preconnect_async
Description:
Start a preconnection to msg.
Once the connection is done, it will remain in idle state so that it can be reused by future requests. If there's already an idle connection
for the given msg host, the operation finishes successfully without creating a new connection. If a new request for the given
msg host is made while the preconnect is still ongoing, the request will take the ownership of the connection and the preconnect
operation will finish successfully (if there's a connection error it will be handled by the request).
The operation finishes when the connection is done or an error occurred.
Parameters:
| this |
a Session |
| msg |
a Message |
| io_priority |
the I/O priority of the request |
| cancellable | |
| callback |
the callback to invoke when the operation finishes |
| user_data |
data for |