/// <summary>
/// advance calculates and returns an updated state for lim resulting from the passage of time.
/// lim is not changed.
/// advance requires that lim.mu is held.
/// </summary>
/// <param name="now">The now.</param>
private (DateTimeOffset newNow, DateTimeOffset newLast, double newTokens) Advance(DateTimeOffset now)
{
lock (_sync)
{
var last = _last;
if (now < last)
{
last = now;
}
// Avoid making delta overflow below when last is very old.
var maxElapsed = _limit.DurationFromTokens(_burst - _tokens);
var elapsed = now - last;
if (elapsed > maxElapsed)
{
elapsed = maxElapsed;
}
// Calculate the new number of tokens, due to time that passed.
var delta = _limit.TokensFromDuration(elapsed);
var tokens = _tokens + delta;
if (tokens > _burst)
{
tokens = _burst;
}
return(now, last, tokens);
}
}
public void TokensFromDuration(double perSecond, double durationSeconds, double tokens)
{
// arrange
var limit = new Limit(perSecond);
// act
var tokensFromDuration = limit.TokensFromDuration(TimeSpan.FromSeconds(durationSeconds));
// assert
tokensFromDuration.ShouldBe(tokens);
}