public async Task Release(SemaphoreContext context)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
var db = multiplexer.GetDatabase(database);
await db.SortedSetRemoveAsync(context.SemaphoreName, context.Identifier);
await db.SortedSetRemoveAsync(context.CounterSet, context.Identifier);
}
/// <summary>
/// Attempts to get a spot in the semaphore without first holding a lock
/// </summary>
/// <param name="semaphoreName"></param>
/// <param name="semaphoreCount"></param>
/// <param name="timeout"></param>
/// <param name="identifier"></param>
/// <returns></returns>
private async Task <(bool wasAcquired, SemaphoreContext ctx)> TryGetSemaphoreUnsafe(
IDatabase db,
string semaphoreName,
long semaphoreCount,
TimeSpan timeout,
string identifier)
{
var counterSetName = semaphoreName + ":owner";
var counterName = semaphoreName + ":counter";
var now = DateTime.UtcNow;
var currentScore = ScoreDateTime(now);
// Anything before the cutoff score has now expired
var cutOffScore = ScoreDateTime(now - timeout);
// remove any entries that no longer have a valid semaphore
_ = await db.SortedSetRemoveRangeByScoreAsync(semaphoreName, 0, cutOffScore);
// propogate any removed entries to the owner set from the timer set
_ = await db.SortedSetCombineAndStoreAsync(
SetOperation.Intersect, counterSetName, new RedisKey[] { counterSetName, semaphoreName }, new double[] { 1, 0 });
// increment the counter and get the latest value
var counter = await db.StringIncrementAsync(counterName);
// add the current time to the timer set
await db.SortedSetAddAsync(semaphoreName, identifier, currentScore);
// add the current count to the owner set
await db.SortedSetAddAsync(counterSetName, identifier, counter);
// check our position in the list
var rank = await db.SortedSetRankAsync(counterSetName, identifier);
var ctx = new SemaphoreContext
{
SemaphoreName = semaphoreName, Identifier = identifier, CounterSet = counterSetName
};
// our rank is low enough (lower is better) so the caller has a spot in the semaphore
if (rank.HasValue && rank.Value < semaphoreCount)
{
return(true, ctx);
}
// we are too far up the semaphore list to be allowed access to the semaphore
// release our handle to the semaphore and fail the call
await Release(ctx);
return(false, null);
}
/// <summary>
/// Extend the semaphore
/// </summary>
/// <param name="context"></param>
/// <returns></returns>
public async Task <bool> TryExtendSemaphore(SemaphoreContext context)
{
var db = multiplexer.GetDatabase(database);
var currentScore = ScoreDateTime(DateTime.UtcNow);
var wasAdded = await db.SortedSetAddAsync(
context.SemaphoreName, context.Identifier, currentScore);
// we still have the semaphore, and have successfully updated it
if (!wasAdded)
{
return(true);
}
// else we added it because we lost the semaphore, so need to delete the just added version
// and return false
await Release(context);
return(false);
}