Go Memory Allocation

What is memory allocation

Memory allocation is the process of how programming languages store or keep track of in-memory data like variables, arguments or any other data in your program’s runtime.

There are two places where the runtime keeps track of memory; Heap & Stack

Heap

A Heap (same name as the data structure but not related at all) is a portion of physical memory on your machine where global variables, arguments or any data used by the runtime is stored. Heaps are generally shared by the entire program meaning that all stacks have access to data stored in the heap.

Data in the heap stays in the heap until it is freed or your program terminates.

Go has aGarbage Collector and it is responsible for freeing up unused data in the heap automatically for us (we can manipulate this behaviour with the runtime package)

Stack

Stack is a short lived memory space to store data that is local to a function or a thread (goroutine).

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Memory in the stack are removed once the function or goroutine returns/terminates.

Any new memory that is created inside of a stack that is passed and used outside of the stack (passed up the stack) is said to have escaped to the heap. This is when the memory is “transferred” over to the heap from the stack.

Passing down the stack

Passing down the stack refers to passing an address of a variable instead of the value of the variable itself down to a function.

Example of Passing down the stack:

package main

func main() {
    num := 2
    add(&num)
}

func add(i int) {
    result := *i + 10
    return result
}

Passing up the stack

Passing up the stack refers to passing an address of a variable instead of the value of the variable itself up/outside the function.

Example of passing up the stack:

package main

func main() {
    num := getNum()
}
func getNum() int {
    number := 7
    // This causes the variable number to be moved to the heap
    return &number 
}