This class is usually preferable to {@link AtomicLong} when multiple threads update a common - * sum that is used for purposes such as collecting statistics, not for fine-grained synchronization - * control. Under low update contention, the two classes have similar characteristics. But under - * high contention, expected throughput of this class is significantly higher, at the expense of - * higher space consumption. - *
- *This class extends {@link Number}, but does not define methods such as {@code - * equals}, {@code hashCode} and {@code compareTo} because instances are expected to be mutated, and - * so are not useful as collection keys. - *
- *jsr166e note: This class is targeted to be placed in java.util.concurrent.atomic. - * - * @author Doug Lea - * @since 1.8 - */ -@SuppressWarnings("all") -class LongAdder extends Striped64 implements Serializable { - private static final long serialVersionUID = 7249069246863182397L; - - /** - * Version of plus for use in retryUpdate - */ - final long fn(long v, long x) { - return v + x; - } - - /** - * Creates a new adder with initial sum of zero. - */ - LongAdder() { - } - - /** - * Adds the given value. - * - * @param x the value to add - */ - public void add(long x) { - Cell[] as; - long b, v; - HashCode hc; - Cell a; - int n; - if ((as = cells) != null || !casBase(b = base, b + x)) { - boolean uncontended = true; - int h = (hc = threadHashCode.get()).code; - if (as == null || (n = as.length) < 1 || - (a = as[(n - 1) & h]) == null || - !(uncontended = a.cas(v = a.value, v + x))) - retryUpdate(x, hc, uncontended); - } - } - - /** - * Equivalent to {@code add(1)}. - */ - public void increment() { - add(1L); - } - - /** - * Equivalent to {@code add(-1)}. - */ - public void decrement() { - add(-1L); - } - - /** - * Returns the current sum. The returned value is NOT an atomic snapshot; invocation - * in the absence of concurrent updates returns an accurate result, but concurrent updates that - * occur while the sum is being calculated might not be incorporated. - * - * @return the sum - */ - public long sum() { - long sum = base; - Cell[] as = cells; - if (as != null) { - int n = as.length; - for (int i = 0; i < n; ++i) { - Cell a = as[i]; - if (a != null) - sum += a.value; - } - } - return sum; - } - - /** - * Resets variables maintaining the sum to zero. This method may be a useful alternative to - * creating a new adder, but is only effective if there are no concurrent updates. Because this - * method is intrinsically racy, it should only be used when it is known that no threads are - * concurrently updating. - */ - public void reset() { - internalReset(0L); - } - - /** - * Equivalent in effect to {@link #sum} followed by {@link #reset}. This method may apply for - * example during quiescent points between multithreaded computations. If there are updates - * concurrent with this method, the returned value is not guaranteed to be the final - * value occurring before the reset. - * - * @return the sum - */ - public long sumThenReset() { - long sum = base; - Cell[] as = cells; - base = 0L; - if (as != null) { - int n = as.length; - for (int i = 0; i < n; ++i) { - Cell a = as[i]; - if (a != null) { - sum += a.value; - a.value = 0L; - } - } - } - return sum; - } - - /** - * Returns the String representation of the {@link #sum}. - * - * @return the String representation of the {@link #sum} - */ - public String toString() { - return Long.toString(sum()); - } - - /** - * Equivalent to {@link #sum}. - * - * @return the sum - */ - public long longValue() { - return sum(); - } - - /** - * Returns the {@link #sum} as an {@code int} after a narrowing primitive conversion. - */ - public int intValue() { - return (int) sum(); - } - - /** - * Returns the {@link #sum} as a {@code float} after a widening primitive conversion. - */ - public float floatValue() { - return (float) sum(); - } - - /** - * Returns the {@link #sum} as a {@code double} after a widening primitive conversion. - */ - public double doubleValue() { - return (double) sum(); - } - - private void writeObject(java.io.ObjectOutputStream s) - throws java.io.IOException { - s.defaultWriteObject(); - s.writeLong(sum()); - } - - private void readObject(java.io.ObjectInputStream s) - throws java.io.IOException, ClassNotFoundException { - s.defaultReadObject(); - busy = 0; - cells = null; - base = s.readLong(); - } -} -// CHECKSTYLE:ON diff --git a/akka-testkit/src/test/java/akka/testkit/metrics/Striped64.java b/akka-testkit/src/test/java/akka/testkit/metrics/Striped64.java deleted file mode 100644 index 3bf5e08c20..0000000000 --- a/akka-testkit/src/test/java/akka/testkit/metrics/Striped64.java +++ /dev/null @@ -1,354 +0,0 @@ -/* - * Written by Doug Lea with assistance from members of JCP JSR-166 - * Expert Group and released to the public domain, as explained at - * http://creativecommons.org/publicdomain/zero/1.0/ - * - * http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/Striped64.java?revision=1.8&view=markup - */ - -package akka.testkit.metrics; - -import java.util.Random; - -// CHECKSTYLE:OFF -/** - * A package-local class holding common representation and mechanics for classes supporting dynamic - * striping on 64bit values. The class extends Number so that concrete subclasses must publicly do - * so. - */ -@SuppressWarnings("all") -abstract class Striped64 extends Number { - /* - * This class maintains a lazily-initialized table of atomically - * updated variables, plus an extra "base" field. The table size - * is a power of two. Indexing uses masked per-thread hash codes. - * Nearly all declarations in this class are package-private, - * accessed directly by subclasses. - * - * Table entries are of class Cell; a variant of AtomicLong padded - * to reduce cache contention on most processors. Padding is - * overkill for most Atomics because they are usually irregularly - * scattered in memory and thus don't interfere much with each - * other. But Atomic objects residing in arrays will tend to be - * placed adjacent to each other, and so will most often share - * cache lines (with a huge negative performance impact) without - * this precaution. - * - * In part because Cells are relatively large, we avoid creating - * them until they are needed. When there is no contention, all - * updates are made to the base field. Upon first contention (a - * failed CAS on base update), the table is initialized to size 2. - * The table size is doubled upon further contention until - * reaching the nearest power of two greater than or equal to the - * number of CPUS. Table slots remain empty (null) until they are - * needed. - * - * A single spinlock ("busy") is used for initializing and - * resizing the table, as well as populating slots with new Cells. - * There is no need for a blocking lock; when the lock is not - * available, threads try other slots (or the base). During these - * retries, there is increased contention and reduced locality, - * which is still better than alternatives. - * - * Per-thread hash codes are initialized to random values. - * Contention and/or table collisions are indicated by failed - * CASes when performing an update operation (see method - * retryUpdate). Upon a collision, if the table size is less than - * the capacity, it is doubled in size unless some other thread - * holds the lock. If a hashed slot is empty, and lock is - * available, a new Cell is created. Otherwise, if the slot - * exists, a CAS is tried. Retries proceed by "double hashing", - * using a secondary hash (Marsaglia XorShift) to try to find a - * free slot. - * - * The table size is capped because, when there are more threads - * than CPUs, supposing that each thread were bound to a CPU, - * there would exist a perfect hash function mapping threads to - * slots that eliminates collisions. When we reach capacity, we - * search for this mapping by randomly varying the hash codes of - * colliding threads. Because search is random, and collisions - * only become known via CAS failures, convergence can be slow, - * and because threads are typically not bound to CPUS forever, - * may not occur at all. However, despite these limitations, - * observed contention rates are typically low in these cases. - * - * It is possible for a Cell to become unused when threads that - * once hashed to it terminate, as well as in the case where - * doubling the table causes no thread to hash to it under - * expanded mask. We do not try to detect or remove such cells, - * under the assumption that for long-running instances, observed - * contention levels will recur, so the cells will eventually be - * needed again; and for short-lived ones, it does not matter. - */ - - /** - * Padded variant of AtomicLong supporting only raw accesses plus CAS. The value field is placed - * between pads, hoping that the JVM doesn't reorder them. - *
- * JVM intrinsics note: It would be possible to use a release-only form of CAS here, if it were - * provided. - */ - static final class Cell { - volatile long p0, p1, p2, p3, p4, p5, p6; - volatile long value; - volatile long q0, q1, q2, q3, q4, q5, q6; - - Cell(long x) { - value = x; - } - - final boolean cas(long cmp, long val) { - return UNSAFE.compareAndSwapLong(this, valueOffset, cmp, val); - } - - // Unsafe mechanics - private static final sun.misc.Unsafe UNSAFE; - private static final long valueOffset; - - static { - try { - UNSAFE = getUnsafe(); - Class ak = Cell.class; - valueOffset = UNSAFE.objectFieldOffset - (ak.getDeclaredField("value")); - } catch (Exception e) { - throw new Error(e); - } - } - - } - - /** - * Holder for the thread-local hash code. The code is initially random, but may be set to a - * different value upon collisions. - */ - static final class HashCode { - static final Random rng = new Random(); - int code; - - HashCode() { - int h = rng.nextInt(); // Avoid zero to allow xorShift rehash - code = (h == 0) ? 1 : h; - } - } - - /** - * The corresponding ThreadLocal class - */ - static final class ThreadHashCode extends ThreadLocal