Connection Pool Lock Performance

[wuttem]

Is there any reason why the ConnectionPool of this Library is locked so that every Bigtable Connection in it can only be used once ? If i understand correct, the Bigtable Connection itself is thread safe and may be used by more than one thread at a time:
googleapis/google-cloud-python#3272
I have a case where a have more worker threads than connections in the pool and i suspect the locking to cause performance issues if threads are waiting on a connection from the pool.