Currently each attempt to load a class in a remote JVM makes a round-trip request to the master, which over a laggy network can make class loading quite slow, thus adding considerable overhead to the first build on a new slave.

      Two possible solutions have been put forward.

      Optimistic prefetch

      The idea: when sending a class file to be loaded, scan its bytecode for other statically linked classes which have not yet been loaded, and send those along as well. In the common case that a network of classes is loaded around the same time, this would avoid some round trips.

      Details

      The first part is for one side to keep track of what classes the other side has already loaded (into which class loader), which is basically memorizing the response from IClassLoader.fetch2.

      The second part is to add Collection<ClassFile> IClassLoader.fetch3 that works like fetch2, except it will also parse the class, figure out some of the referenced classes that are not yet loaded by the other side, then send them along.

      Those prefetched class files would need to be remembered by RemoteClassLoader so that when those are actually requested it can load a class in the right classloader without calling back RemoteClassLoader.proxy. (Assuming there are no side effects, it could also eagerly call RemoteClassLoader.loadClassFile on the prefetched classes.)

      The remoting layer supports talking to an earlier version of the remoting layer. We do this by a bitmask in Capability, so this needs one more bit defined there. There is no point in tracking the classes the other side has loaded if the other side will never call fetch3.

      Bulk transfer

      Send entire JAR files at a time, rather than individual classes; can wind up transferring more than is needed, but the reduction in latency is probably worth it. Since arbitrary class loader graphs might be in use, not just a flat classpath, some custom code needs to be run remotely which will implement the class loader delegation model without hitting the network for each class.

      Details

      An API sketch:

      class Channel {
        void setClassLoaderTrafficCop(TrafficCop cop);
      }
      interface TrafficCop {
        /** do I know/control/own this classloader? */
        boolean controls(ClassLoader cl);
        Set<JarFile> getJarFilesOf(ClassLoader cl);
        RemotePartOfTrafficCop getRemotePart();
      }
      class JarFile {
        String checksum();
        InputStream data();
      }
      /** runs in remote agent */
      interface RemotePartOfTrafficCop implements Serializable {
        /** given a class/resource and an originating loader, what is the defining loader? */
        RemoteClassLoader trafficControl(RemoteClassLoader origin, String resourceName);
      }
      

          [JENKINS-15120] Minimize round trips for slave class loading

          Jesse Glick added a comment -

          Can add a dependency from remoting on ASM via http://kohsuke.org/2012/03/03/potd-package-renamed-asm/ if needed for prefetch.

          Jesse Glick added a comment - Can add a dependency from remoting on ASM via http://kohsuke.org/2012/03/03/potd-package-renamed-asm/ if needed for prefetch.

          Code changed in jenkins
          User: Jesse Glick
          Path:
          src/main/java/hudson/remoting/Channel.java
          http://jenkins-ci.org/commit/remoting/2b1ec8ab152805f01b4063dabc4dcdef64421fed
          Log:
          JENKINS-15120 Kohsuke’s explanation of why preloadJar does not really help.

          SCM/JIRA link daemon added a comment - Code changed in jenkins User: Jesse Glick Path: src/main/java/hudson/remoting/Channel.java http://jenkins-ci.org/commit/remoting/2b1ec8ab152805f01b4063dabc4dcdef64421fed Log: JENKINS-15120 Kohsuke’s explanation of why preloadJar does not really help.

          Jesse Glick added a comment -

          Jesse Glick added a comment - https://github.com/jenkinsci/remoting/pull/10

          Jesse Glick added a comment -

          https://github.com/jenkinsci/mock-slave-plugin useful for testing impact on performance more controllably than simply connecting to some node in the cloud.

          Jesse Glick added a comment - https://github.com/jenkinsci/mock-slave-plugin useful for testing impact on performance more controllably than simply connecting to some node in the cloud.

          Jesse Glick added a comment -

          remoting #37248f1 also suggests using

          sudo tc qdisc add dev lo root netem delay 100ms
          

          to simulate a laggy network.

          Jesse Glick added a comment - remoting #37248f1 also suggests using sudo tc qdisc add dev lo root netem delay 100ms to simulate a laggy network.

          Jesse Glick added a comment -

          Using mock-slave with 10ms latency and building a multimodule Maven project in current trunk I get

          Loading Type Time (s) Count
          Classes 223.8 2993
          Resources 2.7 23

          With prefetch-JENKINS-15120 from Jenkins core checked out (which pulls in a branch of the same name from remoting), this was

          Loading Type Time (s) Count
          Classes 165.5 3361 (prefetch cache: 1651)
          Resources 2.3 26

          though timing is not exactly comparable since the branch currently enables rather verbose logging which slows down the connection.

          Jesse Glick added a comment - Using mock-slave with 10ms latency and building a multimodule Maven project in current trunk I get Loading Type Time (s) Count Classes 223.8 2993 Resources 2.7 23 With prefetch-JENKINS-15120 from Jenkins core checked out (which pulls in a branch of the same name from remoting ), this was Loading Type Time (s) Count Classes 165.5 3361 (prefetch cache: 1651) Resources 2.3 26 though timing is not exactly comparable since the branch currently enables rather verbose logging which slows down the connection.

          Jesse Glick added a comment -

          Retesting with svn up for both builds (originally the first used co), and with verbose logging turned off in the branch. Trunk builds takes 6:02 min (of which the Maven build itself was 1:26):

          Loading Type Time (s) Count
          Classes 243.2 3320
          Resources 2.6 26

          I tried to run the branch build again but this time it failed with a java.lang.OutOfMemoryError: PermGen space (on the master) which is disconcerting; did the branch introduce some kind of class loader leak?

          I retried it, this time succeeding in 4:10 (Maven build 1:06):

          Loading Type Time (s) Count
          Classes 141.0 3323 (prefetch cache: 1633)
          Resources 2.2 26

          So that is a 31% reduction in build time, which I would say is pretty good.

          BTW using https://svn.codehaus.org/mojo/trunk/mojo/nbm-maven as the test project, more or less arbitrarily. Intentionally using a native Maven project since that puts far more load on the remoting layer than a freestyle project.

          Jesse Glick added a comment - Retesting with svn up for both builds (originally the first used co ), and with verbose logging turned off in the branch. Trunk builds takes 6:02 min (of which the Maven build itself was 1:26): Loading Type Time (s) Count Classes 243.2 3320 Resources 2.6 26 I tried to run the branch build again but this time it failed with a java.lang.OutOfMemoryError: PermGen space (on the master) which is disconcerting; did the branch introduce some kind of class loader leak? I retried it, this time succeeding in 4:10 (Maven build 1:06): Loading Type Time (s) Count Classes 141.0 3323 (prefetch cache: 1633) Resources 2.2 26 So that is a 31% reduction in build time, which I would say is pretty good. BTW using https://svn.codehaus.org/mojo/trunk/mojo/nbm-maven as the test project, more or less arbitrarily. Intentionally using a native Maven project since that puts far more load on the remoting layer than a freestyle project.

          Code changed in jenkins
          User: Kohsuke Kawaguchi
          Path:
          changelog.html
          core/src/main/java/hudson/ClassicPluginStrategy.java
          maven-plugin/src/main/java/hudson/maven/Maven3Builder.java
          pom.xml
          http://jenkins-ci.org/commit/jenkins/f7330d7a158eff6705706b1f812993a9b918c351
          Log:
          [FIXED JENKINS-15120]

          • integrated the newer release of remoting
          • jar caching won't work with class file directory, so plugin
            WEB-INF/classes are now exploded as WEB-INF/lib/classes.jar
            (This should also solve the problem of slow plugin extraction in the
            presene of Anti-virus software on Windows.)
          • because the structure of the exploded jar file has changed, I changed
            the up-to-date check timestamp file name to force re-extraction in
            existing installations.

          Compare: https://github.com/jenkinsci/jenkins/compare/b1f5d28f90ca...f7330d7a158e

          SCM/JIRA link daemon added a comment - Code changed in jenkins User: Kohsuke Kawaguchi Path: changelog.html core/src/main/java/hudson/ClassicPluginStrategy.java maven-plugin/src/main/java/hudson/maven/Maven3Builder.java pom.xml http://jenkins-ci.org/commit/jenkins/f7330d7a158eff6705706b1f812993a9b918c351 Log: [FIXED JENKINS-15120] integrated the newer release of remoting jar caching won't work with class file directory, so plugin WEB-INF/classes are now exploded as WEB-INF/lib/classes.jar (This should also solve the problem of slow plugin extraction in the presene of Anti-virus software on Windows.) because the structure of the exploded jar file has changed, I changed the up-to-date check timestamp file name to force re-extraction in existing installations. Compare: https://github.com/jenkinsci/jenkins/compare/b1f5d28f90ca...f7330d7a158e

          dogfood added a comment -

          Integrated in jenkins_main_trunk #2582
          [FIXED JENKINS-15120] (Revision f7330d7a158eff6705706b1f812993a9b918c351)

          Result = UNSTABLE
          kohsuke : f7330d7a158eff6705706b1f812993a9b918c351
          Files :

          • maven-plugin/src/main/java/hudson/maven/Maven3Builder.java
          • pom.xml
          • core/src/main/java/hudson/ClassicPluginStrategy.java
          • changelog.html

          dogfood added a comment - Integrated in jenkins_main_trunk #2582 [FIXED JENKINS-15120] (Revision f7330d7a158eff6705706b1f812993a9b918c351) Result = UNSTABLE kohsuke : f7330d7a158eff6705706b1f812993a9b918c351 Files : maven-plugin/src/main/java/hudson/maven/Maven3Builder.java pom.xml core/src/main/java/hudson/ClassicPluginStrategy.java changelog.html

          Jesse Glick added a comment - Also: https://github.com/jenkinsci/jenkins/compare/f7330d7a158eff6705706b1f812993a9b918c351...cabbe941c73a0db63e59492ff2e3722c41b239f0

          Code changed in jenkins
          User: Kohsuke Kawaguchi
          Path:
          src/main/java/org/jenkinsci/maven/plugins/hpi/AbstractHpiMojo.java
          src/main/java/org/jenkinsci/maven/plugins/hpi/HpiMojo.java
          http://jenkins-ci.org/commit/maven-hpi-plugin/603535119122e820751607812bb7d0bd3b8c3556
          Log:
          Modified to produce a jar file instead of WEB-INF/classes

          Because of the prefetching change in remoting (see JENKINS-15120), it
          is desirable now to produce class files in a jar file, not in a classes
          directory, so that slaves can prefetch them and cache them efficiently.

          Compare: https://github.com/jenkinsci/maven-hpi-plugin/compare/4d27f2880fa5...603535119122

          SCM/JIRA link daemon added a comment - Code changed in jenkins User: Kohsuke Kawaguchi Path: src/main/java/org/jenkinsci/maven/plugins/hpi/AbstractHpiMojo.java src/main/java/org/jenkinsci/maven/plugins/hpi/HpiMojo.java http://jenkins-ci.org/commit/maven-hpi-plugin/603535119122e820751607812bb7d0bd3b8c3556 Log: Modified to produce a jar file instead of WEB-INF/classes Because of the prefetching change in remoting (see JENKINS-15120 ), it is desirable now to produce class files in a jar file, not in a classes directory, so that slaves can prefetch them and cache them efficiently. Compare: https://github.com/jenkinsci/maven-hpi-plugin/compare/4d27f2880fa5...603535119122

          Linards L added a comment - - edited

          Would this work affect freestyle projects using ant / nant / batch builds?

          Linards L added a comment - - edited Would this work affect freestyle projects using ant / nant / batch builds?

          Jesse Glick added a comment -

          Would this work affect freestyle projects using ant / nant / batch builds?

          Some, though not as much as for Maven projects. Depends on the plugins in use during the build, particularly how large their transitive dependencies are.

          Jesse Glick added a comment - Would this work affect freestyle projects using ant / nant / batch builds? Some, though not as much as for Maven projects. Depends on the plugins in use during the build, particularly how large their transitive dependencies are.

          Ulli Hafner added a comment - - edited

          Seems that this new feature breaks class loading of the findbugs plug-in, see JENKINS-18405 and JENKINS-18394 for details...

          Ulli Hafner added a comment - - edited Seems that this new feature breaks class loading of the findbugs plug-in, see JENKINS-18405 and JENKINS-18394 for details...

          kutzi added a comment -

          Maybe also the cause of JENKINS-18401

          kutzi added a comment - Maybe also the cause of JENKINS-18401

          Ulli Hafner added a comment -

          Reopening this issue since it breaks class loading of findbugs plug-in and maven jobs. I can reproduce that issue on my machine, is there anything I can add in my plug-in to prevent these incompatible class exceptions?

          Ulli Hafner added a comment - Reopening this issue since it breaks class loading of findbugs plug-in and maven jobs. I can reproduce that issue on my machine, is there anything I can add in my plug-in to prevent these incompatible class exceptions?

          Process wise, let's leave this bug closed. Instead, if you come across bugs that appear to be related, please link them.

          Kohsuke Kawaguchi added a comment - Process wise, let's leave this bug closed. Instead, if you come across bugs that appear to be related, please link them.

          Code changed in jenkins
          User: Kohsuke Kawaguchi
          Path:
          src/main/java/hudson/remoting/ResourceImageDirect.java
          http://jenkins-ci.org/commit/remoting/781ccaec2e26797bc8fa9e6c982a031988d381e0
          Log:
          JENKINS-18405

          This fixes the 'Unknown url shema' error in the FindBugs plugin.

          Before JENKINS-15120, we used to faithfully recreate the expected
          resource path in a temporary resource file. For some reasons, we lost
          that. This change brings it back by recreting the directory structure.

          Note that this change doesn't address
          "java.lang.IncompatibleClassChangeError: Implementing class" error
          reported also in JENKINS-18405. That is still under investigation.

          SCM/JIRA link daemon added a comment - Code changed in jenkins User: Kohsuke Kawaguchi Path: src/main/java/hudson/remoting/ResourceImageDirect.java http://jenkins-ci.org/commit/remoting/781ccaec2e26797bc8fa9e6c982a031988d381e0 Log: JENKINS-18405 This fixes the 'Unknown url shema' error in the FindBugs plugin. Before JENKINS-15120 , we used to faithfully recreate the expected resource path in a temporary resource file. For some reasons, we lost that. This change brings it back by recreting the directory structure. Note that this change doesn't address "java.lang.IncompatibleClassChangeError: Implementing class" error reported also in JENKINS-18405 . That is still under investigation.

          Yuu Yamashita added a comment -

          This also affects plugins written in JRuby. I created the issue of ruby plugins as JENKINS-18528

          Yuu Yamashita added a comment - This also affects plugins written in JRuby. I created the issue of ruby plugins as JENKINS-18528

          Code changed in jenkins
          User: Nicolas De Loof
          Path:
          src/main/resources/hudson/plugins/ec2/EC2Computer/configure.jelly
          http://jenkins-ci.org/commit/ec2-plugin/995b20442314a3edb615caf803123e77c7c2c9fb
          Log:
          due to JENKINS-15120 relative path isn't supported anymore by st:include

          SCM/JIRA link daemon added a comment - Code changed in jenkins User: Nicolas De Loof Path: src/main/resources/hudson/plugins/ec2/EC2Computer/configure.jelly http://jenkins-ci.org/commit/ec2-plugin/995b20442314a3edb615caf803123e77c7c2c9fb Log: due to JENKINS-15120 relative path isn't supported anymore by st:include

          Code changed in jenkins
          User: Francis Upton
          Path:
          src/main/resources/hudson/plugins/ec2/EC2Computer/configure.jelly
          http://jenkins-ci.org/commit/ec2-plugin/8d5be49e298d130fd4f16db9d5b28a9272825cbe
          Log:
          Merge pull request #62 from ndeloof/master

          due to JENKINS-15120 relative path isn't supported anymore by st:include

          Compare: https://github.com/jenkinsci/ec2-plugin/compare/6a374e309c22...8d5be49e298d

          SCM/JIRA link daemon added a comment - Code changed in jenkins User: Francis Upton Path: src/main/resources/hudson/plugins/ec2/EC2Computer/configure.jelly http://jenkins-ci.org/commit/ec2-plugin/8d5be49e298d130fd4f16db9d5b28a9272825cbe Log: Merge pull request #62 from ndeloof/master due to JENKINS-15120 relative path isn't supported anymore by st:include Compare: https://github.com/jenkinsci/ec2-plugin/compare/6a374e309c22...8d5be49e298d

          Code changed in jenkins
          User: Kohsuke Kawaguchi
          Path:
          src/main/java/hudson/maven/Maven3Builder.java
          http://jenkins-ci.org/commit/maven-plugin/97b452ecc95a5546c471198126834f770a63a249
          Log:
          [FIXED JENKINS-15120]

          • integrated the newer release of remoting
          • jar caching won't work with class file directory, so plugin
            WEB-INF/classes are now exploded as WEB-INF/lib/classes.jar
            (This should also solve the problem of slow plugin extraction in the
            presene of Anti-virus software on Windows.)
          • because the structure of the exploded jar file has changed, I changed
            the up-to-date check timestamp file name to force re-extraction in
            existing installations.

          Originally-Committed-As: f7330d7a158eff6705706b1f812993a9b918c351

          SCM/JIRA link daemon added a comment - Code changed in jenkins User: Kohsuke Kawaguchi Path: src/main/java/hudson/maven/Maven3Builder.java http://jenkins-ci.org/commit/maven-plugin/97b452ecc95a5546c471198126834f770a63a249 Log: [FIXED JENKINS-15120] integrated the newer release of remoting jar caching won't work with class file directory, so plugin WEB-INF/classes are now exploded as WEB-INF/lib/classes.jar (This should also solve the problem of slow plugin extraction in the presene of Anti-virus software on Windows.) because the structure of the exploded jar file has changed, I changed the up-to-date check timestamp file name to force re-extraction in existing installations. Originally-Committed-As: f7330d7a158eff6705706b1f812993a9b918c351

            kohsuke Kohsuke Kawaguchi
            jglick Jesse Glick
            Votes:
            2 Vote for this issue
            Watchers:
            12 Start watching this issue

              Created:
              Updated:
              Resolved: