又一次卡住了。卡的严严实实。

        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - locked <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)
        - waiting to lock <0x00000000868b00b8> (a ch.qos.logback.core.util.CachingDateFormatter)

代码位置 (sdf.format(new Date(now)); )：

/**
 * A synchronized implementation of  SimpleDateFormat which uses caching internally.
 *
 * @author Ceki Gülcü
 * @since 0.9.29
 */
public class CachingDateFormatter {

    long lastTimestamp = -1;
    String cachedStr = null;
    final SimpleDateFormat sdf;

    public CachingDateFormatter(String pattern) {
        sdf = new SimpleDateFormat(pattern);
    }

    public final String format(long now) {

        // SimpleDateFormat is not thread safe.

        // See also the discussion in http://jira.qos.ch/browse/LBCLASSIC-36
        // DateFormattingThreadedThroughputCalculator and SelectiveDateFormattingRunnable
        // are also noteworthy

        // The now == lastTimestamp guard minimizes synchronization
        synchronized (this) {
            if (now != lastTimestamp) {
                lastTimestamp = now;
                cachedStr = sdf.format(new Date(now));
            }
            return cachedStr;
        }
    }