The sharing mode (dwShareMode) parameter of the CreateFile function (used to open files) determines file-sharing. This is typically done through the Task Manager utility. If so, the user may be able to restore file access by manually terminating the malfunctioning program. Improper error-handling in an application program can lead to a scenario where a file is locked (either using "share" access or with byte-range file locking) and cannot be accessed by other applications. The client will observe slower access because read and write operations must be sent to the server where the file is stored. For example, the Windows file-sharing mechanism will typically disable client side caching of a file for all clients when byte-range locks are used by any client. For applications that use the file mapping APIs in Windows, byte-range locks are not enforced (also referred to as advisory locks.) Byte-range locking may also have other side-effects on the Windows system. Note that the region of the file being locked is not required to have data within the file, and applications sometimes exploit this ability to implement their functionality.įor applications that use the file read/write APIs in Windows, byte-range locks are enforced (also referred to as mandatory locks) by the file systems that execute within Windows. Such byte-range locks specify a region of the file (offset and length) and the type of lock (shared or exclusive). Thus, an application must explicitly allow sharing when it opens a file otherwise it has exclusive read, write, and delete access to the file until closed (other types of access, such as those to retrieve the attributes of a file are allowed.)įor a file opened with shared access, applications may then use byte-range locking to control access to specific regions of the file. Windows inherits the semantics of share-access controls from the MS-DOS system, where sharing was introduced in MS-DOS 3.3 .
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