Editing Global variable (section)

==Use==
Interaction mechanisms with global variables are called '''global environment''' (see also '''global state''') mechanisms. The global environment paradigm is contrasted with the [[local environment]] paradigm, where all variables are [[subprogram#Local variables, recursion and reentrancy|local]] with no [[Shared memory (interprocess communication)|shared memory]] (and therefore all interactions can be reconducted to [[message passing]]).

Global variables are used extensively to pass information between sections of code that do not share a caller/callee relation like concurrent threads and signal handlers.  Languages (including C) where each file defines an implicit namespace eliminate most of the problems seen with languages with a global [[namespace]] though some problems may persist without proper encapsulation.  Without proper locking (such as with a [[mutex]]), code using global variables will not be [[thread-safe]] except for read only values in [[protected memory]].