Agilent Technologies FS2010 Podręcznik Użytkownika Pobierz pdf (Strona 88)

88 Agilent VISA User’s Guide

3 Programming with VISA

viLock(vi, lockType, timeout, requestedKey,

accessKey);

The VI_ATTR_RSRC_LOCK_STATE attribute specifies the

current locking state of the resource on the given session,

which can be either VI_NO_LOCK, VI_EXCLUSIVE_LOCK, or

VI_SHARED_LOCK.

The VISA viUnlock function is then used to release the lock

on a resource. If a resource is locked and the current

session does not have the lock, the error

VI_ERROR_RSRC_LOCKED is returned.

VISA Lock Types

VISA defines two different types of locks: Exclusive Lock

and Shared Lock.

Exclusive Lock - A session can lock a VISA resource

using the lock type VI_EXCLUSIVE_LOCK to get exclusive

access privileges to the resource. This exclusive lock type

excludes access to the resource from all other sessions.

If a session has an exclusive lock, other sessions cannot

modify global attributes or invoke operations on the

resource. However, the other sessions can still get

attributes.

Shared Lock - A session can share a lock on a VISA

resource with other sessions by using the lock type

VI_SHARED_LOCK. Shared locks in VISA are similar to

exclusive locks in terms of access privileges, but can still

be shared between multiple sessions.

If a session has a shared lock, other sessions that share

the lock can also modify global attributes and invoke

operations on the resource (of course, unless some other

session has a previous exclusive lock on that resource). A

session that does not share the lock will lack these

capabilities.

Locking a resource restricts access from other sessions, and

in the case where an exclusive lock is acquired, ensures that

operations do not fail because other sessions have acquired

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Agilent Technologies FS2010 Podręcznik Użytkownika Strona 88