public void DurationFromTokens(double perSecond, double durationSeconds, double tokens)
{
// arrange
var limit = new Limit(perSecond);
// act
var durationFromTokens = limit.DurationFromTokens(tokens);
// assert
durationFromTokens.ShouldBe(TimeSpan.FromSeconds(durationSeconds));
}
/// <summary>
/// wait as an asynchronous operation.
/// </summary>
/// <param name="count">The count.</param>
/// <param name="cancellationToken">The cancellation token that can be used by other objects or threads to receive notice of cancellation.</param>
/// <exception cref="Exception">rate: Wait(count={count}) exceeds limiter's burst {burst}.</exception>
/// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
public async Task WaitAsync(int count, CancellationToken cancellationToken)
{
// https://github.com/golang/time/blob/master/rate/rate.go#L226
int burst = default;
Limit limit = default;
lock (_sync)
{
burst = _burst;
limit = _limit;
}
if (count > burst && limit != Limit.Max)
{
throw new Exception($"rate: Wait(count={count}) exceeds limiter's burst {burst}");
}
// Check if ctx is already cancelled
cancellationToken.ThrowIfCancellationRequested();
// Determine wait limit
var waitLimit = limit.DurationFromTokens(count);
while (true)
{
var now = _clock.UtcNow;
var r = ReserveImpl(now, count, waitLimit);
if (r.Ok)
{
var delay = r.DelayFrom(now);
if (delay > TimeSpan.Zero)
{
await Task.Delay(delay, cancellationToken).ConfigureAwait(false);
}
return;
}
await Task.Delay(waitLimit, cancellationToken).ConfigureAwait(false);
}
}
/// <summary>
/// reserveN is a helper method for AllowN, ReserveN, and WaitN.
/// maxFutureReserve specifies the maximum reservation wait duration allowed.
/// reserveN returns Reservation, not *Reservation, to avoid allocation in AllowN and WaitN.
/// </summary>
/// <param name="now">The now.</param>
/// <param name="number">The number.</param>
/// <param name="maxFutureReserve">The maximum future reserve.</param>
/// <returns>Reservation.</returns>
private Reservation ReserveImpl(DateTimeOffset now, int number, TimeSpan maxFutureReserve)
{
lock (_sync)
{
if (_limit == Limit.Max)
{
return(new Reservation(
clock: _clock,
limiter: this,
ok: true,
tokens: number,
timeToAct: now));
}
var(newNow, last, tokens) = Advance(now);
now = newNow;
// Calculate the remaining number of tokens resulting from the request.
tokens -= number;
// Calculate the wait duration
TimeSpan waitDuration = default;
if (tokens < 0)
{
waitDuration = _limit.DurationFromTokens(-tokens);
}
// Decide result
var ok = number <= _burst && waitDuration <= maxFutureReserve;
// Prepare reservation
if (ok)
{
var reservation = new Reservation(
clock: _clock,
limiter: this,
ok: true,
tokens: number,
limit: _limit,
timeToAct: now.Add(waitDuration));
_last = newNow;
_tokens = tokens;
_lastEvent = reservation.TimeToAct;
return(reservation);
}
else
{
var reservation = new Reservation(
clock: _clock,
limiter: this,
ok: false,
limit: _limit);
_last = last;
return(reservation);
}
}
}
