/*
* Written by Cliff Click and released to the public domain, as explained at
* http://creativecommons.org/licenses/publicdomain
*/
package utils.collections;
import sun.misc.Unsafe;
import utils.unsafe.OffHeapMemory;
import java.io.IOException;
import java.io.Serializable;
import java.lang.reflect.Field;
import java.util.*;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
/**
* A lock-free alternate implementation of {@link java.util.concurrent.ConcurrentHashMap}
* with <strong>primitive long keys</strong>, better scaling properties and
* generally lower costs. The use of {@code long} keys allows for faster
* compares and lower memory costs. The Map provides identical correctness
* properties as ConcurrentHashMap. All operations are non-blocking and
* multi-thread safe, including all update operations. {@link
* NonBlockingHashMapLong} scales substatially better than {@link
* java.util.concurrent.ConcurrentHashMap} for high update rates, even with a large
* concurrency factor. Scaling is linear up to 768 CPUs on a 768-CPU Azul
* box, even with 100% updates or 100% reads or any fraction in-between.
* Linear scaling up to all cpus has been observed on a 32-way Sun US2 box,
* 32-way Sun Niagra box, 8-way Intel box and a 4-way Power box.
*
* <p><strong>The main benefit of this class</strong> over using plain {@link
* org.cliffc.high_scale_lib.NonBlockingHashMap} with {@link Long} keys is
* that it avoids the auto-boxing and unboxing costs. Since auto-boxing is
* <em>automatic</em>, it is easy to accidentally cause auto-boxing and negate
* the space and speed benefits.
*
* <p>This class obeys the same functional specification as {@link
* java.util.Hashtable}, and includes versions of methods corresponding to
* each method of <tt>Hashtable</tt>. However, even though all operations are
* thread-safe, operations do <em>not</em> entail locking and there is
* <em>not</em> any support for locking the entire table in a way that
* prevents all access. This class is fully interoperable with
* <tt>Hashtable</tt> in programs that rely on its thread safety but not on
* its synchronization details.
*
* <p> Operations (including <tt>put</tt>) generally do not block, so may
* overlap with other update operations (including other <tt>puts</tt> and
* <tt>removes</tt>). Retrievals reflect the results of the most recently
* <em>completed</em> update operations holding upon their onset. For
* aggregate operations such as <tt>putAll</tt>, concurrent retrievals may
* reflect insertion or removal of only some entries. Similarly, Iterators
* and Enumerations return elements reflecting the state of the hash table at
* some point at or since the creation of the iterator/enumeration. They do
* <em>not</em> throw {@link ConcurrentModificationException}. However,
* iterators are designed to be used by only one thread at a time.
*
* <p> Very full tables, or tables with high reprobe rates may trigger an
* internal resize operation to move into a larger table. Resizing is not
* terribly expensive, but it is not free either; during resize operations
* table throughput may drop somewhat. All threads that visit the table
* during a resize will 'help' the resizing but will still be allowed to
* complete their operation before the resize is finished (i.e., a simple
* 'get' operation on a million-entry table undergoing resizing will not need
* to block until the entire million entries are copied).
*
* <p>This class and its views and iterators implement all of the
* <em>optional</em> methods of the {@link Map} and {@link Iterator}
* interfaces.
*
* <p> Like {@link Hashtable} but unlike {@link HashMap}, this class
* does <em>not</em> allow <tt>null</tt> to be used as a value.
*
*
* @since 1.5
* @author Cliff Click
* @param <TypeV> the type of mapped values
*/
public class NonBlockingHashMapLong<TypeV>
extends AbstractMap<Long,TypeV>
implements ConcurrentMap<Long,TypeV>, Serializable {
private static final long serialVersionUID = 1234123412341234124L;
private static final int REPROBE_LIMIT=10; // Too many reprobes then force a table-resize
// --- Bits to allow Unsafe access to arrays
private static final Unsafe _unsafe = OffHeapMemory.getUnsafe();
private static final int _Obase = _unsafe.arrayBaseOffset(Object[].class);
private static final int _Oscale = _unsafe.arrayIndexScale(Object[].class);
private static long rawIndex(final Object[] ary, final int idx) {
assert idx >= 0 && idx < ary.length;
return _Obase + idx * _Oscale;
}
private static final int _Lbase = _unsafe.arrayBaseOffset(long[].class);
private static final int _Lscale = _unsafe.arrayIndexScale(long[].class);
private static long rawIndex(final long[] ary, final int idx) {
assert idx >= 0 && idx < ary.length;
return _Lbase + idx * _Lscale;
}
// --- Bits to allow Unsafe CAS'ing of the CHM field
private static final long _chm_offset;
private static final long _val_1_offset;
static { // <clinit>
Field f = null;
try { f = NonBlockingHashMapLong.class.getDeclaredField("_chm"); }
catch( java.lang.NoSuchFieldException e ) { throw new RuntimeException(e); }
_chm_offset = _unsafe.objectFieldOffset(f);
try { f = NonBlockingHashMapLong.class.getDeclaredField("_val_1"); }
catch( java.lang.NoSuchFieldException e ) { throw new RuntimeException(e); }
_val_1_offset = _unsafe.objectFieldOffset(f);
}
private final boolean CAS( final long offset, final Object old, final Object nnn ) {
return _unsafe.compareAndSwapObject(this, offset, old, nnn );
}
// --- Adding a 'prime' bit onto Values via wrapping with a junk wrapper class
private static final class Prime {
final Object _V;
Prime( Object V ) { _V = V; }
static Object unbox( Object V ) { return V instanceof Prime ? ((Prime)V)._V : V; }
}
// --- The Hash Table --------------------
private transient CHM _chm;
// This next field holds the value for Key 0 - the special key value which
// is the initial array value, and also means: no-key-inserted-yet.
private transient Object _val_1; // Value for Key: NO_KEY
// Time since last resize
private transient long _last_resize_milli;
// Optimize for space: use a 1/2-sized table and allow more re-probes
private final boolean _opt_for_space;
// --- Minimum table size ----------------
// Pick size 16 K/V pairs, which turns into (16*2)*4+12 = 140 bytes on a
// standard 32-bit HotSpot, and (16*2)*8+12 = 268 bytes on 64-bit Azul.
private static final int MIN_SIZE_LOG=4; //
private static final int MIN_SIZE=(1<<MIN_SIZE_LOG); // Must be power of 2
// --- Sentinels -------------------------
// No-Match-Old - putIfMatch does updates only if it matches the old value,
// and NO_MATCH_OLD basically counts as a wildcard match.
private static final Object NO_MATCH_OLD = new Object(); // Sentinel
// Match-Any-not-null - putIfMatch does updates only if it find a real old
// value.
private static final Object MATCH_ANY = new Object(); // Sentinel
// This K/V pair has been deleted (but the Key slot is forever claimed).
// The same Key can be reinserted with a new value later.
private static final Object TOMBSTONE = new Object();
// Prime'd or box'd version of TOMBSTONE. This K/V pair was deleted, then a
// table resize started. The K/V pair has been marked so that no new
// updates can happen to the old table (and since the K/V pair was deleted
// nothing was copied to the new table).
private static final Prime TOMBPRIME = new Prime(TOMBSTONE);
// I exclude 1 long from the 2^64 possibilities, and test for it before
// entering the main array. The NO_KEY value must be zero, the initial
// value set by Java before it hands me the array.
private static final long NO_KEY = 0L;
// --- dump ----------------------------------------------------------------
/** Verbose printout of table internals, useful for debugging. */
public final void print() {
System.out.println("=========");
print_impl(-99,NO_KEY,_val_1);
_chm.print();
System.out.println("=========");
}
private static final void print_impl(final int i, final long K, final Object V) {
String p = (V instanceof Prime) ? "prime_" : "";
Object V2 = Prime.unbox(V);
String VS = (V2 == TOMBSTONE) ? "tombstone" : V2.toString();
System.out.println("["+i+"]=("+K+","+p+VS+")");
}
private final void print2() {
System.out.println("=========");
print2_impl(-99,NO_KEY,_val_1);
_chm.print();
System.out.println("=========");
}
private static final void print2_impl(final int i, final long K, final Object V) {
if( V != null && Prime.unbox(V) != TOMBSTONE )
print_impl(i,K,V);
}
// Count of reprobes
private transient Counter _reprobes = new Counter();
/** Get and clear the current count of reprobes. Reprobes happen on key
* collisions, and a high reprobe rate may indicate a poor hash function or
* weaknesses in the table resizing function.
* @return the count of reprobes since the last call to {@link #reprobes}
* or since the table was created. */
public long reprobes() { long r = _reprobes.get(); _reprobes = new Counter(); return r; }
// --- reprobe_limit -----------------------------------------------------
// Heuristic to decide if we have reprobed toooo many times. Running over
// the reprobe limit on a 'get' call acts as a 'miss'; on a 'put' call it
// can trigger a table resize. Several places must have exact agreement on
// what the reprobe_limit is, so we share it here.
private static final int reprobe_limit( int len ) {
return REPROBE_LIMIT + (len>>2);
}
// --- NonBlockingHashMapLong ----------------------------------------------
// Constructors
/** Create a new NonBlockingHashMapLong with default minimum size (currently set
* to 8 K/V pairs or roughly 84 bytes on a standard 32-bit JVM). */
public NonBlockingHashMapLong( ) { this(MIN_SIZE,true); }
/** Create a new NonBlockingHashMapLong with initial room for the given
* number of elements, thus avoiding internal resizing operations to reach
* an appropriate size. Large numbers here when used with a small count of
* elements will sacrifice space for a small amount of time gained. The
* initial size will be rounded up internally to the next larger power of 2. */
public NonBlockingHashMapLong( final int initial_sz ) { this(initial_sz,true); }
/** Create a new NonBlockingHashMapLong, setting the space-for-speed
* tradeoff. {@code true} optimizes for space and is the default. {@code
* false} optimizes for speed and doubles space costs for roughly a 10%
* speed improvement. */
public NonBlockingHashMapLong( final boolean opt_for_space ) { this(1,opt_for_space); }
/** Create a new NonBlockingHashMapLong, setting both the initial size and
* the space-for-speed tradeoff. {@code true} optimizes for space and is
* the default. {@code false} optimizes for speed and doubles space costs
* for roughly a 10% speed improvement. */
public NonBlockingHashMapLong( final int initial_sz, final boolean opt_for_space ) {
_opt_for_space = opt_for_space;
initialize(initial_sz);
}
private final void initialize( final int initial_sz ) {
if( initial_sz < 0 ) throw new IllegalArgumentException();
int i; // Convert to next largest power-of-2
for( i=MIN_SIZE_LOG; (1<<i) < initial_sz; i++ ) ;
_chm = new CHM(this,new Counter(),i);
_val_1 = TOMBSTONE; // Always as-if deleted
_last_resize_milli = System.currentTimeMillis();
}
// --- wrappers ------------------------------------------------------------
/** Returns the number of key-value mappings in this map.
* @return the number of key-value mappings in this map */
public int size ( ) { return (_val_1==TOMBSTONE?0:1) + (int)_chm.size(); }
/** Tests if the key in the table.
* @return <tt>true</tt> if the key is in the table */
public boolean containsKey( long key ) { return get(key) != null; }
/** Legacy method testing if some key maps into the specified value in this
* table. This method is identical in functionality to {@link
* #containsValue}, and exists solely to ensure full compatibility with
* class {@link java.util.Hashtable}, which supported this method prior to
* introduction of the Java Collections framework.
* @param val a value to search for
* @return <tt>true</tt> if this map maps one or more keys to the specified value
* @throws NullPointerException if the specified value is null */
public boolean contains ( Object val ) { return containsValue(val); }
/** Maps the specified key to the specified value in the table. The value
* cannot be null. <p> The value can be retrieved by calling {@link #get}
* with a key that is equal to the original key.
* @param key key with which the specified value is to be associated
* @param val value to be associated with the specified key
* @return the previous value associated with <tt>key</tt>, or
* <tt>null</tt> if there was no mapping for <tt>key</tt>
* @throws NullPointerException if the specified value is null */
public TypeV put ( long key, TypeV val ) { return putIfMatch( key, val,NO_MATCH_OLD);}
/** Atomically, do a {@link #put} if-and-only-if the key is not mapped.
* Useful to ensure that only a single mapping for the key exists, even if
* many threads are trying to create the mapping in parallel.
* @return the previous value associated with the specified key,
* or <tt>null</tt> if there was no mapping for the key
* @throws NullPointerException if the specified is value is null */
public TypeV putIfAbsent( long key, TypeV val ) { return putIfMatch( key, val,TOMBSTONE );}
/** Removes the key (and its corresponding value) from this map.
* This method does nothing if the key is not in the map.
* @return the previous value associated with <tt>key</tt>, or
* <tt>null</tt> if there was no mapping for <tt>key</tt>*/
public TypeV remove ( long key ) { return putIfMatch( key,TOMBSTONE,NO_MATCH_OLD);}
/** Atomically do a {@link #remove(long)} if-and-only-if the key is mapped
* to a value which is <code>equals</code> to the given value.
* @throws NullPointerException if the specified value is null */
public boolean remove ( long key,Object val ) { return putIfMatch( key,TOMBSTONE,val ) == val ;}
/** Atomically do a <code>put(key,val)</code> if-and-only-if the key is
* mapped to some value already.
* @throws NullPointerException if the specified value is null */
public TypeV replace ( long key, TypeV val ) { return putIfMatch( key, val,MATCH_ANY );}
/** Atomically do a <code>put(key,newValue)</code> if-and-only-if the key is
* mapped a value which is <code>equals</code> to <code>oldValue</code>.
* @throws NullPointerException if the specified value is null */
public boolean replace ( long key, TypeV oldValue, TypeV newValue ) {
return putIfMatch( key, newValue, oldValue ) == oldValue;
}
private final TypeV putIfMatch( long key, Object newVal, Object oldVal ) {
if (oldVal == null || newVal == null) throw new NullPointerException();
if( key == NO_KEY ) {
final Object curVal = _val_1;
if( oldVal == NO_MATCH_OLD || // Do we care about expected-Value at all?
curVal == oldVal || // No instant match already?
(oldVal == MATCH_ANY && curVal != TOMBSTONE) ||
oldVal.equals(curVal) ) // Expensive equals check
CAS(_val_1_offset,curVal,newVal); // One shot CAS update attempt
return curVal == TOMBSTONE ? null : (TypeV)curVal; // Return the last value present
}
final Object res = _chm.putIfMatch( key, newVal, oldVal );
assert !(res instanceof Prime);
assert res != null;
return res == TOMBSTONE ? null : (TypeV)res;
}
/** Removes all of the mappings from this map. */
public void clear() { // Smack a new empty table down
CHM newchm = new CHM(this,new Counter(),MIN_SIZE_LOG);
while( !CAS(_chm_offset,_chm,newchm) ) // Spin until the clear works
;
CAS(_val_1_offset,_val_1,TOMBSTONE);
}
/** Returns <tt>true</tt> if this Map maps one or more keys to the specified
* value. <em>Note</em>: This method requires a full internal traversal of the
* hash table and is much slower than {@link #containsKey}.
* @param val value whose presence in this map is to be tested
* @return <tt>true</tt> if this Map maps one or more keys to the specified value
* @throws NullPointerException if the specified value is null */
public boolean containsValue( Object val ) {
if( val == null ) return false;
if( val == _val_1 ) return true; // Key 0
for( TypeV V : values() )
if( V == val || V.equals(val) )
return true;
return false;
}
// --- get -----------------------------------------------------------------
/** Returns the value to which the specified key is mapped, or {@code null}
* if this map contains no mapping for the key.
* <p>More formally, if this map contains a mapping from a key {@code k} to
* a value {@code v} such that {@code key==k}, then this method
* returns {@code v}; otherwise it returns {@code null}. (There can be at
* most one such mapping.)
* @throws NullPointerException if the specified key is null */
// Never returns a Prime nor a Tombstone.
public final TypeV get( long key ) {
if( key == NO_KEY ) {
final Object V = _val_1;
return V == TOMBSTONE ? null : (TypeV)V;
}
final Object V = _chm.get_impl(key);
assert !(V instanceof Prime); // Never return a Prime
assert V != TOMBSTONE;
return (TypeV)V;
}
/** Auto-boxing version of {@link #get(long)}. */
public TypeV get ( Object key ) { return (key instanceof Long) ? get (((Long)key).longValue()) : null; }
/** Auto-boxing version of {@link #remove(long)}. */
public TypeV remove ( Object key ) { return (key instanceof Long) ? remove (((Long)key).longValue()) : null; }
/** Auto-boxing version of {@link #remove(long,Object)}. */
public boolean remove ( Object key, Object Val ) { return (key instanceof Long) ? remove (((Long)key).longValue(), Val) : false; }
/** Auto-boxing version of {@link #containsKey(long)}. */
public boolean containsKey( Object key ) { return (key instanceof Long) ? containsKey(((Long)key).longValue()) : false; }
/** Auto-boxing version of {@link #putIfAbsent}. */
public TypeV putIfAbsent( Long key, TypeV val ) { return putIfAbsent( ((Long)key).longValue(), val ); }
/** Auto-boxing version of {@link #replace}. */
public TypeV replace( Long key, TypeV Val ) { return replace(((Long)key).longValue(), Val); }
/** Auto-boxing version of {@link #put}. */
public TypeV put ( Long key, TypeV val ) { return put(key.longValue(),val); }
/** Auto-boxing version of {@link #replace}. */
public boolean replace( Long key, TypeV oldValue, TypeV newValue ) {
return replace(((Long)key).longValue(), oldValue, newValue);
}
// --- help_copy -----------------------------------------------------------
// Help along an existing resize operation. This is just a fast cut-out
// wrapper, to encourage inlining for the fast no-copy-in-progress case. We
// always help the top-most table copy, even if there are nested table
// copies in progress.
private final void help_copy( ) {
// Read the top-level CHM only once. We'll try to help this copy along,
// even if it gets promoted out from under us (i.e., the copy completes
// and another KVS becomes the top-level copy).
CHM topchm = _chm;
if( topchm._newchm == null ) return; // No copy in-progress
topchm.help_copy_impl(false);
}
// --- CHM -----------------------------------------------------------------
// The control structure for the NonBlockingHashMapLong
private static final class CHM<TypeV> implements Serializable {
// Back-pointer to top-level structure
final NonBlockingHashMapLong _nbhml;
// Size in active K,V pairs
private final Counter _size;
public int size () { return (int)_size.get(); }
// ---
// These next 2 fields are used in the resizing heuristics, to judge when
// it is time to resize or copy the table. Slots is a count of used-up
// key slots, and when it nears a large fraction of the table we probably
// end up reprobing too much. Last-resize-milli is the time since the
// last resize; if we are running back-to-back resizes without growing
// (because there are only a few live keys but many slots full of dead
// keys) then we need a larger table to cut down on the churn.
// Count of used slots, to tell when table is full of dead unusable slots
private final Counter _slots;
public int slots() { return (int)_slots.get(); }
// ---
// New mappings, used during resizing.
// The 'next' CHM - created during a resize operation. This represents
// the new table being copied from the old one. It's the volatile
// variable that is read as we cross from one table to the next, to get
// the required memory orderings. It monotonically transits from null to
// set (once).
volatile CHM _newchm;
private static final AtomicReferenceFieldUpdater<CHM,CHM> _newchmUpdater =
AtomicReferenceFieldUpdater.newUpdater(CHM.class,CHM.class, "_newchm");
// Set the _newchm field if we can. AtomicUpdaters do not fail spuriously.
boolean CAS_newchm( CHM newchm ) {
return _newchmUpdater.compareAndSet(this,null,newchm);
}
// Sometimes many threads race to create a new very large table. Only 1
// wins the race, but the losers all allocate a junk large table with
// hefty allocation costs. Attempt to control the overkill here by
// throttling attempts to create a new table. I cannot really block here
// (lest I lose the non-blocking property) but late-arriving threads can
// give the initial resizing thread a little time to allocate the initial
// new table. The Right Long Term Fix here is to use array-lets and
// incrementally create the new very large array. In C I'd make the array
// with malloc (which would mmap under the hood) which would only eat
// virtual-address and not real memory - and after Somebody wins then we
// could in parallel initialize the array. Java does not allow
// un-initialized array creation (especially of ref arrays!).
volatile long _resizers; // count of threads attempting an initial resize
private static final AtomicLongFieldUpdater<CHM> _resizerUpdater =
AtomicLongFieldUpdater.newUpdater(CHM.class, "_resizers");
// --- key,val -------------------------------------------------------------
// Access K,V for a given idx
private final boolean CAS_key( int idx, long old, long key ) {
return _unsafe.compareAndSwapLong ( _keys, rawIndex(_keys, idx), old, key );
}
private final boolean CAS_val( int idx, Object old, Object val ) {
return _unsafe.compareAndSwapObject( _vals, rawIndex(_vals, idx), old, val );
}
final long [] _keys;
final Object [] _vals;
// Simple constructor
CHM( final NonBlockingHashMapLong nbhml, Counter size, final int logsize ) {
_nbhml = nbhml;
_size = size;
_slots= new Counter();
_keys = new long [1<<logsize];
_vals = new Object[1<<logsize];
}
// --- print innards
private final void print() {
for( int i=0; i<_keys.length; i++ ) {
long K = _keys[i];
if( K != NO_KEY )
print_impl(i,K,_vals[i]);
}
CHM newchm = _newchm; // New table, if any
if( newchm != null ) {
System.out.println("----");
newchm.print();
}
}
// --- print only the live objects
private final void print2( ) {
for( int i=0; i<_keys.length; i++ ) {
long K = _keys[i];
if( K != NO_KEY ) // key is sane
print2_impl(i,K,_vals[i]);
}
CHM newchm = _newchm; // New table, if any
if( newchm != null ) {
System.out.println("----");
newchm.print2();
}
}
// --- get_impl ----------------------------------------------------------
// Never returns a Prime nor a Tombstone.
private final Object get_impl ( final long key ) {
final int len = _keys.length;
int idx = (int)(key & (len-1)); // First key hash
// Main spin/reprobe loop, looking for a Key hit
int reprobe_cnt=0;
while( true ) {
final long K = _keys[idx]; // Get key before volatile read, could be NO_KEY
final Object V = _vals[idx]; // Get value before volatile read, could be null or Tombstone or Prime
if( K == NO_KEY ) return null; // A clear miss
// Key-compare
if( key == K ) {
// Key hit! Check for no table-copy-in-progress
if( !(V instanceof Prime) ) { // No copy?
if( V == TOMBSTONE) return null;
// We need a volatile-read between reading a newly inserted Value
// and returning the Value (so the user might end up reading the
// stale Value contents).
final CHM newchm = _newchm; // VOLATILE READ before returning V
return V;
}
// Key hit - but slot is (possibly partially) copied to the new table.
// Finish the copy & retry in the new table.
return copy_slot_and_check(idx,key).get_impl(key); // Retry in the new table
}
// get and put must have the same key lookup logic! But only 'put'
// needs to force a table-resize for a too-long key-reprobe sequence.
// Check for too-many-reprobes on get.
if( ++reprobe_cnt >= reprobe_limit(len) ) // too many probes
return _newchm == null // Table copy in progress?
? null // Nope! A clear miss
: copy_slot_and_check(idx,key).get_impl(key); // Retry in the new table
idx = (idx+1)&(len-1); // Reprobe by 1! (could now prefetch)
}
}
// --- putIfMatch ---------------------------------------------------------
// Put, Remove, PutIfAbsent, etc. Return the old value. If the returned
// value is equal to expVal (or expVal is NO_MATCH_OLD) then the put can
// be assumed to work (although might have been immediately overwritten).
// Only the path through copy_slot passes in an expected value of null,
// and putIfMatch only returns a null if passed in an expected null.
private final Object putIfMatch( final long key, final Object putval, final Object expVal ) {
assert putval != null;
assert !(putval instanceof Prime);
assert !(expVal instanceof Prime);
final int len = _keys.length;
int idx = (int)(key & (len-1)); // The first key
// ---
// Key-Claim stanza: spin till we can claim a Key (or force a resizing).
int reprobe_cnt=0;
long K = NO_KEY;
Object V = null;
while( true ) { // Spin till we get a Key slot
V = _vals[idx]; // Get old value
K = _keys[idx]; // Get current key
if( K == NO_KEY ) { // Slot is free?
// Found an empty Key slot - which means this Key has never been in
// this table. No need to put a Tombstone - the Key is not here!
if( putval == TOMBSTONE ) return putval; // Not-now & never-been in this table
// Claim the zero key-slot
if( CAS_key(idx, NO_KEY, key) ) { // Claim slot for Key
_slots.add(1); // Raise key-slots-used count
break; // Got it!
}
// CAS to claim the key-slot failed.
//
// This re-read of the Key points out an annoying short-coming of Java
// CAS. Most hardware CAS's report back the existing value - so that
// if you fail you have a *witness* - the value which caused the CAS
// to fail. The Java API turns this into a boolean destroying the
// witness. Re-reading does not recover the witness because another
// thread can write over the memory after the CAS. Hence we can be in
// the unfortunate situation of having a CAS fail *for cause* but
// having that cause removed by a later store. This turns a
// non-spurious-failure CAS (such as Azul has) into one that can
// apparently spuriously fail - and we avoid apparent spurious failure
// by not allowing Keys to ever change.
K = _keys[idx]; // CAS failed, get updated value
assert K != NO_KEY ; // If keys[idx] is NO_KEY, CAS shoulda worked
}
// Key slot was not null, there exists a Key here
if( K == key )
break; // Got it!
// get and put must have the same key lookup logic! Lest 'get' give
// up looking too soon.
//topmap._reprobes.add(1);
if( ++reprobe_cnt >= reprobe_limit(len) ) {
// We simply must have a new table to do a 'put'. At this point a
// 'get' will also go to the new table (if any). We do not need
// to claim a key slot (indeed, we cannot find a free one to claim!).
final CHM newchm = resize();
if( expVal != null ) _nbhml.help_copy(); // help along an existing copy
return newchm.putIfMatch(key,putval,expVal);
}
idx = (idx+1)&(len-1); // Reprobe!
} // End of spinning till we get a Key slot
// ---
// Found the proper Key slot, now update the matching Value slot. We
// never put a null, so Value slots monotonically move from null to
// not-null (deleted Values use Tombstone). Thus if 'V' is null we
// fail this fast cutout and fall into the check for table-full.
if( putval == V ) return V; // Fast cutout for no-change
// See if we want to move to a new table (to avoid high average re-probe
// counts). We only check on the initial set of a Value from null to
// not-null (i.e., once per key-insert).
if( (V == null && tableFull(reprobe_cnt,len)) ||
// Or we found a Prime: resize is already in progress. The resize
// call below will do a CAS on _newchm forcing the read.
V instanceof Prime) {
resize(); // Force the new table copy to start
return copy_slot_and_check(idx,expVal).putIfMatch(key,putval,expVal);
}
// ---
// We are finally prepared to update the existing table
while( true ) {
assert !(V instanceof Prime);
// Must match old, and we do not? Then bail out now. Note that either V
// or expVal might be TOMBSTONE. Also V can be null, if we've never
// inserted a value before. expVal can be null if we are called from
// copy_slot.
if( expVal != NO_MATCH_OLD && // Do we care about expected-Value at all?
V != expVal && // No instant match already?
(expVal != MATCH_ANY || V == TOMBSTONE || V == null) &&
!(V==null && expVal == TOMBSTONE) && // Match on null/TOMBSTONE combo
(expVal == null || !expVal.equals(V)) ) // Expensive equals check at the last
return V; // Do not update!
// Actually change the Value in the Key,Value pair
if( CAS_val(idx, V, putval ) ) {
// CAS succeeded - we did the update!
// Both normal put's and table-copy calls putIfMatch, but table-copy
// does not (effectively) increase the number of live k/v pairs.
if( expVal != null ) {
// Adjust sizes - a striped counter
if( (V == null || V == TOMBSTONE) && putval != TOMBSTONE ) _size.add( 1);
if( !(V == null || V == TOMBSTONE) && putval == TOMBSTONE ) _size.add(-1);
}
return (V==null && expVal!=null) ? TOMBSTONE : V;
}
// Else CAS failed
V = _vals[idx]; // Get new value
// If a Prime'd value got installed, we need to re-run the put on the
// new table. Otherwise we lost the CAS to another racing put.
// Simply retry from the start.
if( V instanceof Prime )
return copy_slot_and_check(idx,expVal).putIfMatch(key,putval,expVal);
}
}
// --- tableFull ---------------------------------------------------------
// Heuristic to decide if this table is too full, and we should start a
// new table. Note that if a 'get' call has reprobed too many times and
// decided the table must be full, then always the estimate_sum must be
// high and we must report the table is full. If we do not, then we might
// end up deciding that the table is not full and inserting into the
// current table, while a 'get' has decided the same key cannot be in this
// table because of too many reprobes. The invariant is:
// slots.estimate_sum >= max_reprobe_cnt >= reprobe_limit(len)
private final boolean tableFull( int reprobe_cnt, int len ) {
return
// Do the cheap check first: we allow some number of reprobes always
reprobe_cnt >= REPROBE_LIMIT &&
// More expensive check: see if the table is > 1/4 full.
_slots.estimate_get() >= reprobe_limit(len);
}
// --- resize ------------------------------------------------------------
// Resizing after too many probes. "How Big???" heuristics are here.
// Callers will (not this routine) will 'help_copy' any in-progress copy.
// Since this routine has a fast cutout for copy-already-started, callers
// MUST 'help_copy' lest we have a path which forever runs through
// 'resize' only to discover a copy-in-progress which never progresses.
private final CHM resize() {
// Check for resize already in progress, probably triggered by another thread
CHM newchm = _newchm; // VOLATILE READ
if( newchm != null ) // See if resize is already in progress
return newchm; // Use the new table already
// No copy in-progress, so start one. First up: compute new table size.
int oldlen = _keys.length; // Old count of K,V pairs allowed
int sz = size(); // Get current table count of active K,V pairs
int newsz = sz; // First size estimate
// Heuristic to determine new size. We expect plenty of dead-slots-with-keys
// and we need some decent padding to avoid endless reprobing.
if( _nbhml._opt_for_space ) {
// This heuristic leads to a much denser table with a higher reprobe rate
if( sz >= (oldlen>>1) ) // If we are >50% full of keys then...
newsz = oldlen<<1; // Double size
} else {
if( sz >= (oldlen>>2) ) { // If we are >25% full of keys then...
newsz = oldlen<<1; // Double size
if( sz >= (oldlen>>1) ) // If we are >50% full of keys then...
newsz = oldlen<<2; // Double double size
}
}
// Last (re)size operation was very recent? Then double again; slows
// down resize operations for tables subject to a high key churn rate.
long tm = System.currentTimeMillis();
long q=0;
if( newsz <= oldlen && // New table would shrink or hold steady?
tm <= _nbhml._last_resize_milli+10000 && // Recent resize (less than 1 sec ago)
//(q=_slots.estimate_sum()) >= (sz<<1) ) // 1/2 of keys are dead?
true )
newsz = oldlen<<1; // Double the existing size
// Do not shrink, ever
if( newsz < oldlen ) newsz = oldlen;
//System.out.println("old="+oldlen+" new="+newsz+" size()="+sz+" est_slots()="+q+" millis="+(tm-_nbhml._last_resize_milli));
// Convert to power-of-2
int log2;
for( log2=MIN_SIZE_LOG; (1<<log2) < newsz; log2++ ) ; // Compute log2 of size
// Now limit the number of threads actually allocating memory to a
// handful - lest we have 750 threads all trying to allocate a giant
// resized array.
long r = _resizers;
while( !_resizerUpdater.compareAndSet(this,r,r+1) )
r = _resizers;
// Size calculation: 2 words (K+V) per table entry, plus a handful. We
// guess at 32-bit pointers; 64-bit pointers screws up the size calc by
// 2x but does not screw up the heuristic very much.
int megs = ((((1<<log2)<<1)+4)<<3/*word to bytes*/)>>20/*megs*/;
if( r >= 2 && megs > 0 ) { // Already 2 guys trying; wait and see
newchm = _newchm; // Between dorking around, another thread did it
if( newchm != null ) // See if resize is already in progress
return newchm; // Use the new table already
// TODO - use a wait with timeout, so we'll wakeup as soon as the new table
// is ready, or after the timeout in any case.
//synchronized( this ) { wait(8*megs); } // Timeout - we always wakeup
// For now, sleep a tad and see if the 2 guys already trying to make
// the table actually get around to making it happen.
try { Thread.sleep(8*megs); } catch( Exception e ) { }
}
// Last check, since the 'new' below is expensive and there is a chance
// that another thread slipped in a new thread while we ran the heuristic.
newchm = _newchm;
if( newchm != null ) // See if resize is already in progress
return newchm; // Use the new table already
// New CHM - actually allocate the big arrays
newchm = new CHM(_nbhml,_size,log2);
// Another check after the slow allocation
if( _newchm != null ) // See if resize is already in progress
return _newchm; // Use the new table already
// The new table must be CAS'd in so only 1 winner amongst duplicate
// racing resizing threads. Extra CHM's will be GC'd.
if( CAS_newchm( newchm ) ) { // NOW a resize-is-in-progress!
//notifyAll(); // Wake up any sleepers
//long nano = System.nanoTime();
//System.out.println(" "+nano+" Resize from "+oldlen+" to "+(1<<log2)+" and had "+(_resizers-1)+" extras" );
//System.out.print("["+log2);
} else // CAS failed?
newchm = _newchm; // Reread new table
return newchm;
}
// The next part of the table to copy. It monotonically transits from zero
// to _keys.length. Visitors to the table can claim 'work chunks' by
// CAS'ing this field up, then copying the indicated indices from the old
// table to the new table. Workers are not required to finish any chunk;
// the counter simply wraps and work is copied duplicately until somebody
// somewhere completes the count.
volatile long _copyIdx = 0;
static private final AtomicLongFieldUpdater<CHM> _copyIdxUpdater =
AtomicLongFieldUpdater.newUpdater(CHM.class, "_copyIdx");
// Work-done reporting. Used to efficiently signal when we can move to
// the new table. From 0 to len(oldkvs) refers to copying from the old
// table to the new.
volatile long _copyDone= 0;
static private final AtomicLongFieldUpdater<CHM> _copyDoneUpdater =
AtomicLongFieldUpdater.newUpdater(CHM.class, "_copyDone");
// --- help_copy_impl ----------------------------------------------------
// Help along an existing resize operation. We hope its the top-level
// copy (it was when we started) but this CHM might have been promoted out
// of the top position.
private final void help_copy_impl( final boolean copy_all ) {
final CHM newchm = _newchm;
assert newchm != null; // Already checked by caller
int oldlen = _keys.length; // Total amount to copy
final int MIN_COPY_WORK = Math.min(oldlen,1024); // Limit per-thread work
// ---
int panic_start = -1;
int copyidx=-9999; // Fool javac to think it's initialized
while( _copyDone < oldlen ) { // Still needing to copy?
// Carve out a chunk of work. The counter wraps around so every
// thread eventually tries to copy every slot repeatedly.
// We "panic" if we have tried TWICE to copy every slot - and it still
// has not happened. i.e., twice some thread somewhere claimed they
// would copy 'slot X' (by bumping _copyIdx) but they never claimed to
// have finished (by bumping _copyDone). Our choices become limited:
// we can wait for the work-claimers to finish (and become a blocking
// algorithm) or do the copy work ourselves. Tiny tables with huge
// thread counts trying to copy the table often 'panic'.
if( panic_start == -1 ) { // No panic?
copyidx = (int)_copyIdx;
while( copyidx < (oldlen<<1) && // 'panic' check
!_copyIdxUpdater.compareAndSet(this,copyidx,copyidx+MIN_COPY_WORK) )
copyidx = (int)_copyIdx; // Re-read
if( !(copyidx < (oldlen<<1)) ) // Panic!
panic_start = copyidx; // Record where we started to panic-copy
}
// We now know what to copy. Try to copy.
int workdone = 0;
for( int i=0; i<MIN_COPY_WORK; i++ )
if( copy_slot((copyidx+i)&(oldlen-1)) ) // Made an oldtable slot go dead?
workdone++; // Yes!
if( workdone > 0 ) // Report work-done occasionally
copy_check_and_promote( workdone );// See if we can promote
//for( int i=0; i<MIN_COPY_WORK; i++ )
// if( copy_slot((copyidx+i)&(oldlen-1)) ) // Made an oldtable slot go dead?
// copy_check_and_promote( 1 );// See if we can promote
copyidx += MIN_COPY_WORK;
// Uncomment these next 2 lines to turn on incremental table-copy.
// Otherwise this thread continues to copy until it is all done.
if( !copy_all && panic_start == -1 ) // No panic?
return; // Then done copying after doing MIN_COPY_WORK
}
// Extra promotion check, in case another thread finished all copying
// then got stalled before promoting.
copy_check_and_promote( 0 ); // See if we can promote
}
// --- copy_slot_and_check -----------------------------------------------
// Copy slot 'idx' from the old table to the new table. If this thread
// confirmed the copy, update the counters and check for promotion.
//
// Returns the result of reading the volatile _newchm, mostly as a
// convenience to callers. We come here with 1-shot copy requests
// typically because the caller has found a Prime, and has not yet read
// the _newchm volatile - which must have changed from null-to-not-null
// before any Prime appears. So the caller needs to read the _newchm
// field to retry his operation in the new table, but probably has not
// read it yet.
private final CHM copy_slot_and_check( int idx, Object should_help ) {
// We're only here because the caller saw a Prime, which implies a
// table-copy is in progress.
assert _newchm != null;
if( copy_slot(idx) ) // Copy the desired slot
copy_check_and_promote(1); // Record the slot copied
// Generically help along any copy (except if called recursively from a helper)
if( should_help != null ) _nbhml.help_copy();
return _newchm;
}
// --- copy_check_and_promote --------------------------------------------
private final void copy_check_and_promote( int workdone ) {
int oldlen = _keys.length;
// We made a slot unusable and so did some of the needed copy work
long copyDone = _copyDone;
long nowDone = copyDone+workdone;
assert nowDone <= oldlen;
if( workdone > 0 ) {
while( !_copyDoneUpdater.compareAndSet(this,copyDone,nowDone) ) {
copyDone = _copyDone; // Reload, retry
nowDone = copyDone+workdone;
assert nowDone <= oldlen;
}
//if( (10*copyDone/oldlen) != (10*nowDone/oldlen) )
// System.out.print(" "+nowDone*100/oldlen+"%"+"_"+(_copyIdx*100/oldlen)+"%");
}
// Check for copy being ALL done, and promote. Note that we might have
// nested in-progress copies and manage to finish a nested copy before
// finishing the top-level copy. We only promote top-level copies.
if( nowDone == oldlen && // Ready to promote this table?
_nbhml._chm == this && // Looking at the top-level table?
// Attempt to promote
_nbhml.CAS(_chm_offset,this,_newchm) ) {
_nbhml._last_resize_milli = System.currentTimeMillis(); // Record resize time for next check
//long nano = System.nanoTime();
//System.out.println(" "+nano+" Promote table "+oldlen+" to "+_newchm._keys.length);
//System.out.print("_"+oldlen+"]");
}
}
// --- copy_slot ---------------------------------------------------------
// Copy one K/V pair from oldkvs[i] to newkvs. Returns true if we can
// confirm that the new table guaranteed has a value for this old-table
// slot. We need an accurate confirmed-copy count so that we know when we
// can promote (if we promote the new table too soon, other threads may
// 'miss' on values not-yet-copied from the old table). We don't allow
// any direct updates on the new table, unless they first happened to the
// old table - so that any transition in the new table from null to
// not-null must have been from a copy_slot (or other old-table overwrite)
// and not from a thread directly writing in the new table. Thus we can
// count null-to-not-null transitions in the new table.
private boolean copy_slot( int idx ) {
// Blindly set the key slot from NO_KEY to some key which hashes here,
// to eagerly stop fresh put's from inserting new values in the old
// table when the old table is mid-resize. We don't need to act on the
// results here, because our correctness stems from box'ing the Value
// field. Slamming the Key field is a minor speed optimization.
long key;
while( (key=_keys[idx]) == NO_KEY )
CAS_key(idx, NO_KEY, (idx+_keys.length)/*a non-zero key which hashes here*/);
// ---
// Prevent new values from appearing in the old table.
// Box what we see in the old table, to prevent further updates.
Object oldval = _vals[idx]; // Read OLD table
while( !(oldval instanceof Prime) ) {
final Prime box = (oldval == null || oldval == TOMBSTONE) ? TOMBPRIME : new Prime(oldval);
if( CAS_val(idx,oldval,box) ) { // CAS down a box'd version of oldval
// If we made the Value slot hold a TOMBPRIME, then we both
// prevented further updates here but also the (absent) oldval is
// vaccuously available in the new table. We return with true here:
// any thread looking for a value for this key can correctly go
// straight to the new table and skip looking in the old table.
if( box == TOMBPRIME )
return true;
// Otherwise we boxed something, but it still needs to be
// copied into the new table.
oldval = box; // Record updated oldval
break; // Break loop; oldval is now boxed by us
}
oldval = _vals[idx]; // Else try, try again
}
if( oldval == TOMBPRIME ) return false; // Copy already complete here!
// ---
// Copy the value into the new table, but only if we overwrite a null.
// If another value is already in the new table, then somebody else
// wrote something there and that write is happens-after any value that
// appears in the old table. If putIfMatch does not find a null in the
// new table - somebody else should have recorded the null-not_null
// transition in this copy.
Object old_unboxed = ((Prime)oldval)._V;
assert old_unboxed != TOMBSTONE;
boolean copied_into_new = (_newchm.putIfMatch(key, old_unboxed, null) == null);
// ---
// Finally, now that any old value is exposed in the new table, we can
// forever hide the old-table value by slapping a TOMBPRIME down. This
// will stop other threads from uselessly attempting to copy this slot
// (i.e., it's a speed optimization not a correctness issue).
while( !CAS_val(idx,oldval,TOMBPRIME) )
oldval = _vals[idx];
return copied_into_new;
} // end copy_slot
} // End of CHM
// --- Snapshot ------------------------------------------------------------
private class SnapshotV implements Iterator<TypeV>, Enumeration<TypeV> {
final CHM _sschm;
public SnapshotV() {
CHM topchm;
while( true ) { // Verify no table-copy-in-progress
topchm = _chm;
if( topchm._newchm == null ) // No table-copy-in-progress
break;
// Table copy in-progress - so we cannot get a clean iteration. We
// must help finish the table copy before we can start iterating.
topchm.help_copy_impl(true);
}
// The "linearization point" for the iteration. Every key in this table
// will be visited, but keys added later might be skipped or even be
// added to a following table (also not iterated over).
_sschm = topchm;
// Warm-up the iterator
_idx = -1;
next();
}
int length() { return _sschm._keys.length; }
long key(final int idx) { return _sschm._keys[idx]; }
private int _idx; // -2 for NO_KEY, -1 for CHECK_NEW_TABLE_LONG, 0-keys.length
private long _nextK, _prevK; // Last 2 keys found
private TypeV _nextV, _prevV; // Last 2 values found
public boolean hasNext() { return _nextV != null; }
public TypeV next() {
// 'next' actually knows what the next value will be - it had to
// figure that out last go 'round lest 'hasNext' report true and
// some other thread deleted the last value. Instead, 'next'
// spends all its effort finding the key that comes after the
// 'next' key.
if( _idx != -1 && _nextV == null ) throw new NoSuchElementException();
_prevK = _nextK; // This will become the previous key
_prevV = _nextV; // This will become the previous value
_nextV = null; // We have no more next-key
// Attempt to set <_nextK,_nextV> to the next K,V pair.
// _nextV is the trigger: stop searching when it is != null
if( _idx == -1 ) { // Check for NO_KEY
_idx = 0; // Setup for next phase of search
_nextK = NO_KEY;
if( (_nextV=get(_nextK)) != null ) return _prevV;
}
while( _idx<length() ) { // Scan array
_nextK = key(_idx++); // Get a key that definitely is in the set (for the moment!)
if( _nextK != NO_KEY && // Found something?
(_nextV=get(_nextK)) != null )
break; // Got it! _nextK is a valid Key
} // Else keep scanning
return _prevV; // Return current value.
}
public void remove() {
if( _prevV == null ) throw new IllegalStateException();
_sschm.putIfMatch( _prevK, TOMBSTONE, _prevV );
_prevV = null;
}
public TypeV nextElement() { return next(); }
public boolean hasMoreElements() { return hasNext(); }
}
/** Returns an enumeration of the values in this table.
* @return an enumeration of the values in this table
* @see #values() */
public Enumeration<TypeV> elements() { return new SnapshotV(); }
// --- values --------------------------------------------------------------
/** Returns a {@link Collection} view of the values contained in this map.
* The collection is backed by the map, so changes to the map are reflected
* in the collection, and vice-versa. The collection supports element
* removal, which removes the corresponding mapping from this map, via the
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations.
* It does not support the <tt>add</tt> or <tt>addAll</tt> operations.
*
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator that
* will never throw {@link ConcurrentModificationException}, and guarantees
* to traverse elements as they existed upon construction of the iterator,
* and may (but is not guaranteed to) reflect any modifications subsequent
* to construction. */
public Collection<TypeV> values() {
return new AbstractCollection<TypeV>() {
public void clear ( ) { NonBlockingHashMapLong.this.clear ( ); }
public int size ( ) { return NonBlockingHashMapLong.this.size ( ); }
public boolean contains( Object v ) { return NonBlockingHashMapLong.this.containsValue(v); }
public Iterator<TypeV> iterator() { return new SnapshotV(); }
};
}
// --- keySet --------------------------------------------------------------
/** A class which implements the {@link Iterator} and {@link Enumeration}
* interfaces, generified to the {@link Long} class and supporting a
* <strong>non-auto-boxing</strong> {@link #nextLong} function. */
public class IteratorLong implements LongIterator, Enumeration<Long> {
private final SnapshotV _ss;
/** A new IteratorLong */
public IteratorLong() { _ss = new SnapshotV(); }
/** Remove last key returned by {@link #next} or {@link #nextLong}. */
public void remove() { _ss.remove(); }
/** <strong>Auto-box</strong> and return the next key. */
public Long next () { _ss.next(); return _ss._prevK; }
/** Return the next key as a primitive {@code long}. */
public long nextLong() { _ss.next(); return _ss._prevK; }
/** True if there are more keys to iterate over. */
public boolean hasNext() { return _ss.hasNext(); }
/** <strong>Auto-box</strong> and return the next key. */
public Long nextElement() { return next(); }
/** True if there are more keys to iterate over. */
public boolean hasMoreElements() { return hasNext(); }
}
/** Returns an enumeration of the <strong>auto-boxed</strong> keys in this table.
* <strong>Warning:</strong> this version will auto-box all returned keys.
* @return an enumeration of the auto-boxed keys in this table
* @see #keySet() */
public Enumeration<Long> keys() { return new IteratorLong(); }
/** Returns a {@link Set} view of the keys contained in this map; with care
* the keys may be iterated over <strong>without auto-boxing</strong>. The
* set is backed by the map, so changes to the map are reflected in the
* set, and vice-versa. The set supports element removal, which removes
* the corresponding mapping from this map, via the
* <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, <tt>removeAll</tt>,
* <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not support
* the <tt>add</tt> or <tt>addAll</tt> operations.
*
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator that
* will never throw {@link ConcurrentModificationException}, and guarantees
* to traverse elements as they existed upon construction of the iterator,
* and may (but is not guaranteed to) reflect any modifications subsequent
* to construction. */
public Set<Long> keySet() {
return new AbstractSet<Long> () {
public void clear ( ) { NonBlockingHashMapLong.this.clear ( ); }
public int size ( ) { return NonBlockingHashMapLong.this.size ( ); }
public boolean contains( Object k ) { return NonBlockingHashMapLong.this.containsKey(k); }
public boolean remove ( Object k ) { return NonBlockingHashMapLong.this.remove (k) != null; }
public IteratorLong iterator() { return new IteratorLong(); }
};
}
// --- entrySet ------------------------------------------------------------
// Warning: Each call to 'next' in this iterator constructs a new Long and a
// new NBHMLEntry.
private class NBHMLEntry extends AbstractEntry<Long,TypeV> {
NBHMLEntry( final Long k, final TypeV v ) { super(k,v); }
public TypeV setValue(final TypeV val) {
if (val == null) throw new NullPointerException();
_val = val;
return put(_key, val);
}
}
private class SnapshotE implements Iterator<Map.Entry<Long,TypeV>> {
final SnapshotV _ss;
public SnapshotE() { _ss = new SnapshotV(); }
public void remove() { _ss.remove(); }
public Map.Entry<Long,TypeV> next() { _ss.next(); return new NBHMLEntry(_ss._prevK,_ss._prevV); }
public boolean hasNext() { return _ss.hasNext(); }
}
/** Returns a {@link Set} view of the mappings contained in this map. The
* set is backed by the map, so changes to the map are reflected in the
* set, and vice-versa. The set supports element removal, which removes
* the corresponding mapping from the map, via the
* <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, <tt>removeAll</tt>,
* <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not support
* the <tt>add</tt> or <tt>addAll</tt> operations.
*
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
* that will never throw {@link ConcurrentModificationException},
* and guarantees to traverse elements as they existed upon
* construction of the iterator, and may (but is not guaranteed to)
* reflect any modifications subsequent to construction.
*
* <p><strong>Warning:</strong> the iterator associated with this Set
* requires the creation of {@link java.util.Map.Entry} objects with each
* iteration. The {@link org.cliffc.high_scale_lib.NonBlockingHashMap}
* does not normally create or using {@link java.util.Map.Entry} objects so
* they will be created soley to support this iteration. Iterating using
* {@link #keySet} or {@link #values} will be more efficient. In addition,
* this version requires <strong>auto-boxing</strong> the keys.
*/
public Set<Map.Entry<Long,TypeV>> entrySet() {
return new AbstractSet<Map.Entry<Long,TypeV>>() {
public void clear ( ) { NonBlockingHashMapLong.this.clear( ); }
public int size ( ) { return NonBlockingHashMapLong.this.size ( ); }
public boolean remove( final Object o ) {
if (!(o instanceof Map.Entry)) return false;
final Map.Entry<?,?> e = (Map.Entry<?,?>)o;
return NonBlockingHashMapLong.this.remove(e.getKey(), e.getValue());
}
public boolean contains(final Object o) {
if (!(o instanceof Map.Entry)) return false;
final Map.Entry<?,?> e = (Map.Entry<?,?>)o;
TypeV v = get(e.getKey());
return v.equals(e.getValue());
}
public Iterator<Map.Entry<Long,TypeV>> iterator() { return new SnapshotE(); }
};
}
// --- writeObject -------------------------------------------------------
// Write a NBHML to a stream
private void writeObject(java.io.ObjectOutputStream s) throws IOException {
s.defaultWriteObject(); // Write nothing
for( long K : keySet() ) {
final Object V = get(K); // Do an official 'get'
s.writeLong (K); // Write the <long,TypeV> pair
s.writeObject(V);
}
s.writeLong(NO_KEY); // Sentinel to indicate end-of-data
s.writeObject(null);
}
// --- readObject --------------------------------------------------------
// Read a CHM from a stream
private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException {
s.defaultReadObject(); // Read nothing
initialize(MIN_SIZE);
for (;;) {
final long K = s.readLong();
final TypeV V = (TypeV) s.readObject();
if( K == NO_KEY && V == null ) break;
put(K,V); // Insert with an offical put
}
}
} // End NonBlockingHashMapLong class