core/src/main/java/hudson/model/AsyncAperiodicWork.java [142:243]:
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    protected StreamTaskListener createListener() {
        File f = getLogFile();
        if (!f.getParentFile().isDirectory()) {
            if (!f.getParentFile().mkdirs()) {
                logger.log(getErrorLoggingLevel(), "Could not create directory {0}", f.getParentFile());
            }
        }
        if (f.isFile()) {
            if ((lastRotateMillis + logRotateMillis < System.currentTimeMillis())
                    || (logRotateSize > 0 && f.length() > logRotateSize)) {
                lastRotateMillis = System.currentTimeMillis();
                File prev = null;
                for (int i = 5; i >= 0; i--) {
                    File curr = i == 0 ? f : new File(f.getParentFile(), f.getName() + "." + i);
                    if (curr.isFile()) {
                        if (prev != null && !prev.exists()) {
                            if (!curr.renameTo(prev)) {
                                logger.log(getErrorLoggingLevel(), "Could not rotate log files {0} to {1}",
                                        new Object[]{curr, prev});
                            }
                        } else {
                            if (!curr.delete()) {
                                logger.log(getErrorLoggingLevel(), "Could not delete log file {0} to enable rotation",
                                        curr);
                            }
                        }
                    }
                    prev = curr;
                }
            }
        } else {
            lastRotateMillis = System.currentTimeMillis();
            // migrate old log files the first time we start-up
            File oldFile = new File(Jenkins.get().getRootDir(), f.getName());
            if (oldFile.isFile()) {
                File newFile = new File(f.getParentFile(), f.getName() + ".1");
                if (!newFile.isFile()) {
                    // if there has never been rotation then this is the first time
                    if (oldFile.renameTo(newFile)) {
                        logger.log(getNormalLoggingLevel(), "Moved {0} to {1}", new Object[]{oldFile, newFile});
                    } else {
                        logger.log(getErrorLoggingLevel(), "Could not move {0} to {1}",
                                new Object[]{oldFile, newFile});
                    }
                }
            }
        }
        try {
            return new StreamTaskListener(f, true, null);
        } catch (IOException e) {
            throw new Error(e);
        }
    }

    /**
     * Determines the log file that records the result of this task.
     */
    protected File getLogFile() {
        return new File(getLogsRoot(), "/tasks/" + name + ".log");
    }

    /**
     * Returns the logging level at which normal messages are displayed.
     *
     * @return The logging level.
     * @since 1.651
     */
    protected Level getNormalLoggingLevel() {
        return Level.INFO;
    }

    /**
     * Returns the logging level at which previous task still executing messages is displayed.
     *
     * @return The logging level.
     * @since 1.651
     */
    protected Level getSlowLoggingLevel() {
        return getNormalLoggingLevel();
    }

    /**
     * Returns the logging level at which error messages are displayed.
     *
     * @return The logging level.
     * @since 1.651
     */
    protected Level getErrorLoggingLevel() {
        return Level.SEVERE;
    }

    /**
     * Executes the task.
     *
     * @param listener
     *      Output sent will be reported to the users. (this work is TBD.)
     * @throws InterruptedException
     *      The caller will record the exception and moves on.
     * @throws IOException
     *      The caller will record the exception and moves on.
     */
    protected abstract void execute(TaskListener listener) throws IOException, InterruptedException;
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core/src/main/java/hudson/model/AsyncPeriodicWork.java [127:234]:
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    protected StreamTaskListener createListener() {
        File f = getLogFile();
        if (!f.getParentFile().isDirectory()) {
            if (!f.getParentFile().mkdirs()) {
                logger.log(getErrorLoggingLevel(), "Could not create directory {0}", f.getParentFile());
            }
        }
        if (f.isFile()) {
            if ((lastRotateMillis + logRotateMillis < System.currentTimeMillis())
                    || (logRotateSize > 0 && f.length() > logRotateSize)) {
                lastRotateMillis = System.currentTimeMillis();
                File prev = null;
                for (int i = 5; i >= 0; i--) {
                    File curr = i == 0 ? f : new File(f.getParentFile(), f.getName() + "." + i);
                    if (curr.isFile()) {
                        if (prev != null && !prev.exists()) {
                            if (!curr.renameTo(prev)) {
                                logger.log(getErrorLoggingLevel(), "Could not rotate log files {0} to {1}",
                                        new Object[]{curr, prev});
                            }
                        } else {
                            if (!curr.delete()) {
                                logger.log(getErrorLoggingLevel(), "Could not delete log file {0} to enable rotation",
                                        curr);
                            }
                        }
                    }
                    prev = curr;
                }
            }
        } else {
            lastRotateMillis = System.currentTimeMillis();
            // migrate old log files the first time we start-up
            File oldFile = new File(Jenkins.get().getRootDir(), f.getName());
            if (oldFile.isFile()) {
                File newFile = new File(f.getParentFile(), f.getName() + ".1");
                if (!newFile.isFile()) {
                    // if there has never been rotation then this is the first time
                    if (oldFile.renameTo(newFile)) {
                        logger.log(getNormalLoggingLevel(), "Moved {0} to {1}", new Object[]{oldFile, newFile});
                    } else {
                        logger.log(getErrorLoggingLevel(), "Could not move {0} to {1}",
                                new Object[]{oldFile, newFile});
                    }
                }
            }
        }
        try {
            return new StreamTaskListener(f, true, null);
        } catch (IOException e) {
            throw new Error(e);
        }
    }

    /**
     * Determines the log file that records the result of this task.
     */
    protected File getLogFile() {
        return new File(getLogsRoot(), "/tasks/" + name + ".log");
    }
    
    /**
     * Returns the logging level at which normal messages are displayed.
     * 
     * @return 
     *      The logging level as @Level.
     *
     * @since 1.551
     */
    protected Level getNormalLoggingLevel() {
        return Level.INFO;
    }
    
    /**
     * Returns the logging level at which previous task still executing messages is displayed.
     *
     * @return
     *      The logging level as @Level.
     *
     * @since 1.565
     */
    protected Level getSlowLoggingLevel() {
        return getNormalLoggingLevel();
    }

    /**
     * Returns the logging level at which error messages are displayed.
     * 
     * @return 
     *      The logging level as @Level.
     *
     * @since 1.551
     */
    protected Level getErrorLoggingLevel() {
        return Level.SEVERE;
    }
    
    /**
     * Executes the task.
     *
     * @param listener
     *      Output sent will be reported to the users. (this work is TBD.)
     * @throws InterruptedException
     *      The caller will record the exception and moves on.
     * @throws IOException
     *      The caller will record the exception and moves on.
     */
    protected abstract void execute(TaskListener listener) throws IOException, InterruptedException;
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