/// <summary>
/// The internal lock extender.
/// </summary>
/// <returns></returns>
private async Task LockExtender()
{
while (!_disposeCancellation.IsCancellationRequested)
{
// wait
await Task.Delay(_refreshSpan).ConfigureAwait(false);
// get expiry time
TimeSpan expiryTime = _expirySpan;
// gather all locks that need to be refreshed or expired
RedisLockHandle[] refreshableLocks = null;
IEnumerable <RedisLockHandle> expiredLocks = null;
lock (_handles) {
refreshableLocks = _handles.Where(h => h.RefreshedAt <(DateTime.UtcNow - TimeSpan.FromSeconds(30)) || h.ExpiresAt> DateTime.UtcNow).ToArray();
expiredLocks = _handles.Where(h => h.ExpiresAt < DateTime.UtcNow);
// process any expires locks
foreach (RedisLockHandle handle in expiredLocks)
{
_handles.Remove(handle);
}
}
// build refresh lock tasks
List <Task <bool> > refreshLockTasks = new List <Task <bool> >(refreshableLocks.Length);
Dictionary <Task <bool>, RedisLockHandle> refreshLockHandles = new Dictionary <Task <bool>, RedisLockHandle>();
Dictionary <Task <bool>, DateTime> refreshLockTimes = new Dictionary <Task <bool>, DateTime>();
foreach (RedisLockHandle handle in refreshableLocks)
{
// create task
Task <bool> task = _database.LockExtendAsync($"tandem.{handle.ResourceURI.ToString()}", handle.Token.ToString(), expiryTime);
// add and map
refreshLockTasks.Add(task);
refreshLockHandles[task] = handle;
refreshLockTimes[task] = DateTime.UtcNow;
}
// refresh all locks
try {
await Task.WhenAll(refreshLockTasks).ConfigureAwait(false);
} catch (Exception) { }
// map any sucesses
List <RedisLockHandle> refreshFailures = new List <RedisLockHandle>();
foreach (var task in refreshLockTasks)
{
// find associated handle
RedisLockHandle handle = refreshLockHandles[task];
DateTime time = refreshLockTimes[task];
// ignore faulty refreshes, if it expires eventually we'll catch that too
if (task.IsFaulted)
{
// invoke event
try {
OnInvalidated(new RedisLockInvalidatedEventArgs()
{
Handle = handle
});
} catch (Exception) { }
continue;
}
// check if we successfully refreshed the handle
if (task.Result == true)
{
handle.RefreshedAt = time;
handle.ExpiresAt = time + expiryTime;
}
else
{
refreshFailures.Add(handle);
}
}
lock (_handles) {
foreach (var handle in refreshFailures)
{
try {
_handles.Remove(handle);
} catch (Exception) { }
}
}
}
}
/// <summary>
/// Locks the specified resource.
/// </summary>
/// <param name="resourceUri">The resource URI.</param>
/// <param name="waitTime">The maximum amount of time to wait.</param>
/// <param name="cancellationToken">The cancellation token.</param>
/// <returns>The lock handle or null if the lock could not be obtained.</returns>
public async Task <ILockHandle> LockAsync(Uri resourceUri, TimeSpan waitTime = default(TimeSpan), CancellationToken cancellationToken = default(CancellationToken))
{
if (_disposed == 1)
{
throw new ObjectDisposedException("The lock manager has been disposed");
}
if (!resourceUri.Scheme.Equals("tandem", StringComparison.CurrentCultureIgnoreCase))
{
throw new FormatException("The protocol scheme must be tandem");
}
// generate random token
LockToken token = new LockToken(Guid.NewGuid(), _owner);
// get remaining time
TimeSpan remainingTime = waitTime;
while (remainingTime >= TimeSpan.Zero)
{
// check if cancelled
cancellationToken.ThrowIfCancellationRequested();
// try and get the lock
bool gotLock = await _database.LockTakeAsync($"tandem.{resourceUri.ToString()}", token.ToString(), _expirySpan).ConfigureAwait(false);
if (gotLock)
{
// create handle
RedisLockHandle handle = new RedisLockHandle(this)
{
ResourceURI = resourceUri,
Token = token
};
// add handle
lock (_handles) {
_handles.Add(handle);
}
return(handle);
}
else
{
if (waitTime == TimeSpan.Zero)
{
return(null);
}
if (remainingTime > TimeSpan.FromMilliseconds(3000))
{
// no point waiting anymore, no cigar for the lock
return(null);
}
else
{
// wait 3 seconds until we try again
await Task.Delay(3000, cancellationToken).ConfigureAwait(false);
remainingTime -= TimeSpan.FromSeconds(3);
}
}
}
return(null);
}
