Merge "New option to schedule the Git garbage collection as a background task"

Documentation/rest-api-projects.txt

@@ -844,6 +844,34 @@ The response is the streamed output of the garbage collection.
   done.
 ----
 
+==== Asynchronous Execution
+
+The option `async` allows to schedule a background task that asynchronously
+executes a Git garbage collection.
+
+The `Location` header of the response refers to the link:rest-api-config.html#get-task[background task]
+which allows to inspect the progress of its execution. In case of asynchronous
+execution the `show_progress` option is ignored.
+
+.Request
+----
+  POST /projects/plugins%2Freplication/gc HTTP/1.0
+  Content-Type: application/json;charset=UTF-8
+
+  {
+    "async": true
+  }
+----
+
+The response is empty.
+
+.Response
+----
+  HTTP/1.1 202 Accepted
+  Content-Disposition: attachment
+  Location: https:<host>/a/config/server/tasks/383a0602
+----
+
 [[ban-commit]]
 === Ban Commit
 --
@@ -2212,6 +2240,8 @@ collection.
 Whether progress information should be shown.
 |`aggressive`    |`false` if not set|
 Whether an aggressive garbage collection should be done.
+|`async`         |`false` if not set|
+Whether the garbage collection should run asynchronously.
 |=============================
 
 [[head-input]]

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/restapi/Response.java

@@ -36,6 +36,11 @@ public abstract class Response<T> {
     return new Impl<>(201, value);
   }
 
+  /** HTTP 202 Accepted: accepted as background task. */
+  public static Accepted accepted(String location) {
+    return new Accepted(location);
+  }
+
   /** HTTP 204 No Content: typically used when the resource is deleted. */
   @SuppressWarnings("unchecked")
   public static <T> Response<T> none() {
@@ -168,4 +173,33 @@ public abstract class Response<T> {
       return String.format("[302 Redirect] %s", location);
     }
   }
+
+  /** Accepted as task for asynchronous execution. */
+  public static final class Accepted {
+    private final String location;
+
+    private Accepted(String url) {
+      this.location = url;
+    }
+
+    public String location() {
+      return location;
+    }
+
+    @Override
+    public int hashCode() {
+      return location.hashCode();
+    }
+
+    @Override
+    public boolean equals(Object o) {
+      return o instanceof Accepted
+        && ((Accepted) o).location.equals(location);
+    }
+
+    @Override
+    public String toString() {
+      return String.format("[202 Accepted] %s", location);
+    }
+  }
 }

gerrit-httpd/src/main/java/com/google/gerrit/httpd/restapi/RestApiServlet.java

@@ -18,6 +18,7 @@ import static com.google.common.base.Preconditions.checkNotNull;
 import static java.math.RoundingMode.CEILING;
 import static java.nio.charset.StandardCharsets.ISO_8859_1;
 import static java.nio.charset.StandardCharsets.UTF_8;
+import static javax.servlet.http.HttpServletResponse.SC_ACCEPTED;
 import static javax.servlet.http.HttpServletResponse.SC_BAD_REQUEST;
 import static javax.servlet.http.HttpServletResponse.SC_CONFLICT;
 import static javax.servlet.http.HttpServletResponse.SC_CREATED;
@@ -347,6 +348,11 @@ public class RestApiServlet extends HttpServlet {
         CacheHeaders.setNotCacheable(res);
         res.sendRedirect(((Response.Redirect) result).location());
         return;
+      } else if (result instanceof Response.Accepted) {
+        CacheHeaders.setNotCacheable(res);
+        res.setStatus(SC_ACCEPTED);
+        res.setHeader(HttpHeaders.LOCATION, ((Response.Accepted)result).location());
+        return;
       } else {
         CacheHeaders.setNotCacheable(res);
       }

gerrit-server/src/main/java/com/google/gerrit/server/project/GarbageCollect.java

@@ -20,13 +20,19 @@ import com.google.gerrit.common.data.GarbageCollectionResult;
 import com.google.gerrit.common.data.GlobalCapability;
 import com.google.gerrit.extensions.annotations.RequiresCapability;
 import com.google.gerrit.extensions.restapi.BinaryResult;
+import com.google.gerrit.extensions.restapi.Response;
 import com.google.gerrit.extensions.restapi.RestModifyView;
 import com.google.gerrit.extensions.webui.UiAction;
+import com.google.gerrit.reviewdb.client.Project;
+import com.google.gerrit.server.config.CanonicalWebUrl;
 import com.google.gerrit.server.git.GarbageCollection;
 import com.google.gerrit.server.git.GitRepositoryManager;
 import com.google.gerrit.server.git.LocalDiskRepositoryManager;
+import com.google.gerrit.server.git.WorkQueue;
 import com.google.gerrit.server.project.GarbageCollect.Input;
+import com.google.gerrit.server.util.IdGenerator;
 import com.google.inject.Inject;
+import com.google.inject.Provider;
 import com.google.inject.Singleton;
 
 import java.io.IOException;
@@ -42,22 +48,61 @@ public class GarbageCollect implements RestModifyView<ProjectResource, Input>,
   public static class Input {
     public boolean showProgress;
     public boolean aggressive;
+    public boolean async;
   }
 
   private final boolean canGC;
-  private GarbageCollection.Factory garbageCollectionFactory;
+  private final GarbageCollection.Factory garbageCollectionFactory;
+  private final WorkQueue workQueue;
+  private final Provider<String> canonicalUrl;
 
   @Inject
-  GarbageCollect(
-      GitRepositoryManager repoManager,
-      GarbageCollection.Factory garbageCollectionFactory) {
+  GarbageCollect(GitRepositoryManager repoManager,
+      GarbageCollection.Factory garbageCollectionFactory, WorkQueue workQueue,
+      @CanonicalWebUrl Provider<String> canonicalUrl) {
+    this.workQueue = workQueue;
+    this.canonicalUrl = canonicalUrl;
     this.canGC = repoManager instanceof LocalDiskRepositoryManager;
     this.garbageCollectionFactory = garbageCollectionFactory;
   }
 
-  @SuppressWarnings("resource")
   @Override
-  public BinaryResult apply(final ProjectResource rsrc, final Input input) {
+  public Object apply(ProjectResource rsrc, Input input) {
+    Project.NameKey project = rsrc.getNameKey();
+    if (input.async) {
+      return applyAsync(project, input);
+    } else {
+      return applySync(project, input);
+    }
+  }
+
+  private Response.Accepted applyAsync(final Project.NameKey project, final Input input) {
+    Runnable job = new Runnable() {
+      @Override
+      public void run() {
+       runGC(project, input, null);
+      }
+
+      @Override
+      public String toString() {
+        return "Run " + (input.aggressive ? "aggressive " : "")
+            + "garbage collection on project " + project.get();
+      }
+    };
+
+    @SuppressWarnings("unchecked")
+    WorkQueue.Task<Void> task =
+        (WorkQueue.Task<Void>) workQueue.getDefaultQueue().submit(job);
+
+    String location = canonicalUrl.get() + "a/config/server/tasks/"
+            + IdGenerator.format(task.getTaskId());
+
+    return Response.accepted(location);
+  }
+
+  @SuppressWarnings("resource")
+  private BinaryResult applySync(final Project.NameKey project,
+      final Input input) {
     return new BinaryResult() {
       @Override
       public void writeTo(OutputStream out) throws IOException {
@@ -69,10 +114,8 @@ public class GarbageCollect implements RestModifyView<ProjectResource, Input>,
           }
         };
         try {
-          GarbageCollectionResult result =
-              garbageCollectionFactory.create().run(
-                  Collections.singletonList(rsrc.getNameKey()), input.aggressive,
-                  input.showProgress ? writer : null);
+          PrintWriter progressWriter = input.showProgress ? writer : null;
+          GarbageCollectionResult result = runGC(project, input, progressWriter);
           String msg = "Garbage collection completed successfully.";
           if (result.hasErrors()) {
             for (GarbageCollectionResult.Error e : result.getErrors()) {
@@ -104,6 +147,13 @@ public class GarbageCollect implements RestModifyView<ProjectResource, Input>,
      .disableGzip();
   }
 
+  GarbageCollectionResult runGC(Project.NameKey project,
+      Input input, PrintWriter progressWriter) {
+    return garbageCollectionFactory.create().run(
+        Collections.singletonList(project), input.aggressive,
+        progressWriter);
+  }
+
   @Override
   public UiAction.Description getDescription(ProjectResource rsrc) {
     return new UiAction.Description()