NetWare 4.1/9000 Concepts

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NetWare Glossary
S
NOTE: Normally, only a client can invoke Synchronization Services. However, the NetWare
server will occasionally issue synchronization services calls to perform internal
synchronization on critical data.
NetWare Services provides a simple synchronization mechanism through
the mode in which the file is opened. For example, opening a file in deny-
write mode would prevent other clients from modifying the file, but would
still allow them to read the file. This method of file synchronization is
probably adequate for most simple network applications.
Finer-grained synchronization is provided through four kinds of
synchronization services:
• Whole file synchronization (file locks)
• File segment synchronization (physical or byte-range locks)
• Logical entity synchronization (logical locks)
• Semaphore synchronization (semaphore locks)
Whole file synchronization. When a client issues a file lock on a file,
synchronization occurs on the entire file. While a file lock is held, no other
clients can access the file for read or write.
File segment synchronization. This occurs when a client issues a “physical
lock” on a file. Physical locks allow a client to place a shared or exclusive
lock on a particular range of bytes within the file. This range may extend
beyond the current end of file.
Logical entity synchronization. Logical entity synchronization occurs when
a client issues a “logical lock” on a server entity. A logical lock is a label in
the form of an ASCII string that represents network data and indirectly
controls access to that network data.
Semaphore synchronization. Semaphores, like logical records, are labels in
the form of ASCII strings that individually control network activity. A value
is set when the semaphore is open that indicates how many client can access
the semaphore’s resource at one time.
The NCP engines handle initial lock requests, which completes if there is no
contention for the resource. If the lock is successful, the engine signals the
client. If the lock is not successful, the engine hands it off to one of four lock