public async ValueTask <Dictionary <IDatabase, Task <bool> >?> TryAcquireAsync()
{
this._cancellationToken.ThrowIfCancellationRequested();
var isSynchronous = SyncViaAsync.IsSynchronous;
if (isSynchronous && this._databases.Count == 1)
{
return(this.TrySingleFullySynchronousAcquire());
}
var primitive = this._primitive;
var tryAcquireTasks = this._databases.ToDictionary(
db => db,
db => Helpers.SafeCreateTask(state => state.primitive.TryAcquireAsync(state.db), (primitive, db))
);
var waitForAcquireTask = this.WaitForAcquireAsync(tryAcquireTasks);
var succeeded = false;
try
{
succeeded = await waitForAcquireTask.AwaitSyncOverAsync().ConfigureAwait(false);
}
finally
{
// clean up
if (!succeeded)
{
List <Task>?releaseTasks = null;
foreach (var kvp in tryAcquireTasks)
{
// if the task hasn't finished yet, we don't want to do any releasing now; just
// queue a release command to run when the task eventually completes
if (!kvp.Value.IsCompleted)
{
RedLockHelper.FireAndForgetReleaseUponCompletion(primitive, kvp.Key, kvp.Value);
}
// otherwise, unless we know we failed to acquire, do a release
else if (!RedLockHelper.ReturnedFalse(kvp.Value))
{
if (isSynchronous)
{
try { primitive.Release(kvp.Key, fireAndForget: true); }
catch { }
}
else
{
(releaseTasks ??= new List <Task>())
.Add(Helpers.SafeCreateTask(state => state.primitive.ReleaseAsync(state.Key, fireAndForget: true), (primitive, kvp.Key)));
}
}
}
if (releaseTasks != null)
{
await Task.WhenAll(releaseTasks).ConfigureAwait(false);
}
}
}
return(succeeded ? tryAcquireTasks : null);
}
public async Task <bool?> TryExtendAsync()
{
Invariant.Require(!SyncViaAsync.IsSynchronous, "should only be called from a background renewal thread which is async");
var incompleteTasks = new HashSet <Task>();
foreach (var kvp in this._tryAcquireOrRenewTasks.ToArray())
{
if (kvp.Value.IsCompleted)
{
incompleteTasks.Add(
this._tryAcquireOrRenewTasks[kvp.Key] = Helpers.SafeCreateTask(
state => state.primitive.TryExtendAsync(state.database),
(primitive: this._primitive, database: kvp.Key)
)
);
}
else
{
// if the previous acquire/renew is still going, just keep waiting for that
incompleteTasks.Add(kvp.Value);
}
}
// For extension we use the same timeout as acquire. This ensures the same min validity time which should be
// sufficient to keep extending
using var timeout = new TimeoutTask(this._primitive.AcquireTimeout, this._cancellationToken);
incompleteTasks.Add(timeout.Task);
var databaseCount = this._tryAcquireOrRenewTasks.Count;
var successCount = 0;
var failCount = 0;
while (true)
{
var completed = await Task.WhenAny(incompleteTasks).ConfigureAwait(false);
if (completed == timeout.Task)
{
await completed.ConfigureAwait(false); // propagate cancellation
return(null); // inconclusive
}
if (completed.Status == TaskStatus.RanToCompletion && ((Task <bool>)completed).Result)
{
++successCount;
if (RedLockHelper.HasSufficientSuccesses(successCount, databaseCount))
{
return(true);
}
}
else
{
// note that we treat faulted and failed the same in extend. There's no reason to throw, since
// this is just called by the extend loop. While in theory a fault could indicate some kind of post-success
// failure, most likely it means the db is unreachable and so it is safest to consider it a failure
++failCount;
if (RedLockHelper.HasTooManyFailuresOrFaults(failCount, databaseCount))
{
return(false);
}
}
incompleteTasks.Remove(completed);
}
}
private async Task <bool> WaitForAcquireAsync(IReadOnlyDictionary <IDatabase, Task <bool> > tryAcquireTasks)
{
using var timeout = new TimeoutTask(this._primitive.AcquireTimeout, this._cancellationToken);
var incompleteTasks = new HashSet <Task>(tryAcquireTasks.Values)
{
timeout.Task
};
var successCount = 0;
var failCount = 0;
var faultCount = 0;
while (true)
{
var completed = await Task.WhenAny(incompleteTasks).ConfigureAwait(false);
if (completed == timeout.Task)
{
await completed.ConfigureAwait(false); // propagates cancellation
return(false); // true timeout
}
if (completed.Status == TaskStatus.RanToCompletion)
{
var result = await((Task <bool>)completed).ConfigureAwait(false);
if (result)
{
++successCount;
if (RedLockHelper.HasSufficientSuccesses(successCount, this._databases.Count))
{
return(true);
}
}
else
{
++failCount;
if (RedLockHelper.HasTooManyFailuresOrFaults(failCount, this._databases.Count))
{
return(false);
}
}
}
else // faulted or canceled
{
// if we get too many faults, the lock is not possible to acquire, so we should throw
++faultCount;
if (RedLockHelper.HasTooManyFailuresOrFaults(faultCount, this._databases.Count))
{
var faultingTasks = tryAcquireTasks.Values.Where(t => t.IsCanceled || t.IsFaulted)
.ToArray();
if (faultingTasks.Length == 1)
{
await faultingTasks[0].ConfigureAwait(false); // propagate the error
}
throw new AggregateException(faultingTasks.Select(t => t.Exception ?? new TaskCanceledException(t).As <Exception>()))
.Flatten();
}
++failCount;
if (RedLockHelper.HasTooManyFailuresOrFaults(failCount, this._databases.Count))
{
return(false);
}
}
incompleteTasks.Remove(completed);
Invariant.Require(incompleteTasks.Count > 1, "should be more than just timeout left");
}
}
public async ValueTask ReleaseAsync()
{
var isSynchronous = SyncViaAsync.IsSynchronous;
var unreleasedTryAcquireOrRenewTasks = this._tryAcquireOrRenewTasks.ToDictionary(kvp => kvp.Key, kvp => kvp.Value);
List <Exception>?releaseExceptions = null;
var successCount = 0;
var faultCount = 0;
var databaseCount = unreleasedTryAcquireOrRenewTasks.Count;
try
{
while (true)
{
var releaseableDatabases = unreleasedTryAcquireOrRenewTasks.Where(kvp => kvp.Value.IsCompleted)
// work through non-faulted tasks first
.OrderByDescending(kvp => kvp.Value.Status == TaskStatus.RanToCompletion)
// then start with failed since no action is required to release those
.ThenBy(kvp => kvp.Value.Status == TaskStatus.RanToCompletion && kvp.Value.Result)
.Select(kvp => kvp.Key)
.ToArray();
foreach (var db in releaseableDatabases)
{
var tryAcquireOrRenewTask = unreleasedTryAcquireOrRenewTasks[db];
unreleasedTryAcquireOrRenewTasks.Remove(db);
if (RedLockHelper.ReturnedFalse(tryAcquireOrRenewTask))
{
// if we failed to acquire, we don't need to release
++successCount;
}
else
{
try
{
if (isSynchronous)
{
this._primitive.Release(db, fireAndForget: false);
}
else
{
await this._primitive.ReleaseAsync(db, fireAndForget : false).ConfigureAwait(false);
}
++successCount;
}
catch (Exception ex)
{
(releaseExceptions ??= new List <Exception>()).Add(ex);
++faultCount;
if (RedLockHelper.HasTooManyFailuresOrFaults(faultCount, databaseCount))
{
throw new AggregateException(releaseExceptions !).Flatten();
}
}
}
if (RedLockHelper.HasSufficientSuccesses(successCount, databaseCount))
{
return;
}
}
// if we haven't released enough yet to be done or certain of success or failure, wait for another to finish
if (isSynchronous)
{
Task.WaitAny(unreleasedTryAcquireOrRenewTasks.Values.ToArray());
}
else
{
await Task.WhenAny(unreleasedTryAcquireOrRenewTasks.Values).ConfigureAwait(false);
}
}
}
finally // fire and forget the rest
{
foreach (var kvp in unreleasedTryAcquireOrRenewTasks)
{
RedLockHelper.FireAndForgetReleaseUponCompletion(this._primitive, kvp.Key, kvp.Value);
}
}
}
