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 -

          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: