[SimpleConnectionPool] Add release option to connection pool Lease #4736
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This PR tries to implement eclipse-vertx#4680. A new method, release(Handler<AsyncResult<T>> handler) is added to the Lease interface, with the default implementation calling recycle(). In SimpleConnectionPool, LeaseImpl implements the release() method by invoking slot.pool.release(). The release() method in the Pool reduces slot.usage by 1, and if the usage count reaches 0, it invokes pool.remove(slot). The PR also introduces another member variable within the Slot object, called inactive (boolean). When release() is invoked on a slot, the slot is marked as inactive irrespective of the usage count. inactive is also set to true in Evict, before we remove the slot (when usage count is 0). A new Slot is initialized with inactive as true. The only time inactive gets set to false is when a connection is successfully established for the slot. In pool.acquire, we skip slots that are marked as inactive. This behavior means it is better to invoke pool.connect() whenever a slot is removed, even when there are no Waiters. This change will be made in a follow-up PR. release() can subsequently be used by SqlConnectionPool instead of recycle(), when it determines that a given connection is past its maxLifetime (else it uses recycle()).
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Motivation:
This PR tries to implement #4680.
A new method,
release(Handler<AsyncResult<T>> handler)is added to theLeaseinterface, with the default implementation callingrecycle().In
SimpleConnectionPool,LeaseImplimplements therelease()method by invokingslot.pool.release().The
release()method in the Pool reducesslot.usageby 1, and if the usage count reaches 0, it invokespool.remove(slot).The PR also introduces another member variable within the Slot object, called
inactive (boolean). Whenrelease()is invoked on a slot, the slot is marked as inactive irrespective of the usage count.inactiveis also set to true inEvict, before we remove the slot (when usage count is 0).A new
Slotis initialized withinactiveastrue. The only timeinactivegets set tofalseis when a connection is successfully established for the slot (ConnectSuccess).In
pool.acquire, we skip slots that are marked as inactive. This behavior means it is better to invokepool.connect()whenever a slot isremoved(pool.remove()), even when there are no Waiters. This change will be made in a follow-up PR. Additionally,removecan maintain theminIdleinvariant.release()can subsequently be used by SqlConnectionPool instead of recycle(), when it determines that a given connection is past its maxLifetime (else it uses recycle()).