src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Observable<T> throttleFirst(long skipDuration, TimeUnit unit, Scheduler scheduler) {
        ObjectHelper.requireNonNull(unit, "unit is null");
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
        return RxJavaPlugins.onAssembly(new ObservableThrottleFirstTimed<T>(this, skipDuration, unit, scheduler));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Observable<T> throttleFirst(long skipDuration, TimeUnit unit, Scheduler scheduler) {
        ObjectHelper.requireNonNull(unit, "unit is null");
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
        return RxJavaPlugins.onAssembly(new ObservableThrottleFirstTimed<T>(this, skipDuration, unit, scheduler));
    }
@ CheckReturnValue @ SchedulerSupport ( SchedulerSupport . CUSTOM ) public final Observable < T > throttleFirst ( long skipDuration , TimeUnit unit , Scheduler scheduler ) { ObjectHelper . requireNonNull ( unit , "unit is null" ) ; ObjectHelper . requireNonNull ( scheduler , "scheduler is null" ) ; return RxJavaPlugins . onAssembly ( new ObservableThrottleFirstTimed < T > ( this , skipDuration , unit , scheduler ) ) ; }
Returns an Observable that emits only the first item emitted by the source ObservableSource during sequential
time windows of a specified duration, where the windows are managed by a specified Scheduler.
<p>
This differs from {@link #throttleLast} in that this only tracks passage of time whereas
{@link #throttleLast} ticks at scheduled intervals.
<p>
<img width="640" height="305" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/throttleFirst.s.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>You specify which {@link Scheduler} this operator will use.</dd>
</dl>

@param skipDuration
time to wait before emitting another item after emitting the last item
@param unit
the unit of time of {@code skipDuration}
@param scheduler
the {@link Scheduler} to use internally to manage the timers that handle timeout for each
event
@return an Observable that performs the throttle operation
@see <a href="http://reactivex.io/documentation/operators/sample.html">ReactiveX operators documentation: Sample</a>
Returns an Observable that emits only the first item emitted by the source ObservableSource during sequential time windows of a specified duration where the windows are managed by a specified Scheduler . <p > This differs from { @link #throttleLast } in that this only tracks passage of time whereas { @link #throttleLast } ticks at scheduled intervals . <p > <img width = 640 height = 305 src = https : // raw . github . com / wiki / ReactiveX / RxJava / images / rx - operators / throttleFirst . s . png alt = > <dl > <dt > <b > Scheduler : < / b > < / dt > <dd > You specify which { @link Scheduler } this operator will use . < / dd > < / dl >