private Tuple <long, long, long> Create(RateQuota rateQuota)
{
long limit;
long csii; //信元发送的间隔时间
long cdvt; //信元发送时间间隔的变化容限
switch (rateQuota.PeriodType)
{
case RateLimitPeriod.Min:
csii = TimeSpan.FromTicks(TimeSpan.TicksPerMinute / rateQuota.MaxRate).Ticks;
break;
case RateLimitPeriod.Hour:
csii = TimeSpan.FromTicks(TimeSpan.TicksPerHour / rateQuota.MaxRate).Ticks;
break;
case RateLimitPeriod.Day:
csii = TimeSpan.FromTicks(TimeSpan.TicksPerDay / rateQuota.MaxRate).Ticks;
break;
case RateLimitPeriod.Week:
csii = TimeSpan.FromTicks(TimeSpan.TicksPerDay * 7 / rateQuota.MaxRate).Ticks;
break;
default:
csii = TimeSpan.FromTicks(TimeSpan.TicksPerSecond / rateQuota.MaxRate).Ticks;
break;
}
limit = rateQuota.MaxBurst + 1;
cdvt = csii * limit;
return(Tuple.Create(limit, csii, cdvt));
}
/// <summary>
/// 参数构造函数
/// </summary>
/// <param name="rateQuota"><see cref="RateQuota"/></param>
/// <param name="identity">唯一标识</param>
/// <param name="quantity">总量</param>
/// <returns></returns>
public RateLimitResult RateLimit(RateQuota rateQuota, string identity, int quantity = 1)
{
if (rateQuota.MaxRate < 1)
{
throw new IndexOutOfRangeException("MaxBurst必须大于0");
}
if (rateQuota.MaxBurst < 1)
{
throw new IndexOutOfRangeException("MaxBurst必须大于0");
}
var gcra = Create(rateQuota);
long limit = gcra.Item1, csii = gcra.Item2, cdvt = gcra.Item3;
var result = new RateLimitResult {
MaxLimit = limit, RetryAfter = NoneRetry
};
TimeSpan ttl;
DateTimeOffset tat, newTat;
var i = 0;
while (true)
{
var now = DateTimeOffset.UtcNow;
var existKey = _rateLimitStore.TryGet(identity, out long tatVal);
if (existKey)
{
tat = DateTimeOffset.FromUnixTimeMilliseconds(tatVal);
}
else
{
tat = now;
}
//根据获取数量计算间隔幅度
var increment = quantity * csii;
if (now > tat)
{
newTat = now.AddTicks(increment);
}
else
{
newTat = tat.AddTicks(increment);
}
var allowAt = newTat.AddTicks(-cdvt);
var diff = now.Ticks - allowAt.Ticks;
if (diff < 0)
{
if (increment <= cdvt)
{
result.RetryAfter = TimeSpan.FromTicks(-diff);
}
ttl = tat - now;
result.Limited = true;
break;
}
ttl = newTat - now;
bool updated;
if (existKey)
{
updated = _rateLimitStore.Update(identity, newTat.ToUnixTimeMilliseconds(), ttl);
}
else
{
updated = _rateLimitStore.Add(identity, newTat.ToUnixTimeMilliseconds(), ttl);
}
if (updated)
{
break;
}
i++;
if (i > MaxCASAttempts)
{
throw new CASException($"{identity}速率限制存储更新失败超过{i}次。");
}
}
var next = cdvt - ttl.Ticks;
if (next > -csii)
{
result.Remaining = (int)(next / csii);
}
result.ResetAfter = ttl;
return(result);
}
