Prepare for running relay descriptor downloader twice per hour.

src/org/torproject/ernie/db/bridgedescs/SanitizedBridgesWriter.java

@@ -81,6 +81,13 @@ public class SanitizedBridgesWriter extends Thread {
   private SecureRandom secureRandom;
 
   public void run() {
+
+    if (((System.currentTimeMillis() / 60000L) % 60L) > 30L) {
+      /* Don't start in second half of an hour, when we only want to
+       * process other data. */
+      return;
+    }
+
     File bridgeDirectoriesDirectory =
         new File(config.getBridgeSnapshotsDirectory());
     File sanitizedBridgesDirectory =

src/org/torproject/ernie/db/bridgepools/BridgePoolAssignmentsProcessor.java

@@ -38,6 +38,13 @@ public class BridgePoolAssignmentsProcessor extends Thread {
   }
 
   public void run() {
+
+    if (((System.currentTimeMillis() / 60000L) % 60L) > 30L) {
+      /* Don't start in second half of an hour, when we only want to
+       * process other data. */
+      return;
+    }
+
     File assignmentsDirectory =
         new File(config.getAssignmentsDirectory());
     File sanitizedAssignmentsDirectory =

src/org/torproject/ernie/db/exitlists/ExitListDownloader.java

@@ -27,6 +27,13 @@ public class ExitListDownloader extends Thread {
   }
 
   public void run() {
+
+    if (((System.currentTimeMillis() / 60000L) % 60L) > 30L) {
+      /* Don't start in second half of an hour, when we only want to
+       * process other data. */
+      return;
+    }
+
     Logger logger = Logger.getLogger(ExitListDownloader.class.getName());
     try {
       logger.fine("Downloading exit list...");

src/org/torproject/ernie/db/torperf/TorperfDownloader.java

@@ -42,6 +42,12 @@ public class TorperfDownloader extends Thread {
 
   public void run() {
 
+    if (((System.currentTimeMillis() / 60000L) % 60L) > 30L) {
+      /* Don't start in second half of an hour, when we only want to
+       * process other data. */
+      return;
+    }
+
     File torperfOutputDirectory =
         new File(config.getTorperfOutputDirectory());
     SortedMap<String, String> torperfSources = config.getTorperfSources();