Goroutine在Windows和Linux上的行为有所不同

Question

I`m new to the GO. I have a following legacy code.

var db *sql.DB

func init() {
    go feedChan()

    connString := os.Getenv("DB_CONN")
    var err error

    db, err = sql.Open("postgres", connString)
    if err != nil {
        log.Fatalf("Failed to connect to database at %q: %q
", connString, err)
    }

    // confirm connection
    if err = db.Ping(); err != nil {
        log.Fatalf("Unable to ping database at %q: %q
", connString, err)
    }
}


func feedChan() {
    selectQuery, err := db.Prepare(`
        SELECT id, proxy
        FROM proxy
        WHERE fail_count < 2
        ORDER BY date_added DESC, last_used ASC, fail_count ASC
        LIMIT 5
    `)
    ....

Following code works on linux. But it fails on windows with nil error on

selectQuery, err := db.Prepare(`

Which make sense for me, since db initialized after a launch of feedChan goroutine. What doesnt make sense for me is why it work on linux.

So the question is why this code work at linux without errors?

Answer 1

That's probably a race condition. Import "time", put this line after go feedChan(), and see if it still works on Linux:

time.Sleep(3 * time.Second)

In order to avoid this situation, you could either initialize db before you spawn the routine (which uses db) or use some sort of barrier:

func init() {
    barrier := make(chan int)
    go feedChan(barrier)

    connString := os.Getenv("DB_CONN")
    var err error
    db, err = sql.Open("postgres", connString)

    if err != nil {
        log.Fatalf("Failed to connect to database at %q: %q
", connString, err)
        // Retry.
    } else {
        barrier <- 1 // Opens barrier.
    }
    // ...
}


func feedChan(barrier chan int) {
    <-barrier // Blocks until db is ready.
    selectQuery, err := db.Prepare(`
        SELECT id, proxy
        FROM proxy
        WHERE fail_count < 2
        ORDER BY date_added DESC, last_used ASC, fail_count ASC
        LIMIT 5
    `)
    // ...
}