DropWizard metric support

Gerrit server supports defining and recording metrics.  Metric
reporters for monitoring can be implemented as plugins.  A basic
Graphite reporter is available here:

  https://gerrit-review.googlesource.com/#/c/72202/

Some example metrics are included in this change:

  change/query/query_latency
  (Query latency)

  sshd/sessions/connected
  (SSH sessions connected)

  sshd/sessions/created/count
  (SSH connections created)

  git/upload-pack
  (Upload packs requests)

Partially-by: Gustaf Lundh <gustaflh@axis.com>
Change-Id: I46a07aace57efe236ee724ec8d34c581e2c37965

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

@@ -19,10 +19,14 @@ import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.concurrent.TimeUnit.SECONDS;
 
 import com.google.common.base.Strings;
+import com.google.common.base.Supplier;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
 import com.google.gerrit.common.Version;
 import com.google.gerrit.extensions.events.LifecycleListener;
+import com.google.gerrit.metrics.Counter;
+import com.google.gerrit.metrics.Description;
+import com.google.gerrit.metrics.MetricMaker;
 import com.google.gerrit.server.config.ConfigUtil;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.ssh.SshAdvertisedAddresses;
@@ -126,6 +130,7 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
 
 /**
  * SSH daemon to communicate with Gerrit.
@@ -170,7 +175,8 @@ public class SshDaemon extends SshServer implements SshInfo, LifecycleListener {
       final KeyPairProvider hostKeyProvider, final IdGenerator idGenerator,
       @GerritServerConfig final Config cfg, final SshLog sshLog,
       @SshListenAddresses final List<SocketAddress> listen,
-      @SshAdvertisedAddresses final List<String> advertised) {
+      @SshAdvertisedAddresses final List<String> advertised,
+      MetricMaker metricMaker) {
     setPort(IANA_SSH_PORT /* never used */);
 
     this.cfg = cfg;
@@ -245,10 +251,33 @@ public class SshDaemon extends SshServer implements SshInfo, LifecycleListener {
     setKeyPairProvider(hostKeyProvider);
     setCommandFactory(commandFactory);
     setShellFactory(noShell);
+
+    final AtomicInteger connected = new AtomicInteger();
+    metricMaker.newCallbackMetric(
+        "sshd/sessions/connected",
+        Integer.class,
+        new Description("Currently connected SSH sessions")
+          .setGauge()
+          .setUnit("sessions"),
+        new Supplier<Integer>() {
+          @Override
+          public Integer get() {
+            return connected.get();
+          }
+        });
+
+    final Counter sesssionsCreated = metricMaker.newCounter(
+        "sshd/sessions/created",
+        new Description("Rate of new SSH sessions")
+          .setRate()
+          .setUnit("sessions"));
+
     setSessionFactory(new SessionFactory() {
       @Override
       protected AbstractSession createSession(final IoSession io)
           throws Exception {
+        connected.incrementAndGet();
+        sesssionsCreated.increment();
         if (io instanceof MinaSession) {
           if (((MinaSession) io).getSession()
               .getConfig() instanceof SocketSessionConfig) {
@@ -269,6 +298,7 @@ public class SshDaemon extends SshServer implements SshInfo, LifecycleListener {
         s.addCloseSessionListener(new SshFutureListener<CloseFuture>() {
           @Override
           public void operationComplete(CloseFuture future) {
+            connected.decrementAndGet();
             if (sd.isAuthenticationError()) {
               sshLog.onAuthFail(sd);
             }

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

@@ -20,6 +20,7 @@ import com.google.gerrit.reviewdb.server.ReviewDb;
 import com.google.gerrit.server.git.ChangeCache;
 import com.google.gerrit.server.git.TagCache;
 import com.google.gerrit.server.git.TransferConfig;
+import com.google.gerrit.server.git.UploadPackMetricsHook;
 import com.google.gerrit.server.git.VisibleRefFilter;
 import com.google.gerrit.server.git.validators.UploadValidationException;
 import com.google.gerrit.server.git.validators.UploadValidators;
@@ -58,6 +59,9 @@ final class Upload extends AbstractGitCommand {
   @Inject
   private SshSession session;
 
+  @Inject
+  private UploadPackMetricsHook uploadMetrics;
+
   @Override
   protected void runImpl() throws IOException, Failure {
     if (!projectControl.canRunUploadPack()) {
@@ -71,6 +75,7 @@ final class Upload extends AbstractGitCommand {
     }
     up.setPackConfig(config.getPackConfig());
     up.setTimeout(config.getTimeout());
+    up.setPostUploadHook(uploadMetrics);
 
     List<PreUploadHook> allPreUploadHooks = Lists.newArrayList(preUploadHooks);
     allPreUploadHooks.add(uploadValidatorsFactory.create(project, repo,