Modernizing SCMListener registration.

core/src/main/java/hudson/model/AbstractBuild.java

@@ -605,7 +605,7 @@ public abstract class AbstractBuild<P extends AbstractProject<P,R>,R extends Abs
                     if (project.checkout(build, launcher,listener, changeLogFile)) {
                         // check out succeeded
                         SCM scm = project.getScm();
-                        for (SCMListener l : Jenkins.getInstance().getSCMListeners()) {
+                        for (SCMListener l : SCMListener.all()) {
                             try {
                                 l.onCheckout(build, scm, build.getWorkspace(), listener, changeLogFile, project.pollingBaseline);
                             } catch (Exception e) {
@@ -616,7 +616,7 @@ public abstract class AbstractBuild<P extends AbstractProject<P,R>,R extends Abs
                         build.scm = scm.createChangeLogParser();
                         build.changeSet = new WeakReference<ChangeLogSet<? extends Entry>>(build.calcChangeSet());
 
-                        for (SCMListener l : Jenkins.getInstance().getSCMListeners())
+                        for (SCMListener l : SCMListener.all())
                             try {
                                 l.onChangeLogParsed(build,listener,build.getChangeSet());
                             } catch (Exception e) {

core/src/main/java/hudson/model/listeners/SCMListener.java

@@ -23,6 +23,7 @@
  */
 package hudson.model.listeners;
 
+import hudson.Extension;
 import hudson.ExtensionPoint;
 import hudson.FilePath;
 import hudson.Launcher;
@@ -36,6 +37,10 @@ import hudson.scm.ChangeLogSet;
 import hudson.scm.SCM;
 import hudson.scm.SCMRevisionState;
 import java.io.File;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
 import javax.annotation.CheckForNull;
 import jenkins.model.Jenkins;
 
@@ -113,20 +118,36 @@ public abstract class SCMListener implements ExtensionPoint {
         onChangeLogParsed((Run) build, build.getProject().getScm(), listener, changelog);
     }
 
-    /**
-     * Registers this {@link SCMListener} so that it will start receiving events.
-     */
+    @SuppressWarnings("deprecation")
+    public static Collection<? extends SCMListener> all() {
+        Jenkins j = Jenkins.getInstance();
+        if (j == null) {
+            return Collections.emptySet();
+        }
+        List<SCMListener> r = new ArrayList<SCMListener>(j.getExtensionList(SCMListener.class));
+        for (SCMListener l : j.getSCMListeners()) {
+            r.add(l);
+        }
+        return r;
+    }
+
+    /** @deprecated Use {@link Extension} instead. */
+    @Deprecated
     public final void register() {
-        Jenkins.getInstance().getSCMListeners().add(this);
+        Jenkins j = Jenkins.getInstance();
+        if (j != null) {
+            j.getSCMListeners().add(this);
+        }
     }
 
-    /**
-     * Unregisters this {@link SCMListener} so that it will never receive further events.
-     *
-     * <p>
-     * Unless {@link SCMListener} is unregistered, it will never be a subject of GC.
-     */
+    /** @deprecated Use {@link Extension} instead. */
+    @Deprecated
     public final boolean unregister() {
-        return Jenkins.getInstance().getSCMListeners().remove(this);
+        Jenkins j = Jenkins.getInstance();
+        if (j != null) {
+            return j.getSCMListeners().remove(this);
+        } else {
+            return false;
+        }
     }
 }

core/src/main/java/jenkins/model/Jenkins.java

@@ -1220,9 +1220,8 @@ public class Jenkins extends AbstractCIBase implements DirectlyModifiableTopLeve
         updateComputerList(AUTOMATIC_SLAVE_LAUNCH);
     }
 
-    /**
-     * Gets all the installed {@link SCMListener}s.
-     */
+    /** @deprecated Use {@link SCMListener#all} instead. */
+    @Deprecated
     public CopyOnWriteList<SCMListener> getSCMListeners() {
         return scmListeners;
     }