private static Object getAddressFromNameService(String host, InetAddress reqAddr) throws UnknownHostException { Object obj = null; boolean success = false; UnknownHostException ex = null; // Check whether the host is in the lookupTable. // 1) If the host isn't in the lookupTable when // checkLookupTable() is called, checkLookupTable() // would add the host in the lookupTable and // return null. So we will do the lookup. // 2) If the host is in the lookupTable when // checkLookupTable() is called, the current thread // would be blocked until the host is removed // from the lookupTable. Then this thread // should try to look up the addressCache. // i) if it found the address in the // addressCache, checkLookupTable() would // return the address. // ii) if it didn't find the address in the // addressCache for any reason, // it should add the host in the // lookupTable and return null so the // following code would do a lookup itself. if ((obj = checkLookupTable(host)) == null) { // This is the first thread which looks up the address // this host or the cache entry for this host has been // expired so this thread should do the lookup. for (NameService nameService : nameServices) { try { /* * Do not put the call to lookup() inside the * constructor. if you do you will still be * allocating space when the lookup fails. */ obj = nameService.lookupAllHostAddr(host); success = true; break; } catch (UnknownHostException uhe) { if (host.equalsIgnoreCase("localhost")) { InetAddress[] local = new InetAddress[] {impl.loopbackAddress()}; obj = local; success = true; break; } else { obj = unknown_array; success = false; ex = uhe; } } } // More to do? InetAddress[] addrs = (InetAddress[]) obj; if (reqAddr != null && addrs.length > 1 && !addrs[0].equals(reqAddr)) { // Find it? int i = 1; for (; i < addrs.length; i++) { if (addrs[i].equals(reqAddr)) { break; } } // Rotate if (i < addrs.length) { InetAddress tmp, tmp2 = reqAddr; for (int j = 0; j < i; j++) { tmp = addrs[j]; addrs[j] = tmp2; tmp2 = tmp; } addrs[i] = tmp2; } } // Cache the address. cacheAddress(host, obj, success); // Delete the host from the lookupTable, and // notify all threads waiting for the monitor // for lookupTable. updateLookupTable(host); if (!success && ex != null) throw ex; } return obj; }