public async Task StartShard(IAsyncProjectionShard shard, CancellationToken cancellationToken)
{
if (!_hasStarted)
{
StartNode();
}
// Don't duplicate the shard
if (_agents.ContainsKey(shard.Name.Identity))
{
return;
}
await TryAction(null, async() =>
{
try
{
var agent = new ProjectionAgent(_store, shard, _logger, cancellationToken);
var position = await agent.Start(this);
Tracker.Publish(new ShardState(shard.Name, position)
{
Action = ShardAction.Started
});
_agents[shard.Name.Identity] = agent;
}
catch (Exception e)
{
_logger.LogError(e, "Error when trying to start projection shard '{ShardName}'", shard.Name.Identity);
throw new ShardStartException(shard.Name, e);
}
}, cancellationToken);
}
public async Task StartShard(IAsyncProjectionShard shard)
{
if (!_hasStarted)
{
StartNode();
}
// TODO -- log the start, or error if it fails
var agent = new ProjectionAgent(_store, shard, _logger);
var position = await agent.Start(Tracker);
Tracker.Publish(new ShardState(shard.ProjectionOrShardName, position)
{
Action = ShardAction.Started
});
_agents[shard.ProjectionOrShardName] = agent;
}
internal async Task TryAction(ProjectionAgent projection, Func <Task> action, CancellationToken token, int attempts = 0, TimeSpan delay = default)
{
if (delay != default)
{
await Task.Delay(delay, token);
}
if (token.IsCancellationRequested)
{
return;
}
try
{
await action();
}
catch (Exception ex)
{
if (token.IsCancellationRequested)
{
return;
}
var continuation = Settings.DetermineContinuation(ex, attempts);
switch (continuation)
{
case RetryLater r:
await TryAction(projection, action, token, attempts + 1, r.Delay);
break;
case StopProjection:
if (projection != null)
{
await StopShard(projection.ShardName.Identity, ex);
}
break;
case StopAllProjections:
var tasks = _agents.Keys.ToArray().Select(name =>
{
return(Task.Run(async() =>
{
await StopShard(name, ex);
}, _cancellation.Token));
});
await Task.WhenAll(tasks);
Tracker.Publish(new ShardState(ShardName.All, Tracker.HighWaterMark)
{
Action = ShardAction.Stopped, Exception = ex
});
break;
case PauseProjection pause:
if (projection != null)
{
await projection.Pause(pause.Delay);
}
break;
case PauseAllProjections pauseAll:
var tasks2 = _agents.Values.ToArray().Select(agent =>
{
return(Task.Run(async() =>
{
await agent.Pause(pauseAll.Delay);
}, _cancellation.Token));
});
await Task.WhenAll(tasks2);
break;
case DoNothing:
// Don't do anything.
break;
}
}
}
