a new thread/vm (virtual machine)

call executes code within the same thread

call { sleep 5; };
hint "This will be shown after 5 sec.";

[] spawn { sleep 5; };
hint "This will be shown instantly.";

Local variables are also to be considered. That's why local variables in called code should be made private.

_test = 123;
call { hint format[" %1", _test]; }; // Will display 123
hint format[" %1", _test]; // Will display 123

_test = 123;
call {
private ["_test"];
_test = 456;
hint format[" %1", _test]; // Will display 456
};
hint format[" %1", _test]; // Will display 123

_test = 123;
[] spawn {
_test = 456;
hint format[" %1", _test]; // Will display 456
};
hint format[" %1", _test]; // Will display 123

Has been asked recently here.

[Maurdekye 10]

Thanks for the explanation. I kind of had that sort of idea already, but I wasn't absolutely sure.

[bangabob 41]

Calls can also be used to return values.

This function will return half of any number input.

My_fnc= {
_N=(_this select 0);
_N=_N * 0.5;
_N
};

_newVal = [5] call my_fnc;
Hint str _newVal;