Using a Reentrant lock instead of the intrinsic synchronization lock
permits limiting the blocking time to acquire a lock.
Useful on a very busy Cache concurrently accessed by many threads : when
the time to acquire a lock is too high, getting/storing content on the
cache becomes inefficient, and it is then better to fall back to loading
remote resources.
Illustrated by the CacheTest stress test and some traces reported in
mantis 751 ( http://mantis.tokeek.de/view.php?id=751 )
When starting a crawl from a file containing thousands of links,
configuration setting "crawler.MaxActiveThreads" is effective to prevent
saturating the system with too many outgoing HTTP connections threads
launched by the crawler.
But robots.txt was not affected by this setting and was indefinitely
increasing the number of concurrently loading threads until most ot the
connections timed out.
To improve performance control, added a pool of threads for Robots.txt,
consistently used in its ensureExist() and massCrawlCheck() methods.
The Robots.txt threads pool max size can now be configured in the
/PerformanceQueus_p.html page, or with the new
"robots.txt.MaxActiveThreads" setting, initialized with the same default
value as the crawler.
with file:// protocol, 2 hostqueues accessing same cache file concurrently
http://mantis.tokeek.de/view.php?id=668
Reason seems to be diff. hosthash key of hostqueues on reopen.
Internal queue key and external representation (directoryname currently hostname.port) must be adjusted to fix it (not done yet).
luccioman