Composite State of a Lock Table Entry

The term “composite state” was previously introduced to depict the cumulative state, in terms of shared or exclusive, of a resource request queue. This same term can be used to describe the state of a coupling facility lock table entry. Whereas the composite state of a resource request queue reflects the state of all owners and requestors of a particular resource, the composite state of a lock table entry denotes the state of the owners and requestors of ALL resources mapping to that lock table entry. Similar to a resource request queue, a lock table entry can be in one of three composite states — free, shared, or exclusive.

Free - There are currently no owners or waiters for any resource that maps to this lock table entry.
Shared - All owners and waiters for resources that map to this lock table entry are in the shared state.
Exclusive - There is at least one owner or waiter for a resource mapping to the lock table entry in the exclusive state.

The same rules used to determine compatibility of requests that are added to a resource request queue can also be used to determine the effect of a resource request on the state of the corresponding lock table entry. Figure 1 illustrated this concept.

For example, Figure 1 depicts a four-entry lock table with multiple owners of resources that hash to lock table entry 2. The composite state of this lock entry is determined to be “exclusive” because there is at least one exclusive owner of a resource mapping to this entry. Additionally, the lock entry is recognized as being incompatible because the resources (XYZ and JKL) that map to this entry are owned in conflicting states.