upload-pack: Delay reserving database connection until executing

We don't want to check out a connection from the connection pool
until we know we have been granted a thread from the thread pool
to execute on.  If we grab the connection when the Upload object is
created, and we have to wait 5 seconds to get a thread for runImpl()
to execute on, we'll simply be tieing up that connection for the
entire duration of the wait.  So use a Provider instead so we can
defer obtaining the connection.

Change-Id: I9ac360981fb1ad3e09e77ad579e9203686b14494
Signed-off-by: Shawn O. Pearce <sop@google.com>
Reviewed-by: Nico Sallembien <nsallembien@google.com>

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

@@ -18,6 +18,7 @@ import com.google.gerrit.reviewdb.ReviewDb;
 import com.google.gerrit.server.git.VisibleRefFilter;
 import com.google.gerrit.sshd.AbstractGitCommand;
 import com.google.inject.Inject;
+import com.google.inject.Provider;
 
 import org.eclipse.jgit.transport.UploadPack;
 
@@ -25,15 +26,14 @@ import java.io.IOException;
 
 /** Publishes Git repositories over SSH using the Git upload-pack protocol. */
 final class Upload extends AbstractGitCommand {
-
   @Inject
-  private ReviewDb db;
+  private Provider<ReviewDb> db;
 
   @Override
   protected void runImpl() throws IOException {
     final UploadPack up = new UploadPack(repo);
     if (!projectControl.allRefsAreVisible()) {
-      up.setRefFilter(new VisibleRefFilter(repo, projectControl, db));
+      up.setRefFilter(new VisibleRefFilter(repo, projectControl, db.get()));
     }
     up.upload(in, out, err);
   }