Modes
You can set up plug-ins in synchronous or asynchronous mode.
Synchronous mode starts the execution of the plug-in when the event is fired and blocks the CRM application process until the executed method finishes. This option is not recommended if you are performing a process that might take a long time to execute. Regardless of the method used, synchronous or asynchronous, there is a timeout limit of 2 minutes for plugin executions. If your process needs more time, then you will have to consider using a workflow or another custom background process.
Tip
If you want to prevent a record from being created or updated, this should be the desired mode in conjunction with the Pre stage (see the next section for stages).
Asynchronous mode releases ...