show-queue cannot be starved for admins

When admin executes the show-queue command a new thread will be
created to make sure that the commmand is always executed even if
the thread pool is exhausted.

Bug: issue 570

gerrit-sshd/src/main/java/com/google/gerrit/sshd/AdminHighPriorityCommand.java

@@ -0,0 +1,31 @@
+// Copyright (C) 2009 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.sshd;
+
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+/**
+ * Annotation tagged on a concrete Command that requires
+ * high priority thread creation whenever called by administrators users.
+ * <p>
+ */
+@Target( {ElementType.TYPE})
+@Retention(RUNTIME)
+public @interface AdminHighPriorityCommand {
+}

gerrit-sshd/src/main/java/com/google/gerrit/sshd/BaseCommand.java

@@ -238,7 +238,8 @@ public abstract class BaseCommand implements Command {
    */
   protected synchronized void startThread(final CommandRunnable thunk) {
     final TaskThunk tt = new TaskThunk(thunk);
-    if (isAdminCommand()) {
+
+    if (isAdminCommand()||(isAdminHighPriorityCommand() && userProvider.get().isAdministrator())) {
       // Admin commands should not block the main work threads (there
       // might be an interactive shell there), nor should they wait
       // for the main work threads.
@@ -253,6 +254,10 @@ public abstract class BaseCommand implements Command {
     return getClass().getAnnotation(AdminCommand.class) != null;
   }
 
+  private final boolean isAdminHighPriorityCommand() {
+    return getClass().getAnnotation(AdminHighPriorityCommand.class) != null;
+  }
+
   /**
    * Terminate this command and return a result code to the remote client.
    * <p>

gerrit-sshd/src/main/java/com/google/gerrit/sshd/commands/ShowQueue.java

@@ -22,6 +22,7 @@ import com.google.gerrit.server.git.WorkQueue.Task;
 import com.google.gerrit.server.project.ProjectCache;
 import com.google.gerrit.server.project.ProjectState;
 import com.google.gerrit.server.util.IdGenerator;
+import com.google.gerrit.sshd.AdminHighPriorityCommand;
 import com.google.gerrit.sshd.BaseCommand;
 import com.google.inject.Inject;
 
@@ -37,6 +38,7 @@ import java.util.List;
 import java.util.concurrent.TimeUnit;
 
 /** Display the current work queue. */
+@AdminHighPriorityCommand
 final class ShowQueue extends BaseCommand {
   @Option(name = "-w", usage = "display without line width truncation")
   private boolean wide;