implement MinMaxCounter and Gauge, include them in the InstrumentFactory

10 files changed, 1001 insertions, 31 deletions

diff --git a/kamon-core/src/main/java/kamon/jsr166/LongAdder.java b/kamon-core/src/main/java/kamon/jsr166/LongAdder.java
new file mode 100644
index 00000000..7e47ae63
--- /dev/null
+++ b/kamon-core/src/main/java/kamon/jsr166/LongAdder.java
@@ -0,0 +1,224 @@
+/*
+
+Note: this was copied from Doug Lea's CVS repository
+	http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/
+
+LongAdder.java version 1.14
+
+*/
+
+
+/*
+ * 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/
+ */
+
+package kamon.jsr166;
+
+import java.io.Serializable;
+
+/**
+ * One or more variables that together maintain an initially zero
+ * {@code long} sum.  When updates (method {@link #add}) are contended
+ * across threads, the set of variables may grow dynamically to reduce
+ * contention. Method {@link #sum} (or, equivalently, {@link
+ * #longValue}) returns the current total combined across the
+ * variables maintaining the sum.
+ *
+ * <p>This class is usually preferable to {@link java.util.concurrent.atomic.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.
+ *
+ * <p>This class extends {@link Number}, but does <em>not</em> 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.
+ *
+ * <p><em>jsr166e note: This class is targeted to be placed in
+ * java.util.concurrent.atomic.</em>
+ *
+ * @since 1.8
+ * @author Doug Lea
+ */
+public 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.
+     */
+    public 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 <em>NOT</em> 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
+     * <em>not</em> 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;
+    }
+
+    public long sumAndReset() {
+        long sum = getAndSetBase(0L);
+        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.getAndSet(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();
+    }
+
+}
diff --git a/kamon-core/src/main/java/kamon/jsr166/LongMaxUpdater.java b/kamon-core/src/main/java/kamon/jsr166/LongMaxUpdater.java
new file mode 100644
index 00000000..fc9ea4e5
--- /dev/null
+++ b/kamon-core/src/main/java/kamon/jsr166/LongMaxUpdater.java
@@ -0,0 +1,191 @@
+/*
+ * 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/
+ */
+
+package kamon.jsr166;
+import java.io.Serializable;
+
+/**
+ * One or more variables that together maintain a running {@code long}
+ * maximum with initial value {@code Long.MIN_VALUE}.  When updates
+ * (method {@link #update}) are contended across threads, the set of
+ * variables may grow dynamically to reduce contention.  Method {@link
+ * #max} (or, equivalently, {@link #longValue}) returns the current
+ * maximum across the variables maintaining updates.
+ *
+ * <p>This class extends {@link Number}, but does <em>not</em> 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.
+ *
+ * <p><em>jsr166e note: This class is targeted to be placed in
+ * java.util.concurrent.atomic.</em>
+ *
+ * @since 1.8
+ * @author Doug Lea
+ */
+public class LongMaxUpdater extends Striped64 implements Serializable {
+    private static final long serialVersionUID = 7249069246863182397L;
+
+    /**
+     * Version of max for use in retryUpdate
+     */
+    final long fn(long v, long x) { return v > x ? v : x; }
+
+    /**
+     * Creates a new instance with initial maximum of {@code
+     * Long.MIN_VALUE}.
+     */
+    public LongMaxUpdater() {
+        base = Long.MIN_VALUE;
+    }
+
+    /**
+     * Creates a new instance with the given initialValue
+     */
+    public LongMaxUpdater(long initialValue) {
+        base = initialValue;
+    }
+
+
+    /**
+     * Updates the maximum to be at least the given value.
+     *
+     * @param x the value to update
+     */
+    public void update(long x) {
+        Cell[] as; long b, v; HashCode hc; Cell a; int n;
+        if ((as = cells) != null ||
+            (b = base) < x && !casBase(b, x)) {
+            boolean uncontended = true;
+            int h = (hc = threadHashCode.get()).code;
+            if (as == null || (n = as.length) < 1 ||
+                (a = as[(n - 1) & h]) == null ||
+                ((v = a.value) < x && !(uncontended = a.cas(v, x))))
+                retryUpdate(x, hc, uncontended);
+        }
+    }
+
+    /**
+     * Returns the current maximum.  The returned value is
+     * <em>NOT</em> an atomic snapshot; invocation in the absence of
+     * concurrent updates returns an accurate result, but concurrent
+     * updates that occur while the value is being calculated might
+     * not be incorporated.
+     *
+     * @return the maximum
+     */
+    public long max() {
+        Cell[] as = cells;
+        long max = base;
+        if (as != null) {
+            int n = as.length;
+            long v;
+            for (int i = 0; i < n; ++i) {
+                Cell a = as[i];
+                if (a != null && (v = a.value) > max)
+                    max = v;
+            }
+        }
+        return max;
+    }
+
+    /**
+     * Resets variables maintaining updates to {@code Long.MIN_VALUE}.
+     * This method may be a useful alternative to creating a new
+     * updater, 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(Long.MIN_VALUE);
+    }
+
+    /**
+     * Equivalent in effect to {@link #max} 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
+     * <em>not</em> guaranteed to be the final value occurring before
+     * the reset.
+     *
+     * @return the maximum
+     */
+    public long maxThenReset(long newValue) {
+        Cell[] as = cells;
+        long max = base;
+        base = newValue;
+        if (as != null) {
+            int n = as.length;
+            for (int i = 0; i < n; ++i) {
+                Cell a = as[i];
+                if (a != null) {
+                    long v = a.value;
+                    a.value = newValue;
+                    if (v > max)
+                        max = v;
+                }
+            }
+        }
+        return max;
+    }
+
+    /**
+     * Returns the String representation of the {@link #max}.
+     * @return the String representation of the {@link #max}
+     */
+    public String toString() {
+        return Long.toString(max());
+    }
+
+    /**
+     * Equivalent to {@link #max}.
+     *
+     * @return the maximum
+     */
+    public long longValue() {
+        return max();
+    }
+
+    /**
+     * Returns the {@link #max} as an {@code int} after a narrowing
+     * primitive conversion.
+     */
+    public int intValue() {
+        return (int)max();
+    }
+
+    /**
+     * Returns the {@link #max} as a {@code float}
+     * after a widening primitive conversion.
+     */
+    public float floatValue() {
+        return (float)max();
+    }
+
+    /**
+     * Returns the {@link #max} as a {@code double} after a widening
+     * primitive conversion.
+     */
+    public double doubleValue() {
+        return (double)max();
+    }
+
+    private void writeObject(java.io.ObjectOutputStream s)
+        throws java.io.IOException {
+        s.defaultWriteObject();
+        s.writeLong(max());
+    }
+
+    private void readObject(java.io.ObjectInputStream s)
+        throws java.io.IOException, ClassNotFoundException {
+        s.defaultReadObject();
+        busy = 0;
+        cells = null;
+        base = s.readLong();
+    }
+
+}
diff --git a/kamon-core/src/main/java/kamon/jsr166/Striped64.java b/kamon-core/src/main/java/kamon/jsr166/Striped64.java
new file mode 100644
index 00000000..8fbfa4ba
--- /dev/null
+++ b/kamon-core/src/main/java/kamon/jsr166/Striped64.java
@@ -0,0 +1,371 @@
+/*
+
+Note: this was copied from Doug Lea's CVS repository
+	http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/
+
+Striped64.java version 1.8
+
+*/
+
+
+/*
+ * 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/
+ */
+
+package kamon.jsr166;
+
+import java.util.Random;
+
+/**
+ * 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.
+ */
+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);
+        }
+
+        final long getAndSet(long val) {
+            long v;
+            do {
+                v = UNSAFE.getLongVolatile(this, valueOffset);
+            } while (!UNSAFE.compareAndSwapLong(this, valueOffset, v, val));
+            return v;
+        }
+
+        // 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<HashCode> {
+        public HashCode initialValue() { return new HashCode(); }
+    }
+
+    /**
+     * Static per-thread hash codes. Shared across all instances to
+     * reduce ThreadLocal pollution and because adjustments due to
+     * collisions in one table are likely to be appropriate for
+     * others.
+     */
+    static final ThreadHashCode threadHashCode = new ThreadHashCode();
+
+    /** Number of CPUS, to place bound on table size */
+    static final int NCPU = Runtime.getRuntime().availableProcessors();
+
+    /**
+     * Table of cells. When non-null, size is a power of 2.
+     */
+    transient volatile Cell[] cells;
+
+    /**
+     * Base value, used mainly when there is no contention, but also as
+     * a fallback during table initialization races. Updated via CAS.
+     */
+    transient volatile long base;
+
+    /**
+     * Spinlock (locked via CAS) used when resizing and/or creating Cells.
+     */
+    transient volatile int busy;
+
+    /**
+     * Package-private default constructor
+     */
+    Striped64() {
+    }
+
+    /**
+     * CASes the base field.
+     */
+    final boolean casBase(long cmp, long val) {
+        return UNSAFE.compareAndSwapLong(this, baseOffset, cmp, val);
+    }
+
+    /**
+     * CASes the base field.
+     */
+    final long getAndSetBase(long val) {
+        long v;
+        do {
+            v = UNSAFE.getLongVolatile(this, baseOffset);
+        } while (!UNSAFE.compareAndSwapLong(this, baseOffset, v, val));
+        return v;
+    }
+
+    /**
+     * CASes the busy field from 0 to 1 to acquire lock.
+     */
+    final boolean casBusy() {
+        return UNSAFE.compareAndSwapInt(this, busyOffset, 0, 1);
+    }
+
+    /**
+     * Computes the function of current and new value. Subclasses
+     * should open-code this update function for most uses, but the
+     * virtualized form is needed within retryUpdate.
+     *
+     * @param currentValue the current value (of either base or a cell)
+     * @param newValue the argument from a user update call
+     * @return result of the update function
+     */
+    abstract long fn(long currentValue, long newValue);
+
+    /**
+     * Handles cases of updates involving initialization, resizing,
+     * creating new Cells, and/or contention. See above for
+     * explanation. This method suffers the usual non-modularity
+     * problems of optimistic retry code, relying on rechecked sets of
+     * reads.
+     *
+     * @param x the value
+     * @param hc the hash code holder
+     * @param wasUncontended false if CAS failed before call
+     */
+    final void retryUpdate(long x, HashCode hc, boolean wasUncontended) {
+        int h = hc.code;
+        boolean collide = false;                // True if last slot nonempty
+        for (;;) {
+            Cell[] as; Cell a; int n; long v;
+            if ((as = cells) != null && (n = as.length) > 0) {
+                if ((a = as[(n - 1) & h]) == null) {
+                    if (busy == 0) {            // Try to attach new Cell
+                        Cell r = new Cell(x);   // Optimistically create
+                        if (busy == 0 && casBusy()) {
+                            boolean created = false;
+                            try {               // Recheck under lock
+                                Cell[] rs; int m, j;
+                                if ((rs = cells) != null &&
+                                    (m = rs.length) > 0 &&
+                                    rs[j = (m - 1) & h] == null) {
+                                    rs[j] = r;
+                                    created = true;
+                                }
+                            } finally {
+                                busy = 0;
+                            }
+                            if (created)
+                                break;
+                            continue;           // Slot is now non-empty
+                        }
+                    }
+                    collide = false;
+                }
+                else if (!wasUncontended)       // CAS already known to fail
+                    wasUncontended = true;      // Continue after rehash
+                else if (a.cas(v = a.value, fn(v, x)))
+                    break;
+                else if (n >= NCPU || cells != as)
+                    collide = false;            // At max size or stale
+                else if (!collide)
+                    collide = true;
+                else if (busy == 0 && casBusy()) {
+                    try {
+                        if (cells == as) {      // Expand table unless stale
+                            Cell[] rs = new Cell[n << 1];
+                            for (int i = 0; i < n; ++i)
+                                rs[i] = as[i];
+                            cells = rs;
+                        }
+                    } finally {
+                        busy = 0;
+                    }
+                    collide = false;
+                    continue;                   // Retry with expanded table
+                }
+                h ^= h << 13;                   // Rehash
+                h ^= h >>> 17;
+                h ^= h << 5;
+            }
+            else if (busy == 0 && cells == as && casBusy()) {
+                boolean init = false;
+                try {                           // Initialize table
+                    if (cells == as) {
+                        Cell[] rs = new Cell[2];
+                        rs[h & 1] = new Cell(x);
+                        cells = rs;
+                        init = true;
+                    }
+                } finally {
+                    busy = 0;
+                }
+                if (init)
+                    break;
+            }
+            else if (casBase(v = base, fn(v, x)))
+                break;                          // Fall back on using base
+        }
+        hc.code = h;                            // Record index for next time
+    }
+
+
+    /**
+     * Sets base and all cells to the given value.
+     */
+    final void internalReset(long initialValue) {
+        Cell[] as = cells;
+        base = initialValue;
+        if (as != null) {
+            int n = as.length;
+            for (int i = 0; i < n; ++i) {
+                Cell a = as[i];
+                if (a != null)
+                    a.value = initialValue;
+            }
+        }
+    }
+
+    // Unsafe mechanics
+    private static final sun.misc.Unsafe UNSAFE;
+    private static final long baseOffset;
+    private static final long busyOffset;
+    static {
+        try {
+            UNSAFE = getUnsafe();
+            Class<?> sk = Striped64.class;
+            baseOffset = UNSAFE.objectFieldOffset
+                (sk.getDeclaredField("base"));
+            busyOffset = UNSAFE.objectFieldOffset
+                (sk.getDeclaredField("busy"));
+        } catch (Exception e) {
+            throw new Error(e);
+        }
+    }
+
+    /**
+     * Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
+     * Replace with a simple call to Unsafe.getUnsafe when integrating
+     * into a jdk.
+     *
+     * @return a sun.misc.Unsafe
+     */
+    private static sun.misc.Unsafe getUnsafe() {
+        try {
+            return sun.misc.Unsafe.getUnsafe();
+        } catch (SecurityException tryReflectionInstead) {}
+        try {
+            return java.security.AccessController.doPrivileged
+            (new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
+                public sun.misc.Unsafe run() throws Exception {
+                    Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
+                    for (java.lang.reflect.Field f : k.getDeclaredFields()) {
+                        f.setAccessible(true);
+                        Object x = f.get(null);
+                        if (k.isInstance(x))
+                            return k.cast(x);
+                    }
+                    throw new NoSuchFieldError("the Unsafe");
+                }});
+        } catch (java.security.PrivilegedActionException e) {
+            throw new RuntimeException("Could not initialize intrinsics",
+                                       e.getCause());
+        }
+    }
+}
diff --git a/kamon-core/src/main/java/kamon/util/GlobPathFilter.java b/kamon-core/src/main/java/kamon/util/GlobPathFilter.java
new file mode 100644
index 00000000..1bfbaefc
--- /dev/null
+++ b/kamon-core/src/main/java/kamon/util/GlobPathFilter.java
@@ -0,0 +1,110 @@
+/*
+ * =========================================================================================
+ * Copyright  2013-2014 the kamon project <http://kamon.io/>
+ *
+ * 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 kamon.util;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * Default implementation of PathFilter.  Uses glob based includes and excludes to determine whether to export.
+ *
+ * @author John E. Bailey
+ * @author <a href="mailto:david.lloyd@redhat.com">David M. Lloyd</a>
+ */
+public final class GlobPathFilter   {
+    private static final Pattern GLOB_PATTERN = Pattern.compile("(\\*\\*?)|(\\?)|(\\\\.)|(/+)|([^*?]+)");
+
+    private final String glob;
+    private final Pattern pattern;
+
+    /**
+     * Construct a new instance.
+     *
+     * @param glob the path glob to match
+     */
+    public GlobPathFilter(final String glob) {
+        pattern = getGlobPattern(glob);
+        this.glob = glob;
+    }
+
+    /**
+     * Determine whether a path should be accepted.
+     *
+     * @param path the path to check
+     * @return true if the path should be accepted, false if not
+     */
+    public boolean accept(final String path) {
+        return pattern.matcher(path).matches();
+    }
+
+    /**
+     * Get a regular expression pattern which accept any path names which match the given glob.  The glob patterns
+     * function similarly to {@code ant} file patterns.  Valid metacharacters in the glob pattern include:
+     * <ul>
+     * <li><code>"\"</code> - escape the next character (treat it literally, even if it is itself a recognized metacharacter)</li>
+     * <li><code>"?"</code> - match any non-slash character</li>
+     * <li><code>"*"</code> - match zero or more non-slash characters</li>
+     * <li><code>"**"</code> - match zero or more characters, including slashes</li>
+     * <li><code>"/"</code> - match one or more slash characters.  Consecutive {@code /} characters are collapsed down into one.</li>
+     * </ul>
+     * In addition, any glob pattern matches all subdirectories thereof.  A glob pattern ending in {@code /} is equivalent
+     * to a glob pattern ending in <code>/**</code> in that the named directory is not itself included in the glob.
+     * <p/>
+     * <b>See also:</b> <a href="http://ant.apache.org/manual/dirtasks.html#patterns">"Patterns" in the Ant Manual</a>
+     *
+     * @param glob the glob to match
+     *
+     * @return the pattern
+     */
+    private static Pattern getGlobPattern(final String glob) {
+        StringBuilder patternBuilder = new StringBuilder();
+        final Matcher m = GLOB_PATTERN.matcher(glob);
+        boolean lastWasSlash = false;
+        while (m.find()) {
+            lastWasSlash = false;
+            String grp;
+            if ((grp = m.group(1)) != null) {
+                // match a * or **
+                if (grp.length() == 2) {
+                    // it's a *workers are able to process multiple metrics*
+                    patternBuilder.append(".*");
+                } else {
+                    // it's a *
+                    patternBuilder.append("[^/]*");
+                }
+            } else if ((grp = m.group(2)) != null) {
+                // match a '?' glob pattern; any non-slash character
+                patternBuilder.append("[^/]");
+            } else if ((grp = m.group(3)) != null) {
+                // backslash-escaped value
+                patternBuilder.append(Pattern.quote(m.group().substring(1)));
+            } else if ((grp = m.group(4)) != null) {
+                // match any number of / chars
+                patternBuilder.append("/+");
+                lastWasSlash = true;
+            } else {
+                // some other string
+                patternBuilder.append(Pattern.quote(m.group()));
+            }
+        }
+        if (lastWasSlash) {
+            // ends in /, append **
+            patternBuilder.append(".*");
+        }
+        return Pattern.compile(patternBuilder.toString());
+    }
+}
diff --git a/kamon-core/src/main/scala/kamon/metric/snapshot/EntitySnapshot.scala b/kamon-core/src/main/scala/kamon/metric/EntitySnapshot.scala
index 41fde2c0..e51e80cc 100644
--- a/kamon-core/src/main/scala/kamon/metric/snapshot/EntitySnapshot.scala
+++ b/kamon-core/src/main/scala/kamon/metric/EntitySnapshot.scala
@@ -1,6 +1,5 @@
-package kamon.metric.snapshot
+package kamon.metric
 
-import kamon.metric.Entity
 import kamon.metric.instrument.{DistributionSnapshot, SingleValueSnapshot}
 
 trait EntitySnapshot {
diff --git a/kamon-core/src/main/scala/kamon/metric/snapshot/TickSnapshot.scala b/kamon-core/src/main/scala/kamon/metric/TickSnapshot.scala
index a1bdd6b1..4248180c 100644
--- a/kamon-core/src/main/scala/kamon/metric/snapshot/TickSnapshot.scala
+++ b/kamon-core/src/main/scala/kamon/metric/TickSnapshot.scala
@@ -1,4 +1,4 @@
-package kamon.metric.snapshot
+package kamon.metric
 
 import java.time.Instant
 
diff --git a/kamon-core/src/main/scala/kamon/metric/instrument/Gauge.scala b/kamon-core/src/main/scala/kamon/metric/instrument/Gauge.scala
index bb31e30a..5263d258 100644
--- a/kamon-core/src/main/scala/kamon/metric/instrument/Gauge.scala
+++ b/kamon-core/src/main/scala/kamon/metric/instrument/Gauge.scala
@@ -1,5 +1,7 @@
 package kamon.metric.instrument
 
+import java.util.concurrent.atomic.AtomicLong
+
 import kamon.metric.Entity
 import kamon.util.MeasurementUnit
 
@@ -13,6 +15,27 @@ trait Gauge {
   def set(value: Long): Unit
 }
 
-object Gauge {
-  def apply(entity: Entity, name: String): Gauge = ???
+
+class AtomicLongGauge(entity: Entity, name: String, val measurementUnit: MeasurementUnit)
+  extends Gauge with SingleValueSnapshotInstrument  {
+
+  private val currentValue = new AtomicLong(0L)
+
+  def increment(): Unit =
+    currentValue.incrementAndGet()
+
+  def increment(times: Long): Unit =
+    currentValue.addAndGet(times)
+
+  def decrement(): Unit =
+    currentValue.decrementAndGet()
+
+  def decrement(times: Long): Unit =
+    currentValue.addAndGet(-times)
+
+  def set(value: Long): Unit =
+    currentValue.set(value)
+
+  def snapshot(): SingleValueSnapshot =
+    SingleValueSnapshot(name, measurementUnit, currentValue.get())
 }
diff --git a/kamon-core/src/main/scala/kamon/metric/instrument/InstrumentFactory.scala b/kamon-core/src/main/scala/kamon/metric/instrument/InstrumentFactory.scala
index 1ccd5899..fb6dfe27 100644
--- a/kamon-core/src/main/scala/kamon/metric/instrument/InstrumentFactory.scala
+++ b/kamon-core/src/main/scala/kamon/metric/instrument/InstrumentFactory.scala
@@ -16,7 +16,7 @@ private[metric] class InstrumentFactory private (
     customSettings: Map[(String, String), CustomInstrumentSettings]) {
 
   def buildHistogram(entity: Entity, name: String, dynamicRange: DynamicRange = defaultHistogramDynamicRange,
-      measurementUnit: MeasurementUnit = MeasurementUnit.none): Histogram = {
+      measurementUnit: MeasurementUnit = MeasurementUnit.none): Histogram with DistributionSnapshotInstrument = {
 
     new HdrHistogram(
       entity,
@@ -29,16 +29,17 @@ private[metric] class InstrumentFactory private (
   def buildMinMaxCounter(entity: Entity, name: String, dynamicRange: DynamicRange = defaultMMCounterDynamicRange,
       sampleInterval: Duration = defaultMMCounterSampleRate, measurementUnit: MeasurementUnit = MeasurementUnit.none): MinMaxCounter = {
 
-    MinMaxCounter(
+    val underlyingHistogram = buildHistogram(entity, name, dynamicRange, measurementUnit)
+    new PaddedMinMaxCounter(
       entity,
       name,
-      instrumentDynamicRange(entity, name, dynamicRange),
+      underlyingHistogram,
       instrumentSampleInterval(entity, name, sampleInterval)
     )
   }
 
-  def buildGauge(entity: Entity, name: String, measurementUnit: MeasurementUnit = MeasurementUnit.none): Gauge =
-    Gauge(entity, name)
+  def buildGauge(entity: Entity, name: String, measurementUnit: MeasurementUnit = MeasurementUnit.none): Gauge with SingleValueSnapshotInstrument =
+    new AtomicLongGauge(entity, name, measurementUnit)
 
   def buildCounter(entity: Entity, name: String, measurementUnit: MeasurementUnit = MeasurementUnit.none): Counter with SingleValueSnapshotInstrument =
     new LongAdderCounter(entity, name, measurementUnit)
diff --git a/kamon-core/src/main/scala/kamon/metric/instrument/InstrumentSnapshot.scala b/kamon-core/src/main/scala/kamon/metric/instrument/InstrumentSnapshot.scala
index 58e10c54..ffb00080 100644
--- a/kamon-core/src/main/scala/kamon/metric/instrument/InstrumentSnapshot.scala
+++ b/kamon-core/src/main/scala/kamon/metric/instrument/InstrumentSnapshot.scala
@@ -2,21 +2,18 @@ package kamon.metric.instrument
 
 import kamon.util.MeasurementUnit
 
-
+/**
+  * Snapshot for instruments that internally track a single value. Meant to be used for counters and gauges.
+  *
+  */
 case class SingleValueSnapshot(name: String, measurementUnit: MeasurementUnit, value: Long)
 
+/**
+  * Snapshot for instruments that internally the distribution of values in a defined dynamic range. Meant to be used
+  * with histograms and min max counters.
+  */
 case class DistributionSnapshot(name: String, measurementUnit: MeasurementUnit, dynamicRange: DynamicRange, distribution: Distribution)
 
-trait DistributionSnapshotInstrument {
-  def snapshot(): DistributionSnapshot
-}
-
-trait SingleValueSnapshotInstrument {
-  def snapshot(): SingleValueSnapshot
-}
-
-
-
 
 trait Distribution {
   def buckets: Seq[Bucket]
@@ -42,3 +39,12 @@ trait Percentile {
   def value: Long
   def countUnderQuantile: Long
 }
+
+
+trait DistributionSnapshotInstrument {
+  private[kamon] def snapshot(): DistributionSnapshot
+}
+
+trait SingleValueSnapshotInstrument {
+  private[kamon] def snapshot(): SingleValueSnapshot
+}
diff --git a/kamon-core/src/main/scala/kamon/metric/instrument/MinMaxCounter.scala b/kamon-core/src/main/scala/kamon/metric/instrument/MinMaxCounter.scala
index 8a43865f..cddd8ed9 100644
--- a/kamon-core/src/main/scala/kamon/metric/instrument/MinMaxCounter.scala
+++ b/kamon-core/src/main/scala/kamon/metric/instrument/MinMaxCounter.scala
@@ -1,7 +1,10 @@
 package kamon.metric.instrument
 
+import java.lang.Math.abs
 import java.time.Duration
+import java.util.concurrent.atomic.{AtomicLong, AtomicReference}
 
+import kamon.jsr166.LongMaxUpdater
 import kamon.metric.Entity
 import kamon.util.MeasurementUnit
 
@@ -14,18 +17,60 @@ trait MinMaxCounter {
   def increment(times: Long): Unit
   def decrement(): Unit
   def decrement(times: Long): Unit
+  def sample(): Unit
 }
 
-object MinMaxCounter {
-  def apply(entity: Entity, name: String, dynamicRange2: DynamicRange, sampleInterval2: Duration): MinMaxCounter = new MinMaxCounter {
 
-    override def measurementUnit: MeasurementUnit = ???
+class PaddedMinMaxCounter(entity: Entity, name: String, underlyingHistogram: Histogram with DistributionSnapshotInstrument,
+    val sampleInterval: Duration) extends MinMaxCounter with DistributionSnapshotInstrument {
 
-    override def sampleInterval: Duration = sampleInterval2
-    override def increment(): Unit = ???
-    override def increment(times: Long): Unit = ???
-    override def decrement(): Unit = ???
-    override def decrement(times: Long): Unit = ???
-    override def dynamicRange: DynamicRange = dynamicRange2
+  private val min = new LongMaxUpdater(0L)
+  private val max = new LongMaxUpdater(0L)
+  private val sum = new AtomicLong()
+
+  def dynamicRange: DynamicRange =
+    underlyingHistogram.dynamicRange
+
+  def measurementUnit: MeasurementUnit =
+    underlyingHistogram.measurementUnit
+
+  private[kamon] def snapshot(): DistributionSnapshot =
+    underlyingHistogram.snapshot()
+
+  def increment(): Unit =
+    increment(1L)
+
+  def increment(times: Long): Unit = {
+    val currentValue = sum.addAndGet(times)
+    max.update(currentValue)
   }
-}
+
+  def decrement(): Unit =
+    decrement(1L)
+
+  def decrement(times: Long): Unit = {
+    val currentValue = sum.addAndGet(-times)
+    min.update(-currentValue)
+  }
+
+  def sample(): Unit = {
+    val currentValue = {
+      val value = sum.get()
+      if (value <= 0) 0 else value
+    }
+
+    val currentMin = {
+      val rawMin = min.maxThenReset(-currentValue)
+      if (rawMin >= 0)
+        0
+      else
+        abs(rawMin)
+    }
+
+    val currentMax = max.maxThenReset(currentValue)
+
+    underlyingHistogram.record(currentValue)
+    underlyingHistogram.record(currentMin)
+    underlyingHistogram.record(currentMax)
+  }
+}
\ No newline at end of file