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/*
 *  Copyright 2001-2012 Stephen Colebourne
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.joda.time.tz;

import org.joda.time.DateTimeZone;

/**
 * Improves the performance of requesting time zone offsets and name keys by
 * caching the results. Time zones that have simple rules or are fixed should
 * not be cached, as it is unlikely to improve performance.
 * 

* CachedDateTimeZone is thread-safe and immutable. * * @author Brian S O'Neill * @since 1.0 */ public class CachedDateTimeZone extends DateTimeZone { private static final long serialVersionUID = 5472298452022250685L; private static final int cInfoCacheMask; static { Integer i; try { i = Integer.getInteger("org.joda.time.tz.CachedDateTimeZone.size"); } catch (SecurityException e) { i = null; } int cacheSize; if (i == null) { // With a cache size of 512, dates that lie within any 69.7 year // period have no cache collisions. cacheSize = 512; // (1 << 9) } else { cacheSize = i.intValue(); // Ensure cache size is even power of 2. cacheSize--; int shift = 0; while (cacheSize > 0) { shift++; cacheSize >>= 1; } cacheSize = 1 << shift; } cInfoCacheMask = cacheSize - 1; } /** * Returns a new CachedDateTimeZone unless given zone is already cached. */ public static CachedDateTimeZone forZone(DateTimeZone zone) { if (zone instanceof CachedDateTimeZone) { return (CachedDateTimeZone)zone; } return new CachedDateTimeZone(zone); } /* * Caching is performed by breaking timeline down into periods of 2^32 * milliseconds, or about 49.7 days. A year has about 7.3 periods, usually * with only 2 time zone offset periods. Most of the 49.7 day periods will * have no transition, about one quarter have one transition, and very rare * cases have multiple transitions. */ private final DateTimeZone iZone; private final transient Info[] iInfoCache = new Info[cInfoCacheMask + 1]; private CachedDateTimeZone(DateTimeZone zone) { super(zone.getID()); iZone = zone; } /** * Returns the DateTimeZone being wrapped. */ public DateTimeZone getUncachedZone() { return iZone; } public String getNameKey(long instant) { return getInfo(instant).getNameKey(instant); } public int getOffset(long instant) { return getInfo(instant).getOffset(instant); } public int getStandardOffset(long instant) { return getInfo(instant).getStandardOffset(instant); } public boolean isFixed() { return iZone.isFixed(); } public long nextTransition(long instant) { return iZone.nextTransition(instant); } public long previousTransition(long instant) { return iZone.previousTransition(instant); } public int hashCode() { return iZone.hashCode(); } public boolean equals(Object obj) { if (this == obj) { return true; } if (obj instanceof CachedDateTimeZone) { return iZone.equals(((CachedDateTimeZone)obj).iZone); } return false; } // Although accessed by multiple threads, this method doesn't need to be // synchronized. private Info getInfo(long millis) { int period = (int)(millis >> 32); Info[] cache = iInfoCache; int index = period & cInfoCacheMask; Info info = cache[index]; if (info == null || (int)((info.iPeriodStart >> 32)) != period) { info = createInfo(millis); cache[index] = info; } return info; } private Info createInfo(long millis) { long periodStart = millis & (0xffffffffL << 32); Info info = new Info(iZone, periodStart); long end = periodStart | 0xffffffffL; Info chain = info; while (true) { long next = iZone.nextTransition(periodStart); if (next == periodStart || next > end) { break; } periodStart = next; chain = (chain.iNextInfo = new Info(iZone, periodStart)); } return info; } private final static class Info { // For first Info in chain, iPeriodStart's lower 32 bits are clear. public final long iPeriodStart; public final DateTimeZone iZoneRef; Info iNextInfo; private String iNameKey; private int iOffset = Integer.MIN_VALUE; private int iStandardOffset = Integer.MIN_VALUE; Info(DateTimeZone zone, long periodStart) { iPeriodStart = periodStart; iZoneRef = zone; } public String getNameKey(long millis) { if (iNextInfo == null || millis < iNextInfo.iPeriodStart) { if (iNameKey == null) { iNameKey = iZoneRef.getNameKey(iPeriodStart); } return iNameKey; } return iNextInfo.getNameKey(millis); } public int getOffset(long millis) { if (iNextInfo == null || millis < iNextInfo.iPeriodStart) { if (iOffset == Integer.MIN_VALUE) { iOffset = iZoneRef.getOffset(iPeriodStart); } return iOffset; } return iNextInfo.getOffset(millis); } public int getStandardOffset(long millis) { if (iNextInfo == null || millis < iNextInfo.iPeriodStart) { if (iStandardOffset == Integer.MIN_VALUE) { iStandardOffset = iZoneRef.getStandardOffset(iPeriodStart); } return iStandardOffset; } return iNextInfo.getStandardOffset(millis); } } }





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