When the resource is defined and the locks are added, the build gets a configuration parameter with the name of the lock and with the value of the resource string (
teamcity.locks.writeLock.<lockName>), e.g. the parameter name can be:
Locks for resources with custom values cannot be added to composite builds: TW-54381
Locks for resources in composite builds
Shared resources (except ones with custom values) can now be locked for composite builds as well. A lock on the specified resource will be acquired when a composite build starts (when the first build of the composite build chain starts); the lock will be released when the composite build finishes (the last build in its chain is finished).
Clicking the resource name takes you back to the the shared resources configuration page on the project level.