private static List<String> findPIDs(final Collection<File> files, final PrintWriter output) {
    int[] pidTable = new int[files.size()];
    int[] pidTableCounter = new int[pidTable.length];
    List<String> nickNames = new ArrayList<>();
    char fileSeparatorChar = File.separatorChar;

    for (File file : files) {
      String name = file.getPath();

      String slashdotslash = fileSeparatorChar + "." + fileSeparatorChar;
      int startIdx = name.lastIndexOf(slashdotslash);

      // get rid of the parent directories and any /./ in the path
      if (startIdx > 0) {
        name = name.substring(startIdx + slashdotslash.length());
      }

      startIdx = name.lastIndexOf(fileSeparatorChar);

      // first see if there's a number at the end of the file's directory name
      if (startIdx > 0) {
        startIdx--;
        char c = name.charAt(startIdx);
        if (!('0' <= c && c <= '9')) {
          startIdx = 0;
        } else {
          // see if this is a hydra-generated test directory name, like parReg-0504-161349
          int testIdx = startIdx - 1;
          while (testIdx > 0 && '0' <= name.charAt(testIdx) && name.charAt(testIdx) <= '9') {
            testIdx--;
          }
          if (testIdx < 1 || name.charAt(testIdx) == '-') {
            startIdx = 0;
          }
        }
      }

      // if there's no number in the directory name, use the file name
      if (startIdx <= 0) {
        startIdx = name.length() - 1;
        if (startIdx > 6 && name.charAt(startIdx) == 'z' && name.charAt(startIdx - 1) == 'g'
            && name.charAt(startIdx - 2) == '.' && name.charAt(startIdx - 3) == 'g'
            && name.charAt(startIdx - 4) == 'o' && name.charAt(startIdx - 5) == 'l'
            && name.charAt(startIdx - 6) == '.') {
          startIdx -= 7;
        } else if (startIdx > 3 && name.charAt(startIdx) == 'g' && name.charAt(startIdx - 1) == 'o'
            && name.charAt(startIdx - 2) == 'l' && name.charAt(startIdx - 3) == '.') {
          startIdx -= 4;
        }
      }

      // find the string of numbers at the end of the test area and use it as a PID
      for (int i = startIdx; i >= 0; i--) {
        char c = name.charAt(i);
        if (!('0' <= c && c <= '9')) {
          if (i < name.length() - 1) { // have a number
            // there's a number - assume it's a PID if it's not zero
            String PID = name.substring(i + 1, startIdx + 1);
            try {
              int iPID = Integer.parseInt(PID);
              if (iPID > 0) {
                int p = 0;
                // find the PID in the table of those seen so far, or assign it
                // a new slot. increment the number of files for this PID and
                // assign a nickname for the file
                for (; p < pidTable.length; p++) {
                  if (pidTable[p] == 0) {
                    pidTable[p] = iPID;
                    pidTableCounter[p] = 1;
                    break;
                  }
                  if (pidTable[p] == iPID) {
                    pidTableCounter[p]++;
                    break;
                  }
                }
                Assert.assertTrue(p < pidTableCounter.length);
                nickNames.add(iPID + "-" + pidTableCounter[p]);
                output.println("nickname " + iPID + "-" + pidTableCounter[p] + ": " + name);
              } else {
                nickNames.add(null);
              }
            } catch (NumberFormatException nfe) {
              nickNames.add(null);
            }
          } else {
            nickNames.add(null);
          }
          break;
        }
      }
    }
    return nickNames;
  }
hydra log files usually have the process's PID in their path name. This method extracts the PID
number and assigns the corresponding File a nickname using the PID and the position of the File
in the list of those also having this PID.
<p>
e.g., bgexec32414_1043.log --> 1043-1<br>
gemfire_1043/system.log --> 1043-2<br>
gemfire_1043/system_01_00.log --> 1043-3<br>
geode-core/src/main/java/org/apache/geode/internal/logging/MergeLogFiles.java