bool button1Int=0;
int button1Time=0;

ISR(INT0_vect) {
    EIMSK &= ~(1<<INT0); //disable this interrupt
    button1Int=1;
}
void button1Click() {
    Serial.print("test ");
}
void loop() {
    if (button1Int) {
        if(button1Time==0)
            button1Time = millis();
        if ((millis() - button1Time) > 20) {
            button1Time = 0;
            button1Int = 0;
            button1Click();
            EIFR |= 1<<INTF0; //clear iterrupt flag
            EIMSK |= 1 << INT0; //re-enable interrupt
        }
    }
}