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/*
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* Copyright (c) 2016, 2018, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package jdk.jfr.internal;
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import java.util.concurrent.ConcurrentHashMap;
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import java.util.concurrent.atomic.AtomicLong;
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import jdk.internal.misc.Unsafe;
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public final class StringPool {
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private static final Unsafe unsafe = Unsafe.getUnsafe();
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static final int MIN_LIMIT = 16;
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static final int MAX_LIMIT = 128; /* 0 MAX means disabled */
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private static final long epochAddress;
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private static final SimpleStringIdPool sp = new SimpleStringIdPool();
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static {
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epochAddress = JVM.getJVM().getEpochAddress();
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sp.reset();
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}
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public static long addString(String s) {
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return sp.addString(s);
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}
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private static boolean getCurrentEpoch() {
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return unsafe.getByte(epochAddress) == 1;
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}
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private static class SimpleStringIdPool {
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/* string id index */
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private final AtomicLong sidIdx = new AtomicLong();
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/* epoch of cached strings */
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private boolean poolEpoch;
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/* the cache */
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private final ConcurrentHashMap<String, Long> cache;
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/* max size */
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private final int MAX_SIZE = 32*1024;
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/* max size bytes*/
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private final long MAX_SIZE_UTF16 = 16*1024*1024;
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/* max size bytes*/
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private long currentSizeUTF16;
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/* looking at a biased data set 4 is a good value */
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private final String[] preCache = new String[]{"", "" , "" ,""};
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/* index of oldest */
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private int preCacheOld = 0;
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/* loop mask */
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private static final int preCacheMask = 0x03;
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SimpleStringIdPool() {
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cache = new ConcurrentHashMap<>(MAX_SIZE, 0.75f);
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}
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void reset() {
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reset(getCurrentEpoch());
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}
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private void reset(boolean epoch) {
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this.cache.clear();
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this.poolEpoch = epoch;
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this.currentSizeUTF16 = 0;
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}
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private long addString(String s) {
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boolean currentEpoch = getCurrentEpoch();
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if (poolEpoch == currentEpoch) {
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/* pool is for current chunk */
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Long lsid = this.cache.get(s);
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if (lsid != null) {
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return lsid.longValue();
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}
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} else {
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/* pool is for an old chunk */
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reset(currentEpoch);
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}
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if (!preCache(s)) {
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/* we should not pool this string */
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return -1;
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}
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if (cache.size() > MAX_SIZE || currentSizeUTF16 > MAX_SIZE_UTF16) {
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/* pool was full */
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reset(currentEpoch);
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}
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return storeString(s);
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}
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private long storeString(String s) {
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long sid = this.sidIdx.getAndIncrement();
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/* we can race but it is ok */
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this.cache.put(s, sid);
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boolean currentEpoch;
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synchronized(SimpleStringIdPool.class) {
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currentEpoch = JVM.addStringConstant(poolEpoch, sid, s);
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currentSizeUTF16 += s.length();
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}
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/* did we write in chunk that this pool represent */
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return currentEpoch == poolEpoch ? sid : -1;
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}
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private boolean preCache(String s) {
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if (preCache[0].equals(s)) {
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return true;
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}
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if (preCache[1].equals(s)) {
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return true;
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}
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if (preCache[2].equals(s)) {
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return true;
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}
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if (preCache[3].equals(s)) {
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return true;
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}
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preCacheOld = (preCacheOld - 1) & preCacheMask;
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preCache[preCacheOld] = s;
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return false;
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}
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}
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}
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