When some file request is handled by the callback/event handler (eg. OnReadFile), are other requests for the same file waiting or callback/event handlers can be called for those requests at the same time?
By default all requests for one file are handled sequentially (i.e. the next callback/event handler is called only after the previous one has been finished). For different files requests can be handled in parallel (this depends on how SerializeCallbacks and ThreadPoolSize properties are set).
In version 4 new property has been introduced - ParallelProcessingAllowed (boolean, default value is false). If this property is set to true, any request that doesn't change the filesystem state (file read, directory enumeration, get file attributes, etc) can be called in parallel to other similar requests for the same file. For example, if the process reads from file in multiple threads (to speed up file reading), with ParallelProcessingAllowed property set to true you can get multiple OnReadFile callback/event handlers called in parallel.