--- /dev/null
+/*\r
+ * Written by Cliff Click and released to the public domain, as explained at\r
+ * http://creativecommons.org/licenses/publicdomain\r
+ */\r
+\r
+package org.cliffc.high_scale_lib;\r
+import java.io.IOException;\r
+import java.io.Serializable;\r
+import java.lang.reflect.Field;\r
+import java.util.*;\r
+import java.util.concurrent.ConcurrentMap;\r
+import java.util.concurrent.atomic.*;\r
+import sun.misc.Unsafe;\r
+\r
+/**\r
+ * A lock-free alternate implementation of {@link java.util.concurrent.ConcurrentHashMap}\r
+ * with better scaling properties and generally lower costs to mutate the Map.\r
+ * It provides identical correctness properties as ConcurrentHashMap. All\r
+ * operations are non-blocking and multi-thread safe, including all update\r
+ * operations. {@link NonBlockingHashMap} scales substatially better than\r
+ * {@link java.util.concurrent.ConcurrentHashMap} for high update rates, even with a\r
+ * large concurrency factor. Scaling is linear up to 768 CPUs on a 768-CPU\r
+ * Azul box, even with 100% updates or 100% reads or any fraction in-between.\r
+ * Linear scaling up to all cpus has been observed on a 32-way Sun US2 box,\r
+ * 32-way Sun Niagra box, 8-way Intel box and a 4-way Power box.\r
+ *\r
+ * This class obeys the same functional specification as {@link\r
+ * java.util.Hashtable}, and includes versions of methods corresponding to\r
+ * each method of <tt>Hashtable</tt>. However, even though all operations are\r
+ * thread-safe, operations do <em>not</em> entail locking and there is\r
+ * <em>not</em> any support for locking the entire table in a way that\r
+ * prevents all access. This class is fully interoperable with\r
+ * <tt>Hashtable</tt> in programs that rely on its thread safety but not on\r
+ * its synchronization details.\r
+ *\r
+ * <p> Operations (including <tt>put</tt>) generally do not block, so may\r
+ * overlap with other update operations (including other <tt>puts</tt> and\r
+ * <tt>removes</tt>). Retrievals reflect the results of the most recently\r
+ * <em>completed</em> update operations holding upon their onset. For\r
+ * aggregate operations such as <tt>putAll</tt>, concurrent retrievals may\r
+ * reflect insertion or removal of only some entries. Similarly, Iterators\r
+ * and Enumerations return elements reflecting the state of the hash table at\r
+ * some point at or since the creation of the iterator/enumeration. They do\r
+ * <em>not</em> throw {@link ConcurrentModificationException}. However,\r
+ * iterators are designed to be used by only one thread at a time.\r
+ *\r
+ * <p> Very full tables, or tables with high reprobe rates may trigger an\r
+ * internal resize operation to move into a larger table. Resizing is not\r
+ * terribly expensive, but it is not free either; during resize operations\r
+ * table throughput may drop somewhat. All threads that visit the table\r
+ * during a resize will 'help' the resizing but will still be allowed to\r
+ * complete their operation before the resize is finished (i.e., a simple\r
+ * 'get' operation on a million-entry table undergoing resizing will not need\r
+ * to block until the entire million entries are copied).\r
+ *\r
+ * <p>This class and its views and iterators implement all of the\r
+ * <em>optional</em> methods of the {@link Map} and {@link Iterator}\r
+ * interfaces.\r
+ *\r
+ * <p> Like {@link Hashtable} but unlike {@link HashMap}, this class\r
+ * does <em>not</em> allow <tt>null</tt> to be used as a key or value.\r
+ *\r
+ *\r
+ * @since 1.5\r
+ * @author Cliff Click\r
+ * @param <TypeK> the type of keys maintained by this map\r
+ * @param <TypeV> the type of mapped values\r
+ *\r
+ * @version 1.1.2\r
+ * @author Prashant Deva - moved hash() function out of get_impl() so it is\r
+ * not calculated multiple times.\r
+ */\r
+\r
+public class NonBlockingHashMap<TypeK, TypeV>\r
+ extends AbstractMap<TypeK, TypeV>\r
+ implements ConcurrentMap<TypeK, TypeV>, Cloneable, Serializable {\r
+\r
+ private static final long serialVersionUID = 1234123412341234123L;\r
+\r
+ private static final int REPROBE_LIMIT=10; // Too many reprobes then force a table-resize\r
+\r
+ // --- Bits to allow Unsafe access to arrays\r
+ private static final Unsafe _unsafe = UtilUnsafe.getUnsafe();\r
+ private static final int _Obase = _unsafe.arrayBaseOffset(Object[].class);\r
+ private static final int _Oscale = _unsafe.arrayIndexScale(Object[].class);\r
+ private static long rawIndex(final Object[] ary, final int idx) {\r
+ assert idx >= 0 && idx < ary.length;\r
+ return _Obase + idx * _Oscale;\r
+ }\r
+\r
+ // --- Setup to use Unsafe\r
+ private static final long _kvs_offset;\r
+ static { // <clinit>\r
+ Field f = null;\r
+ try { f = NonBlockingHashMap.class.getDeclaredField("_kvs"); }\r
+ catch( java.lang.NoSuchFieldException e ) { throw new RuntimeException(e); }\r
+ _kvs_offset = _unsafe.objectFieldOffset(f);\r
+ }\r
+ private final boolean CAS_kvs( final Object[] oldkvs, final Object[] newkvs ) {\r
+ return _unsafe.compareAndSwapObject(this, _kvs_offset, oldkvs, newkvs );\r
+ }\r
+\r
+ // --- Adding a 'prime' bit onto Values via wrapping with a junk wrapper class\r
+ private static final class Prime {\r
+ final Object _V;\r
+ Prime( Object V ) { _V = V; }\r
+ static Object unbox( Object V ) { return V instanceof Prime ? ((Prime)V)._V : V; }\r
+ }\r
+\r
+ // --- hash ----------------------------------------------------------------\r
+ // Helper function to spread lousy hashCodes\r
+ private static final int hash(final Object key) {\r
+ int h = key.hashCode(); // The real hashCode call\r
+ // Spread bits to regularize both segment and index locations,\r
+ // using variant of single-word Wang/Jenkins hash.\r
+ h += (h << 15) ^ 0xffffcd7d;\r
+ h ^= (h >>> 10);\r
+ h += (h << 3);\r
+ h ^= (h >>> 6);\r
+ h += (h << 2) + (h << 14);\r
+ return h ^ (h >>> 16);\r
+ }\r
+\r
+ // --- The Hash Table --------------------\r
+ // Slot 0 is always used for a 'CHM' entry below to hold the interesting\r
+ // bits of the hash table. Slot 1 holds full hashes as an array of ints.\r
+ // Slots {2,3}, {4,5}, etc hold {Key,Value} pairs. The entire hash table\r
+ // can be atomically replaced by CASing the _kvs field.\r
+ //\r
+ // Why is CHM buried inside the _kvs Object array, instead of the other way\r
+ // around? The CHM info is used during resize events and updates, but not\r
+ // during standard 'get' operations. I assume 'get' is much more frequent\r
+ // than 'put'. 'get' can skip the extra indirection of skipping through the\r
+ // CHM to reach the _kvs array.\r
+ private transient Object[] _kvs;\r
+ private static final CHM chm (Object[] kvs) { return (CHM )kvs[0]; }\r
+ private static final int[] hashes(Object[] kvs) { return (int[])kvs[1]; }\r
+ // Number of K,V pairs in the table\r
+ private static final int len(Object[] kvs) { return (kvs.length-2)>>1; }\r
+\r
+ // Time since last resize\r
+ private transient long _last_resize_milli;\r
+\r
+ // --- Minimum table size ----------------\r
+ // Pick size 8 K/V pairs, which turns into (8*2+2)*4+12 = 84 bytes on a\r
+ // standard 32-bit HotSpot, and (8*2+2)*8+12 = 156 bytes on 64-bit Azul.\r
+ private static final int MIN_SIZE_LOG=3; //\r
+ private static final int MIN_SIZE=(1<<MIN_SIZE_LOG); // Must be power of 2\r
+\r
+ // --- Sentinels -------------------------\r
+ // No-Match-Old - putIfMatch does updates only if it matches the old value,\r
+ // and NO_MATCH_OLD basically counts as a wildcard match.\r
+ private static final Object NO_MATCH_OLD = new Object(); // Sentinel\r
+ // Match-Any-not-null - putIfMatch does updates only if it find a real old\r
+ // value.\r
+ private static final Object MATCH_ANY = new Object(); // Sentinel\r
+ // This K/V pair has been deleted (but the Key slot is forever claimed).\r
+ // The same Key can be reinserted with a new value later.\r
+ private static final Object TOMBSTONE = new Object();\r
+ // Prime'd or box'd version of TOMBSTONE. This K/V pair was deleted, then a\r
+ // table resize started. The K/V pair has been marked so that no new\r
+ // updates can happen to the old table (and since the K/V pair was deleted\r
+ // nothing was copied to the new table).\r
+ private static final Prime TOMBPRIME = new Prime(TOMBSTONE);\r
+\r
+ // --- key,val -------------------------------------------------------------\r
+ // Access K,V for a given idx\r
+ //\r
+ // Note that these are static, so that the caller is forced to read the _kvs\r
+ // field only once, and share that read across all key/val calls - lest the\r
+ // _kvs field move out from under us and back-to-back key & val calls refer\r
+ // to different _kvs arrays.\r
+ private static final Object key(Object[] kvs,int idx) { return kvs[(idx<<1)+2]; }\r
+ private static final Object val(Object[] kvs,int idx) { return kvs[(idx<<1)+3]; }\r
+ private static final boolean CAS_key( Object[] kvs, int idx, Object old, Object key ) {\r
+ return _unsafe.compareAndSwapObject( kvs, rawIndex(kvs,(idx<<1)+2), old, key );\r
+ }\r
+ private static final boolean CAS_val( Object[] kvs, int idx, Object old, Object val ) {\r
+ return _unsafe.compareAndSwapObject( kvs, rawIndex(kvs,(idx<<1)+3), old, val );\r
+ }\r
+\r
+\r
+ // --- dump ----------------------------------------------------------------\r
+ /** Verbose printout of table internals, useful for debugging. */\r
+ public final void print() {\r
+ System.out.println("=========");\r
+ print2(_kvs);\r
+ System.out.println("=========");\r
+ }\r
+ // print the entire state of the table\r
+ private final void print( Object[] kvs ) {\r
+ for( int i=0; i<len(kvs); i++ ) {\r
+ Object K = key(kvs,i);\r
+ if( K != null ) {\r
+ String KS = (K == TOMBSTONE) ? "XXX" : K.toString();\r
+ Object V = val(kvs,i);\r
+ Object U = Prime.unbox(V);\r
+ String p = (V==U) ? "" : "prime_";\r
+ String US = (U == TOMBSTONE) ? "tombstone" : U.toString();\r
+ System.out.println(""+i+" ("+KS+","+p+US+")");\r
+ }\r
+ }\r
+ Object[] newkvs = chm(kvs)._newkvs; // New table, if any\r
+ if( newkvs != null ) {\r
+ System.out.println("----");\r
+ print(newkvs);\r
+ }\r
+ }\r
+ // print only the live values, broken down by the table they are in\r
+ private final void print2( Object[] kvs) {\r
+ for( int i=0; i<len(kvs); i++ ) {\r
+ Object key = key(kvs,i);\r
+ Object val = val(kvs,i);\r
+ Object U = Prime.unbox(val);\r
+ if( key != null && key != TOMBSTONE && // key is sane\r
+ val != null && U != TOMBSTONE ) { // val is sane\r
+ String p = (val==U) ? "" : "prime_";\r
+ System.out.println(""+i+" ("+key+","+p+val+")");\r
+ }\r
+ }\r
+ Object[] newkvs = chm(kvs)._newkvs; // New table, if any\r
+ if( newkvs != null ) {\r
+ System.out.println("----");\r
+ print2(newkvs);\r
+ }\r
+ }\r
+\r
+ // Count of reprobes\r
+ private transient Counter _reprobes = new Counter();\r
+ /** Get and clear the current count of reprobes. Reprobes happen on key\r
+ * collisions, and a high reprobe rate may indicate a poor hash function or\r
+ * weaknesses in the table resizing function.\r
+ * @return the count of reprobes since the last call to {@link #reprobes}\r
+ * or since the table was created. */\r
+ public long reprobes() { long r = _reprobes.get(); _reprobes = new Counter(); return r; }\r
+\r
+\r
+ // --- reprobe_limit -----------------------------------------------------\r
+ // Heuristic to decide if we have reprobed toooo many times. Running over\r
+ // the reprobe limit on a 'get' call acts as a 'miss'; on a 'put' call it\r
+ // can trigger a table resize. Several places must have exact agreement on\r
+ // what the reprobe_limit is, so we share it here.\r
+ private static final int reprobe_limit( int len ) {\r
+ return REPROBE_LIMIT + (len>>2);\r
+ }\r
+\r
+ // --- NonBlockingHashMap --------------------------------------------------\r
+ // Constructors\r
+\r
+ /** Create a new NonBlockingHashMap with default minimum size (currently set\r
+ * to 8 K/V pairs or roughly 84 bytes on a standard 32-bit JVM). */\r
+ public NonBlockingHashMap( ) { this(MIN_SIZE); }\r
+\r
+ /** Create a new NonBlockingHashMap with initial room for the given number of\r
+ * elements, thus avoiding internal resizing operations to reach an\r
+ * appropriate size. Large numbers here when used with a small count of\r
+ * elements will sacrifice space for a small amount of time gained. The\r
+ * initial size will be rounded up internally to the next larger power of 2. */\r
+ public NonBlockingHashMap( final int initial_sz ) { initialize(initial_sz); }\r
+ private final void initialize( int initial_sz ) {\r
+ if( initial_sz < 0 ) throw new IllegalArgumentException();\r
+ int i; // Convert to next largest power-of-2\r
+ if( initial_sz > 1024*1024 ) initial_sz = 1024*1024;\r
+ for( i=MIN_SIZE_LOG; (1<<i) < (initial_sz<<2); i++ ) ;\r
+ // Double size for K,V pairs, add 1 for CHM and 1 for hashes\r
+ _kvs = new Object[((1<<i)<<1)+2];\r
+ _kvs[0] = new CHM(new Counter()); // CHM in slot 0\r
+ _kvs[1] = new int[1<<i]; // Matching hash entries\r
+ _last_resize_milli = System.currentTimeMillis();\r
+ }\r
+ // Version for subclassed readObject calls, to be called after the defaultReadObject\r
+ protected final void initialize() { initialize(MIN_SIZE); }\r
+\r
+ // --- wrappers ------------------------------------------------------------\r
+\r
+ /** Returns the number of key-value mappings in this map.\r
+ * @return the number of key-value mappings in this map */\r
+ @Override \r
+ public int size ( ) { return chm(_kvs).size(); }\r
+ /** Returns <tt>size() == 0</tt>.\r
+ * @return <tt>size() == 0</tt> */\r
+ @Override \r
+ public boolean isEmpty ( ) { return size() == 0; }\r
+\r
+ /** Tests if the key in the table using the <tt>equals</tt> method.\r
+ * @return <tt>true</tt> if the key is in the table using the <tt>equals</tt> method\r
+ * @throws NullPointerException if the specified key is null */\r
+ @Override \r
+ public boolean containsKey( Object key ) { return get(key) != null; }\r
+\r
+ /** Legacy method testing if some key maps into the specified value in this\r
+ * table. This method is identical in functionality to {@link\r
+ * #containsValue}, and exists solely to ensure full compatibility with\r
+ * class {@link java.util.Hashtable}, which supported this method prior to\r
+ * introduction of the Java Collections framework.\r
+ * @param val a value to search for\r
+ * @return <tt>true</tt> if this map maps one or more keys to the specified value\r
+ * @throws NullPointerException if the specified value is null */\r
+ public boolean contains ( Object val ) { return containsValue(val); }\r
+\r
+ /** Maps the specified key to the specified value in the table. Neither key\r
+ * nor value can be null.\r
+ * <p> The value can be retrieved by calling {@link #get} with a key that is\r
+ * equal to the original key.\r
+ * @param key key with which the specified value is to be associated\r
+ * @param val value to be associated with the specified key\r
+ * @return the previous value associated with <tt>key</tt>, or\r
+ * <tt>null</tt> if there was no mapping for <tt>key</tt>\r
+ * @throws NullPointerException if the specified key or value is null */\r
+ @Override\r
+ public TypeV put ( TypeK key, TypeV val ) { return putIfMatch( key, val, NO_MATCH_OLD); }\r
+\r
+ /** Atomically, do a {@link #put} if-and-only-if the key is not mapped.\r
+ * Useful to ensure that only a single mapping for the key exists, even if\r
+ * many threads are trying to create the mapping in parallel.\r
+ * @return the previous value associated with the specified key,\r
+ * or <tt>null</tt> if there was no mapping for the key\r
+ * @throws NullPointerException if the specified key or value is null */\r
+ public TypeV putIfAbsent( TypeK key, TypeV val ) { return putIfMatch( key, val, TOMBSTONE ); }\r
+\r
+ /** Removes the key (and its corresponding value) from this map.\r
+ * This method does nothing if the key is not in the map.\r
+ * @return the previous value associated with <tt>key</tt>, or\r
+ * <tt>null</tt> if there was no mapping for <tt>key</tt>\r
+ * @throws NullPointerException if the specified key is null */\r
+ @Override\r
+ public TypeV remove ( Object key ) { return putIfMatch( key,TOMBSTONE, NO_MATCH_OLD); }\r
+\r
+ /** Atomically do a {@link #remove(Object)} if-and-only-if the key is mapped\r
+ * to a value which is <code>equals</code> to the given value.\r
+ * @throws NullPointerException if the specified key or value is null */\r
+ public boolean remove ( Object key,Object val ) { return putIfMatch( key,TOMBSTONE, val ) == val; }\r
+\r
+ /** Atomically do a <code>put(key,val)</code> if-and-only-if the key is\r
+ * mapped to some value already.\r
+ * @throws NullPointerException if the specified key or value is null */\r
+ public TypeV replace ( TypeK key, TypeV val ) { return putIfMatch( key, val,MATCH_ANY ); }\r
+\r
+ /** Atomically do a <code>put(key,newValue)</code> if-and-only-if the key is\r
+ * mapped a value which is <code>equals</code> to <code>oldValue</code>.\r
+ * @throws NullPointerException if the specified key or value is null */\r
+ public boolean replace ( TypeK key, TypeV oldValue, TypeV newValue ) {\r
+ return putIfMatch( key, newValue, oldValue ) == oldValue;\r
+ }\r
+\r
+ private final TypeV putIfMatch( Object key, Object newVal, Object oldVal ) {\r
+ if (oldVal == null || newVal == null) throw new NullPointerException();\r
+ final Object res = putIfMatch( this, _kvs, key, newVal, oldVal );\r
+ assert !(res instanceof Prime);\r
+ assert res != null;\r
+ return res == TOMBSTONE ? null : (TypeV)res;\r
+ }\r
+\r
+\r
+ /** Copies all of the mappings from the specified map to this one, replacing\r
+ * any existing mappings.\r
+ * @param m mappings to be stored in this map */\r
+ @Override\r
+ public void putAll(Map<? extends TypeK, ? extends TypeV> m) {\r
+ for (Map.Entry<? extends TypeK, ? extends TypeV> e : m.entrySet())\r
+ put(e.getKey(), e.getValue());\r
+ }\r
+\r
+ /** Removes all of the mappings from this map. */\r
+ @Override\r
+ public void clear() { // Smack a new empty table down\r
+ Object[] newkvs = new NonBlockingHashMap(MIN_SIZE)._kvs;\r
+ while( !CAS_kvs(_kvs,newkvs) ) // Spin until the clear works\r
+ ;\r
+ }\r
+\r
+ /** Returns <tt>true</tt> if this Map maps one or more keys to the specified\r
+ * value. <em>Note</em>: This method requires a full internal traversal of the\r
+ * hash table and is much slower than {@link #containsKey}.\r
+ * @param val value whose presence in this map is to be tested\r
+ * @return <tt>true</tt> if this map maps one or more keys to the specified value\r
+ * @throws NullPointerException if the specified value is null */\r
+ @Override\r
+ public boolean containsValue( final Object val ) {\r
+ if( val == null ) throw new NullPointerException();\r
+ for( TypeV V : values() )\r
+ if( V == val || V.equals(val) )\r
+ return true;\r
+ return false;\r
+ }\r
+\r
+ // This function is supposed to do something for Hashtable, and the JCK\r
+ // tests hang until it gets called... by somebody ... for some reason,\r
+ // any reason....\r
+ protected void rehash() {\r
+ }\r
+\r
+ /**\r
+ * Creates a shallow copy of this hashtable. All the structure of the\r
+ * hashtable itself is copied, but the keys and values are not cloned.\r
+ * This is a relatively expensive operation.\r
+ *\r
+ * @return a clone of the hashtable.\r
+ */\r
+ @Override\r
+ public Object clone() {\r
+ try {\r
+ // Must clone, to get the class right; NBHM might have been\r
+ // extended so it would be wrong to just make a new NBHM.\r
+ NonBlockingHashMap<TypeK,TypeV> t = (NonBlockingHashMap<TypeK,TypeV>) super.clone();\r
+ // But I don't have an atomic clone operation - the underlying _kvs\r
+ // structure is undergoing rapid change. If I just clone the _kvs\r
+ // field, the CHM in _kvs[0] won't be in sync.\r
+ //\r
+ // Wipe out the cloned array (it was shallow anyways).\r
+ t.clear();\r
+ // Now copy sanely\r
+ for( TypeK K : keySet() ) {\r
+ final TypeV V = get(K); // Do an official 'get'\r
+ t.put(K,V);\r
+ }\r
+ return t;\r
+ } catch (CloneNotSupportedException e) {\r
+ // this shouldn't happen, since we are Cloneable\r
+ throw new InternalError();\r
+ }\r
+ }\r
+\r
+ /**\r
+ * Returns a string representation of this map. The string representation\r
+ * consists of a list of key-value mappings in the order returned by the\r
+ * map's <tt>entrySet</tt> view's iterator, enclosed in braces\r
+ * (<tt>"{}"</tt>). Adjacent mappings are separated by the characters\r
+ * <tt>", "</tt> (comma and space). Each key-value mapping is rendered as\r
+ * the key followed by an equals sign (<tt>"="</tt>) followed by the\r
+ * associated value. Keys and values are converted to strings as by\r
+ * {@link String#valueOf(Object)}.\r
+ *\r
+ * @return a string representation of this map\r
+ */\r
+ @Override\r
+ public String toString() {\r
+ Iterator<Entry<TypeK,TypeV>> i = entrySet().iterator();\r
+ if( !i.hasNext())\r
+ return "{}";\r
+\r
+ StringBuilder sb = new StringBuilder();\r
+ sb.append('{');\r
+ for (;;) {\r
+ Entry<TypeK,TypeV> e = i.next();\r
+ TypeK key = e.getKey();\r
+ TypeV value = e.getValue();\r
+ sb.append(key == this ? "(this Map)" : key);\r
+ sb.append('=');\r
+ sb.append(value == this ? "(this Map)" : value);\r
+ if( !i.hasNext())\r
+ return sb.append('}').toString();\r
+ sb.append(", ");\r
+ }\r
+ }\r
+\r
+ // --- keyeq ---------------------------------------------------------------\r
+ // Check for key equality. Try direct pointer compare first, then see if\r
+ // the hashes are unequal (fast negative test) and finally do the full-on\r
+ // 'equals' v-call.\r
+ private static boolean keyeq( Object K, Object key, int[] hashes, int hash, int fullhash ) {\r
+ return\r
+ K==key || // Either keys match exactly OR\r
+ // hash exists and matches? hash can be zero during the install of a\r
+ // new key/value pair.\r
+ ((hashes[hash] == 0 || hashes[hash] == fullhash) &&\r
+ // Do not call the users' "equals()" call with a Tombstone, as this can\r
+ // surprise poorly written "equals()" calls that throw exceptions\r
+ // instead of simply returning false.\r
+ K != TOMBSTONE && // Do not call users' equals call with a Tombstone\r
+ // Do the match the hard way - with the users' key being the loop-\r
+ // invariant "this" pointer. I could have flipped the order of\r
+ // operands (since equals is commutative), but I'm making mega-morphic\r
+ // v-calls in a reprobing loop and nailing down the 'this' argument\r
+ // gives both the JIT and the hardware a chance to prefetch the call target.\r
+ key.equals(K)); // Finally do the hard match\r
+ }\r
+\r
+ // --- get -----------------------------------------------------------------\r
+ /** Returns the value to which the specified key is mapped, or {@code null}\r
+ * if this map contains no mapping for the key.\r
+ * <p>More formally, if this map contains a mapping from a key {@code k} to\r
+ * a value {@code v} such that {@code key.equals(k)}, then this method\r
+ * returns {@code v}; otherwise it returns {@code null}. (There can be at\r
+ * most one such mapping.)\r
+ * @throws NullPointerException if the specified key is null */\r
+ // Never returns a Prime nor a Tombstone.\r
+ @Override\r
+ public TypeV get( Object key ) {\r
+ final int fullhash= hash (key); // throws NullPointerException if key is null\r
+ final Object V = get_impl(this,_kvs,key,fullhash);\r
+ assert !(V instanceof Prime); // Never return a Prime\r
+ return (TypeV)V;\r
+ }\r
+\r
+ private static final Object get_impl( final NonBlockingHashMap topmap, final Object[] kvs, final Object key, final int fullhash ) {\r
+ final int len = len (kvs); // Count of key/value pairs, reads kvs.length\r
+ final CHM chm = chm (kvs); // The CHM, for a volatile read below; reads slot 0 of kvs\r
+ final int[] hashes=hashes(kvs); // The memoized hashes; reads slot 1 of kvs\r
+\r
+ int idx = fullhash & (len-1); // First key hash\r
+\r
+ // Main spin/reprobe loop, looking for a Key hit\r
+ int reprobe_cnt=0;\r
+ while( true ) {\r
+ // Probe table. Each read of 'val' probably misses in cache in a big\r
+ // table; hopefully the read of 'key' then hits in cache.\r
+ final Object K = key(kvs,idx); // Get key before volatile read, could be null\r
+ final Object V = val(kvs,idx); // Get value before volatile read, could be null or Tombstone or Prime\r
+ if( K == null ) return null; // A clear miss\r
+\r
+ // We need a volatile-read here to preserve happens-before semantics on\r
+ // newly inserted Keys. If the Key body was written just before inserting\r
+ // into the table a Key-compare here might read the uninitalized Key body.\r
+ // Annoyingly this means we have to volatile-read before EACH key compare.\r
+ // .\r
+ // We also need a volatile-read between reading a newly inserted Value\r
+ // and returning the Value (so the user might end up reading the stale\r
+ // Value contents). Same problem as with keys - and the one volatile\r
+ // read covers both.\r
+ final Object[] newkvs = chm._newkvs; // VOLATILE READ before key compare\r
+\r
+ // Key-compare\r
+ if( keyeq(K,key,hashes,idx,fullhash) ) {\r
+ // Key hit! Check for no table-copy-in-progress\r
+ if( !(V instanceof Prime) ) // No copy?\r
+ return (V == TOMBSTONE) ? null : V; // Return the value\r
+ // Key hit - but slot is (possibly partially) copied to the new table.\r
+ // Finish the copy & retry in the new table.\r
+ return get_impl(topmap,chm.copy_slot_and_check(topmap,kvs,idx,key),key,fullhash); // Retry in the new table\r
+ }\r
+ // get and put must have the same key lookup logic! But only 'put'\r
+ // needs to force a table-resize for a too-long key-reprobe sequence.\r
+ // Check for too-many-reprobes on get - and flip to the new table.\r
+ // ???? Why a TOMBSTONE key means no more keys in this table\r
+ // because a TOMBSTONE key should be null before\r
+ if( ++reprobe_cnt >= reprobe_limit(len) || // too many probes\r
+ key == TOMBSTONE ) // found a TOMBSTONE key, means no more keys in this table\r
+ return newkvs == null ? null : get_impl(topmap,topmap.help_copy(newkvs),key,fullhash); // Retry in the new table\r
+\r
+ idx = (idx+1)&(len-1); // Reprobe by 1! (could now prefetch)\r
+ }\r
+ }\r
+\r
+ // --- putIfMatch ---------------------------------------------------------\r
+ // Put, Remove, PutIfAbsent, etc. Return the old value. If the returned\r
+ // value is equal to expVal (or expVal is NO_MATCH_OLD) then the put can be\r
+ // assumed to work (although might have been immediately overwritten). Only\r
+ // the path through copy_slot passes in an expected value of null, and\r
+ // putIfMatch only returns a null if passed in an expected null.\r
+ private static final Object putIfMatch( final NonBlockingHashMap topmap, final Object[] kvs, final Object key, final Object putval, final Object expVal ) {\r
+ assert putval != null;\r
+ assert !(putval instanceof Prime);\r
+ assert !(expVal instanceof Prime);\r
+ final int fullhash = hash (key); // throws NullPointerException if key null\r
+ final int len = len (kvs); // Count of key/value pairs, reads kvs.length\r
+ final CHM chm = chm (kvs); // Reads kvs[0]\r
+ final int[] hashes = hashes(kvs); // Reads kvs[1], read before kvs[0]\r
+ int idx = fullhash & (len-1);\r
+\r
+ // ---\r
+ // Key-Claim stanza: spin till we can claim a Key (or force a resizing).\r
+ int reprobe_cnt=0;\r
+ Object K=null, V=null;\r
+ Object[] newkvs=null;\r
+ while( true ) { // Spin till we get a Key slot\r
+ V = val(kvs,idx); // Get old value (before volatile read below!)\r
+ K = key(kvs,idx); // Get current key\r
+ if( K == null ) { // Slot is free?\r
+ // Found an empty Key slot - which means this Key has never been in\r
+ // this table. No need to put a Tombstone - the Key is not here!\r
+ if( putval == TOMBSTONE ) return putval; // Not-now & never-been in this table\r
+ // Claim the null key-slot\r
+ if( CAS_key(kvs,idx, null, key ) ) { // Claim slot for Key\r
+ chm._slots.add(1); // Raise key-slots-used count\r
+ hashes[idx] = fullhash; // Memoize fullhash\r
+ break; // Got it!\r
+ }\r
+ // CAS to claim the key-slot failed.\r
+ //\r
+ // This re-read of the Key points out an annoying short-coming of Java\r
+ // CAS. Most hardware CAS's report back the existing value - so that\r
+ // if you fail you have a *witness* - the value which caused the CAS\r
+ // to fail. The Java API turns this into a boolean destroying the\r
+ // witness. Re-reading does not recover the witness because another\r
+ // thread can write over the memory after the CAS. Hence we can be in\r
+ // the unfortunate situation of having a CAS fail *for cause* but\r
+ // having that cause removed by a later store. This turns a\r
+ // non-spurious-failure CAS (such as Azul has) into one that can\r
+ // apparently spuriously fail - and we avoid apparent spurious failure\r
+ // by not allowing Keys to ever change.\r
+ K = key(kvs,idx); // CAS failed, get updated value\r
+ assert K != null; // If keys[idx] is null, CAS shoulda worked\r
+ }\r
+ // Key slot was not null, there exists a Key here\r
+\r
+ // We need a volatile-read here to preserve happens-before semantics on\r
+ // newly inserted Keys. If the Key body was written just before inserting\r
+ // into the table a Key-compare here might read the uninitalized Key body.\r
+ // Annoyingly this means we have to volatile-read before EACH key compare.\r
+ newkvs = chm._newkvs; // VOLATILE READ before key compare\r
+\r
+ if( keyeq(K,key,hashes,idx,fullhash) )\r
+ break; // Got it!\r
+\r
+ // get and put must have the same key lookup logic! Lest 'get' give\r
+ // up looking too soon.\r
+ //topmap._reprobes.add(1);\r
+ if( ++reprobe_cnt >= reprobe_limit(len) || // too many probes or\r
+ key == TOMBSTONE ) { // found a TOMBSTONE key, means no more keys\r
+ // We simply must have a new table to do a 'put'. At this point a\r
+ // 'get' will also go to the new table (if any). We do not need\r
+ // to claim a key slot (indeed, we cannot find a free one to claim!).\r
+ newkvs = chm.resize(topmap,kvs);\r
+ if( expVal != null ) topmap.help_copy(newkvs); // help along an existing copy\r
+ return putIfMatch(topmap,newkvs,key,putval,expVal);\r
+ }\r
+\r
+ idx = (idx+1)&(len-1); // Reprobe!\r
+ } // End of spinning till we get a Key slot\r
+\r
+ // ---\r
+ // Found the proper Key slot, now update the matching Value slot. We\r
+ // never put a null, so Value slots monotonically move from null to\r
+ // not-null (deleted Values use Tombstone). Thus if 'V' is null we\r
+ // fail this fast cutout and fall into the check for table-full.\r
+ if( putval == V ) return V; // Fast cutout for no-change\r
+\r
+ // See if we want to move to a new table (to avoid high average re-probe\r
+ // counts). We only check on the initial set of a Value from null to\r
+ // not-null (i.e., once per key-insert). Of course we got a 'free' check\r
+ // of newkvs once per key-compare (not really free, but paid-for by the\r
+ // time we get here).\r
+ if( newkvs == null && // New table-copy already spotted?\r
+ // Once per fresh key-insert check the hard way\r
+ ((V == null && chm.tableFull(reprobe_cnt,len)) ||\r
+ // Or we found a Prime, but the JMM allowed reordering such that we\r
+ // did not spot the new table (very rare race here: the writing\r
+ // thread did a CAS of _newkvs then a store of a Prime. This thread\r
+ // reads the Prime, then reads _newkvs - but the read of Prime was so\r
+ // delayed (or the read of _newkvs was so accelerated) that they\r
+ // swapped and we still read a null _newkvs. The resize call below\r
+ // will do a CAS on _newkvs forcing the read.\r
+ V instanceof Prime) )\r
+ newkvs = chm.resize(topmap,kvs); // Force the new table copy to start\r
+ // See if we are moving to a new table.\r
+ // If so, copy our slot and retry in the new table.\r
+ if( newkvs != null )\r
+ return putIfMatch(topmap,chm.copy_slot_and_check(topmap,kvs,idx,expVal),key,putval,expVal);\r
+\r
+ // ---\r
+ // We are finally prepared to update the existing table\r
+ while( true ) {\r
+ assert !(V instanceof Prime);\r
+\r
+ // Must match old, and we do not? Then bail out now. Note that either V\r
+ // or expVal might be TOMBSTONE. Also V can be null, if we've never\r
+ // inserted a value before. expVal can be null if we are called from\r
+ // copy_slot.\r
+\r
+ if( expVal != NO_MATCH_OLD && // Do we care about expected-Value at all?\r
+ V != expVal && // No instant match already?\r
+ (expVal != MATCH_ANY || V == TOMBSTONE || V == null) &&\r
+ !(V==null && expVal == TOMBSTONE) && // Match on null/TOMBSTONE combo\r
+ (expVal == null || !expVal.equals(V)) ) // Expensive equals check at the last\r
+ return V; // Do not update!\r
+\r
+ // Actually change the Value in the Key,Value pair\r
+ if( CAS_val(kvs, idx, V, putval ) ) {\r
+ // CAS succeeded - we did the update!\r
+ // Both normal put's and table-copy calls putIfMatch, but table-copy\r
+ // does not (effectively) increase the number of live k/v pairs.\r
+ if( expVal != null ) {\r
+ // Adjust sizes - a striped counter\r
+ if( (V == null || V == TOMBSTONE) && putval != TOMBSTONE ) chm._size.add( 1);\r
+ if( !(V == null || V == TOMBSTONE) && putval == TOMBSTONE ) chm._size.add(-1);\r
+ }\r
+ return (V==null && expVal!=null) ? TOMBSTONE : V;\r
+ } \r
+ // Else CAS failed\r
+ V = val(kvs,idx); // Get new value\r
+ // If a Prime'd value got installed, we need to re-run the put on the\r
+ // new table. Otherwise we lost the CAS to another racing put.\r
+ // Simply retry from the start.\r
+ if( V instanceof Prime )\r
+ return putIfMatch(topmap,chm.copy_slot_and_check(topmap,kvs,idx,expVal),key,putval,expVal);\r
+ }\r
+ }\r
+\r
+ // --- help_copy ---------------------------------------------------------\r
+ // Help along an existing resize operation. This is just a fast cut-out\r
+ // wrapper, to encourage inlining for the fast no-copy-in-progress case. We\r
+ // always help the top-most table copy, even if there are nested table\r
+ // copies in progress.\r
+ private final Object[] help_copy( Object[] helper ) {\r
+ // Read the top-level KVS only once. We'll try to help this copy along,\r
+ // even if it gets promoted out from under us (i.e., the copy completes\r
+ // and another KVS becomes the top-level copy).\r
+ Object[] topkvs = _kvs;\r
+ CHM topchm = chm(topkvs);\r
+ if( topchm._newkvs == null ) return helper; // No copy in-progress\r
+ topchm.help_copy_impl(this,topkvs,false);\r
+ return helper;\r
+ }\r
+\r
+\r
+ // --- CHM -----------------------------------------------------------------\r
+ // The control structure for the NonBlockingHashMap\r
+ private static final class CHM<TypeK,TypeV> {\r
+ // Size in active K,V pairs\r
+ private final Counter _size;\r
+ public int size () { return (int)_size.get(); }\r
+\r
+ // ---\r
+ // These next 2 fields are used in the resizing heuristics, to judge when\r
+ // it is time to resize or copy the table. Slots is a count of used-up\r
+ // key slots, and when it nears a large fraction of the table we probably\r
+ // end up reprobing too much. Last-resize-milli is the time since the\r
+ // last resize; if we are running back-to-back resizes without growing\r
+ // (because there are only a few live keys but many slots full of dead\r
+ // keys) then we need a larger table to cut down on the churn.\r
+\r
+ // Count of used slots, to tell when table is full of dead unusable slots\r
+ private final Counter _slots;\r
+ public int slots() { return (int)_slots.get(); }\r
+\r
+ // ---\r
+ // New mappings, used during resizing.\r
+ // The 'new KVs' array - created during a resize operation. This\r
+ // represents the new table being copied from the old one. It's the\r
+ // volatile variable that is read as we cross from one table to the next,\r
+ // to get the required memory orderings. It monotonically transits from\r
+ // null to set (once).\r
+ volatile Object[] _newkvs;\r
+ private final AtomicReferenceFieldUpdater<CHM,Object[]> _newkvsUpdater =\r
+ AtomicReferenceFieldUpdater.newUpdater(CHM.class,Object[].class, "_newkvs");\r
+ // Set the _next field if we can.\r
+ boolean CAS_newkvs( Object[] newkvs ) {\r
+ while( _newkvs == null )\r
+ if( _newkvsUpdater.compareAndSet(this,null,newkvs) )\r
+ return true;\r
+ return false;\r
+ }\r
+ // Sometimes many threads race to create a new very large table. Only 1\r
+ // wins the race, but the losers all allocate a junk large table with\r
+ // hefty allocation costs. Attempt to control the overkill here by\r
+ // throttling attempts to create a new table. I cannot really block here\r
+ // (lest I lose the non-blocking property) but late-arriving threads can\r
+ // give the initial resizing thread a little time to allocate the initial\r
+ // new table. The Right Long Term Fix here is to use array-lets and\r
+ // incrementally create the new very large array. In C I'd make the array\r
+ // with malloc (which would mmap under the hood) which would only eat\r
+ // virtual-address and not real memory - and after Somebody wins then we\r
+ // could in parallel initialize the array. Java does not allow\r
+ // un-initialized array creation (especially of ref arrays!).\r
+ volatile long _resizers; // count of threads attempting an initial resize\r
+ private static final AtomicLongFieldUpdater<CHM> _resizerUpdater =\r
+ AtomicLongFieldUpdater.newUpdater(CHM.class, "_resizers");\r
+\r
+ // ---\r
+ // Simple constructor\r
+ CHM( Counter size ) {\r
+ _size = size;\r
+ _slots= new Counter();\r
+ }\r
+\r
+ // --- tableFull ---------------------------------------------------------\r
+ // Heuristic to decide if this table is too full, and we should start a\r
+ // new table. Note that if a 'get' call has reprobed too many times and\r
+ // decided the table must be full, then always the estimate_sum must be\r
+ // high and we must report the table is full. If we do not, then we might\r
+ // end up deciding that the table is not full and inserting into the\r
+ // current table, while a 'get' has decided the same key cannot be in this\r
+ // table because of too many reprobes. The invariant is:\r
+ // slots.estimate_sum >= max_reprobe_cnt >= reprobe_limit(len)\r
+ private final boolean tableFull( int reprobe_cnt, int len ) {\r
+ return\r
+ // Do the cheap check first: we allow some number of reprobes always\r
+ reprobe_cnt >= REPROBE_LIMIT &&\r
+ // More expensive check: see if the table is > 1/4 full.\r
+ _slots.estimate_get() >= reprobe_limit(len);\r
+ }\r
+\r
+ // --- resize ------------------------------------------------------------\r
+ // Resizing after too many probes. "How Big???" heuristics are here.\r
+ // Callers will (not this routine) will 'help_copy' any in-progress copy.\r
+ // Since this routine has a fast cutout for copy-already-started, callers\r
+ // MUST 'help_copy' lest we have a path which forever runs through\r
+ // 'resize' only to discover a copy-in-progress which never progresses.\r
+ private final Object[] resize( NonBlockingHashMap topmap, Object[] kvs) {\r
+ assert chm(kvs) == this;\r
+\r
+ // Check for resize already in progress, probably triggered by another thread\r
+ Object[] newkvs = _newkvs; // VOLATILE READ\r
+ if( newkvs != null ) // See if resize is already in progress\r
+ return newkvs; // Use the new table already\r
+\r
+ // No copy in-progress, so start one. First up: compute new table size.\r
+ int oldlen = len(kvs); // Old count of K,V pairs allowed\r
+ int sz = size(); // Get current table count of active K,V pairs\r
+ int newsz = sz; // First size estimate\r
+\r
+ // Heuristic to determine new size. We expect plenty of dead-slots-with-keys\r
+ // and we need some decent padding to avoid endless reprobing.\r
+ if( sz >= (oldlen>>2) ) { // If we are >25% full of keys then...\r
+ newsz = oldlen<<1; // Double size\r
+ if( sz >= (oldlen>>1) ) // If we are >50% full of keys then...\r
+ newsz = oldlen<<2; // Double double size\r
+ }\r
+ // This heuristic in the next 2 lines leads to a much denser table\r
+ // with a higher reprobe rate\r
+ //if( sz >= (oldlen>>1) ) // If we are >50% full of keys then...\r
+ // newsz = oldlen<<1; // Double size\r
+\r
+ // Last (re)size operation was very recent? Then double again; slows\r
+ // down resize operations for tables subject to a high key churn rate.\r
+ long tm = System.currentTimeMillis();\r
+ long q=0;\r
+ if( newsz <= oldlen && // New table would shrink or hold steady?\r
+ tm <= topmap._last_resize_milli+10000 && // Recent resize (less than 1 sec ago)\r
+ (q=_slots.estimate_get()) >= (sz<<1) ) // 1/2 of keys are dead?\r
+ newsz = oldlen<<1; // Double the existing size\r
+\r
+ // Do not shrink, ever\r
+ if( newsz < oldlen ) newsz = oldlen;\r
+\r
+ // Convert to power-of-2\r
+ int log2;\r
+ for( log2=MIN_SIZE_LOG; (1<<log2) < newsz; log2++ ) ; // Compute log2 of size\r
+\r
+ // Now limit the number of threads actually allocating memory to a\r
+ // handful - lest we have 750 threads all trying to allocate a giant\r
+ // resized array.\r
+ long r = _resizers;\r
+ while( !_resizerUpdater.compareAndSet(this,r,r+1) )\r
+ r = _resizers;\r
+ // Size calculation: 2 words (K+V) per table entry, plus a handful. We\r
+ // guess at 32-bit pointers; 64-bit pointers screws up the size calc by\r
+ // 2x but does not screw up the heuristic very much.\r
+ int megs = ((((1<<log2)<<1)+4)<<3/*word to bytes*/)>>20/*megs*/;\r
+ if( r >= 2 && megs > 0 ) { // Already 2 guys trying; wait and see\r
+ newkvs = _newkvs; // Between dorking around, another thread did it\r
+ if( newkvs != null ) // See if resize is already in progress\r
+ return newkvs; // Use the new table already\r
+ // TODO - use a wait with timeout, so we'll wakeup as soon as the new table\r
+ // is ready, or after the timeout in any case.\r
+ //synchronized( this ) { wait(8*megs); } // Timeout - we always wakeup\r
+ // For now, sleep a tad and see if the 2 guys already trying to make\r
+ // the table actually get around to making it happen.\r
+ try { Thread.sleep(8*megs); } catch( Exception e ) { }\r
+ }\r
+ // Last check, since the 'new' below is expensive and there is a chance\r
+ // that another thread slipped in a new thread while we ran the heuristic.\r
+ newkvs = _newkvs;\r
+ if( newkvs != null ) // See if resize is already in progress\r
+ return newkvs; // Use the new table already\r
+\r
+ // Double size for K,V pairs, add 1 for CHM\r
+ newkvs = new Object[((1<<log2)<<1)+2]; // This can get expensive for big arrays\r
+ newkvs[0] = new CHM(_size); // CHM in slot 0\r
+ newkvs[1] = new int[1<<log2]; // hashes in slot 1\r
+\r
+ // Another check after the slow allocation\r
+ if( _newkvs != null ) // See if resize is already in progress\r
+ return _newkvs; // Use the new table already\r
+\r
+ // The new table must be CAS'd in so only 1 winner amongst duplicate\r
+ // racing resizing threads. Extra CHM's will be GC'd.\r
+ if( CAS_newkvs( newkvs ) ) { // NOW a resize-is-in-progress!\r
+ //notifyAll(); // Wake up any sleepers\r
+ //long nano = System.nanoTime();\r
+ //System.out.println(" "+nano+" Resize from "+oldlen+" to "+(1<<log2)+" and had "+(_resizers-1)+" extras" );\r
+ //if( System.out != null ) System.out.print("["+log2);\r
+ topmap.rehash(); // Call for Hashtable's benefit\r
+ } else // CAS failed?\r
+ newkvs = _newkvs; // Reread new table\r
+ return newkvs;\r
+ }\r
+\r
+\r
+ // The next part of the table to copy. It monotonically transits from zero\r
+ // to _kvs.length. Visitors to the table can claim 'work chunks' by\r
+ // CAS'ing this field up, then copying the indicated indices from the old\r
+ // table to the new table. Workers are not required to finish any chunk;\r
+ // the counter simply wraps and work is copied duplicately until somebody\r
+ // somewhere completes the count.\r
+ volatile long _copyIdx = 0;\r
+ static private final AtomicLongFieldUpdater<CHM> _copyIdxUpdater =\r
+ AtomicLongFieldUpdater.newUpdater(CHM.class, "_copyIdx");\r
+\r
+ // Work-done reporting. Used to efficiently signal when we can move to\r
+ // the new table. From 0 to len(oldkvs) refers to copying from the old\r
+ // table to the new.\r
+ volatile long _copyDone= 0;\r
+ static private final AtomicLongFieldUpdater<CHM> _copyDoneUpdater =\r
+ AtomicLongFieldUpdater.newUpdater(CHM.class, "_copyDone");\r
+\r
+ // --- help_copy_impl ----------------------------------------------------\r
+ // Help along an existing resize operation. We hope its the top-level\r
+ // copy (it was when we started) but this CHM might have been promoted out\r
+ // of the top position.\r
+ private final void help_copy_impl( NonBlockingHashMap topmap, Object[] oldkvs, boolean copy_all ) {\r
+ assert chm(oldkvs) == this;\r
+ Object[] newkvs = _newkvs;\r
+ assert newkvs != null; // Already checked by caller\r
+ int oldlen = len(oldkvs); // Total amount to copy\r
+ final int MIN_COPY_WORK = Math.min(oldlen,1024); // Limit per-thread work\r
+\r
+ // ---\r
+ int panic_start = -1;\r
+ int copyidx=-9999; // Fool javac to think it's initialized\r
+ while( _copyDone < oldlen ) { // Still needing to copy?\r
+ // Carve out a chunk of work. The counter wraps around so every\r
+ // thread eventually tries to copy every slot repeatedly.\r
+\r
+ // We "panic" if we have tried TWICE to copy every slot - and it still\r
+ // has not happened. i.e., twice some thread somewhere claimed they\r
+ // would copy 'slot X' (by bumping _copyIdx) but they never claimed to\r
+ // have finished (by bumping _copyDone). Our choices become limited:\r
+ // we can wait for the work-claimers to finish (and become a blocking\r
+ // algorithm) or do the copy work ourselves. Tiny tables with huge\r
+ // thread counts trying to copy the table often 'panic'.\r
+ if( panic_start == -1 ) { // No panic?\r
+ copyidx = (int)_copyIdx;\r
+ while( copyidx < (oldlen<<1) && // 'panic' check\r
+ !_copyIdxUpdater.compareAndSet(this,copyidx,copyidx+MIN_COPY_WORK) )\r
+ copyidx = (int)_copyIdx; // Re-read\r
+ if( !(copyidx < (oldlen<<1)) ) // Panic!\r
+ panic_start = copyidx; // Record where we started to panic-copy\r
+ }\r
+\r
+ // We now know what to copy. Try to copy.\r
+ int workdone = 0;\r
+ for( int i=0; i<MIN_COPY_WORK; i++ )\r
+ if( copy_slot(topmap,(copyidx+i)&(oldlen-1),oldkvs,newkvs) ) // Made an oldtable slot go dead?\r
+ workdone++; // Yes!\r
+ if( workdone > 0 ) // Report work-done occasionally\r
+ copy_check_and_promote( topmap, oldkvs, workdone );// See if we can promote\r
+ //for( int i=0; i<MIN_COPY_WORK; i++ )\r
+ // if( copy_slot(topmap,(copyidx+i)&(oldlen-1),oldkvs,newkvs) ) // Made an oldtable slot go dead?\r
+ // copy_check_and_promote( topmap, oldkvs, 1 );// See if we can promote\r
+\r
+ copyidx += MIN_COPY_WORK;\r
+ // Uncomment these next 2 lines to turn on incremental table-copy.\r
+ // Otherwise this thread continues to copy until it is all done.\r
+ if( !copy_all && panic_start == -1 ) // No panic?\r
+ return; // Then done copying after doing MIN_COPY_WORK\r
+ }\r
+ // Extra promotion check, in case another thread finished all copying\r
+ // then got stalled before promoting.\r
+ copy_check_and_promote( topmap, oldkvs, 0 );// See if we can promote\r
+ }\r
+\r
+\r
+ // --- copy_slot_and_check -----------------------------------------------\r
+ // Copy slot 'idx' from the old table to the new table. If this thread\r
+ // confirmed the copy, update the counters and check for promotion.\r
+ //\r
+ // Returns the result of reading the volatile _newkvs, mostly as a\r
+ // convenience to callers. We come here with 1-shot copy requests\r
+ // typically because the caller has found a Prime, and has not yet read\r
+ // the _newkvs volatile - which must have changed from null-to-not-null\r
+ // before any Prime appears. So the caller needs to read the _newkvs\r
+ // field to retry his operation in the new table, but probably has not\r
+ // read it yet.\r
+ private final Object[] copy_slot_and_check( NonBlockingHashMap topmap, Object[] oldkvs, int idx, Object should_help ) {\r
+ assert chm(oldkvs) == this;\r
+ Object[] newkvs = _newkvs; // VOLATILE READ\r
+ // We're only here because the caller saw a Prime, which implies a\r
+ // table-copy is in progress.\r
+ assert newkvs != null;\r
+ if( copy_slot(topmap,idx,oldkvs,_newkvs) ) // Copy the desired slot\r
+ copy_check_and_promote(topmap, oldkvs, 1); // Record the slot copied\r
+ // Generically help along any copy (except if called recursively from a helper)\r
+ return (should_help == null) ? newkvs : topmap.help_copy(newkvs);\r
+ }\r
+\r
+ // --- copy_check_and_promote --------------------------------------------\r
+ private final void copy_check_and_promote( NonBlockingHashMap topmap, Object[] oldkvs, int workdone ) {\r
+ assert chm(oldkvs) == this;\r
+ int oldlen = len(oldkvs);\r
+ // We made a slot unusable and so did some of the needed copy work\r
+ long copyDone = _copyDone;\r
+ assert (copyDone+workdone) <= oldlen;\r
+ if( workdone > 0 ) {\r
+ while( !_copyDoneUpdater.compareAndSet(this,copyDone,copyDone+workdone) ) {\r
+ copyDone = _copyDone; // Reload, retry\r
+ assert (copyDone+workdone) <= oldlen;\r
+ }\r
+ //if( (10*copyDone/oldlen) != (10*(copyDone+workdone)/oldlen) )\r
+ //System.out.print(" "+(copyDone+workdone)*100/oldlen+"%"+"_"+(_copyIdx*100/oldlen)+"%");\r
+ }\r
+\r
+ // Check for copy being ALL done, and promote. Note that we might have\r
+ // nested in-progress copies and manage to finish a nested copy before\r
+ // finishing the top-level copy. We only promote top-level copies.\r
+ if( copyDone+workdone == oldlen && // Ready to promote this table?\r
+ topmap._kvs == oldkvs && // Looking at the top-level table?\r
+ // Attempt to promote\r
+ topmap.CAS_kvs(oldkvs,_newkvs) ) {\r
+ topmap._last_resize_milli = System.currentTimeMillis(); // Record resize time for next check\r
+ //long nano = System.nanoTime();\r
+ //System.out.println(" "+nano+" Promote table to "+len(_newkvs));\r
+ //if( System.out != null ) System.out.print("]");\r
+ }\r
+ }\r
+ // --- copy_slot ---------------------------------------------------------\r
+ // Copy one K/V pair from oldkvs[i] to newkvs. Returns true if we can\r
+ // confirm that the new table guaranteed has a value for this old-table\r
+ // slot. We need an accurate confirmed-copy count so that we know when we\r
+ // can promote (if we promote the new table too soon, other threads may\r
+ // 'miss' on values not-yet-copied from the old table). We don't allow\r
+ // any direct updates on the new table, unless they first happened to the\r
+ // old table - so that any transition in the new table from null to\r
+ // not-null must have been from a copy_slot (or other old-table overwrite)\r
+ // and not from a thread directly writing in the new table. Thus we can\r
+ // count null-to-not-null transitions in the new table.\r
+ private boolean copy_slot( NonBlockingHashMap topmap, int idx, Object[] oldkvs, Object[] newkvs ) {\r
+ // Blindly set the key slot from null to TOMBSTONE, to eagerly stop\r
+ // fresh put's from inserting new values in the old table when the old\r
+ // table is mid-resize. We don't need to act on the results here,\r
+ // because our correctness stems from box'ing the Value field. Slamming\r
+ // the Key field is a minor speed optimization.\r
+ Object key;\r
+ while( (key=key(oldkvs,idx)) == null )\r
+ CAS_key(oldkvs,idx, null, TOMBSTONE);\r
+\r
+ // ---\r
+ // Prevent new values from appearing in the old table.\r
+ // Box what we see in the old table, to prevent further updates.\r
+ Object oldval = val(oldkvs,idx); // Read OLD table\r
+ while( !(oldval instanceof Prime) ) {\r
+ final Prime box = (oldval == null || oldval == TOMBSTONE) ? TOMBPRIME : new Prime(oldval);\r
+ if( CAS_val(oldkvs,idx,oldval,box) ) { // CAS down a box'd version of oldval\r
+ // If we made the Value slot hold a TOMBPRIME, then we both\r
+ // prevented further updates here but also the (absent)\r
+ // oldval is vaccuously available in the new table. We\r
+ // return with true here: any thread looking for a value for\r
+ // this key can correctly go straight to the new table and\r
+ // skip looking in the old table.\r
+ if( box == TOMBPRIME )\r
+ return true;\r
+ // Otherwise we boxed something, but it still needs to be\r
+ // copied into the new table.\r
+ oldval = box; // Record updated oldval\r
+ break; // Break loop; oldval is now boxed by us\r
+ }\r
+ oldval = val(oldkvs,idx); // Else try, try again\r
+ }\r
+ if( oldval == TOMBPRIME ) return false; // Copy already complete here!\r
+\r
+ // ---\r
+ // Copy the value into the new table, but only if we overwrite a null.\r
+ // If another value is already in the new table, then somebody else\r
+ // wrote something there and that write is happens-after any value that\r
+ // appears in the old table. If putIfMatch does not find a null in the\r
+ // new table - somebody else should have recorded the null-not_null\r
+ // transition in this copy.\r
+ Object old_unboxed = ((Prime)oldval)._V;\r
+ assert old_unboxed != TOMBSTONE;\r
+ boolean copied_into_new = (putIfMatch(topmap, newkvs, key, old_unboxed, null) == null);\r
+\r
+ // ---\r
+ // Finally, now that any old value is exposed in the new table, we can\r
+ // forever hide the old-table value by slapping a TOMBPRIME down. This\r
+ // will stop other threads from uselessly attempting to copy this slot\r
+ // (i.e., it's a speed optimization not a correctness issue).\r
+ while( !CAS_val(oldkvs,idx,oldval,TOMBPRIME) )\r
+ oldval = val(oldkvs,idx);\r
+\r
+ return copied_into_new;\r
+ } // end copy_slot\r
+ } // End of CHM\r
+\r
+\r
+ // --- Snapshot ------------------------------------------------------------\r
+ // The main class for iterating over the NBHM. It "snapshots" a clean\r
+ // view of the K/V array.\r
+ private class SnapshotV implements Iterator<TypeV>, Enumeration<TypeV> {\r
+ final Object[] _sskvs;\r
+ public SnapshotV() {\r
+ while( true ) { // Verify no table-copy-in-progress\r
+ Object[] topkvs = _kvs;\r
+ CHM topchm = chm(topkvs);\r
+ if( topchm._newkvs == null ) { // No table-copy-in-progress\r
+ // The "linearization point" for the iteration. Every key in this\r
+ // table will be visited, but keys added later might be skipped or\r
+ // even be added to a following table (also not iterated over).\r
+ _sskvs = topkvs;\r
+ break;\r
+ }\r
+ // Table copy in-progress - so we cannot get a clean iteration. We\r
+ // must help finish the table copy before we can start iterating.\r
+ topchm.help_copy_impl(NonBlockingHashMap.this,topkvs,true);\r
+ }\r
+ // Warm-up the iterator\r
+ next();\r
+ }\r
+ int length() { return len(_sskvs); }\r
+ Object key(int idx) { return NonBlockingHashMap.key(_sskvs,idx); }\r
+ private int _idx; // Varies from 0-keys.length\r
+ private Object _nextK, _prevK; // Last 2 keys found\r
+ private TypeV _nextV, _prevV; // Last 2 values found\r
+ public boolean hasNext() { return _nextV != null; }\r
+ public TypeV next() {\r
+ // 'next' actually knows what the next value will be - it had to\r
+ // figure that out last go-around lest 'hasNext' report true and\r
+ // some other thread deleted the last value. Instead, 'next'\r
+ // spends all its effort finding the key that comes after the\r
+ // 'next' key.\r
+ if( _idx != 0 && _nextV == null ) throw new NoSuchElementException();\r
+ _prevK = _nextK; // This will become the previous key\r
+ _prevV = _nextV; // This will become the previous value\r
+ _nextV = null; // We have no more next-key\r
+ // Attempt to set <_nextK,_nextV> to the next K,V pair.\r
+ // _nextV is the trigger: stop searching when it is != null\r
+ while( _idx<length() ) { // Scan array\r
+ _nextK = key(_idx++); // Get a key that definitely is in the set (for the moment!)\r
+ if( _nextK != null && // Found something?\r
+ _nextK != TOMBSTONE &&\r
+ (_nextV=get(_nextK)) != null )\r
+ break; // Got it! _nextK is a valid Key\r
+ } // Else keep scanning\r
+ return _prevV; // Return current value.\r
+ }\r
+ public void remove() {\r
+ if( _prevV == null ) throw new IllegalStateException();\r
+ putIfMatch( NonBlockingHashMap.this, _sskvs, _prevK, TOMBSTONE, _prevV );\r
+ _prevV = null;\r
+ }\r
+\r
+ public TypeV nextElement() { return next(); }\r
+ public boolean hasMoreElements() { return hasNext(); }\r
+ }\r
+\r
+ /** Returns an enumeration of the values in this table.\r
+ * @return an enumeration of the values in this table\r
+ * @see #values() */\r
+ public Enumeration<TypeV> elements() { return new SnapshotV(); }\r
+\r
+ // --- values --------------------------------------------------------------\r
+ /** Returns a {@link Collection} view of the values contained in this map.\r
+ * The collection is backed by the map, so changes to the map are reflected\r
+ * in the collection, and vice-versa. The collection supports element\r
+ * removal, which removes the corresponding mapping from this map, via the\r
+ * <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,\r
+ * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations.\r
+ * It does not support the <tt>add</tt> or <tt>addAll</tt> operations.\r
+ *\r
+ * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator that\r
+ * will never throw {@link ConcurrentModificationException}, and guarantees\r
+ * to traverse elements as they existed upon construction of the iterator,\r
+ * and may (but is not guaranteed to) reflect any modifications subsequent\r
+ * to construction. */\r
+ @Override\r
+ public Collection<TypeV> values() {\r
+ return new AbstractCollection<TypeV>() {\r
+ @Override public void clear ( ) { NonBlockingHashMap.this.clear ( ); }\r
+ @Override public int size ( ) { return NonBlockingHashMap.this.size ( ); }\r
+ @Override public boolean contains( Object v ) { return NonBlockingHashMap.this.containsValue(v); }\r
+ @Override public Iterator<TypeV> iterator() { return new SnapshotV(); }\r
+ };\r
+ }\r
+\r
+ // --- keySet --------------------------------------------------------------\r
+ private class SnapshotK implements Iterator<TypeK>, Enumeration<TypeK> {\r
+ final SnapshotV _ss;\r
+ public SnapshotK() { _ss = new SnapshotV(); }\r
+ public void remove() { _ss.remove(); }\r
+ public TypeK next() { _ss.next(); return (TypeK)_ss._prevK; }\r
+ public boolean hasNext() { return _ss.hasNext(); }\r
+ public TypeK nextElement() { return next(); }\r
+ public boolean hasMoreElements() { return hasNext(); }\r
+ }\r
+\r
+ /** Returns an enumeration of the keys in this table.\r
+ * @return an enumeration of the keys in this table\r
+ * @see #keySet() */\r
+ public Enumeration<TypeK> keys() { return new SnapshotK(); }\r
+\r
+ /** Returns a {@link Set} view of the keys contained in this map. The set\r
+ * is backed by the map, so changes to the map are reflected in the set,\r
+ * and vice-versa. The set supports element removal, which removes the\r
+ * corresponding mapping from this map, via the <tt>Iterator.remove</tt>,\r
+ * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and\r
+ * <tt>clear</tt> operations. It does not support the <tt>add</tt> or\r
+ * <tt>addAll</tt> operations.\r
+ *\r
+ * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator that\r
+ * will never throw {@link ConcurrentModificationException}, and guarantees\r
+ * to traverse elements as they existed upon construction of the iterator,\r
+ * and may (but is not guaranteed to) reflect any modifications subsequent\r
+ * to construction. */\r
+ @Override\r
+ public Set<TypeK> keySet() {\r
+ return new AbstractSet<TypeK> () {\r
+ @Override public void clear ( ) { NonBlockingHashMap.this.clear ( ); }\r
+ @Override public int size ( ) { return NonBlockingHashMap.this.size ( ); }\r
+ @Override public boolean contains( Object k ) { return NonBlockingHashMap.this.containsKey(k); }\r
+ @Override public boolean remove ( Object k ) { return NonBlockingHashMap.this.remove (k) != null; }\r
+ @Override public Iterator<TypeK> iterator() { return new SnapshotK(); }\r
+ };\r
+ }\r
+\r
+\r
+ // --- entrySet ------------------------------------------------------------\r
+ // Warning: Each call to 'next' in this iterator constructs a new NBHMEntry.\r
+ private class NBHMEntry extends AbstractEntry<TypeK,TypeV> {\r
+ NBHMEntry( final TypeK k, final TypeV v ) { super(k,v); }\r
+ public TypeV setValue(final TypeV val) {\r
+ if( val == null ) throw new NullPointerException();\r
+ _val = val;\r
+ return put(_key, val);\r
+ }\r
+ }\r
+\r
+ private class SnapshotE implements Iterator<Map.Entry<TypeK,TypeV>> {\r
+ final SnapshotV _ss;\r
+ public SnapshotE() { _ss = new SnapshotV(); }\r
+ public void remove() { _ss.remove(); }\r
+ public Map.Entry<TypeK,TypeV> next() { _ss.next(); return new NBHMEntry((TypeK)_ss._prevK,_ss._prevV); }\r
+ public boolean hasNext() { return _ss.hasNext(); }\r
+ }\r
+\r
+ /** Returns a {@link Set} view of the mappings contained in this map. The\r
+ * set is backed by the map, so changes to the map are reflected in the\r
+ * set, and vice-versa. The set supports element removal, which removes\r
+ * the corresponding mapping from the map, via the\r
+ * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, <tt>removeAll</tt>,\r
+ * <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not support\r
+ * the <tt>add</tt> or <tt>addAll</tt> operations.\r
+ *\r
+ * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator\r
+ * that will never throw {@link ConcurrentModificationException},\r
+ * and guarantees to traverse elements as they existed upon\r
+ * construction of the iterator, and may (but is not guaranteed to)\r
+ * reflect any modifications subsequent to construction.\r
+ *\r
+ * <p><strong>Warning:</strong> the iterator associated with this Set\r
+ * requires the creation of {@link java.util.Map.Entry} objects with each\r
+ * iteration. The {@link NonBlockingHashMap} does not normally create or\r
+ * using {@link java.util.Map.Entry} objects so they will be created soley\r
+ * to support this iteration. Iterating using {@link #keySet} or {@link\r
+ * #values} will be more efficient.\r
+ */\r
+ @Override\r
+ public Set<Map.Entry<TypeK,TypeV>> entrySet() {\r
+ return new AbstractSet<Map.Entry<TypeK,TypeV>>() {\r
+ @Override public void clear ( ) { NonBlockingHashMap.this.clear( ); }\r
+ @Override public int size ( ) { return NonBlockingHashMap.this.size ( ); }\r
+ @Override public boolean remove( final Object o ) {\r
+ if( !(o instanceof Map.Entry)) return false;\r
+ final Map.Entry<?,?> e = (Map.Entry<?,?>)o;\r
+ return NonBlockingHashMap.this.remove(e.getKey(), e.getValue());\r
+ }\r
+ @Override public boolean contains(final Object o) {\r
+ if( !(o instanceof Map.Entry)) return false;\r
+ final Map.Entry<?,?> e = (Map.Entry<?,?>)o;\r
+ TypeV v = get(e.getKey());\r
+ return v.equals(e.getValue());\r
+ }\r
+ @Override public Iterator<Map.Entry<TypeK,TypeV>> iterator() { return new SnapshotE(); }\r
+ };\r
+ }\r
+\r
+ // --- writeObject -------------------------------------------------------\r
+ // Write a NBHM to a stream\r
+ private void writeObject(java.io.ObjectOutputStream s) throws IOException {\r
+ s.defaultWriteObject(); // Nothing to write\r
+ for( Object K : keySet() ) {\r
+ final Object V = get(K); // Do an official 'get'\r
+ s.writeObject(K); // Write the <TypeK,TypeV> pair\r
+ s.writeObject(V);\r
+ }\r
+ s.writeObject(null); // Sentinel to indicate end-of-data\r
+ s.writeObject(null);\r
+ }\r
+\r
+ // --- readObject --------------------------------------------------------\r
+ // Read a CHM from a stream\r
+ private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException {\r
+ s.defaultReadObject(); // Read nothing\r
+ initialize(MIN_SIZE);\r
+ for(;;) {\r
+ final TypeK K = (TypeK) s.readObject();\r
+ final TypeV V = (TypeV) s.readObject();\r
+ if( K == null ) break;\r
+ put(K,V); // Insert with an offical put\r
+ }\r
+ }\r
+\r
+} // End NonBlockingHashMap class\r
projects / cdsspec-compiler.git / blobdiff