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package java.util.concurrent; |
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|
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import java.util.*; |
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import java.io.Serializable; |
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import java.io.IOException; |
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import java.io.ObjectInputStream; |
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import java.io.ObjectOutputStream; |
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|
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/** |
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* A version of Hashtable supporting |
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* concurrency for both retrievals and updates. |
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* |
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* <dl> |
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* <dt> Retrievals |
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* |
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* <dd> Retrievals may overlap updates. Successful retrievals using |
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* get(key) and containsKey(key) usually run without |
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* locking. Unsuccessful retrievals (i.e., when the key is not |
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* present) do involve brief synchronization (locking). Because |
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* retrieval operations can ordinarily overlap with update operations |
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* (i.e., put, remove, and their derivatives), retrievals can only be |
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* guaranteed to return the results of the most recently |
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* <em>completed</em> operations holding upon their onset. Retrieval |
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* operations may or may not return results reflecting in-progress |
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* writing operations. However, the retrieval operations do always |
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* return consistent results -- either those holding before any single |
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* modification or after it, but never a nonsense result. For |
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* aggregate operations such as putAll and clear, concurrent reads may |
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* reflect insertion or removal of only some entries. <p> |
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* |
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* Iterators and Enumerations (i.e., those returned by |
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* keySet().iterator(), entrySet().iterator(), values().iterator(), |
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* keys(), and elements()) return elements reflecting the state of the |
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* hash table at some point at or since the creation of the |
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* iterator/enumeration. They will return at most one instance of |
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* each element (via next()/nextElement()), but might or might not |
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* reflect puts and removes that have been processed since they were |
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* created. They do <em>not</em> throw ConcurrentModificationException. |
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* However, these iterators are designed to be used by only one |
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* thread at a time. Passing an iterator across multiple threads may |
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* lead to unpredictable results if the table is being concurrently |
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* modified. <p> |
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* |
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* |
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* <dt> Updates |
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* |
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* <dd> This class supports a hard-wired preset <em>concurrency |
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* level</em> of 32. This allows a maximum of 32 put and/or remove |
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* operations to proceed concurrently. This level is an upper bound on |
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* concurrency, not a guarantee, since it interacts with how |
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* well-strewn elements are across bins of the table. (The preset |
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* value in part reflects the fact that even on large multiprocessors, |
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* factors other than synchronization tend to be bottlenecks when more |
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* than 32 threads concurrently attempt updates.) |
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* Additionally, operations triggering internal resizing and clearing |
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* do not execute concurrently with any operation. |
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* <p> |
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* |
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* There is <em>NOT</em> any support for locking the entire table to |
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* prevent updates. This makes it imposssible, for example, to |
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* add an element only if it is not already present, since another |
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* thread may be in the process of doing the same thing. |
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* |
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* </dl> |
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* |
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* |
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* This class may be used as a direct replacement for |
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* java.util.Hashtable in any application that does not rely |
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* on the ability to lock the entire table to prevent updates. |
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* As of this writing, it performs much faster than Hashtable in |
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* typical multi-threaded applications with multiple readers and writers. |
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* Like Hashtable but unlike java.util.HashMap, |
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* this class does NOT allow <tt>null</tt> to be used as a key or |
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* value. |
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* <p> |
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* |
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* |
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**/ |
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public class ConcurrentHashMap<K, V> extends AbstractMap<K, V> |
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implements ConcurrentMap<K, V>, Cloneable, Serializable { |
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|
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/* |
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The basic strategy is an optimistic-style scheme based on |
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the guarantee that the hash table and its lists are always |
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kept in a consistent enough state to be read without locking: |
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|
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* Read operations first proceed without locking, by traversing the |
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apparently correct list of the apparently correct bin. If an |
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entry is found, but not invalidated (value field null), it is |
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returned. If not found, operations must recheck (after a memory |
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barrier) to make sure they are using both the right list and |
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the right table (which can change under resizes). If |
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invalidated, reads must acquire main update lock to wait out |
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the update, and then re-traverse. |
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|
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* All list additions are at the front of each bin, making it easy |
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to check changes, and also fast to traverse. Entry next |
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pointers are never assigned. Remove() builds new nodes when |
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necessary to preserve this. |
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|
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* Remove() (also clear()) invalidates removed nodes to alert read |
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operations that they must wait out the full modifications. |
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|
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* Locking for puts, removes (and, when necessary gets, etc) |
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is controlled by Segments, each covering a portion of the |
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table. During operations requiring global exclusivity (mainly |
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resize and clear), ALL of these locks are acquired at once. |
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Note that these segments are NOT contiguous -- they are based |
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on the least 5 bits of hashcodes. This ensures that the same |
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segment controls the same slots before and after resizing, which |
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is necessary for supporting concurrent retrievals. This |
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comes at the price of a mismatch of logical vs physical locality, |
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but this seems not to be a performance problem in practice. |
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|
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*/ |
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|
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/** |
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* The hash table data. |
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*/ |
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private transient Entry<K,V>[] table; |
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|
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|
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/** |
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* The number of concurrency control segments. |
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* The value can be at most 32 since ints are used |
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* as bitsets over segments. Emprically, it doesn't |
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* seem to pay to decrease it either, so the value should be at least 32. |
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* In other words, do not redefine this :-) |
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**/ |
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private static final int CONCURRENCY_LEVEL = 32; |
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|
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/** |
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* Mask value for indexing into segments |
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**/ |
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private static final int SEGMENT_MASK = CONCURRENCY_LEVEL - 1; |
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|
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/** |
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* Bookkeeping for each concurrency control segment. |
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* Each segment contains a local count of the number of |
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* elements in its region. |
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* However, the main use of a Segment is for its lock. |
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**/ |
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private final static class Segment { |
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/** |
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* The number of elements in this segment's region. |
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* It is always updated within synchronized blocks. |
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**/ |
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private int count; |
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|
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/** |
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* Get the count under synch. |
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**/ |
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private synchronized int getCount() { return count; } |
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|
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/** |
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* Force a synchronization |
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**/ |
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private synchronized void synch() {} |
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} |
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|
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/** |
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* The array of concurrency control segments. |
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**/ |
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private final Segment[] segments = new Segment[CONCURRENCY_LEVEL]; |
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|
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|
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/** |
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* The default initial number of table slots for this table (32). |
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* Used when not otherwise specified in constructor. |
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**/ |
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public static int DEFAULT_INITIAL_CAPACITY = 32; |
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|
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|
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/** |
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* The minimum capacity, used if a lower value is implicitly specified |
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* by either of the constructors with arguments. |
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* MUST be a power of two. |
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*/ |
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private static final int MINIMUM_CAPACITY = 32; |
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|
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/** |
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* The maximum capacity, used if a higher value is implicitly specified |
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* by either of the constructors with arguments. |
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* MUST be a power of two <= 1<<30. |
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*/ |
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private static final int MAXIMUM_CAPACITY = 1 << 30; |
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|
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/** |
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* The default load factor for this table (0.75) |
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* Used when not otherwise specified in constructor. |
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**/ |
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public static final float DEFAULT_LOAD_FACTOR = 0.75f; |
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|
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/** |
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* The load factor for the hash table. |
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* |
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* @serial |
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*/ |
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private final float loadFactor; |
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|
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/** |
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* Per-segment resize threshold. |
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* |
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* @serial |
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*/ |
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private int threshold; |
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|
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|
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/** |
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* Number of segments voting for resize. The table is |
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* doubled when 1/4 of the segments reach threshold. |
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* Volatile but updated without synch since this is just a heuristic. |
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**/ |
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private transient volatile int votesForResize; |
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|
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|
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/** |
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* Return the number of set bits in w. |
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* For a derivation of this algorithm, see |
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* "Algorithms and data structures with applications to |
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* graphics and geometry", by Jurg Nievergelt and Klaus Hinrichs, |
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* Prentice Hall, 1993. |
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* See also notes by Torsten Sillke at |
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* http://www.mathematik.uni-bielefeld.de/~sillke/PROBLEMS/bitcount |
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**/ |
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private static int bitcount(int w) { |
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w -= (0xaaaaaaaa & w) >>> 1; |
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w = (w & 0x33333333) + ((w >>> 2) & 0x33333333); |
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w = (w + (w >>> 4)) & 0x0f0f0f0f; |
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w += w >>> 8; |
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w += w >>> 16; |
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return w & 0xff; |
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} |
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|
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/** |
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* Returns the appropriate capacity (power of two) for the specified |
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* initial capacity argument. |
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*/ |
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private int p2capacity(int initialCapacity) { |
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int cap = initialCapacity; |
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|
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// Compute the appropriate capacity |
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int result; |
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if (cap > MAXIMUM_CAPACITY || cap < 0) { |
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result = MAXIMUM_CAPACITY; |
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} else { |
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result = MINIMUM_CAPACITY; |
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while (result < cap) |
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result <<= 1; |
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} |
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return result; |
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} |
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|
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/** |
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* Return hash code for Object x. Since we are using power-of-two |
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* tables, it is worth the effort to improve hashcode via |
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* the same multiplicative scheme as used in IdentityHashMap. |
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*/ |
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private static int hash(Object x) { |
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int h = x.hashCode(); |
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// Multiply by 127 (quickly, via shifts), and mix in some high |
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// bits to help guard against bunching of codes that are |
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// consecutive or equally spaced. |
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return ((h << 7) - h + (h >>> 9) + (h >>> 17)); |
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} |
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|
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|
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/** |
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* Check for equality of non-null references x and y. |
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**/ |
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private boolean eq(Object x, Object y) { |
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return x == y || x.equals(y); |
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} |
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|
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/** Create table array and set the per-segment threshold **/ |
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private Entry<K,V>[] newTable(int capacity) { |
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threshold = (int)(capacity * loadFactor / CONCURRENCY_LEVEL) + 1; |
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return new Entry<K,V>[capacity]; |
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} |
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|
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/** |
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* Constructs a new, empty map with the specified initial |
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* capacity and the specified load factor. |
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* |
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* @param initialCapacity the initial capacity. |
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* The actual initial capacity is rounded up to the nearest power of two. |
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* @param loadFactor the load factor threshold, used to control resizing. |
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* This value is used in an approximate way: When at least |
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* a quarter of the segments of the table reach per-segment threshold, or |
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* one of the segments itself exceeds overall threshold, |
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* the table is doubled. |
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* This will on average cause resizing when the table-wide |
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* load factor is slightly less than the threshold. If you'd like |
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* to avoid resizing, you can set this to a ridiculously large |
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* value. |
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* @throws IllegalArgumentException if the load factor is nonpositive. |
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*/ |
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public ConcurrentHashMap(int initialCapacity, float loadFactor) { |
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if (!(loadFactor > 0)) |
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throw new IllegalArgumentException("Illegal Load factor: "+ loadFactor); |
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this.loadFactor = loadFactor; |
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for (int i = 0; i < segments.length; ++i) |
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segments[i] = new Segment(); |
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int cap = p2capacity(initialCapacity); |
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table = newTable(cap); |
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} |
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|
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/** |
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* Constructs a new, empty map with the specified initial |
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* capacity and default load factor. |
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* |
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* @param initialCapacity the initial capacity of the |
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* ConcurrentHashMap. |
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* @throws IllegalArgumentException if the initial maximum number |
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* of elements is less |
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* than zero. |
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*/ |
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public ConcurrentHashMap(int initialCapacity) { |
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this(initialCapacity, DEFAULT_LOAD_FACTOR); |
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} |
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|
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/** |
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* Constructs a new, empty map with a default initial capacity |
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* and default load factor. |
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*/ |
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public ConcurrentHashMap() { |
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this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR); |
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} |
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|
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/** |
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* Constructs a new map with the same mappings as the given map. The |
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* map is created with a capacity of twice the number of mappings in |
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* the given map or 32 (whichever is greater), and a default load factor. |
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*/ |
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public <A extends K, B extends V> ConcurrentHashMap(Map<A,B> t) { |
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this(Math.max((int) (t.size() / DEFAULT_LOAD_FACTOR) + 1, |
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MINIMUM_CAPACITY), |
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DEFAULT_LOAD_FACTOR); |
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putAll(t); |
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} |
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|
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/** |
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* Returns the number of key-value mappings in this map. |
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* |
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* @return the number of key-value mappings in this map. |
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*/ |
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public int size() { |
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int c = 0; |
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for (int i = 0; i < segments.length; ++i) |
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c += segments[i].getCount(); |
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return c; |
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} |
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|
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/** |
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* Returns <tt>true</tt> if this map contains no key-value mappings. |
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* |
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* @return <tt>true</tt> if this map contains no key-value mappings. |
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*/ |
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public boolean isEmpty() { |
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for (int i = 0; i < segments.length; ++i) |
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if (segments[i].getCount() != 0) |
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return false; |
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return true; |
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} |
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|
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|
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/** |
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* Returns the value to which the specified key is mapped in this table. |
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* |
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* @param key a key in the table. |
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* @return the value to which the key is mapped in this table; |
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* <code>null</code> if the key is not mapped to any value in |
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* this table. |
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* @exception NullPointerException if the key is |
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* <code>null</code>. |
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* @see #put(Object, Object) |
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*/ |
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public V get(Object key) { |
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int hash = hash(key); // throws null pointer exception if key null |
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|
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// Try first without locking... |
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Entry<K,V>[] tab = table; |
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int index = hash & (tab.length - 1); |
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Entry<K,V> first = tab[index]; |
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Entry<K,V> e; |
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|
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for (e = first; e != null; e = e.next) { |
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if (e.hash == hash && eq(key, e.key)) { |
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V value = e.value; |
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if (value != null) |
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return value; |
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else |
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break; |
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} |
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} |
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|
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// Recheck under synch if key apparently not there or interference |
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Segment seg = segments[hash & SEGMENT_MASK]; |
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synchronized(seg) { |
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tab = table; |
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index = hash & (tab.length - 1); |
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Entry<K,V> newFirst = tab[index]; |
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if (e != null || first != newFirst) { |
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for (e = newFirst; e != null; e = e.next) { |
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if (e.hash == hash && eq(key, e.key)) |
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return e.value; |
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} |
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} |
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return null; |
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} |
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} |
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|
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/** |
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* Tests if the specified object is a key in this table. |
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* |
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* @param key possible key. |
417 |
* @return <code>true</code> if and only if the specified object |
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* is a key in this table, as determined by the |
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* <tt>equals</tt> method; <code>false</code> otherwise. |
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* @exception NullPointerException if the key is |
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* <code>null</code>. |
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* @see #contains(Object) |
423 |
*/ |
424 |
public boolean containsKey(Object key) { |
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return get(key) != null; |
426 |
} |
427 |
|
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|
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/** |
430 |
* Maps the specified <code>key</code> to the specified |
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* <code>value</code> in this table. Neither the key nor the |
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* value can be <code>null</code>. (Note that this policy is |
433 |
* the same as for java.util.Hashtable, but unlike java.util.HashMap, |
434 |
* which does accept nulls as valid keys and values.)<p> |
435 |
* |
436 |
* The value can be retrieved by calling the <code>get</code> method |
437 |
* with a key that is equal to the original key. |
438 |
* |
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* @param key the table key. |
440 |
* @param value the value. |
441 |
* @return the previous value of the specified key in this table, |
442 |
* or <code>null</code> if it did not have one. |
443 |
* @exception NullPointerException if the key or value is |
444 |
* <code>null</code>. |
445 |
* @see Object#equals(Object) |
446 |
* @see #get(Object) |
447 |
*/ |
448 |
public V put(K key, V value) { |
449 |
if (value == null) |
450 |
throw new NullPointerException(); |
451 |
|
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int hash = hash(key); |
453 |
Segment seg = segments[hash & SEGMENT_MASK]; |
454 |
int segcount; |
455 |
Entry<K,V>[] tab; |
456 |
int votes; |
457 |
|
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synchronized(seg) { |
459 |
tab = table; |
460 |
int index = hash & (tab.length-1); |
461 |
Entry<K,V> first = tab[index]; |
462 |
|
463 |
for (Entry<K,V> e = first; e != null; e = e.next) { |
464 |
if (e.hash == hash && eq(key, e.key)) { |
465 |
V oldValue = e.value; |
466 |
e.value = value; |
467 |
return oldValue; |
468 |
} |
469 |
} |
470 |
|
471 |
// Add to front of list |
472 |
Entry<K,V> newEntry = new Entry<K,V>(hash, key, value, first); |
473 |
tab[index] = newEntry; |
474 |
|
475 |
if ((segcount = ++seg.count) < threshold) |
476 |
return null; |
477 |
|
478 |
int bit = (1 << (hash & SEGMENT_MASK)); |
479 |
votes = votesForResize; |
480 |
if ((votes & bit) == 0) |
481 |
votes = votesForResize |= bit; |
482 |
} |
483 |
|
484 |
// Attempt resize if 1/4 segs vote, |
485 |
// or if this seg itself reaches the overall threshold. |
486 |
// (The latter check is just a safeguard to avoid pathological cases.) |
487 |
if (bitcount(votes) >= CONCURRENCY_LEVEL / 4 || |
488 |
segcount > (threshold * CONCURRENCY_LEVEL)) |
489 |
resize(0, tab); |
490 |
|
491 |
return null; |
492 |
} |
493 |
|
494 |
public V putIfAbsent(K key, V value) { |
495 |
if (value == null) |
496 |
throw new NullPointerException(); |
497 |
|
498 |
int hash = hash(key); |
499 |
Segment seg = segments[hash & SEGMENT_MASK]; |
500 |
int segcount; |
501 |
Entry<K,V>[] tab; |
502 |
int votes; |
503 |
|
504 |
synchronized(seg) { |
505 |
tab = table; |
506 |
int index = hash & (tab.length-1); |
507 |
Entry<K,V> first = tab[index]; |
508 |
|
509 |
for (Entry<K,V> e = first; e != null; e = e.next) { |
510 |
if (e.hash == hash && eq(key, e.key)) { |
511 |
V oldValue = e.value; |
512 |
return oldValue; |
513 |
} |
514 |
} |
515 |
|
516 |
// Add to front of list |
517 |
Entry<K,V> newEntry = new Entry<K,V>(hash, key, value, first); |
518 |
tab[index] = newEntry; |
519 |
|
520 |
if ((segcount = ++seg.count) < threshold) |
521 |
return null; |
522 |
|
523 |
int bit = (1 << (hash & SEGMENT_MASK)); |
524 |
votes = votesForResize; |
525 |
if ((votes & bit) == 0) |
526 |
votes = votesForResize |= bit; |
527 |
} |
528 |
|
529 |
// Attempt resize if 1/4 segs vote, |
530 |
// or if this seg itself reaches the overall threshold. |
531 |
// (The latter check is just a safeguard to avoid pathological cases.) |
532 |
if (bitcount(votes) >= CONCURRENCY_LEVEL / 4 || |
533 |
segcount > (threshold * CONCURRENCY_LEVEL)) |
534 |
resize(0, tab); |
535 |
|
536 |
return value; |
537 |
} |
538 |
|
539 |
/** |
540 |
* Gather all locks in order to call rehash, by |
541 |
* recursing within synch blocks for each segment index. |
542 |
* @param index the current segment. initially call value must be 0 |
543 |
* @param assumedTab the state of table on first call to resize. If |
544 |
* this changes on any call, the attempt is aborted because the |
545 |
* table has already been resized by another thread. |
546 |
*/ |
547 |
private void resize(int index, Entry<K,V>[] assumedTab) { |
548 |
Segment seg = segments[index]; |
549 |
synchronized(seg) { |
550 |
if (assumedTab == table) { |
551 |
int next = index+1; |
552 |
if (next < segments.length) |
553 |
resize(next, assumedTab); |
554 |
else |
555 |
rehash(); |
556 |
} |
557 |
} |
558 |
} |
559 |
|
560 |
/** |
561 |
* Rehashes the contents of this map into a new table |
562 |
* with a larger capacity. |
563 |
*/ |
564 |
private void rehash() { |
565 |
votesForResize = 0; // reset |
566 |
|
567 |
Entry<K,V>[] oldTable = table; |
568 |
int oldCapacity = oldTable.length; |
569 |
|
570 |
if (oldCapacity >= MAXIMUM_CAPACITY) { |
571 |
threshold = Integer.MAX_VALUE; // avoid retriggering |
572 |
return; |
573 |
} |
574 |
|
575 |
int newCapacity = oldCapacity << 1; |
576 |
Entry<K,V>[] newTable = newTable(newCapacity); |
577 |
int mask = newCapacity - 1; |
578 |
|
579 |
/* |
580 |
* Reclassify nodes in each list to new Map. Because we are |
581 |
* using power-of-two expansion, the elements from each bin |
582 |
* must either stay at same index, or move to |
583 |
* oldCapacity+index. We also eliminate unnecessary node |
584 |
* creation by catching cases where old nodes can be reused |
585 |
* because their next fields won't change. Statistically, at |
586 |
* the default threshhold, only about one-sixth of them need |
587 |
* cloning. (The nodes they replace will be garbage |
588 |
* collectable as soon as they are no longer referenced by any |
589 |
* reader thread that may be in the midst of traversing table |
590 |
* right now.) |
591 |
*/ |
592 |
|
593 |
for (int i = 0; i < oldCapacity ; i++) { |
594 |
// We need to guarantee that any existing reads of old Map can |
595 |
// proceed. So we cannot yet null out each bin. |
596 |
Entry<K,V> e = oldTable[i]; |
597 |
|
598 |
if (e != null) { |
599 |
int idx = e.hash & mask; |
600 |
Entry<K,V> next = e.next; |
601 |
|
602 |
// Single node on list |
603 |
if (next == null) |
604 |
newTable[idx] = e; |
605 |
|
606 |
else { |
607 |
// Reuse trailing consecutive sequence of all same bit |
608 |
Entry<K,V> lastRun = e; |
609 |
int lastIdx = idx; |
610 |
for (Entry<K,V> last = next; last != null; last = last.next) { |
611 |
int k = last.hash & mask; |
612 |
if (k != lastIdx) { |
613 |
lastIdx = k; |
614 |
lastRun = last; |
615 |
} |
616 |
} |
617 |
newTable[lastIdx] = lastRun; |
618 |
|
619 |
// Clone all remaining nodes |
620 |
for (Entry<K,V> p = e; p != lastRun; p = p.next) { |
621 |
int k = p.hash & mask; |
622 |
newTable[k] = new Entry<K,V>(p.hash, p.key, |
623 |
p.value, newTable[k]); |
624 |
} |
625 |
} |
626 |
} |
627 |
} |
628 |
|
629 |
table = newTable; |
630 |
} |
631 |
|
632 |
|
633 |
/** |
634 |
* Removes the key (and its corresponding value) from this |
635 |
* table. This method does nothing if the key is not in the table. |
636 |
* |
637 |
* @param key the key that needs to be removed. |
638 |
* @return the value to which the key had been mapped in this table, |
639 |
* or <code>null</code> if the key did not have a mapping. |
640 |
* @exception NullPointerException if the key is |
641 |
* <code>null</code>. |
642 |
*/ |
643 |
public V remove(Object key) { |
644 |
return remove(key, null); |
645 |
} |
646 |
|
647 |
|
648 |
/** |
649 |
* Removes the (key, value) pair from this |
650 |
* table. This method does nothing if the key is not in the table, |
651 |
* or if the key is associated with a different value. This method |
652 |
* is needed by EntrySet. |
653 |
* |
654 |
* @param key the key that needs to be removed. |
655 |
* @param value the associated value. If the value is null, |
656 |
* it means "any value". |
657 |
* @return the value to which the key had been mapped in this table, |
658 |
* or <code>null</code> if the key did not have a mapping. |
659 |
* @exception NullPointerException if the key is |
660 |
* <code>null</code>. |
661 |
*/ |
662 |
private V remove(Object key, V value) { |
663 |
/* |
664 |
Find the entry, then |
665 |
1. Set value field to null, to force get() to retry |
666 |
2. Rebuild the list without this entry. |
667 |
All entries following removed node can stay in list, but |
668 |
all preceeding ones need to be cloned. Traversals rely |
669 |
on this strategy to ensure that elements will not be |
670 |
repeated during iteration. |
671 |
*/ |
672 |
|
673 |
int hash = hash(key); |
674 |
Segment seg = segments[hash & SEGMENT_MASK]; |
675 |
|
676 |
synchronized(seg) { |
677 |
Entry<K,V>[] tab = table; |
678 |
int index = hash & (tab.length-1); |
679 |
Entry<K,V> first = tab[index]; |
680 |
Entry<K,V> e = first; |
681 |
|
682 |
for (;;) { |
683 |
if (e == null) |
684 |
return null; |
685 |
if (e.hash == hash && eq(key, e.key)) |
686 |
break; |
687 |
e = e.next; |
688 |
} |
689 |
|
690 |
V oldValue = e.value; |
691 |
if (value != null && !value.equals(oldValue)) |
692 |
return null; |
693 |
|
694 |
e.value = null; |
695 |
|
696 |
Entry<K,V> head = e.next; |
697 |
for (Entry<K,V> p = first; p != e; p = p.next) |
698 |
head = new Entry<K,V>(p.hash, p.key, p.value, head); |
699 |
tab[index] = head; |
700 |
seg.count--; |
701 |
return oldValue; |
702 |
} |
703 |
} |
704 |
|
705 |
|
706 |
/** |
707 |
* Returns <tt>true</tt> if this map maps one or more keys to the |
708 |
* specified value. Note: This method requires a full internal |
709 |
* traversal of the hash table, and so is much slower than |
710 |
* method <tt>containsKey</tt>. |
711 |
* |
712 |
* @param value value whose presence in this map is to be tested. |
713 |
* @return <tt>true</tt> if this map maps one or more keys to the |
714 |
* specified value. |
715 |
* @exception NullPointerException if the value is <code>null</code>. |
716 |
*/ |
717 |
public boolean containsValue(Object value) { |
718 |
|
719 |
if (value == null) throw new NullPointerException(); |
720 |
|
721 |
for (int s = 0; s < segments.length; ++s) { |
722 |
Segment seg = segments[s]; |
723 |
Entry<K,V>[] tab; |
724 |
synchronized(seg) { tab = table; } |
725 |
for (int i = s; i < tab.length; i+= segments.length) { |
726 |
for (Entry<K,V> e = tab[i]; e != null; e = e.next) |
727 |
if (value.equals(e.value)) |
728 |
return true; |
729 |
} |
730 |
} |
731 |
return false; |
732 |
} |
733 |
|
734 |
/** |
735 |
* Tests if some key maps into the specified value in this table. |
736 |
* This operation is more expensive than the <code>containsKey</code> |
737 |
* method.<p> |
738 |
* |
739 |
* Note that this method is identical in functionality to containsValue, |
740 |
* (which is part of the Map interface in the collections framework). |
741 |
* |
742 |
* @param value a value to search for. |
743 |
* @return <code>true</code> if and only if some key maps to the |
744 |
* <code>value</code> argument in this table as |
745 |
* determined by the <tt>equals</tt> method; |
746 |
* <code>false</code> otherwise. |
747 |
* @exception NullPointerException if the value is <code>null</code>. |
748 |
* @see #containsKey(Object) |
749 |
* @see #containsValue(Object) |
750 |
* @see Map |
751 |
*/ |
752 |
public boolean contains(V value) { |
753 |
return containsValue(value); |
754 |
} |
755 |
|
756 |
/** |
757 |
* Copies all of the mappings from the specified map to this one. |
758 |
* |
759 |
* These mappings replace any mappings that this map had for any of the |
760 |
* keys currently in the specified Map. |
761 |
* |
762 |
* @param t Mappings to be stored in this map. |
763 |
*/ |
764 |
public <A extends K, B extends V> void putAll(Map<A, B> t) { |
765 |
int n = t.size(); |
766 |
if (n == 0) |
767 |
return; |
768 |
|
769 |
// Expand enough to hold at least n elements without resizing. |
770 |
// We can only resize table by factor of two at a time. |
771 |
// It is faster to rehash with fewer elements, so do it now. |
772 |
for(;;) { |
773 |
Entry<K,V>[] tab; |
774 |
int max; |
775 |
synchronized(segments[0]) { // must synch on some segment. pick 0. |
776 |
tab = table; |
777 |
max = threshold * CONCURRENCY_LEVEL; |
778 |
} |
779 |
if (n < max) |
780 |
break; |
781 |
resize(0, tab); |
782 |
} |
783 |
|
784 |
for (Iterator<Map.Entry<A,B>> it = t.entrySet().iterator(); it.hasNext();) { |
785 |
Map.Entry<A,B> entry = (Map.Entry<A,B>) it.next(); |
786 |
put(entry.getKey(), entry.getValue()); |
787 |
} |
788 |
} |
789 |
|
790 |
/** |
791 |
* Removes all mappings from this map. |
792 |
*/ |
793 |
public void clear() { |
794 |
// We don't need all locks at once so long as locks |
795 |
// are obtained in low to high order |
796 |
for (int s = 0; s < segments.length; ++s) { |
797 |
Segment seg = segments[s]; |
798 |
synchronized(seg) { |
799 |
Entry<K,V>[] tab = table; |
800 |
for (int i = s; i < tab.length; i+= segments.length) { |
801 |
for (Entry<K,V> e = tab[i]; e != null; e = e.next) |
802 |
e.value = null; |
803 |
tab[i] = null; |
804 |
seg.count = 0; |
805 |
} |
806 |
} |
807 |
} |
808 |
} |
809 |
|
810 |
/** |
811 |
* Returns a shallow copy of this |
812 |
* <tt>ConcurrentHashMap</tt> instance: the keys and |
813 |
* values themselves are not cloned. |
814 |
* |
815 |
* @return a shallow copy of this map. |
816 |
*/ |
817 |
public Object clone() { |
818 |
// We cannot call super.clone, since it would share final segments array, |
819 |
// and there's no way to reassign finals. |
820 |
return new ConcurrentHashMap<K,V>(this); |
821 |
} |
822 |
|
823 |
// Views |
824 |
|
825 |
private transient Set<K> keySet = null; |
826 |
private transient Set<Map.Entry<K,V>> entrySet = null; |
827 |
private transient Collection<V> values = null; |
828 |
|
829 |
/** |
830 |
* Returns a set view of the keys contained in this map. The set is |
831 |
* backed by the map, so changes to the map are reflected in the set, and |
832 |
* vice-versa. The set supports element removal, which removes the |
833 |
* corresponding mapping from this map, via the <tt>Iterator.remove</tt>, |
834 |
* <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and |
835 |
* <tt>clear</tt> operations. It does not support the <tt>add</tt> or |
836 |
* <tt>addAll</tt> operations. |
837 |
* |
838 |
* @return a set view of the keys contained in this map. |
839 |
*/ |
840 |
public Set<K> keySet() { |
841 |
Set<K> ks = keySet; |
842 |
return (ks != null)? ks : (keySet = new KeySet()); |
843 |
} |
844 |
|
845 |
private class KeySet extends AbstractSet<K> { |
846 |
public Iterator<K> iterator() { |
847 |
return new KeyIterator(); |
848 |
} |
849 |
public int size() { |
850 |
return ConcurrentHashMap.this.size(); |
851 |
} |
852 |
public boolean contains(Object o) { |
853 |
return ConcurrentHashMap.this.containsKey(o); |
854 |
} |
855 |
public boolean remove(Object o) { |
856 |
return ConcurrentHashMap.this.remove(o) != null; |
857 |
} |
858 |
public void clear() { |
859 |
ConcurrentHashMap.this.clear(); |
860 |
} |
861 |
} |
862 |
|
863 |
/** |
864 |
* Returns a collection view of the values contained in this map. The |
865 |
* collection is backed by the map, so changes to the map are reflected in |
866 |
* the collection, and vice-versa. The collection supports element |
867 |
* removal, which removes the corresponding mapping from this map, via the |
868 |
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, |
869 |
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations. |
870 |
* It does not support the <tt>add</tt> or <tt>addAll</tt> operations. |
871 |
* |
872 |
* @return a collection view of the values contained in this map. |
873 |
*/ |
874 |
public Collection<V> values() { |
875 |
Collection<V> vs = values; |
876 |
return (vs != null)? vs : (values = new Values()); |
877 |
} |
878 |
|
879 |
private class Values extends AbstractCollection<V> { |
880 |
public Iterator<V> iterator() { |
881 |
return new ValueIterator(); |
882 |
} |
883 |
public int size() { |
884 |
return ConcurrentHashMap.this.size(); |
885 |
} |
886 |
public boolean contains(Object o) { |
887 |
return ConcurrentHashMap.this.containsValue(o); |
888 |
} |
889 |
public void clear() { |
890 |
ConcurrentHashMap.this.clear(); |
891 |
} |
892 |
} |
893 |
|
894 |
/** |
895 |
* Returns a collection view of the mappings contained in this map. Each |
896 |
* element in the returned collection is a <tt>Map.Entry</tt>. The |
897 |
* collection is backed by the map, so changes to the map are reflected in |
898 |
* the collection, and vice-versa. The collection supports element |
899 |
* removal, which removes the corresponding mapping from the map, via the |
900 |
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, |
901 |
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations. |
902 |
* It does not support the <tt>add</tt> or <tt>addAll</tt> operations. |
903 |
* |
904 |
* @return a collection view of the mappings contained in this map. |
905 |
*/ |
906 |
public Set<Map.Entry<K,V>> entrySet() { |
907 |
Set<Map.Entry<K,V>> es = entrySet; |
908 |
return (es != null) ? es : (entrySet = new EntrySet()); |
909 |
} |
910 |
|
911 |
private class EntrySet extends AbstractSet<Map.Entry<K,V>> { |
912 |
public Iterator<Map.Entry<K,V>> iterator() { |
913 |
return new EntryIterator(); |
914 |
} |
915 |
public boolean contains(Map.Entry<K,V> entry) { |
916 |
V v = ConcurrentHashMap.this.get(entry.getKey()); |
917 |
return v != null && v.equals(entry.getValue()); |
918 |
} |
919 |
public boolean remove(Map.Entry<K,V> e) { |
920 |
return ConcurrentHashMap.this.remove(e.getKey(), e.getValue()) != null; |
921 |
} |
922 |
public int size() { |
923 |
return ConcurrentHashMap.this.size(); |
924 |
} |
925 |
public void clear() { |
926 |
ConcurrentHashMap.this.clear(); |
927 |
} |
928 |
} |
929 |
|
930 |
/** |
931 |
* Returns an enumeration of the keys in this table. |
932 |
* |
933 |
* @return an enumeration of the keys in this table. |
934 |
* @see Enumeration |
935 |
* @see #elements() |
936 |
* @see #keySet() |
937 |
* @see Map |
938 |
*/ |
939 |
public Enumeration keys() { |
940 |
return new KeyIterator(); |
941 |
} |
942 |
|
943 |
/** |
944 |
* Returns an enumeration of the values in this table. |
945 |
* Use the Enumeration methods on the returned object to fetch the elements |
946 |
* sequentially. |
947 |
* |
948 |
* @return an enumeration of the values in this table. |
949 |
* @see java.util.Enumeration |
950 |
* @see #keys() |
951 |
* @see #values() |
952 |
* @see Map |
953 |
*/ |
954 |
public Enumeration elements() { |
955 |
return new ValueIterator(); |
956 |
} |
957 |
|
958 |
/** |
959 |
* ConcurrentHashMap collision list entry. |
960 |
*/ |
961 |
private static class Entry<K,V> implements Map.Entry<K,V> { |
962 |
/* |
963 |
The use of volatile for value field ensures that |
964 |
we can detect status changes without synchronization. |
965 |
The other fields are never changed, and are |
966 |
marked as final. |
967 |
*/ |
968 |
|
969 |
private final K key; |
970 |
private volatile V value; |
971 |
private final int hash; |
972 |
private final Entry<K,V> next; |
973 |
|
974 |
Entry(int hash, K key, V value, Entry<K,V> next) { |
975 |
this.value = value; |
976 |
this.hash = hash; |
977 |
this.key = key; |
978 |
this.next = next; |
979 |
} |
980 |
|
981 |
// Map.Entry Ops |
982 |
|
983 |
public K getKey() { |
984 |
return key; |
985 |
} |
986 |
|
987 |
/** |
988 |
* Get the value. Note: In an entrySet or entrySet.iterator, |
989 |
* unless you can guarantee lack of concurrent modification, |
990 |
* <tt>getValue</tt> <em>might</em> return null, reflecting the |
991 |
* fact that the entry has been concurrently removed. However, |
992 |
* there are no assurances that concurrent removals will be |
993 |
* reflected using this method. |
994 |
* |
995 |
* @return the current value, or null if the entry has been |
996 |
* detectably removed. |
997 |
**/ |
998 |
public V getValue() { |
999 |
return value; |
1000 |
} |
1001 |
|
1002 |
/** |
1003 |
* Set the value of this entry. Note: In an entrySet or |
1004 |
* entrySet.iterator), unless you can guarantee lack of concurrent |
1005 |
* modification, <tt>setValue</tt> is not strictly guaranteed to |
1006 |
* actually replace the value field obtained via the <tt>get</tt> |
1007 |
* operation of the underlying hash table in multithreaded |
1008 |
* applications. If iterator-wide synchronization is not used, |
1009 |
* and any other concurrent <tt>put</tt> or <tt>remove</tt> |
1010 |
* operations occur, sometimes even to <em>other</em> entries, |
1011 |
* then this change is not guaranteed to be reflected in the hash |
1012 |
* table. (It might, or it might not. There are no assurances |
1013 |
* either way.) |
1014 |
* |
1015 |
* @param value the new value. |
1016 |
* @return the previous value, or null if entry has been detectably |
1017 |
* removed. |
1018 |
* @exception NullPointerException if the value is <code>null</code>. |
1019 |
* |
1020 |
**/ |
1021 |
public V setValue(V value) { |
1022 |
if (value == null) |
1023 |
throw new NullPointerException(); |
1024 |
V oldValue = this.value; |
1025 |
this.value = value; |
1026 |
return oldValue; |
1027 |
} |
1028 |
|
1029 |
public boolean equals(Object o) { |
1030 |
if (!(o instanceof Map.Entry)) |
1031 |
return false; |
1032 |
Map.Entry e = (Map.Entry)o; |
1033 |
return (key.equals(e.getKey()) && value.equals(e.getValue())); |
1034 |
} |
1035 |
|
1036 |
public int hashCode() { |
1037 |
return key.hashCode() ^ value.hashCode(); |
1038 |
} |
1039 |
|
1040 |
public String toString() { |
1041 |
return key + "=" + value; |
1042 |
} |
1043 |
|
1044 |
} |
1045 |
|
1046 |
private abstract class HashIterator<T> implements Iterator<T>, Enumeration { |
1047 |
private final Entry<K,V>[] tab; // snapshot of table |
1048 |
private int index; // current slot |
1049 |
Entry<K,V> entry = null; // current node of slot |
1050 |
K currentKey; // key for current node |
1051 |
V currentValue; // value for current node |
1052 |
private Entry lastReturned = null; // last node returned by next |
1053 |
|
1054 |
private HashIterator() { |
1055 |
// force all segments to synch |
1056 |
synchronized(segments[0]) { tab = table; } |
1057 |
for (int i = 1; i < segments.length; ++i) segments[i].synch(); |
1058 |
index = tab.length - 1; |
1059 |
} |
1060 |
|
1061 |
public boolean hasMoreElements() { return hasNext(); } |
1062 |
public Object nextElement() { return next(); } |
1063 |
|
1064 |
public boolean hasNext() { |
1065 |
/* |
1066 |
currentkey and currentValue are set here to ensure that next() |
1067 |
returns normally if hasNext() returns true. This avoids |
1068 |
surprises especially when final element is removed during |
1069 |
traversal -- instead, we just ignore the removal during |
1070 |
current traversal. |
1071 |
*/ |
1072 |
|
1073 |
while (true) { |
1074 |
if (entry != null) { |
1075 |
V v = entry.value; |
1076 |
if (v != null) { |
1077 |
currentKey = entry.key; |
1078 |
currentValue = v; |
1079 |
return true; |
1080 |
} |
1081 |
else |
1082 |
entry = entry.next; |
1083 |
} |
1084 |
|
1085 |
while (entry == null && index >= 0) |
1086 |
entry = tab[index--]; |
1087 |
|
1088 |
if (entry == null) { |
1089 |
currentKey = null; |
1090 |
currentValue = null; |
1091 |
return false; |
1092 |
} |
1093 |
} |
1094 |
} |
1095 |
|
1096 |
abstract T returnValueOfNext(); |
1097 |
|
1098 |
public T next() { |
1099 |
if (currentKey == null && !hasNext()) |
1100 |
throw new NoSuchElementException(); |
1101 |
|
1102 |
T result = returnValueOfNext(); |
1103 |
lastReturned = entry; |
1104 |
currentKey = null; |
1105 |
currentValue = null; |
1106 |
entry = entry.next; |
1107 |
return result; |
1108 |
} |
1109 |
|
1110 |
public void remove() { |
1111 |
if (lastReturned == null) |
1112 |
throw new IllegalStateException(); |
1113 |
ConcurrentHashMap.this.remove(lastReturned.key); |
1114 |
lastReturned = null; |
1115 |
} |
1116 |
|
1117 |
} |
1118 |
|
1119 |
private class KeyIterator extends HashIterator<K> { |
1120 |
K returnValueOfNext() { return currentKey; } |
1121 |
public K next() { return super.next(); } |
1122 |
} |
1123 |
|
1124 |
private class ValueIterator extends HashIterator<V> { |
1125 |
V returnValueOfNext() { return currentValue; } |
1126 |
public V next() { return super.next(); } |
1127 |
} |
1128 |
|
1129 |
private class EntryIterator extends HashIterator<Map.Entry<K,V>> { |
1130 |
Map.Entry<K,V> returnValueOfNext() { return entry; } |
1131 |
public Map.Entry<K,V> next() { return super.next(); } |
1132 |
} |
1133 |
|
1134 |
/** |
1135 |
* Save the state of the <tt>ConcurrentHashMap</tt> |
1136 |
* instance to a stream (i.e., |
1137 |
* serialize it). |
1138 |
* |
1139 |
* @serialData |
1140 |
* An estimate of the table size, followed by |
1141 |
* the key (Object) and value (Object) |
1142 |
* for each key-value mapping, followed by a null pair. |
1143 |
* The key-value mappings are emitted in no particular order. |
1144 |
*/ |
1145 |
private void writeObject(java.io.ObjectOutputStream s) throws IOException { |
1146 |
// Write out the loadfactor, and any hidden stuff |
1147 |
s.defaultWriteObject(); |
1148 |
|
1149 |
// Write out capacity estimate. It is OK if this |
1150 |
// changes during the write, since it is only used by |
1151 |
// readObject to set initial capacity, to avoid needless resizings. |
1152 |
|
1153 |
int cap; |
1154 |
synchronized(segments[0]) { cap = table.length; } |
1155 |
s.writeInt(cap); |
1156 |
|
1157 |
// Write out keys and values (alternating) |
1158 |
for (int k = 0; k < segments.length; ++k) { |
1159 |
Segment seg = segments[k]; |
1160 |
Entry[] tab; |
1161 |
synchronized(seg) { tab = table; } |
1162 |
for (int i = k; i < tab.length; i+= segments.length) { |
1163 |
for (Entry e = tab[i]; e != null; e = e.next) { |
1164 |
s.writeObject(e.key); |
1165 |
s.writeObject(e.value); |
1166 |
} |
1167 |
} |
1168 |
} |
1169 |
|
1170 |
s.writeObject(null); |
1171 |
s.writeObject(null); |
1172 |
} |
1173 |
|
1174 |
/** |
1175 |
* Reconstitute the <tt>ConcurrentHashMap</tt> |
1176 |
* instance from a stream (i.e., |
1177 |
* deserialize it). |
1178 |
*/ |
1179 |
private void readObject(java.io.ObjectInputStream s) |
1180 |
throws IOException, ClassNotFoundException { |
1181 |
|
1182 |
// Read in the threshold, loadfactor, and any hidden stuff |
1183 |
s.defaultReadObject(); |
1184 |
|
1185 |
int cap = s.readInt(); |
1186 |
table = newTable(cap); |
1187 |
for (int i = 0; i < segments.length; ++i) |
1188 |
segments[i] = new Segment(); |
1189 |
|
1190 |
|
1191 |
// Read the keys and values, and put the mappings in the table |
1192 |
while (true) { |
1193 |
K key = (K) s.readObject(); |
1194 |
V value = (V) s.readObject(); |
1195 |
if (key == null) |
1196 |
break; |
1197 |
put(key, value); |
1198 |
} |
1199 |
} |
1200 |
} |