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https://issues.apache.org/jira/browse/NUTCH-2578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16499137#comment-16499137
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ASF GitHub Bot commented on NUTCH-2578:
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sebastian-nagel opened a new pull request #338: NUTCH-2578 Avoid lock by
MimeUtil in constructor of protocol.Content
URL: https://github.com/apache/nutch/pull/338
- avoid creation of new Tika object in constructor of MimeUtil (cache in
ObjectCache) - suggested by @YossiTamari. Thanks!
- also hold MimeUtil object in protocol implementation (protocol plugin) and
pass it to constructor of Content. This avoids any locks (also those by
ObjectCache) in a highly concurrent fetcher. Note that the current MimeUtil
implementation and the Tika detector are thread-safe.
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> Avoid lock by MimeUtil in constructor of protocol.Content
> ---------------------------------------------------------
>
> Key: NUTCH-2578
> URL: https://issues.apache.org/jira/browse/NUTCH-2578
> Project: Nutch
> Issue Type: Improvement
> Components: protocol
> Affects Versions: 1.14
> Reporter: Sebastian Nagel
> Priority: Major
> Fix For: 1.15
>
>
> The constructor of the class o.a.n.protocol.Content instantiates a new
> MimeUtil object. That's not cheap as it always creates a new Tika object and
> there is a lock on the job/jar file when config files are read:
> {noformat}
> "FetcherThread" #146 daemon prio=5 os_prio=0 tid=0x00007f70523c3800
> nid=0x1de2 waiting for monitor entry [0x00007f70193a8000]
> java.lang.Thread.State: BLOCKED (on object monitor)
> at java.util.zip.ZipFile.getEntry(ZipFile.java:314)
> - waiting to lock <0x00000005e0285758> (a java.util.jar.JarFile)
> at java.util.jar.JarFile.getEntry(JarFile.java:240)
> at java.util.jar.JarFile.getJarEntry(JarFile.java:223)
> at sun.misc.URLClassPath$JarLoader.getResource(URLClassPath.java:1042)
> at
> sun.misc.URLClassPath$JarLoader.findResource(URLClassPath.java:1020)
> at sun.misc.URLClassPath$1.next(URLClassPath.java:267)
> at sun.misc.URLClassPath$1.hasMoreElements(URLClassPath.java:277)
> at java.net.URLClassLoader$3$1.run(URLClassLoader.java:601)
> at java.net.URLClassLoader$3$1.run(URLClassLoader.java:599)
> at java.security.AccessController.doPrivileged(Native Method)
> at java.net.URLClassLoader$3.next(URLClassLoader.java:598)
> at java.net.URLClassLoader$3.hasMoreElements(URLClassLoader.java:623)
> at sun.misc.CompoundEnumeration.next(CompoundEnumeration.java:45)
> at
> sun.misc.CompoundEnumeration.hasMoreElements(CompoundEnumeration.java:54)
> at java.util.Collections.list(Collections.java:5239)
> at
> org.apache.tika.config.ServiceLoader.identifyStaticServiceProviders(ServiceLoader.java:325)
> at
> org.apache.tika.config.ServiceLoader.loadStaticServiceProviders(ServiceLoader.java:352)
> at
> org.apache.tika.config.ServiceLoader.loadServiceProviders(ServiceLoader.java:274)
> at
> org.apache.tika.detect.DefaultEncodingDetector.<init>(DefaultEncodingDetector.java:45)
> at
> org.apache.tika.config.TikaConfig.getDefaultEncodingDetector(TikaConfig.java:92)
> at org.apache.tika.config.TikaConfig.<init>(TikaConfig.java:248)
> at
> org.apache.tika.config.TikaConfig.getDefaultConfig(TikaConfig.java:386)
> at org.apache.tika.Tika.<init>(Tika.java:116)
> at org.apache.nutch.util.MimeUtil.<init>(MimeUtil.java:69)
> at org.apache.nutch.protocol.Content.<init>(Content.java:83)
> at
> org.apache.nutch.protocol.http.api.HttpBase.getProtocolOutput(HttpBase.java:316)
> at org.apache.nutch.fetcher.FetcherThread.run(FetcherThread.java:341)
> {noformat}
> If there are many Fetcher threads this may cause a significant bottleneck,
> running a Fetcher with 120 threads I've found up to 50 threads waiting for
> this lock:
> {noformat}
> # pid 7195 is a Fetcher map task
> % sudo -u yarn jstack 7195 \
> | grep -A25 'waiting to lock' \
> | grep -F 'org.apache.tika.Tika.<init>' \
> | wc -l
> 49
> {noformat}
> As MimeUtil is thread-safe [including the called Tika
> detector|https://www.mail-archive.com/[email protected]/msg00296.html],
> the best solution seems to cache the MimeUtil object in the actual protocol
> implementation as it is done in Nutch 2.x ([lib-http HttpBase, line
> #151|https://github.com/apache/nutch/blob/2.x/src/plugin/lib-http/src/java/org/apache/nutch/protocol/http/api/HttpBase.java#L151]).
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