Package com.tangosol.util

Class SegmentedHashMap

  • All Implemented Interfaces:
    Map
    Direct Known Subclasses:
    SegmentedConcurrentMap
    public class SegmentedHashMap
extends Base
implements Map
    An implementation of java.util.Map that is optimized for heavy concurrent use.

    Retrieval and update operations to the map (e.g. get, put) are non-blocking and uncontended and will reflect some state of the map. Insert and remove operations to the map (e.g. put, remove) do require internal locking.

    The entries in the map are internally segmented so as to permit a high level of concurrent "locked" operations without contention.

    Retrievals and updates that run concurrently with bulk operations (e.g. putAll, clear may reflect insertion or removal of only some entries. Iterators on the Map may also reflect concurrent updates made since the Iterator was created. However, Iterators will not throw ConcurrentModificationException.

    Since:
    Coherence 3.5
    Author:
    rhl 2008.12.01

    • Field Detail

      • PRIME_MODULO

        protected static final int[] PRIME_MODULO
        A list of possible modulos to use.

      • DEFAULT_INITIALSIZE

        public static final int DEFAULT_INITIALSIZE
        Default initial size provides a prime modulo and is large enough that resize is not immediate. (A hash map probably uses less than 128 bytes initially.)

      • BIGGEST_MODULO

        protected static final int BIGGEST_MODULO
        Biggest possible modulo.

      • DEFAULT_LOADFACTOR

        public static final float DEFAULT_LOADFACTOR
        The default load factor is 100%, which means that the hash map will not resize until there is (on average) one entry in every bucket. The cost of scanning a linked list in a particular bucket is very low, so there is little reason for having this value below 1.0, and the goal is constant order access, so assuming a perfect hash this will provide the optimal access speed relative to size.
        See Also:
        Constant Field Values

      • DEFAULT_GROWTHRATE

        public static final float DEFAULT_GROWTHRATE
        Using the default growth rate, the bucket array will grow by a factor of four. The relatively high growth rate helps to ensure less resize operations, an important consideration in a high-concurrency map.
        See Also:
        Constant Field Values

      • MIN_SEGMENT_CAPACITY

        protected static final int MIN_SEGMENT_CAPACITY
        The minimum segment capacity.
        See Also:
        Constant Field Values

      • SEGMENT_COUNT

        protected static final int SEGMENT_COUNT
        The number of segments to partition the hash buckets into. There is a single lock for each segment. This number is specially chosen as 61 is the largest prime number smaller than 64 (the size of the datatype used to represent the lock).
        See Also:
        Constant Field Values

      • LOCK_COUNT

        protected static final int LOCK_COUNT
        The number of segment-locks. Each segment has its own lock and there is a global "intention" lock.
        See Also:
        Constant Field Values

      • LOCKS_NONE

        protected static final long LOCKS_NONE
        The lock representation used to indicate that no locks are set.
        See Also:
        Constant Field Values

      • LOCKS_ALL

        protected static final long LOCKS_ALL
        The lock representation used to indicate that all mutexes are locked.
        See Also:
        Constant Field Values

      • LOCK_ALL_PENDING_IDX

        protected static final int LOCK_ALL_PENDING_IDX
        The mutex number used to indicate that a lock-all is pending.
        See Also:
        Constant Field Values

      • LOCK_ALL_PENDING

        protected static final long LOCK_ALL_PENDING
        The bit-mask used to indicate that a lock-all is pending.
        See Also:
        Constant Field Values

      • SEGMENT_LOCK_MAX_SPIN

        protected static final int SEGMENT_LOCK_MAX_SPIN
        Maximum number of times to spin while trying to acquire a segment lock before waiting.
        See Also:
        Constant Field Values

      • PUTALL_THRESHOLD

        protected static final int PUTALL_THRESHOLD
        Size threshold used by the putAll operation.
        See Also:
        Constant Field Values

      • NO_VALUE

        protected static final Object NO_VALUE
        Object to be used as a value representing that the Entry object is "synthetic" and while logically associated with a key, does not represent a key-value mapping in the Map.

      • EMPTY

        public static final Map<?,​?> EMPTY
        An empty, immutable SegmentedHashMap instance.

      • RESIZING

        protected final Object RESIZING
        When resizing completes, a notification is issued against this object.

      • m_atomicLocks

        protected final AtomicLong m_atomicLocks
        The "segment-locks". This AtomicCounter is actually used just as an "Atomic Long" value, with each of the first 61 bits being used to represent a segment-lock. In this case, the number of "buckets" is fixed to 61 (the largest prime smaller than 64).

      • m_aSegment

        protected final SegmentedHashMap.Segment[] m_aSegment
        An array of the control-structures for the Map's segments.

      • m_aeBucket

        protected volatile SegmentedHashMap.Entry[] m_aeBucket
        The array of hash buckets. This field is declared volatile in order to reduce synchronization.

      • m_cSegmentCapacity

        protected int m_cSegmentCapacity
        The capacity of each segment (the point at which we should resize).

      • m_flLoadFactor

        protected final float m_flLoadFactor
        The determining factor for the hash map capacity given a certain number of buckets, such that capacity = bucketcount * loadfactor.

      • m_flGrowthRate

        protected final float m_flGrowthRate
        The rate of growth as a fraction of the current number of buckets, 0 < n, such that the hash map grows to bucketcount * (1 + growth-rate).

      • m_oIterActive

        protected Object m_oIterActive
        A holder for active Iterator(s): either WeakReference(<Iterator>) or WeakHashMap(<Iterator> null)

    • Constructor Detail

      • SegmentedHashMap

        public SegmentedHashMap()
        Default constructor.

      • SegmentedHashMap

        public SegmentedHashMap​(int cInitialBuckets,
                        float flLoadFactor,
                        float flGrowthRate)
        Construct a thread-safe hash map using the specified settings.
        Parameters:
        cInitialBuckets - the initial number of hash buckets, 0 < n
        flLoadFactor - the acceptable load factor before resizing occurs, 0 < n, such that a load factor of 1.0 causes resizing when the number of entries exceeds the number of buckets
        flGrowthRate - the rate of bucket growth when a resize occurs, 0 < n, such that a growth rate of 1.0 will double the number of buckets: bucketcount = bucketcount * (1 + growthrate)

    • Method Detail

      • getInsertAction

        protected SegmentedHashMap.InsertAction getInsertAction()
        Return the registered action for insert.
        Returns:
        the registered action for insert

      • setInsertAction

        protected void setInsertAction​(SegmentedHashMap.InsertAction action)
        Specify the action for insert.
        Parameters:
        action - the action for insert

      • getGetEntryAction

        protected SegmentedHashMap.GetEntryAction getGetEntryAction()
        Return the registered action for getEntryInternal.
        Returns:
        the registered action for getEntryInternal

      • setGetEntryAction

        protected void setGetEntryAction​(SegmentedHashMap.GetEntryAction action)
        Specify the action for getEntryInternal.
        Parameters:
        action - the action for getEntryInternal

      • getRemoveAction

        protected SegmentedHashMap.RemoveAction getRemoveAction()
        Return the registered action for remove().
        Returns:
        the registered action for remove()

      • setRemoveAction

        protected void setRemoveAction​(SegmentedHashMap.RemoveAction action)
        Specify the action for remove().
        Parameters:
        action - the action for remove()

      • getContainsValueAction

        protected SegmentedHashMap.ContainsValueAction getContainsValueAction()
        Return the registered action for containsValue().
        Returns:
        the registered action for containsValue()

      • setContainsValueAction

        protected void setContainsValueAction​(SegmentedHashMap.ContainsValueAction action)
        Specify the action for containsValue().
        Parameters:
        action - the action for containsValue()

      • equals

        public boolean equals​(Object oThat)
        Compares the specified object with this map for equality. Returns true if the given object is also a map and the two maps represent the same mappings. More formally, two maps t1 and t2 represent the same mappings if t1.keySet().equals(t2.keySet()) and for every key k in t1.keySet(), (t1.get(k)==null ? t2.get(k)==null : t1.get(k).equals(t2.get(k))) . This ensures that the equals method works properly across different implementations of the map interface.
        Specified by:
        equals in interface Map
        Overrides:
        equals in class Object
        Parameters:
        oThat - object to be compared for equality with this Map
        Returns:
        true if the specified object is equal to this Map

      • hashCode

        public int hashCode()
        Returns the hash code value for this Map. The hash code of a Map is defined to be the sum of the hash codes of each entry in the Map's entrySet() view. This ensures that t1.equals(t2) implies that t1.hashCode()==t2.hashCode() for any two maps t1 and t2, as required by the general contract of Object.hashCode.
        Specified by:
        hashCode in interface Map
        Overrides:
        hashCode in class Object
        Returns:
        the hash code value for this Map

      • toString

        public String toString()
        Returns a String representation of this map.
        Overrides:
        toString in class Object
        Returns:
        a String representation of this map

      • size

        public int size()
        Returns the number of key-value mappings in this map.

        Note: Unlike some Map implementations, the size() operation on this map may be relatively expensive.

        Specified by:
        size in interface Map
        Returns:
        the number of key-value mappings in this map

      • isEmpty

        public boolean isEmpty()
        Returns true if this map contains no key-value mappings.
        Specified by:
        isEmpty in interface Map
        Returns:
        true if this map contains no key-value mappings

      • containsKey

        public boolean containsKey​(Object oKey)
        Returns true iff this map contains a mapping for the specified key.
        Specified by:
        containsKey in interface Map
        Parameters:
        oKey - key whose presence in this map is to be tested
        Returns:
        true iff this map contains a mapping for the specified key

      • containsValue

        public boolean containsValue​(Object oValue)
        Returns true if this map maps one or more keys to the specified value.
        Specified by:
        containsValue in interface Map
        Parameters:
        oValue - value whose presence in this map is to be tested
        Returns:
        true if this map maps one or more keys to the specified value

      • get

        public Object get​(Object oKey)
        Returns the value to which this map maps the specified key. Returns null if the map contains no mapping for this key. A return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.
        Specified by:
        get in interface Map
        Parameters:
        oKey - key whose associated value is to be returned
        Returns:
        the value to which this map maps the specified key, or null if the map contains no mapping for this key

      • getEntry

        public Map.Entry getEntry​(Object key)
        Locate an Entry in the this map based on its key.
        Parameters:
        key - the key object to search for
        Returns:
        the Entry or null if the entry does not exist

      • put

        public Object put​(Object oKey,
                  Object oValue)
        Associates the specified value with the specified key in this map. If the map previously contained a mapping for this key, the old value is replaced.
        Specified by:
        put in interface Map
        Parameters:
        oKey - key with which the specified value is to be associated
        oValue - value to be associated with the specified key
        Returns:
        previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the map previously associated null with the specified key

      • putAll

        public void putAll​(Map mapOther)
        Copies all of the mappings from the specified map to this map. putAll is semantically equivalent to: 
         for (Iterator iter = mapOther.entrySet().iterator(); iter.hasNext(); )
     {
     Map.Entry entry = (Map.Entry) iter.next();
     put(entry.getKey(), entry.getValue());
     }
        Specified by:
        putAll in interface Map
        Parameters:
        mapOther - mappings to be stored in this map

      • remove

        public Object remove​(Object oKey)
        Removes the mapping for this key from this map if present.
        Specified by:
        remove in interface Map
        Parameters:
        oKey - key whose mapping is to be removed from the map
        Returns:
        previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the map previously associated null with the specified key

      • clear

        public void clear()
        Removes all mappings from this map.
        Specified by:
        clear in interface Map

      • entrySet

        public Set entrySet()
        Returns a set view of the mappings contained in this map. Each element in the returned set is a Map.Entry. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress, the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.
        Specified by:
        entrySet in interface Map
        Returns:
        a set view of the mappings contained in this map.

      • keySet

        public Set keySet()
        Returns a Set view of the keys contained in this map. The Set is backed by the map, so changes to the map are reflected in the Set, and vice-versa. (If the map is modified while an iteration over the Set is in progress, the results of the iteration are undefined.) The Set supports element removal, which removes the corresponding entry from the map, via the Iterator.remove, Set.remove, removeAll retainAll, and clear operations. It does not support the add or addAll operations.
        Specified by:
        keySet in interface Map
        Returns:
        a Set view of the keys contained in this map

      • values

        public Collection values()
        Returns a collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. If the map is modified while an iteration over the collection is in progress, the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.
        Specified by:
        values in interface Map
        Returns:
        a collection view of the values contained in this map

      • initializeActions

        protected void initializeActions()
        Initialize the EntryAction's for this map.

      • getEntryInternal

        protected SegmentedHashMap.Entry getEntryInternal​(Object oKey)
        Locate an Entry in the hash map based on its key.
        Parameters:
        oKey - the key object to search for
        Returns:
        the Entry or null

      • getEntryInternal

        protected SegmentedHashMap.Entry getEntryInternal​(Object oKey,
                                                  boolean fSynthetic)
        Locate an Entry in the hash map based on its key.
        Parameters:
        oKey - the key object to search for
        fSynthetic - include synthetic Entry objects representing keys that are not contained in the map
        Returns:
        the Entry or null

      • putInternal

        protected Object putInternal​(Object oKey,
                             Object oValue)
        Associates the specified value with the specified key in this map. If the map previously contained a mapping for this key, the old value is replaced.
        Parameters:
        oKey - key with which the specified value is to be associated
        oValue - value to be associated with the specified key
        Returns:
        previous value associated with specified key, or NO_VALUE if there was no mapping for key. A null return indicates that the map previously associated null with the specified key

      • putInternal

        protected Object putInternal​(Object oKey,
                             Object oValue,
                             boolean fOnlyIfAbsent)
        Associates the specified value with the specified key in this map. If the map previously contained a mapping for this key, the old value is replaced.
        Parameters:
        oKey - key with which the specified value is to be associated
        oValue - value to be associated with the specified key
        fOnlyIfAbsent - if true, perform a logical insert only; no action if the key already exists
        Returns:
        previous value associated with specified key, or NO_VALUE if there was no mapping for key. A null return indicates that the map previously associated null with the specified key

      • removeInternal

        protected Object removeInternal​(Object oKey,
                                SegmentedHashMap.EntryAction actionRemove,
                                Object oContext)
        Removes the mapping for this key from this map if present.
        Parameters:
        oKey - key whose mapping is to be removed from the map
        actionRemove - the EntryAction to apply
        oContext - the context for the remove action
        Returns:
        previous value associated with specified key, or NO_VALUE if there was no mapping for key. A null return indicates that the map previously associated null with the specified key.

      • toArrayInternal

        protected Object[] toArrayInternal​(SegmentedHashMap.IterableEntryAction action,
                                   Object[] a)
        Apply the specified toArray() action to the entries in the map. The toArray() action is not applied under any segment lock and is expected to accept a List instance as a context.
        Parameters:
        action - the toArray() action
        a - the array into which the elements of the Collection are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose
        Returns:
        an array containing the elements returned by the specified action
        Throws:
        ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of the elements returned by the specified action

      • ensureLoadFactor

        protected void ensureLoadFactor​(SegmentedHashMap.Segment segment)
        Check whether or not the specified segment is overloaded and if so, grow the bucket array (which suggests with high probability that the per-segment load will decrease).
        Parameters:
        segment - the segment to ensure the load-factor for

      • grow

        protected void grow()
        Resize the bucket array, rehashing all Entries.

        Note: caller of this method is expected to hold locks on all segments of the map while making this call.

      • grow

        protected void grow​(int cNew)
        Resize the bucket array to the specified size, rehashing all Entries.

        Note: caller of this method is expected to hold locks on all segments of the map while making this call.

        Parameters:
        cNew - the minimum size to attempt to grow to

      • invokeOnAllKeys

        protected Object invokeOnAllKeys​(Object oContext,
                                 boolean fLock,
                                 SegmentedHashMap.IterableEntryAction actionEntry)
        Perform an action on all Entries in the map. The action is provided as an EntryAction and (if the fLock is specified) it are invoked while holding the locks for all segments.

        The semantics of invokeOnAllKeys are equivalent to: 

         for (Iterator iter = entrySet().iterator(); iter.hasNext(); )
     {
     Entry entry = (Entry) iter.next();
     actionEntry.invokeFound(...);
     }
 return oContext;
        Except that if fLock is specified, it is performed atomically while holding all segment-locks.
        Parameters:
        oContext - opaque context for the specified action
        fLock - true if all segment-locks should be acquired before invoking the specified action
        actionEntry - the action to perform for each entry
        Returns:
        the specified opaque context

      • invokeOnKey

        protected Object invokeOnKey​(Object oKey,
                             Object oContext,
                             boolean fLock,
                             SegmentedHashMap.EntryAction action)
        Perform an action on the specified key. The action operation is provided as an EntryAction and (if fLock is specified), is invoked while holding the appropriate segment lock for the key.

        The semantics of invokeOnKey are equivalent to: 

         Object oResult;
 if (containsKey(oKey))
     {
     oResult = action.invokeFound(...);
     }
 else
     {
     oResult = action.invokeNotFound(...);
     }
 return oResult;
        Except that if fLock is specified, it is performed atomically while holding the segment-lock.
        Parameters:
        oKey - the key to act on
        oContext - opaque context for the specified action
        fLock - true iff the segment should be locked before invoking the specified action
        action - the action to invoke
        Returns:
        the result of performing the action

      • getBucketIndex

        protected int getBucketIndex​(int nHash,
                             int cBuckets)
        Calculate the bucket number for a particular hash code.
        Parameters:
        nHash - the hash code
        cBuckets - the number of buckets
        Returns:
        the bucket index for the specified hash code

      • getSegmentIndex

        protected int getSegmentIndex​(int nBucket)
        Calculate the segment index for the the specified bucket.
        Parameters:
        nBucket - the bucket number
        Returns:
        the segment index

      • getSegmentForKey

        protected SegmentedHashMap.Segment getSegmentForKey​(Object oKey)
        Return the Segment object for the specified key.
        Parameters:
        oKey - the key
        Returns:
        the Segment for the specified key

      • getStableBucketArray

        protected SegmentedHashMap.Entry[] getStableBucketArray()
        Get the bucket array, or if a resize is occurring, wait for the resize to complete and return the new bucket array.
        Returns:
        the latest bucket array

      • iteratorActivated

        protected void iteratorActivated​(Iterator iter)
        Register the activation of an Iterator.

        Note: The map will not grow while there are any active iterators.

        Parameters:
        iter - the activated iterator

      • releaseIterator

        public void releaseIterator​(Iterator iter)
        Release the (formerly-active) Iterator.

        Note: This method could be used to accelerate the destruction of unexhausted iterators.

        Parameters:
        iter - the iterator to be released

      • isActiveIterator

        protected boolean isActiveIterator()
        Determine if there are any active Iterators, which may mean that they are in the middle of iterating over the Map.
        Returns:
        true iff there is at least one active Iterator

      • lockBucket

        protected boolean lockBucket​(int nBucket)
        Attempt to lock the segment corresponding to the specified bucket.
        Parameters:
        nBucket - the bucket index
        Returns:
        true iff the segment was successfully locked

      • lockSegment

        protected boolean lockSegment​(int nSegment,
                              boolean fBlock)
        Attempt to lock the specified segment.
        Parameters:
        nSegment - the segment to lock
        fBlock - should we block on trying to lock the segment
        Returns:
        true iff the segment was successfully locked

      • unlockBucket

        protected void unlockBucket​(int nBucket)
        Unlock the segment corresponding to the specified bucket that was previously locked using the lockBucket(int) method.
        Parameters:
        nBucket - the bucket to unlock

      • unlockSegment

        protected void unlockSegment​(int nSegment)
        Unlock the specified segment previously locked using the lockSegment(int, boolean) method.
        Parameters:
        nSegment - the segment to unlock

      • contendForSegment

        protected void contendForSegment​(int nSegment)
        Wait for a segment to be unlocked.
        Parameters:
        nSegment - the segment-lock to be waited for

      • lockAllBuckets

        protected void lockAllBuckets()
        Lock everything. This method will not return until the lock is placed. It must not be called on a thread that could already hold a lock.

      • lockAllBuckets

        protected boolean lockAllBuckets​(int nBucketAlreadyLocked)
        Lock everything, assuming that the segment for the specified bucket has already been locked.
        Parameters:
        nBucketAlreadyLocked - the bucket that was already locked.
        Returns:
        false if the operation failed because another thread was also trying to lock everything (indicating potential deadlock)

      • unlockAllBuckets

        protected void unlockAllBuckets()
        Unlock everything.

      • unlockAllBuckets

        protected void unlockAllBuckets​(int nBucketLeaveLocked)
        Unlock everything, leaving only the segment for the specified bucket locked.
        Parameters:
        nBucketLeaveLocked - the bucket that was already locked

      • lockAllSegments

        protected boolean lockAllSegments​(long lLocksHeld)
        Lock all segments except for the specified segments that have already been locked by the calling thread.
        Parameters:
        lLocksHeld - the bit-mask representing all segment-locks that the calling thread already holds
        Returns:
        false if the operation failed because another thread was also trying to lock everything (indicating potential deadlock)

      • unlockAllSegments

        protected void unlockAllSegments​(long lLocksKeep)
        Unlock all segments, except the segment-locks indicated by the specified bit-vector. This method must only be called by a thread if that thread has successfully called lockAllSegments(long).
        Parameters:
        lLocksKeep - the segment-locks to keep locked

      • instantiateEntry

        protected SegmentedHashMap.Entry instantiateEntry​(Object oKey,
                                                  Object oValue,
                                                  int nHash)
        Factory for Entry.
        Parameters:
        oKey - the key
        oValue - the value
        nHash - the hashCode value of the key
        Returns:
        a new instance of the Entry class (or a subclass thereof)

      • entryFromBucket

        protected static SegmentedHashMap.Entry entryFromBucket​(SegmentedHashMap.Entry[] aeBucket,
                                                        int nBucket)
        Return the first non-synthetic Entry object contained by in the specified bucket.
        Parameters:
        aeBucket - the array of hash buckets
        nBucket - the bucket index
        Returns:
        the first non-synthetic Entry in the specified bucket or null

      • instantiateEntrySet

        protected SegmentedHashMap.EntrySet instantiateEntrySet()
        Factory for EntrySet
        Returns:
        a new instance of the EntrySet class (or a subclass thereof)

      • instantiateKeySet

        protected SegmentedHashMap.KeySet instantiateKeySet()
        Factory for KeySet.
        Returns:
        a new instance of the KeySet class (or subclass thereof)

      • instantiateValuesCollection

        protected SegmentedHashMap.ValuesCollection instantiateValuesCollection()
        Factory for ValuesCollection.
        Returns:
        a new instance of the ValuesCollection class (or subclass thereof)