Hi, I'm not sure what the answer is here,
What I am sure of is that the goal of close should be a graceful shutdown. Once a resource is closed then it should not accept new requests. Descendant resources may or may not continue to be operational, for instance you may allow ongoing transactions to complete but that is implementation dependent.
The question is after calling close when how can you be sure that all descendant resources are finished before returning to the user? Only by keeping references to all spawned resources can you tell.
Perhaps Graph.close() should return a Future. That way you can block until the graph is actually closed.
Bryn On 05/10/15 20:56, Stephen Mallette wrote:
There are two tickets in JIRA that relate to the semantics of closing and releasing resources in the Graph hierarchy: + Graph + TraversalSource + TraversalStrategy + GraphTraversal + Transaction https://issues.apache.org/jira/browse/TINKERPOP3-789 https://issues.apache.org/jira/browse/TINKERPOP3-790 There's been some discussion on them already. I bring this to everyone's attention as the change could have wide repercussions depending on the direction it goes. The short of the matter is that currently: 1. Graph implements AutoCloseable, but we don't enforce the notion of close() itself in the test suite. 2. TraversalSource should likely implement AutoCloseable as there are sometimes resources that need to be released when a TraversalSource is no longer in use. 3. Transaction implements AutoCloseable but it applies in the context of how a Transaction will behave when Graph.close() is called. Where is this all going? Matt Frantz summarized the thought points nicely in this comment: https://issues.apache.org/jira/browse/TINKERPOP3-790?focusedCommentId=14710389&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14710389 Basically, there's two options Matt identified: 1. Making it so that Graph.close() would release resources and effectively close() all things it spawned is one approach, but I''m not sure how straightforward/practical to implement that is. I suspect it will complicate Graph implementations as well. 2. The alternative is that the things in this hierarchy can have their own expensive resources which can be independently closed. I think that this approach more closely fits with the code as we have it now and won't unduly burden implementers. TinkerPop Developers will have to know when to call close() (e.g. if a TraversalStrategy has expensive resources and the user assumes that a call to TraversalSource.close() will release those resources, then they might be wrong - depends on the approach we decide on). When I first created 790, i had the second option in mind, but since Matt brought wrote that comment, i figured it was worth thinking through as a whole. Once that is decided then we should figure out 789 which is how to enforce the semantics of close() (e.g. what does a Graph do when it's closed and someone calls graph.traversal()?). Thoughts?
