InterSystems Programming Tools Index
Locks
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Read lock table information programmatically; remove locks; query and adjust lock table parameters.
Background Information
An important feature of any multi-process system is concurrency control, the ability to prevent different processes from changing a specific element of data at the same time, resulting in corruption. Thus Caché ObjectScript, Caché SQL, Caché MVBasic, and Caché Basic each provide commands for working with locks, which you use for concurrency control.
The %Persistent class provides a way to control concurrent access to objects, namely, the concurrency argument to %OpenId() and other methods of this class. These methods ultimately use the Caché ObjectScript LOCK command. All persistent objects inherit these methods.
Internally, the in-memory lock table contains the current locks, along with information about the processes that hold those locks. You can use the Management Portal to view the lock table and (if necessary) remove locks; see Monitoring Locks in the Caché Monitoring Guide.
For more information on locks, see the article Locking and Concurrency Control.
Available Tools
In addition, InterSystems provides the following tools:
^$LOCK
This structured system variable returns information about locks.
Availability: All namespaces.
%SYS.LockQuery class
Enables you to read lock table information. This class provides details and examples.
Availability: All namespaces.
SYS.Lock class
Enables you to remove locks. Also enables you to query and adjust lock table parameters. This class provides methods like the following:
Availability: %SYS namespace.
See Also