[java] pick random port outside of well-known ranges of ephemeral ports

java/src/org/openqa/selenium/net/PortProber.java

@@ -64,22 +64,42 @@ public static int findFreePort() {
   }
 
   /**
-   * Returns a random port within the systems ephemeral port range <p/>
-   * See https://en.wikipedia.org/wiki/Ephemeral_ports for more information. <p/>
-   * If the system provides a too short range (mostly on old windows systems)
-   * the port range suggested from Internet Assigned Numbers Authority will be used.
+   * Returns a port that is within a probable free range. <p/> Based on the ports in
+   * http://en.wikipedia.org/wiki/Ephemeral_ports, this method stays away from all well-known
+   * ephemeral port ranges, since they can arbitrarily race with the operating system in
+   * allocations. Due to the port-greedy nature of selenium this happens fairly frequently.
+   * Staying within the known safe range increases the probability tests will run green quite
+   * significantly.
    *
    * @return a random port number
    */
   private static int createAcceptablePort() {
     synchronized (random) {
-      int FIRST_PORT = Math.max(START_OF_USER_PORTS, ephemeralRangeDetector.getLowestEphemeralPort());
-      int LAST_PORT = Math.min(HIGHEST_PORT, ephemeralRangeDetector.getHighestEphemeralPort());
+      final int FIRST_PORT;
+      final int LAST_PORT;
 
-      if (LAST_PORT - FIRST_PORT < 5000) {
+      int ephemeralStart = Math.max(START_OF_USER_PORTS, ephemeralRangeDetector.getLowestEphemeralPort());
+      int ephemeralEnd = Math.min(HIGHEST_PORT, ephemeralRangeDetector.getHighestEphemeralPort());
+
+      /*
+       * If the system provides a too short range of ephemeral ports (mostly on old windows systems)
+       * use the range suggested from Internet Assigned Numbers Authority as ephemeral port range.
+       */
+      if (ephemeralEnd - ephemeralStart < 5000) {
         EphemeralPortRangeDetector ianaRange = new FixedIANAPortRange();
-        FIRST_PORT = ianaRange.getLowestEphemeralPort();
-        LAST_PORT = ianaRange.getHighestEphemeralPort();
+        ephemeralStart = ianaRange.getLowestEphemeralPort();
+        ephemeralEnd = ianaRange.getHighestEphemeralPort();
+      }
+
+      int freeAbove = HIGHEST_PORT - ephemeralEnd;
+      int freeBelow = Math.max(0, ephemeralStart - START_OF_USER_PORTS);
+
+      if (freeAbove > freeBelow) {
+        FIRST_PORT = ephemeralEnd;
+        LAST_PORT = 65535;
+      } else {
+        FIRST_PORT = 1024;
+        LAST_PORT = ephemeralStart;
       }
 
       if (FIRST_PORT == LAST_PORT) {