reduce synchronization bottleneck in processing date/time values by using a…

reduce synchronization bottleneck in processing date/time values by using a ThreadLocal for the cached Calendar object

h2/src/main/org/h2/util/DateTimeUtils.java

@@ -52,31 +52,22 @@ public class DateTimeUtils {
     private static final int[] DAYS_OFFSET = { 0, 31, 61, 92, 122, 153, 184,
             214, 245, 275, 306, 337, 366 };
 
-    private static int zoneOffset;
-    private static Calendar cachedCalendar;
+    private static final ThreadLocal<Calendar> cachedCalendar = new ThreadLocal<Calendar>() {
+    	@Override
+    	protected Calendar initialValue() {
+            return Calendar.getInstance();
+    	}
+    };
 
     private DateTimeUtils() {
         // utility class
     }
 
-    static {
-        getCalendar();
-    }
-
     /**
      * Reset the calendar, for example after changing the default timezone.
      */
     public static void resetCalendar() {
-        cachedCalendar = null;
-        getCalendar();
-    }
-
-    private static Calendar getCalendar() {
-        if (cachedCalendar == null) {
-            cachedCalendar = Calendar.getInstance();
-            zoneOffset = cachedCalendar.get(Calendar.ZONE_OFFSET);
-        }
-        return cachedCalendar;
+        cachedCalendar.remove();
     }
 
     /**
@@ -388,17 +379,15 @@ public class DateTimeUtils {
             int millis) {
         Calendar c;
         if (tz == TimeZone.getDefault()) {
-            c = getCalendar();
+            c = cachedCalendar.get();
         } else {
             c = Calendar.getInstance(tz);
         }
-        synchronized (c) {
         c.clear();
         c.setLenient(lenient);
         setCalendarFields(c, year, month, day, hour, minute, second, millis);
         return c.getTime().getTime();
     }
-    }
 
     private static void setCalendarFields(Calendar cal, int year, int month,
             int day, int hour, int minute, int second, int millis) {
@@ -427,8 +416,7 @@ public class DateTimeUtils {
      * @return the value
      */
     public static int getDatePart(java.util.Date d, int field) {
-        Calendar c = getCalendar();
-        synchronized (c) {
+        Calendar c = cachedCalendar.get();
         c.setTime(d);
         if (field == Calendar.YEAR) {
             return getYear(c);
@@ -439,7 +427,6 @@ public class DateTimeUtils {
         }
         return value;
     }
-    }
 
     /**
      * Get the year (positive or negative) from a calendar.
@@ -463,7 +450,7 @@ public class DateTimeUtils {
      * @return the milliseconds
      */
     public static long getTimeLocalWithoutDst(java.util.Date d) {
-        return d.getTime() + zoneOffset;
+        return d.getTime() + cachedCalendar.get().get(Calendar.ZONE_OFFSET);
     }
 
     /**
@@ -474,7 +461,7 @@ public class DateTimeUtils {
      * @return the number of milliseconds in UTC
      */
     public static long getTimeUTCWithoutDst(long millis) {
-        return millis - zoneOffset;
+        return millis - cachedCalendar.get().get(Calendar.ZONE_OFFSET);
     }
 
     /**
@@ -744,13 +731,11 @@ public class DateTimeUtils {
      * @return the date value
      */
     public static long dateValueFromDate(long ms) {
-        Calendar cal = getCalendar();
-        synchronized (cal) {
+        Calendar cal = cachedCalendar.get();
         cal.clear();
         cal.setTimeInMillis(ms);
         return dateValueFromCalendar(cal);
     }
-    }
 
     /**
      * Calculate the date value from a given calendar.
@@ -774,13 +759,11 @@ public class DateTimeUtils {
      * @return the nanoseconds
      */
     public static long nanosFromDate(long ms) {
-        Calendar cal = getCalendar();
-        synchronized (cal) {
+        Calendar cal = cachedCalendar.get();
         cal.clear();
         cal.setTimeInMillis(ms);
         return nanosFromCalendar(cal);
     }
-    }
 
     /**
      * Calculate the nanoseconds since midnight from a given calendar.