Are deferred functions called when calling log.Fatalln?

Question

db, err := sql.Open("postgres", "…")
if err != nil {
    log.Fatalln(err)
}
defer db.Close()

tpl, err := template.ParseGlob("")
if err != nil {
    log.Fatalln(err)
}

If template.ParseGlob("") returns an error, is db.Close() still being called?

Martellato

No. If you need deferred functions running, use log.Panicln – Spineless

Answer 1

No, the deferred functions aren't run.

Here's the description of log.Fatal :

Fatal is equivalent to Print() followed by a call to os.Exit(1).

log.Fatal calls os.Exit, whose description is here :

Exit causes the current program to exit with the given status code. Conventionally, code zero indicates success, non-zero an error. The program terminates immediately; deferred functions are not run.

Demonstration

If you really need to properly close resources or do some tasks before the program finishes, then don't use log.Fatal.

Bike

If calling log.Fatalln in main(), you could instead call log.Println followed by return. – Scalade

Answer 2

If you want deferred functions to be considered use "log.Panic", "log.Panicf" or "log.Panicln"

Appenzell