com.mongodb.internal.async.client.KeyManagementService constructs a {{ TlsChannelStreamFactoryFactory}} but never closes it. This class is expensive because every instance starts a thread (or maybe two). It slows down our tests a lot because every FLE spec test creates one of these, so by the end there are hundreds.

This can be fixed by making it Closeable and calling close from Crypt.close().

At the same time we should update com.mongodb.reactivestreams.client.ClientSideEncryptionTest and org.mongodb.scala.ClientSideEncryptionTest to close the MongoClient instance they own.