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package org.jctools.counters;
import static org.jctools.util.UnsafeAccess.UNSAFE;
import java.util.concurrent.ThreadLocalRandom;
import org.jctools.util.PortableJvmInfo;
import org.jctools.util.Pow2;
/**
* Basic class representing static striped long counter with
* common mechanics for implementors.
*
* @author Tolstopyatov Vsevolod
*/
abstract class FixedSizeStripedLongCounterPrePad {
byte b000,b001,b002,b003,b004,b005,b006,b007;// 8b
byte b010,b011,b012,b013,b014,b015,b016,b017;// 16b
byte b020,b021,b022,b023,b024,b025,b026,b027;// 24b
byte b030,b031,b032,b033,b034,b035,b036,b037;// 32b
byte b040,b041,b042,b043,b044,b045,b046,b047;// 40b
byte b050,b051,b052,b053,b054,b055,b056,b057;// 48b
byte b060,b061,b062,b063,b064,b065,b066,b067;// 56b
byte b070,b071,b072,b073,b074,b075,b076,b077;// 64b
byte b100,b101,b102,b103,b104,b105,b106,b107;// 72b
byte b110,b111,b112,b113,b114,b115,b116,b117;// 80b
byte b120,b121,b122,b123,b124,b125,b126,b127;// 88b
byte b130,b131,b132,b133,b134,b135,b136,b137;// 96b
byte b140,b141,b142,b143,b144,b145,b146,b147;//104b
byte b150,b151,b152,b153,b154,b155,b156,b157;//112b
byte b160,b161,b162,b163,b164,b165,b166,b167;//120b
// byte b170,b171,b172,b173,b174,b175,b176,b177;//128b
}
abstract class FixedSizeStripedLongCounterFields extends FixedSizeStripedLongCounterPrePad {
protected static final int CACHE_LINE_IN_LONGS = PortableJvmInfo.CACHE_LINE_SIZE / 8;
// place first element at the end of the cache line of the array object
protected static final long COUNTER_ARRAY_BASE = Math.max(UNSAFE.arrayBaseOffset(long[].class), PortableJvmInfo.CACHE_LINE_SIZE - 8);
// element shift is enlarged to include the padding, still aligned to long
protected static final long ELEMENT_SHIFT = Integer.numberOfTrailingZeros(PortableJvmInfo.CACHE_LINE_SIZE);
// we pad each element in the array to effectively write a counter in each cache line
protected final long[] cells;
protected final int mask;
protected FixedSizeStripedLongCounterFields(int stripesCount) {
if (stripesCount <= 0) {
throw new IllegalArgumentException("Expecting a stripesCount that is larger than 0");
}
int size = Pow2.roundToPowerOfTwo(stripesCount);
cells = new long[CACHE_LINE_IN_LONGS * size];
mask = (size - 1);
}
}
public abstract class FixedSizeStripedLongCounter extends FixedSizeStripedLongCounterFields implements Counter {
byte b000,b001,b002,b003,b004,b005,b006,b007;// 8b
byte b010,b011,b012,b013,b014,b015,b016,b017;// 16b
byte b020,b021,b022,b023,b024,b025,b026,b027;// 24b
byte b030,b031,b032,b033,b034,b035,b036,b037;// 32b
byte b040,b041,b042,b043,b044,b045,b046,b047;// 40b
byte b050,b051,b052,b053,b054,b055,b056,b057;// 48b
byte b060,b061,b062,b063,b064,b065,b066,b067;// 56b
byte b070,b071,b072,b073,b074,b075,b076,b077;// 64b
byte b100,b101,b102,b103,b104,b105,b106,b107;// 72b
byte b110,b111,b112,b113,b114,b115,b116,b117;// 80b
byte b120,b121,b122,b123,b124,b125,b126,b127;// 88b
byte b130,b131,b132,b133,b134,b135,b136,b137;// 96b
byte b140,b141,b142,b143,b144,b145,b146,b147;//104b
byte b150,b151,b152,b153,b154,b155,b156,b157;//112b
byte b160,b161,b162,b163,b164,b165,b166,b167;//120b
//byte b170,b171,b172,b173,b174,b175,b176,b177;//128b
private static final long PROBE = getProbeOffset();
private static long getProbeOffset() {
try {
return UNSAFE.objectFieldOffset(Thread.class.getDeclaredField("threadLocalRandomProbe"));
} catch (NoSuchFieldException e) {
return -1L;
}
}
public FixedSizeStripedLongCounter(int stripesCount) {
super(stripesCount);
}
@Override
public void inc() {
inc(1L);
}
@Override
public void inc(long delta) {
inc(cells, counterOffset(index()), delta);
}
@Override
public long get() {
long result = 0L;
long[] cells = this.cells;
int length = mask + 1;
for (int i = 0; i < length; i++) {
result += UNSAFE.getLongVolatile(cells, counterOffset(i));
}
return result;
}
private long counterOffset(long i) {
return COUNTER_ARRAY_BASE + (i << ELEMENT_SHIFT);
}
@Override
public long getAndReset() {
long result = 0L;
long[] cells = this.cells;
int length = mask + 1;
for (int i = 0; i < length; i++) {
result += getAndReset(cells, counterOffset(i));
}
return result;
}
protected abstract void inc(long[] cells, long offset, long value);
protected abstract long getAndReset(long[] cells, long offset);
private int index() {
return probe() & mask;
}
/**
* Returns the probe value for the current thread.
* If target JDK version is 7 or higher, than ThreadLocalRandom-specific
* value will be used, xorshift with thread id otherwise.
*/
private int probe() {
// Fast path for reliable well-distributed probe, available from JDK 7+.
// As long as PROBE is final static this branch will be constant folded
// (i.e removed).
if (PROBE != -1) {
int probe;
if ((probe = UNSAFE.getInt(Thread.currentThread(), PROBE)) == 0) {
ThreadLocalRandom.current(); // force initialization
probe = UNSAFE.getInt(Thread.currentThread(), PROBE);
}
return probe;
}
/*
* Else use much worse (for values distribution) method:
* Mix thread id with golden ratio and then xorshift it
* to spread consecutive ids (see Knuth multiplicative method as reference).
*/
int probe = (int) ((Thread.currentThread().getId() * 0x9e3779b9) & Integer.MAX_VALUE);
// xorshift
probe ^= probe << 13;
probe ^= probe >>> 17;
probe ^= probe << 5;
return probe;
}
}
