Since the CBFS class's events are typically tied directly to requests from the OS itself, it's critical that event handlers complete quickly in order to prevent the system from being blocked. To help prevent such blocking, the CBFS Connect system driver can enforce request timeouts on a per-virtual-drive basis.
A virtual drive's request timeout interval is specified by passing the desired number of milliseconds to the Timeout parameter when calling the mount_media method. The value passed to the Timeout parameter must either be a positive value greater than or equal to 3000; or 0, indicating that timeouts should not be enforced, in which case events may take as long as necessary to execute.
When timeout enforcement is in effect, and an event executes long enough for its timeout to expire, the driver cancels the underlying request by reporting an error to the OS. The tardy event still runs to completion, but any results it returns once finished are ignored since the underlying request has already been handled.
If an event handler knows it will require additional time to complete an operation, it can call the reset_timeout method (before the current timeout expires) to restart the timeout timer.
Applications should always strive to ensure that all event handlers complete quickly, even if request timeouts are disabled. Don't perform time-consuming work, especially network operations, within event handlers; offload such work to background threads. For example, a viable strategy for writing to a remote file would be to pass the data to be written to a background thread, then immediately finish the event handler. Similarly, to read from a remote file, an application could pre-cache some of its data with the help of a worker thread, then return the cached data when it is requested.