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Posted to dev@nutch.apache.org by "Jacob Brunson (JIRA)" <ji...@apache.org> on 2006/08/10 06:22:16 UTC
[jira] Commented: (NUTCH-344) Fetcher threads blocked on
synchronized block in cleanExpiredServerBlocks
[ http://issues.apache.org/jira/browse/NUTCH-344?page=comments#action_12427096 ]
Jacob Brunson commented on NUTCH-344:
-------------------------------------
I'm having problems with the patch committed in revision #429779. I used to be having the "fetch aborted with X hung threads" problem. After updating to this revision, fetching goes fine for a while, but then I get this error on just about every page fetch attempt:
2006-08-09 23:27:28,548 INFO fetcher.Fetcher - fetching http://www.xmission.com/~nelsonb/resources.htm
2006-08-09 23:27:28,549 ERROR http.Http - java.lang.NullPointerException
2006-08-09 23:27:28,549 ERROR http.Http - at org.apache.nutch.protocol.http.api.HttpBase.cleanExpiredServerBlocks(HttpBase.java:382)
2006-08-09 23:27:28,549 ERROR http.Http - at org.apache.nutch.protocol.http.api.HttpBase.blockAddr(HttpBase.java:323)
2006-08-09 23:27:28,549 ERROR http.Http - at org.apache.nutch.protocol.http.api.HttpBase.getProtocolOutput(HttpBase.java:188)
2006-08-09 23:27:28,549 ERROR http.Http - at org.apache.nutch.fetcher.Fetcher$FetcherThread.run(Fetcher.java:144)
2006-08-09 23:27:28,549 INFO fetcher.Fetcher - fetch of http://www.xmission.com/~nelsonb/resources.htm failed with: java.lang.NullPointerException
> Fetcher threads blocked on synchronized block in cleanExpiredServerBlocks
> -------------------------------------------------------------------------
>
> Key: NUTCH-344
> URL: http://issues.apache.org/jira/browse/NUTCH-344
> Project: Nutch
> Issue Type: Bug
> Components: fetcher
> Affects Versions: 0.8.1, 0.9.0, 0.8
> Environment: All
> Reporter: Greg Kim
> Fix For: 0.8.1, 0.9.0
>
> Attachments: cleanExpiredServerBlocks.patch, HttpBase.patch
>
>
> With the recent change to the following code in HttpBase.java has tendencies to block fetcher threads while one thread busy waits...
> private static void cleanExpiredServerBlocks() {
> synchronized (BLOCKED_ADDR_TO_TIME) {
> while (!BLOCKED_ADDR_QUEUE.isEmpty()) { <===== LINE 3:
> String host = (String) BLOCKED_ADDR_QUEUE.getLast();
> long time = ((Long) BLOCKED_ADDR_TO_TIME.get(host)).longValue();
> if (time <= System.currentTimeMillis()) {
> BLOCKED_ADDR_TO_TIME.remove(host);
> BLOCKED_ADDR_QUEUE.removeLast();
> }
> }
> }
> }
> LINE3: As long as there are *any* entries in the BLOCKED_ADDR_QUEUE, the thread that first enters this block busy-waits until it becomes empty while all other threads block on the synchronized block. This leads to extremely poor fetcher performance.
> Since the checkin to respect crawlDelay in robots.txt, we are no longer guranteed that BLOCKED_ADDR_TO_TIME queue is a fifo list. The simple fix is to iterate the queue once rather than busy waiting...
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