问题
I know this is a very basic question, but I would like a deeper understanding of what "busy" means. I have done a double check that I close all my connections. I know that in c3p0, "the pool will intercept the call to close() and check the underlying Connection back into the pool." I would expect the number of busy connections to trend to zero, but this does not happen. Any ideas why? How long does a connection stay in the "busy" state? Shouldn't the connection become unbusy when I close it? Thx in advance.
回答1:
OK... I finally figured this out by watching the DEBUG log statements from mchange. There is a "check for expired resources" every 5 seconds. If you get and use a connection just before that window and then you call "getNumConnectionsDefaultUser()" within that window you may not get an accurate count because the connection could be marked s busy and become unbusy before the window closes.
Essentially (I think), c3p0 does not maintain its own counters based on a change in status, it cycles through the collection of connections every five seconds checking current status.
来源：https://stackoverflow.com/questions/49450547/c3p0-getnumbusyconnectionsdefaultuser-what-does-busy-mean