[ https://issues.apache.org/jira/browse/HTTPCLIENT-1165?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Oleg Kalnichevski updated HTTPCLIENT-1165: ------------------------------------------ Labels: stuck volunteers-wanted (was: ) Fix Version/s: (was: Future) Stuck > Cache allows multipe requests to retrieve the same cacheable resource from > the server in multithreaded environment due to lack of proper locking > ------------------------------------------------------------------------------------------------------------------------------------------------ > > Key: HTTPCLIENT-1165 > URL: https://issues.apache.org/jira/browse/HTTPCLIENT-1165 > Project: HttpComponents HttpClient > Issue Type: Improvement > Components: HttpCache > Affects Versions: Snapshot > Reporter: Manish Tripathi > Labels: stuck, volunteers-wanted > Fix For: Stuck > > > Consider the following scenario: > Two separate threads are launched at the same time with identical Http > requests through CachingHttpClient. > Both threads look up the same URI in the cache at [almost] the same time and > find no cached response for that URI. > Both threads fall back to backend HttpClient and make identical requests to > the server. > Both threads retrieve the resource and attempt to store it in the cache. > The same resource gets retrieved from the server twice and is stored in the > cache twice. > Obviously, the described algorithm is inefficient > Suggested fix: introduce read-write locking mechanism which would block > multiple requests to retrieve the same URI until one of the concurrent > requests has either received a response header indicating that the response > is not cacheable, or until cacheable response has been fully retrieved and > stored in the cache. The proposed pseudo-code follows: > cachingClient.execute(url) { > if (lock_count(url)>0) > lock=lockingFactory.acquireReadLock(url); > else > lock=lockingFactory.acquireWriteLock(url); > response=satisfyFromCache(url); > if (response==null) { > if (lock.isReadLock()) { lock.release(); > lock=lockingFactory.acquireWriteLock(url); } > response=satisfyFromServerAndStoreInCache(url); > } > lock.release(); > return response; > } > where lockingFactory instance is shared by multiple instances of > CachingHttpClient. -- This message was sent by Atlassian JIRA (v6.3.15#6346) --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@hc.apache.org For additional commands, e-mail: dev-h...@hc.apache.org