The caller is responsible himself that a file is not being read before it is completely written.
The caller is also responsible for making sure the stream gets closed, otherwise resource
might leak (thus: always in a try-catch block!).
Suspends all write operations to the blob store, after calling this method
only read operation will be allowed. This method only returns after all
active write operations have been finished.
Parameters: msecs - max time to wait for active write operations to finish