private async ValueTask StoreOrDisposeLockAsync(string connectionString, MultiplexedConnectionLock @lock, bool shouldDispose)
{
if (shouldDispose)
{
try { await @lock.DisposeAsync().ConfigureAwait(false); }
catch { /* swallow */ }
}
using (await this._lock.AcquireAsync(CancellationToken.None).ConfigureAwait(false))
{
++this._storeCountSinceLastPrune;
if (shouldDispose)
{
// If we're about to dispose the lock, check if it has an empty pool that can be removed from our dictionary.
// By itself this doesn't guarantee cleanup: after a successful acquire we'll have an empty lock left over that won't
// go away unless we use THAT connection string again. To help with this, we have pruning
if (this._poolsByConnectionString.TryGetValue(connectionString, out var pool) && pool.Count == 0)
{
this._poolsByConnectionString.Remove(connectionString);
}
}
else // otherwise, store the lock
{
++this._pooledLockCount;
if (this._poolsByConnectionString.TryGetValue(connectionString, out var existing))
{
existing.Enqueue(@lock);
}
else
{
var newPool = new Queue <MultiplexedConnectionLock>();
newPool.Enqueue(@lock);
this._poolsByConnectionString.Add(connectionString, newPool);
}
}
if (this.IsDueForPruningNoLock())
{
await this.PrunePoolsNoLockAsync().ConfigureAwait(false);
}
}
}
public Handle(MultiplexedConnectionLock @lock, IDbSynchronizationStrategy <TLockCookie> strategy, string name, TLockCookie lockCookie)
{
this._name = name;
this._box = RefBox.Create((@lock, strategy, lockCookie, default(IDatabaseConnectionMonitoringHandle)));
}
public async ValueTask <IDistributedSynchronizationHandle?> TryAcquireAsync <TLockCookie>(
string connectionString,
string name,
TimeoutValue timeout,
IDbSynchronizationStrategy <TLockCookie> strategy,
TimeoutValue keepaliveCadence,
CancellationToken cancellationToken)
where TLockCookie : class
{
// opportunistic phase: see if we can use a connection that is already holding a lock
// to acquire the current lock
var existingLock = await this.GetExistingLockOrDefaultAsync(connectionString).ConfigureAwait(false);
if (existingLock != null)
{
var canSafelyDisposeExistingLock = false;
try
{
var opportunisticResult = await TryAcquireAsync(existingLock, opportunistic : true).ConfigureAwait(false);
if (opportunisticResult.Handle != null)
{
return(opportunisticResult.Handle);
}
// this will always be false if handle is non-null, so we can set if afterwards
canSafelyDisposeExistingLock = opportunisticResult.CanSafelyDispose;
switch (opportunisticResult.Retry)
{
case MultiplexedConnectionLockRetry.NoRetry:
return(null);
case MultiplexedConnectionLockRetry.RetryOnThisLock:
var retryOnThisLockResult = await TryAcquireAsync(existingLock, opportunistic : false).ConfigureAwait(false);
canSafelyDisposeExistingLock = retryOnThisLockResult.CanSafelyDispose;
return(retryOnThisLockResult.Handle);
case MultiplexedConnectionLockRetry.Retry:
break;
default:
throw new InvalidOperationException("unexpected retry");
}
}
finally
{
// since we took this lock from the pool, always return it to the pool
await this.StoreOrDisposeLockAsync(connectionString, existingLock, shouldDispose : canSafelyDisposeExistingLock).ConfigureAwait(false);
}
}
// normal phase: if we were not able to be opportunistic, ensure that we have a lock
var @lock = new MultiplexedConnectionLock(this.ConnectionFactory(connectionString));
MultiplexedConnectionLock.Result?result = null;
try
{
result = await TryAcquireAsync(@lock, opportunistic : false).ConfigureAwait(false);
Invariant.Require(result !.Value.Retry == MultiplexedConnectionLockRetry.NoRetry, "Acquire on fresh lock should not recommend a retry");
}
finally
{
// if we failed to even acquire a result on a brand new lock, then there's definitely no reason to store it
await this.StoreOrDisposeLockAsync(connectionString, @lock, shouldDispose : result?.CanSafelyDispose ?? true).ConfigureAwait(false);
}
return(result.Value.Handle);
ValueTask <MultiplexedConnectionLock.Result> TryAcquireAsync(MultiplexedConnectionLock @lock, bool opportunistic) =>
@lock.TryAcquireAsync(name, timeout, strategy, keepaliveCadence, cancellationToken, opportunistic);
}
