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goexception-safety

Are deferred functions called when calling log.Fatalln?

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?

Solution

  • 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.