Comment by p_ing

From the NT Design Workbook, oplocks.

> Because the NT OS/2 I/O system is asynchronous by nature, the ability to make a request and then have it completed at a later time makes it natural for implementing oplocks. Further, because synchronization is required by the file system to determine when the caller has completed its oplock update transfers, the file system can use this feature to block open requests to a file by queueing the I/O Request Packet (IRP) to its internal file control structure until the oplock owner lets it know that it is finished.