[infinispan-issues] [JBoss JIRA] Created: (ISPN-650) DefaultCacheManager.getCache(...) should block until cache newly created cache is started

[Paul Ferraro (JIRA)]

DefaultCacheManager.getCache(...) should block until cache newly created cache is started
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                 Key: ISPN-650
                 URL: https://jira.jboss.org/browse/ISPN-650
             Project: Infinispan
          Issue Type: Feature Request
          Components: Core API
    Affects Versions: 4.2.0.ALPHA1
            Reporter: Paul Ferraro
            Assignee: Manik Surtani
            Priority: Minor


Currently, DefaultCacheManager stores it's caches in a concurrent map.  When a call to getCache(...) is made for a cache that does not yet exist, the cache is created, put into the map (via putIfAbsent()) and then the cache is started.  Consequently, a subsequent, but concurrent thread calling getCache(...) with the same cache name may end up with a cache that is not yet ready for use, leading to unexpected behavior.

Ideally, calls to getCache(...) should block if the requested cache is newly created, but not yet started.  Requests for an already started cache should not block.

A possible implementation might involve storing the cache along side a volatile single-use thread gate (e.g. new CountDownLatch(1)) in the concurrent map.  The algorithm might look like:
1. Lookup the map entry (i.e. cache + gate) using the cache name
2. If the map entry exists, but no gate is present, return the cache.
3. If the map entry exists, and a latch is present, wait on the latch (ideally with a timeout) and return the cache.
4. If the map entry does not exist, create the cache and put it into the map (if absent) with a new thread gate.
4a. If the put was not successful (i.e. an entry already existed), goto 1.
5. Start the cache - if start fails, stop the cache and remove the map entry (threads waiting on it's gate will timeout, oh well)
6. Open the gate
7. Remove the gate from the map entry
8. Return the cache

A horridly generic version of the above can be found in the HA-JDBC source code:
http://ha-jdbc.svn.sourceforge.net/viewvc/ha-jdbc/trunk/src/main/java/net/sf/hajdbc/util/concurrent/Registry.java?revision=2399&view=markup
and an example demonstrating use of a Registry with a MapRegistryStoreFactory can be found here:
http://ha-jdbc.svn.sourceforge.net/viewvc/ha-jdbc/trunk/src/main/java/net/sf/hajdbc/sql/Driver.java?revision=2414&view=markup

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