private static IAGLink4 VerifyConnectivity(AgLinkPlc plc, ICollection <IPlcItem> plcItems, PlcItemUsageType usageType)
{
var underlyingPlc = plc.UnderlyingPlc;
if (underlyingPlc is null)
{
var itemDescriptions = Plc.GetPlcItemDescription(plcItems);
throw new NotConnectedPlcException($"Cannot {usageType.ToString().ToLower()} the plc items ({itemDescriptions}) because {plc:LOG} is not connected. All items will be put on hold.");
}
return(underlyingPlc);
}
private async Task <bool> ExecuteReadWriteAsync(ICollection <IPlcItem> plcItems, PlcItemUsageType usageType, CancellationToken cancellationToken)
{
// Allow only items that have a length greater than zero. This is mostly needed for dynamic items.
plcItems = plcItems.Where(item => item.Value.Length > 0).ToList();
if (!plcItems.Any())
{
return(true);
}
var cancellationTokenSource = this.BuildLinkedTokenSource(cancellationToken);
cancellationToken = cancellationTokenSource.Token;
try
{
while (true)
{
try
{
cancellationToken.ThrowIfCancellationRequested();
lock (_connectionStateChangeLock)
{
// If no active connection is available, then throw an exception.
/*!
* This means, that reading/writing items while the plc is not connected, will result in the calling function to indefinitely wait,
* because no reconnect will be made when the connection was deliberately not established.
*/
if (this.ConnectionState == PlcConnectionState.Disconnected)
{
var itemDescriptions = Plc.GetPlcItemDescription(plcItems);
throw new NotConnectedPlcException($"Cannot {usageType.ToString().ToLower()} the plc items ({itemDescriptions}) because {this:LOG} is not connected. All items will be put on hold.");
}
}
await Task.Run(() => this.PerformReadWriteAsync(plcItems, usageType, cancellationToken), cancellationToken);
break;
}
// This handles task cancellation.
catch (OperationCanceledException)
{
if (_disposeToken.IsCancellationRequested)
{
if (usageType == PlcItemUsageType.Read)
{
throw new DisposedReadPlcException(plcItems);
}
else
{
throw new DisposedWritePlcException(plcItems);
}
}
return(false);
}
// Handle not connected exceptions by trying to re-connect and halting the items until a connection was established.
catch (NotConnectedPlcException ex)
{
this.Logger.Error(ex.Message);
// Create a cancellation token source for this handle callback that is linked to the external one.
var sleepCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
_waitQueue.Enqueue(sleepCancellationTokenSource);
var sleepCancellationToken = sleepCancellationTokenSource.Token;
// Check if a reconnection could be useful.
lock (_connectionStateChangeLock)
{
// Don't reconnect if the connection is disconnected to begin with.
if (this.ConnectionState != PlcConnectionState.Disconnected)
{
this.OnInterrupted(executeReconnect: true);
}
}
// Indefinitely wait until the task gets canceled.
try
{
await Task.Delay(Timeout.Infinite, sleepCancellationToken);
}
catch (OperationCanceledException)
{
// Throw special dispose exception if the dispose token was canceled.
if (_disposeToken.IsCancellationRequested)
{
if (usageType == PlcItemUsageType.Read)
{
throw new DisposedReadPlcException(plcItems);
}
else
{
throw new DisposedWritePlcException(plcItems);
}
}
// Stop execution if the original (external) token was canceled.
else if (cancellationToken.IsCancellationRequested)
{
return(false);
}
// In all other cases just keep going.
else
{
/* ignore */
}
}
this.Logger.Info($"The previously suspended plc items of {this:LOG} will now be handled again.");
}
// Throw on read or write exceptions.
catch (ReadOrWritePlcException)
{
throw;
}
}
return(true);
}
finally
{
cancellationTokenSource.Dispose();
cancellationTokenSource = null;
#if DEBUG
this.LinkedTokenWasCanceled();
#endif
}
}