Factory interface, allows
Cache to use different transactional systems. Names of implementors of
this class can be configured using
Configuration#setTransactionManagerLookupClass.
Thread safety: it is possible for the same instance of this class to be used by multiple caches at the same time e.g.
when the same instance is passed to multiple configurations:
org.infinispan.configuration.cache.TransactionConfigurationBuilder#transactionManagerLookup(TransactionManagerLookup).
As infinispan supports parallel test startup, it might be possible for multiple threads to invoke the
getTransactionManager() method concurrently, so it is highly recommended for instances of this class to be thread safe.