Πού βρίσκεται η μεταβλητή όταν επισημαίνεται σε μια goroutine;

A variable can be allocated either on a goroutine's stack or on the heap. This is determined by the escape analysis mechanism of the Go compiler.

Basic principles of escape analysis:

• If the compiler can prove that the variable only lives within a single function call or only within the stack of a goroutine (i.e., it is not referenced from outside), it is allocated on that goroutine's stack. This is faster, as the stack is managed automatically and does not require garbage collection.
• If the compiler cannot prove that the variable is limited to the stack, or if there are references to it from outside (e.g., passed by pointer to another function, written into a global variable, returned from a function via a pointer), it is allocated on the heap. The heap requires garbage collection, which can slow down execution.

Example of stack allocation:

// The variable 'x' is allocated on the goroutine's stack because it is only used within the function.
func exampleStack() int {
	x := 10
	return x
}

Example of heap allocation:

// The variable 'p' (pointer to int) and the int it points to can be allocated on the heap.
// This happens because the pointer is returned from the function and can be used externally.
func exampleHeap() *int {
	x := 20 // The value 20 can be allocated on the heap
	return &x // Return the address of variable x
}

Escape analysis occurs during compilation. It can be checked using the -gcflags "-m" flag:

// Build command with escape analysis flag
go build -gcflags "-m" your_package_name

The compiler output will show which variables "escape to heap".

Therefore, the location of the variable (stack vs heap) is not determined by whether the variable is allocated in a goroutine, but by how the Go compiler analyzes its lifecycle and scope.