Possible Network Data Corruption If Locking Not Used

The information in this article applies to:

• Microsoft Windows 95

SYMPTOMS

When you use certain programs to access a common data file over the network from multiple workstations, the data may be read incorrectly or may become damaged.

CAUSE

The Microsoft Client for Microsoft Networks and Microsoft Client for NetWare Networks cache some network data on the client computer for enhanced network performance. If the program does not use locking calls to guarantee data synchronization and integrity, this cached data may not be kept in synchronization with the data on the network server.

If an opened file is not locked, it may be cached by the client. If the file is then modified by a second client, the first client may read incorrect file data from the cache, instead of reading the current file data from the network server. Subequent writes by the first client may result in incorrect data being written to the file, and damage to the file data.

RESOLUTION

Contact the program's manufacturer for additional information about using the program with Windows 95.

When you create a multiple-user program that allows for multiple users concurrently accessing and modifying a common data source, use locking calls when reading and writing data to ensure data integrity.

STATUS

Microsoft has confirmed this to be a problem in Microsoft Windows 95 and OEM Service Release 2 (OSR2). An update to address this problem is now available, but is not fully regression-tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft does not recommend implementing this update at this time. Contact Microsoft Technical Support for additional information about the availability of this update.

MORE INFORMATION

When locking calls are not used, the integrity of data cannot be guaranteed by a network client that employs caching for enhanced performance. Such network clients include the Microsoft Client for NetWare Networks and the Microsoft Client for Microsoft Networks included in Windows 95.

If a program locks the file or range of bytes that it intends to read from or write to, the server locks that file, or that range of the file. This denies access to that data to other users, and forces the client to read the current data from the server instead of from the cache. This technique is advised for maintaining data integrity when required, while providing the performance benefits of caching when it is safe to do so.