[JENKINS-35098] Disable AutoBrowserHolder by default to improve the changelog rendering performance

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

@@ -63,6 +63,7 @@
 import static hudson.scm.PollingResult.*;
 import hudson.scm.SCM;
 import hudson.scm.SCMRevisionState;
+import hudson.scm.SCMS;
 import hudson.search.SearchIndexBuilder;
 import hudson.security.ACL;
 import hudson.security.Permission;
@@ -1860,7 +1861,7 @@ protected void submit(StaplerRequest req, StaplerResponse rsp) throws IOExceptio
 
         authToken = BuildAuthorizationToken.create(req);
 
-        setScm(req.bindJSON(SCM.class, json.getJSONObject("scm")));
+        setScm(SCMS.parseSCM(req,this));
 
         for (Trigger t : triggers())
             t.stop();

core/src/main/java/hudson/scm/AutoBrowserHolder.java

@@ -0,0 +1,88 @@
+/*
+ * The MIT License
+ * 
+ * Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package hudson.scm;
+
+import hudson.model.AbstractProject;
+import jenkins.model.Jenkins;
+
+/**
+ * Maintains the automatically inferred {@link RepositoryBrowser} instance.
+ *
+ * <p>
+ * To reduce the user's work, Hudson tries to infer applicable {@link RepositoryBrowser}
+ * from configurations of other jobs. But this needs caution &mdash; for example,
+ * such inferred {@link RepositoryBrowser} must be recalculated whenever
+ * a job configuration changes somewhere.
+ *
+ * <p>
+ * This class makes such tracking easy by hiding this logic.
+ * @deprecated Disabled by default: JENKINS-35098
+ */
+@Deprecated
+final class AutoBrowserHolder {
+    private int cacheGeneration;
+    private RepositoryBrowser cache;
+    private SCM owner;
+
+    public AutoBrowserHolder(SCM owner) {
+        this.owner = owner;
+    }
+
+    public RepositoryBrowser get() {
+        if (cacheGeneration == -1) {
+            return cache;
+        }
+        SCMDescriptor<?> d = owner.getDescriptor();
+        RepositoryBrowser<?> dflt = owner.guessBrowser();
+        if (dflt != null) {
+            cache = dflt;
+            cacheGeneration = -1;
+            return cache;
+        }
+        int g = d.generation;
+        if(g!=cacheGeneration) {
+            cacheGeneration = g;
+            cache = infer();
+        }
+        return cache;
+    }
+
+    /**
+     * Picks up a {@link RepositoryBrowser} that matches the
+     * given {@link SCM} from existing other jobs.
+     *
+     * @return
+     *      null if no applicable configuration was found.
+     */
+    private RepositoryBrowser infer() {
+        for( AbstractProject p : Jenkins.getInstance().getAllItems(AbstractProject.class) ) {
+            SCM scm = p.getScm();
+            if (scm!=null && scm.getClass()==owner.getClass() && scm.getBrowser()!=null &&
+                    ((SCMDescriptor)scm.getDescriptor()).isBrowserReusable(scm,owner)) {
+                return scm.getBrowser();
+            }
+        }
+        return null;
+    }
+}

core/src/main/java/hudson/scm/SCM.java

@@ -85,6 +85,15 @@
 @ExportedBean
 public abstract class SCM implements Describable<SCM>, ExtensionPoint {
 
+    /** JENKINS-35098: discouraged */
+    @SuppressWarnings("FieldMayBeFinal")
+    private static boolean useAutoBrowserHolder = Boolean.getBoolean(SCM.class.getName() + ".useAutoBrowserHolder");
+    /**
+     * Stores {@link AutoBrowserHolder}. Lazily created.
+     * @deprecated Unused by default.
+     */
+    private transient AutoBrowserHolder autoBrowserHolder;
+
     /**
      * Expose {@link SCM} to the remote API.
      */
@@ -121,12 +130,20 @@ public String getType() {
      * controlled by this {@link SCM}.
      * @see #guessBrowser
      */
+    @SuppressWarnings("deprecation")
     @Exported(name="browser")
     public final @CheckForNull RepositoryBrowser<?> getEffectiveBrowser() {
         RepositoryBrowser<?> b = getBrowser();
         if(b!=null)
             return b;
-        return guessBrowser();
+        if (useAutoBrowserHolder) {
+            if (autoBrowserHolder == null) {
+                autoBrowserHolder = new AutoBrowserHolder(this);
+            }
+            return autoBrowserHolder.get();
+        } else {
+            return guessBrowser();
+        }
     }
 
     /**

core/src/main/java/hudson/scm/SCMDescriptor.java

@@ -53,7 +53,7 @@ public abstract class SCMDescriptor<T extends SCM> extends Descriptor<SCM> {
      * This is used to invalidate cache of {@link SCM#getEffectiveBrowser}. Due to the lack of synchronization and serialization,
      * this field doesn't really count the # of instances created to date,
      * but it's good enough for the cache invalidation.
-     * @deprecated No longer used.
+     * @deprecated No longer used by default.
      */
     @Deprecated
     public volatile int generation = 1;
@@ -104,7 +104,7 @@ public void load() {
      * @return
      *      true if the two given SCM configurations are similar enough
      *      that they can reuse {@link RepositoryBrowser} between them.
-     * @deprecated No longer used. {@link SCM#getKey} could be used to implement similar features if needed.
+     * @deprecated No longer used by default. {@link SCM#getKey} could be used to implement similar features if needed.
      */
     @Deprecated
     public boolean isBrowserReusable(T x, T y) {

core/src/main/java/hudson/scm/SCMS.java

@@ -38,9 +38,7 @@
  * List of all installed SCMs.
  * 
  * @author Kohsuke Kawaguchi
- * @deprecated No longer contains anything nondeprecated.
  */
-@Deprecated
 public class SCMS {
     /**
      * List of all installed SCMs.
@@ -55,16 +53,12 @@ public class SCMS {
      *
      * @param target
      *      The project for which this SCM is configured to.
-     * @deprecated Suffices to use {@link StaplerRequest#bindJSON(java.lang.Class, net.sf.json.JSONObject)}
      */
-    @Deprecated
+    @SuppressWarnings("deprecation")
     public static SCM parseSCM(StaplerRequest req, AbstractProject target) throws FormException, ServletException {
-        String scm = req.getParameter("scm");
-        if(scm==null)   return new NullSCM();
-
-        int scmidx = Integer.parseInt(scm);
-        SCMDescriptor<?> d = SCM._for(target).get(scmidx);
-        return d.newInstance(req, req.getSubmittedForm().getJSONObject("scm"));
+        SCM scm = req.bindJSON(SCM.class, req.getSubmittedForm().getJSONObject("scm"));
+        scm.getDescriptor().generation++;
+        return scm;
     }
 
     /**