Introduction

VISA introduces locks for access control of resources. In VISA, applications can open multiple sessions to a resource simultaneously and can access the resource through these different sessions concurrently. In some cases, applications accessing a resource must restrict other sessions from accessing that resource. For example, an application may need to execute a write and a read operation as a single step so that no other operations intervene between the write and read operations. The application can lock the resource before invoking the write operation and unlock it after the read operation, to execute them as a single step. VISA defines a locking mechanism to restrict accesses to resources for such special circumstances.

The VISA locking mechanism enforces arbitration of accesses to resources on an individual basis. If a session locks a resource, operations invoked by other sessions are serviced or returned with a locking error, depending on the operation and the type of lock used.