We are using EWS Managed API 2.2 to detect when new messages are received in multiple email account hosted in Office365. We've adapted this sample program.
Using Streaming Notifications with Exchange 2010
Basically this windows command line application will contact an Exchange server and wait for new messages to arrive. This is done using a single instance of ExchangeService. To get notifications we use the StreamingSubscription object to perform a hanging HTTP Get.
The sample program works great, until we attempt to connect to multiple accounts. With each instance in its own Thread, with two different exchange accounts, with two ExchangeService and two StreamingSubscription, the exact same code throws errors.
The error is thrown in different locations but let's focus on this one for now.
In the StreamingSubscription OnNotificationEvent callback, this code will throw "the operation has timed out".
ExchangeService.SyncFolderItems(folderId,PropertySet.IdOnly,null,5,SyncFolderItemsScope.NormalItems, State);
If we catch this error and ignore it on subsequent calls we see these errors:
"Unable to retrieve events for this subscription. The subscription must be recreated., The events couldn't be read"
"Microsoft.Exchange.WebServices.Data.ServiceLocalException: You must add at least one subscription to this connection before it can be opened"
Now we understand that the EWS library is NOT THREAD SAFE, but we are creating two totally parallel instances where no objects in another thread is changed.
We also have found that if the code is run in two separate Processes not Threads, the error disappears.
Our theories are:
- Simple Bug or use of static in StreamingSubscription?
- Could the ExchangeService Affinity cookies somehow be overwritten, so the information about which slot in the CAS server is being reused by the second thread?
Is this the right way to accomplish our goal? In the video:
Exchange Web Services Affinity and Throttling at minute 47:00
They discuss a process architecture where subscriptions are managed in multiple processes and mailbox access is managed in a separate process. The speaker states that this is a load balancing strategy and not a requirement of use.
Any help would be appreciated.
Update:
We found that it appears possible to damage the account if two users run the two same email accounts at the same time.
user 1 : runs account 1,account 2
user 2: runs account 1,account 2
Now both users experience timeouts for the same account.
