// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
//
/*============================================================
**
**
**
** Purpose: A scalable dictionary for concurrent access
**
**
===========================================================*/
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Diagnostics.Contracts;
using System.Runtime.InteropServices;
using System.Runtime.Serialization;
using System.Text;
using System.Threading;
using System.Security;
namespace System.Collections.Concurrent
{
///
/// Represents a thread-safe collection of keys and values.
///
/// The type of the keys in the dictionary.
/// The type of the values in the dictionary.
///
/// All public and protected members of are thread-safe and may be used
/// concurrently from multiple threads.
///
[DebuggerTypeProxy(typeof(Mscorlib_DictionaryDebugView<,>))]
[DebuggerDisplay("Count = {Count}")]
internal class ConcurrentDictionary : IDictionary, IDictionary, IReadOnlyDictionary
{
///
/// Tables that hold the internal state of the ConcurrentDictionary
///
/// Wrapping the three tables in a single object allows us to atomically
/// replace all tables at once.
///
private class Tables
{
internal readonly Node[] m_buckets; // A singly-linked list for each bucket.
internal readonly object[] m_locks; // A set of locks, each guarding a section of the table.
internal volatile int[] m_countPerLock; // The number of elements guarded by each lock.
internal readonly IEqualityComparer m_comparer; // Key equality comparer
internal Tables(Node[] buckets, object[] locks, int[] countPerLock, IEqualityComparer comparer)
{
m_buckets = buckets;
m_locks = locks;
m_countPerLock = countPerLock;
m_comparer = comparer;
}
}
private volatile Tables m_tables; // Internal tables of the dictionary
// NOTE: this is only used for compat reasons to serialize the comparer.
// This should not be accessed from anywhere else outside of the serialization methods.
internal IEqualityComparer m_comparer;
private readonly bool m_growLockArray; // Whether to dynamically increase the size of the striped lock
// How many times we resized becaused of collisions.
// This is used to make sure we don't resize the dictionary because of multi-threaded Add() calls
// that generate collisions. Whenever a GrowTable() should be the only place that changes this
private int m_keyRehashCount;
private int m_budget; // The maximum number of elements per lock before a resize operation is triggered
// The default concurrency level is DEFAULT_CONCURRENCY_MULTIPLIER * #CPUs. The higher the
// DEFAULT_CONCURRENCY_MULTIPLIER, the more concurrent writes can take place without interference
// and blocking, but also the more expensive operations that require all locks become (e.g. table
// resizing, ToArray, Count, etc). According to brief benchmarks that we ran, 4 seems like a good
// compromise.
private const int DEFAULT_CONCURRENCY_MULTIPLIER = 4;
// The default capacity, i.e. the initial # of buckets. When choosing this value, we are making
// a trade-off between the size of a very small dictionary, and the number of resizes when
// constructing a large dictionary. Also, the capacity should not be divisible by a small prime.
private const int DEFAULT_CAPACITY = 31;
// The maximum size of the striped lock that will not be exceeded when locks are automatically
// added as the dictionary grows. However, the user is allowed to exceed this limit by passing
// a concurrency level larger than MAX_LOCK_NUMBER into the constructor.
private const int MAX_LOCK_NUMBER = 1024;
// Whether TValue is a type that can be written atomically (i.e., with no danger of torn reads)
private static readonly bool s_isValueWriteAtomic = IsValueWriteAtomic();
///
/// Determines whether type TValue can be written atomically
///
private static bool IsValueWriteAtomic()
{
Type valueType = typeof(TValue);
//
// Section 12.6.6 of ECMA CLI explains which types can be read and written atomically without
// the risk of tearing.
//
// See http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-335.pdf
//
bool isAtomic =
(valueType.IsClass)
|| valueType == typeof(Boolean)
|| valueType == typeof(Char)
|| valueType == typeof(Byte)
|| valueType == typeof(SByte)
|| valueType == typeof(Int16)
|| valueType == typeof(UInt16)
|| valueType == typeof(Int32)
|| valueType == typeof(UInt32)
|| valueType == typeof(Single);
if (!isAtomic && IntPtr.Size == 8)
{
isAtomic |= valueType == typeof(Double) || valueType == typeof(Int64);
}
return isAtomic;
}
///
/// Initializes a new instance of the
/// class that is empty, has the default concurrency level, has the default initial capacity, and
/// uses the default comparer for the key type.
///
public ConcurrentDictionary() : this(DefaultConcurrencyLevel, DEFAULT_CAPACITY, true, EqualityComparer.Default) { }
internal ConcurrentDictionary(int concurrencyLevel, int capacity, bool growLockArray, IEqualityComparer comparer)
{
if (concurrencyLevel < 1)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.concurrencyLevel, ExceptionResource.ConcurrentDictionary_ConcurrencyLevelMustBePositive);
}
if (capacity < 0)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.capacity, ExceptionResource.ConcurrentDictionary_CapacityMustNotBeNegative);
}
if (comparer == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.comparer);
// The capacity should be at least as large as the concurrency level. Otherwise, we would have locks that don't guard
// any buckets.
if (capacity < concurrencyLevel)
{
capacity = concurrencyLevel;
}
object[] locks = new object[concurrencyLevel];
for (int i = 0; i < locks.Length; i++)
{
locks[i] = new object();
}
int[] countPerLock = new int[locks.Length];
Node[] buckets = new Node[capacity];
m_tables = new Tables(buckets, locks, countPerLock, comparer);
m_growLockArray = growLockArray;
m_budget = buckets.Length / locks.Length;
}
///
/// Attempts to add the specified key and value to the .
///
/// The key of the element to add.
/// The value of the element to add. The value can be a null reference (Nothing
/// in Visual Basic) for reference types.
/// true if the key/value pair was added to the
/// successfully; otherwise, false.
/// is null reference
/// (Nothing in Visual Basic).
/// The
/// contains too many elements.
public bool TryAdd(TKey key, TValue value)
{
if (key == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
TValue dummy;
return TryAddInternal(key, value, false, true, out dummy);
}
///
/// Determines whether the contains the specified
/// key.
///
/// The key to locate in the .
/// true if the contains an element with
/// the specified key; otherwise, false.
/// is a null reference
/// (Nothing in Visual Basic).
public bool ContainsKey(TKey key)
{
if (key == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
TValue throwAwayValue;
return TryGetValue(key, out throwAwayValue);
}
///
/// Attempts to remove and return the the value with the specified key from the
/// .
///
/// The key of the element to remove and return.
/// When this method returns, contains the object removed from the
/// or the default value of
/// if the operation failed.
/// true if an object was removed successfully; otherwise, false.
/// is a null reference
/// (Nothing in Visual Basic).
public bool TryRemove(TKey key, out TValue value)
{
if (key == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
return TryRemoveInternal(key, out value, false, default(TValue));
}
///
/// Removes the specified key from the dictionary if it exists and returns its associated value.
/// If matchValue flag is set, the key will be removed only if is associated with a particular
/// value.
///
/// The key to search for and remove if it exists.
/// The variable into which the removed value, if found, is stored.
/// Whether removal of the key is conditional on its value.
/// The conditional value to compare against if is true
///
[SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "Reviewed for thread safety")]
private bool TryRemoveInternal(TKey key, out TValue value, bool matchValue, TValue oldValue)
{
while (true)
{
Tables tables = m_tables;
IEqualityComparer comparer = tables.m_comparer;
int bucketNo, lockNo;
GetBucketAndLockNo(comparer.GetHashCode(key), out bucketNo, out lockNo, tables.m_buckets.Length, tables.m_locks.Length);
lock (tables.m_locks[lockNo])
{
// If the table just got resized, we may not be holding the right lock, and must retry.
// This should be a rare occurence.
if (tables != m_tables)
{
continue;
}
Node prev = null;
for (Node curr = tables.m_buckets[bucketNo]; curr != null; curr = curr.m_next)
{
Assert((prev == null && curr == tables.m_buckets[bucketNo]) || prev.m_next == curr);
if (comparer.Equals(curr.m_key, key))
{
if (matchValue)
{
bool valuesMatch = EqualityComparer.Default.Equals(oldValue, curr.m_value);
if (!valuesMatch)
{
value = default(TValue);
return false;
}
}
if (prev == null)
{
Volatile.Write(ref tables.m_buckets[bucketNo], curr.m_next);
}
else
{
prev.m_next = curr.m_next;
}
value = curr.m_value;
tables.m_countPerLock[lockNo]--;
return true;
}
prev = curr;
}
}
value = default(TValue);
return false;
}
}
///
/// Attempts to get the value associated with the specified key from the .
///
/// The key of the value to get.
/// When this method returns, contains the object from
/// the
/// with the specified key or the default value of
/// , if the operation failed.
/// true if the key was found in the ;
/// otherwise, false.
/// is a null reference
/// (Nothing in Visual Basic).
[SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "Reviewed for thread safety")]
public bool TryGetValue(TKey key, out TValue value)
{
if (key == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
int bucketNo, lockNoUnused;
// We must capture the m_buckets field in a local variable. It is set to a new table on each table resize.
Tables tables = m_tables;
IEqualityComparer comparer = tables.m_comparer;
GetBucketAndLockNo(comparer.GetHashCode(key), out bucketNo, out lockNoUnused, tables.m_buckets.Length, tables.m_locks.Length);
// We can get away w/out a lock here.
// The Volatile.Read ensures that the load of the fields of 'n' doesn't move before the load from buckets[i].
Node n = Volatile.Read(ref tables.m_buckets[bucketNo]);
while (n != null)
{
if (comparer.Equals(n.m_key, key))
{
value = n.m_value;
return true;
}
n = n.m_next;
}
value = default(TValue);
return false;
}
///
/// Removes all keys and values from the .
///
public void Clear()
{
int locksAcquired = 0;
try
{
AcquireAllLocks(ref locksAcquired);
Tables newTables = new Tables(new Node[DEFAULT_CAPACITY], m_tables.m_locks, new int[m_tables.m_countPerLock.Length], m_tables.m_comparer);
m_tables = newTables;
m_budget = Math.Max(1, newTables.m_buckets.Length / newTables.m_locks.Length);
}
finally
{
ReleaseLocks(0, locksAcquired);
}
}
///
/// Copies the elements of the to an array of
/// type , starting at the
/// specified array index.
///
/// The one-dimensional array of type
/// that is the destination of the elements copied from the . The array must have zero-based indexing.
/// The zero-based index in at which copying
/// begins.
/// is a null reference
/// (Nothing in Visual Basic).
/// is less than
/// 0.
/// is equal to or greater than
/// the length of the . -or- The number of elements in the source
/// is greater than the available space from to the end of the destination
/// .
[SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "ConcurrencyCop just doesn't know about these locks")]
void ICollection>.CopyTo(KeyValuePair[] array, int index)
{
if (array == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
if (index < 0) ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ConcurrentDictionary_IndexIsNegative);
int locksAcquired = 0;
try
{
AcquireAllLocks(ref locksAcquired);
int count = 0;
for (int i = 0; i < m_tables.m_locks.Length && count >= 0; i++)
{
count += m_tables.m_countPerLock[i];
}
if (array.Length - count < index || count < 0) //"count" itself or "count + index" can overflow
{
ThrowHelper.ThrowArgumentException(ExceptionResource.ConcurrentDictionary_ArrayNotLargeEnough);
}
CopyToPairs(array, index);
}
finally
{
ReleaseLocks(0, locksAcquired);
}
}
///
/// Copies the key and value pairs stored in the to a
/// new array.
///
/// A new array containing a snapshot of key and value pairs copied from the .
[SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "ConcurrencyCop just doesn't know about these locks")]
public KeyValuePair[] ToArray()
{
int locksAcquired = 0;
try
{
AcquireAllLocks(ref locksAcquired);
int count = 0;
checked
{
for (int i = 0; i < m_tables.m_locks.Length; i++)
{
count += m_tables.m_countPerLock[i];
}
}
KeyValuePair[] array = new KeyValuePair[count];
CopyToPairs(array, 0);
return array;
}
finally
{
ReleaseLocks(0, locksAcquired);
}
}
///
/// Copy dictionary contents to an array - shared implementation between ToArray and CopyTo.
///
/// Important: the caller must hold all locks in m_locks before calling CopyToPairs.
///
private void CopyToPairs(KeyValuePair[] array, int index)
{
Node[] buckets = m_tables.m_buckets;
for (int i = 0; i < buckets.Length; i++)
{
for (Node current = buckets[i]; current != null; current = current.m_next)
{
array[index] = new KeyValuePair(current.m_key, current.m_value);
index++; //this should never flow, CopyToPairs is only called when there's no overflow risk
}
}
}
///
/// Copy dictionary contents to an array - shared implementation between ToArray and CopyTo.
///
/// Important: the caller must hold all locks in m_locks before calling CopyToEntries.
///
private void CopyToEntries(DictionaryEntry[] array, int index)
{
Node[] buckets = m_tables.m_buckets;
for (int i = 0; i < buckets.Length; i++)
{
for (Node current = buckets[i]; current != null; current = current.m_next)
{
array[index] = new DictionaryEntry(current.m_key, current.m_value);
index++; //this should never flow, CopyToEntries is only called when there's no overflow risk
}
}
}
///
/// Copy dictionary contents to an array - shared implementation between ToArray and CopyTo.
///
/// Important: the caller must hold all locks in m_locks before calling CopyToObjects.
///
private void CopyToObjects(object[] array, int index)
{
Node[] buckets = m_tables.m_buckets;
for (int i = 0; i < buckets.Length; i++)
{
for (Node current = buckets[i]; current != null; current = current.m_next)
{
array[index] = new KeyValuePair(current.m_key, current.m_value);
index++; //this should never flow, CopyToObjects is only called when there's no overflow risk
}
}
}
/// Returns an enumerator that iterates through the .
/// An enumerator for the .
///
/// The enumerator returned from the dictionary is safe to use concurrently with
/// reads and writes to the dictionary, however it does not represent a moment-in-time snapshot
/// of the dictionary. The contents exposed through the enumerator may contain modifications
/// made to the dictionary after was called.
///
public IEnumerator> GetEnumerator()
{
Node[] buckets = m_tables.m_buckets;
for (int i = 0; i < buckets.Length; i++)
{
// The Volatile.Read ensures that the load of the fields of 'current' doesn't move before the load from buckets[i].
Node current = Volatile.Read(ref buckets[i]);
while (current != null)
{
yield return new KeyValuePair(current.m_key, current.m_value);
current = current.m_next;
}
}
}
///
/// Shared internal implementation for inserts and updates.
/// If key exists, we always return false; and if updateIfExists == true we force update with value;
/// If key doesn't exist, we always add value and return true;
///
[SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "Reviewed for thread safety")]
private bool TryAddInternal(TKey key, TValue value, bool updateIfExists, bool acquireLock, out TValue resultingValue)
{
while (true)
{
int bucketNo, lockNo;
int hashcode;
Tables tables = m_tables;
IEqualityComparer comparer = tables.m_comparer;
hashcode = comparer.GetHashCode(key);
GetBucketAndLockNo(hashcode, out bucketNo, out lockNo, tables.m_buckets.Length, tables.m_locks.Length);
bool resizeDesired = false;
bool lockTaken = false;
try
{
if (acquireLock)
Monitor.Enter(tables.m_locks[lockNo], ref lockTaken);
// If the table just got resized, we may not be holding the right lock, and must retry.
// This should be a rare occurence.
if (tables != m_tables)
{
continue;
}
// Try to find this key in the bucket
Node prev = null;
for (Node node = tables.m_buckets[bucketNo]; node != null; node = node.m_next)
{
Assert((prev == null && node == tables.m_buckets[bucketNo]) || prev.m_next == node);
if (comparer.Equals(node.m_key, key))
{
// The key was found in the dictionary. If updates are allowed, update the value for that key.
// We need to create a new node for the update, in order to support TValue types that cannot
// be written atomically, since lock-free reads may be happening concurrently.
if (updateIfExists)
{
if (s_isValueWriteAtomic)
{
node.m_value = value;
}
else
{
Node newNode = new Node(node.m_key, value, hashcode, node.m_next);
if (prev == null)
{
tables.m_buckets[bucketNo] = newNode;
}
else
{
prev.m_next = newNode;
}
}
resultingValue = value;
}
else
{
resultingValue = node.m_value;
}
return false;
}
prev = node;
}
// The key was not found in the bucket. Insert the key-value pair.
Volatile.Write(ref tables.m_buckets[bucketNo], new Node(key, value, hashcode, tables.m_buckets[bucketNo]));
checked
{
tables.m_countPerLock[lockNo]++;
}
//
// If the number of elements guarded by this lock has exceeded the budget, resize the bucket table.
// It is also possible that GrowTable will increase the budget but won't resize the bucket table.
// That happens if the bucket table is found to be poorly utilized due to a bad hash function.
//
if (tables.m_countPerLock[lockNo] > m_budget)
{
resizeDesired = true;
}
}
finally
{
if (lockTaken)
Monitor.Exit(tables.m_locks[lockNo]);
}
//
// The fact that we got here means that we just performed an insertion. If necessary, we will grow the table.
//
// Concurrency notes:
// - Notice that we are not holding any locks at when calling GrowTable. This is necessary to prevent deadlocks.
// - As a result, it is possible that GrowTable will be called unnecessarily. But, GrowTable will obtain lock 0
// and then verify that the table we passed to it as the argument is still the current table.
//
if (resizeDesired)
{
#if FEATURE_RANDOMIZED_STRING_HASHING
GrowTable(tables, tables.m_comparer, false, m_keyRehashCount);
#else
GrowTable(tables, tables.m_comparer, false, m_keyRehashCount);
#endif
}
resultingValue = value;
return true;
}
}
///
/// Gets or sets the value associated with the specified key.
///
/// The key of the value to get or set.
/// The value associated with the specified key. If the specified key is not found, a get
/// operation throws a
/// , and a set operation creates a new
/// element with the specified key.
/// is a null reference
/// (Nothing in Visual Basic).
/// The property is retrieved and
///
/// does not exist in the collection.
public TValue this[TKey key]
{
get
{
TValue value;
if (!TryGetValue(key, out value))
{
ThrowHelper.ThrowKeyNotFoundException();
}
return value;
}
set
{
if (key == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
TValue dummy;
TryAddInternal(key, value, true, true, out dummy);
}
}
///
/// Gets the number of key/value pairs contained in the .
///
/// The dictionary contains too many
/// elements.
/// The number of key/value paris contained in the .
/// Count has snapshot semantics and represents the number of items in the
/// at the moment when Count was accessed.
public int Count
{
[SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "ConcurrencyCop just doesn't know about these locks")]
get
{
int count = 0;
int acquiredLocks = 0;
try
{
// Acquire all locks
AcquireAllLocks(ref acquiredLocks);
// Compute the count, we allow overflow
for (int i = 0; i < m_tables.m_countPerLock.Length; i++)
{
count += m_tables.m_countPerLock[i];
}
}
finally
{
// Release locks that have been acquired earlier
ReleaseLocks(0, acquiredLocks);
}
return count;
}
}
///
/// Gets a value that indicates whether the is empty.
///
/// true if the is empty; otherwise,
/// false.
public bool IsEmpty
{
[SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "ConcurrencyCop just doesn't know about these locks")]
get
{
int acquiredLocks = 0;
try
{
// Acquire all locks
AcquireAllLocks(ref acquiredLocks);
for (int i = 0; i < m_tables.m_countPerLock.Length; i++)
{
if (m_tables.m_countPerLock[i] != 0)
{
return false;
}
}
}
finally
{
// Release locks that have been acquired earlier
ReleaseLocks(0, acquiredLocks);
}
return true;
}
}
#region IDictionary members
///
/// Adds the specified key and value to the .
///
/// The object to use as the key of the element to add.
/// The object to use as the value of the element to add.
/// is a null reference
/// (Nothing in Visual Basic).
/// The dictionary contains too many
/// elements.
///
/// An element with the same key already exists in the .
void IDictionary.Add(TKey key, TValue value)
{
if (!TryAdd(key, value))
{
ThrowHelper.ThrowArgumentException(ExceptionResource.ConcurrentDictionary_KeyAlreadyExisted);
}
}
///
/// Removes the element with the specified key from the .
///
/// The key of the element to remove.
/// true if the element is successfully remove; otherwise false. This method also returns
/// false if
/// was not found in the original .
///
/// is a null reference
/// (Nothing in Visual Basic).
bool IDictionary.Remove(TKey key)
{
TValue throwAwayValue;
return TryRemove(key, out throwAwayValue);
}
///
/// Gets a collection containing the keys in the .
///
/// An containing the keys in the
/// .
public ICollection Keys
{
get { return GetKeys(); }
}
///
/// Gets an containing the keys of
/// the .
///
/// An containing the keys of
/// the .
IEnumerable IReadOnlyDictionary.Keys
{
get { return GetKeys(); }
}
///
/// Gets a collection containing the values in the .
///
/// An containing the values in
/// the
/// .
public ICollection Values
{
get { return GetValues(); }
}
///
/// Gets an containing the values
/// in the .
///
/// An containing the
/// values in the .
IEnumerable IReadOnlyDictionary.Values
{
get { return GetValues(); }
}
#endregion
#region ICollection> Members
///
/// Adds the specified value to the
/// with the specified key.
///
/// The
/// structure representing the key and value to add to the .
/// The of is null.
/// The
/// contains too many elements.
/// An element with the same key already exists in the
///
void ICollection>.Add(KeyValuePair keyValuePair)
{
((IDictionary)this).Add(keyValuePair.Key, keyValuePair.Value);
}
///
/// Determines whether the
/// contains a specific key and value.
///
/// The
/// structure to locate in the .
/// true if the is found in the ; otherwise, false.
bool ICollection>.Contains(KeyValuePair keyValuePair)
{
TValue value;
if (!TryGetValue(keyValuePair.Key, out value))
{
return false;
}
return EqualityComparer.Default.Equals(value, keyValuePair.Value);
}
///
/// Gets a value indicating whether the dictionary is read-only.
///
/// true if the is
/// read-only; otherwise, false. For , this property always returns
/// false.
bool ICollection>.IsReadOnly
{
get { return false; }
}
///
/// Removes a key and value from the dictionary.
///
/// The
/// structure representing the key and value to remove from the .
/// true if the key and value represented by is successfully
/// found and removed; otherwise, false.
/// The Key property of is a null reference (Nothing in Visual Basic).
bool ICollection>.Remove(KeyValuePair keyValuePair)
{
if (keyValuePair.Key == null) ThrowHelper.ThrowArgumentNullException(ExceptionResource.ConcurrentDictionary_ItemKeyIsNull);
TValue throwAwayValue;
return TryRemoveInternal(keyValuePair.Key, out throwAwayValue, true, keyValuePair.Value);
}
#endregion
#region IEnumerable Members
/// Returns an enumerator that iterates through the .
/// An enumerator for the .
///
/// The enumerator returned from the dictionary is safe to use concurrently with
/// reads and writes to the dictionary, however it does not represent a moment-in-time snapshot
/// of the dictionary. The contents exposed through the enumerator may contain modifications
/// made to the dictionary after was called.
///
IEnumerator IEnumerable.GetEnumerator()
{
return ((ConcurrentDictionary)this).GetEnumerator();
}
#endregion
#region IDictionary Members
///
/// Adds the specified key and value to the dictionary.
///
/// The object to use as the key.
/// The object to use as the value.
/// is a null reference
/// (Nothing in Visual Basic).
/// The dictionary contains too many
/// elements.
///
/// is of a type that is not assignable to the key type of the . -or-
/// is of a type that is not assignable to ,
/// the type of values in the .
/// -or- A value with the same key already exists in the .
///
void IDictionary.Add(object key, object value)
{
if (key == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
if (!(key is TKey)) ThrowHelper.ThrowArgumentException(ExceptionResource.ConcurrentDictionary_TypeOfKeyIncorrect);
TValue typedValue = default(TValue);
try
{
typedValue = (TValue)value;
}
catch (InvalidCastException)
{
ThrowHelper.ThrowArgumentException(ExceptionResource.ConcurrentDictionary_TypeOfValueIncorrect);
}
((IDictionary)this).Add((TKey)key, typedValue);
}
///
/// Gets whether the contains an
/// element with the specified key.
///
/// The key to locate in the .
/// true if the contains
/// an element with the specified key; otherwise, false.
/// is a null reference
/// (Nothing in Visual Basic).
bool IDictionary.Contains(object key)
{
if (key == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
return (key is TKey) && ((ConcurrentDictionary)this).ContainsKey((TKey)key);
}
/// Provides an for the
/// .
/// An for the .
IDictionaryEnumerator IDictionary.GetEnumerator()
{
return new DictionaryEnumerator(this);
}
///
/// Gets a value indicating whether the has a fixed size.
///
/// true if the has a
/// fixed size; otherwise, false. For , this property always
/// returns false.
bool IDictionary.IsFixedSize
{
get { return false; }
}
///
/// Gets a value indicating whether the is read-only.
///
/// true if the is
/// read-only; otherwise, false. For , this property always
/// returns false.
bool IDictionary.IsReadOnly
{
get { return false; }
}
///
/// Gets an containing the keys of the .
///
/// An containing the keys of the .
ICollection IDictionary.Keys
{
get { return GetKeys(); }
}
///
/// Removes the element with the specified key from the .
///
/// The key of the element to remove.
/// is a null reference
/// (Nothing in Visual Basic).
void IDictionary.Remove(object key)
{
if (key == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
TValue throwAwayValue;
if (key is TKey)
{
this.TryRemove((TKey)key, out throwAwayValue);
}
}
///
/// Gets an containing the values in the .
///
/// An containing the values in the .
ICollection IDictionary.Values
{
get { return GetValues(); }
}
///
/// Gets or sets the value associated with the specified key.
///
/// The key of the value to get or set.
/// The value associated with the specified key, or a null reference (Nothing in Visual Basic)
/// if is not in the dictionary or is of a type that is
/// not assignable to the key type of the .
/// is a null reference
/// (Nothing in Visual Basic).
///
/// A value is being assigned, and is of a type that is not assignable to the
/// key type of the . -or- A value is being
/// assigned, and is of a type that is not assignable to the value type
/// of the
///
object IDictionary.this[object key]
{
get
{
if (key == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
TValue value;
if (key is TKey && this.TryGetValue((TKey)key, out value))
{
return value;
}
return null;
}
set
{
if (key == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
if (!(key is TKey)) ThrowHelper.ThrowArgumentException(ExceptionResource.ConcurrentDictionary_TypeOfKeyIncorrect);
if (!(value is TValue)) ThrowHelper.ThrowArgumentException(ExceptionResource.ConcurrentDictionary_TypeOfValueIncorrect);
((ConcurrentDictionary)this)[(TKey)key] = (TValue)value;
}
}
#endregion
#region ICollection Members
///
/// Copies the elements of the to an array, starting
/// at the specified array index.
///
/// The one-dimensional array that is the destination of the elements copied from
/// the . The array must have zero-based
/// indexing.
/// The zero-based index in at which copying
/// begins.
/// is a null reference
/// (Nothing in Visual Basic).
/// is less than
/// 0.
/// is equal to or greater than
/// the length of the . -or- The number of elements in the source
/// is greater than the available space from to the end of the destination
/// .
[SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "ConcurrencyCop just doesn't know about these locks")]
void ICollection.CopyTo(Array array, int index)
{
if (array == null) ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
if (index < 0) ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index, ExceptionResource.ConcurrentDictionary_IndexIsNegative);
int locksAcquired = 0;
try
{
AcquireAllLocks(ref locksAcquired);
Tables tables = m_tables;
int count = 0;
for (int i = 0; i < tables.m_locks.Length && count >= 0; i++)
{
count += tables.m_countPerLock[i];
}
if (array.Length - count < index || count < 0) //"count" itself or "count + index" can overflow
{
ThrowHelper.ThrowArgumentException(ExceptionResource.ConcurrentDictionary_ArrayNotLargeEnough);
}
// To be consistent with the behavior of ICollection.CopyTo() in Dictionary,
// we recognize three types of target arrays:
// - an array of KeyValuePair structs
// - an array of DictionaryEntry structs
// - an array of objects
KeyValuePair[] pairs = array as KeyValuePair[];
if (pairs != null)
{
CopyToPairs(pairs, index);
return;
}
DictionaryEntry[] entries = array as DictionaryEntry[];
if (entries != null)
{
CopyToEntries(entries, index);
return;
}
object[] objects = array as object[];
if (objects != null)
{
CopyToObjects(objects, index);
return;
}
ThrowHelper.ThrowArgumentException(ExceptionResource.ConcurrentDictionary_ArrayIncorrectType, ExceptionArgument.array);
}
finally
{
ReleaseLocks(0, locksAcquired);
}
}
///
/// Gets a value indicating whether access to the is
/// synchronized with the SyncRoot.
///
/// true if access to the is synchronized
/// (thread safe); otherwise, false. For , this property always
/// returns false.
bool ICollection.IsSynchronized
{
get { return false; }
}
///
/// Gets an object that can be used to synchronize access to the . This property is not supported.
///
/// The SyncRoot property is not supported.
object ICollection.SyncRoot
{
get
{
ThrowHelper.ThrowNotSupportedException(ExceptionResource.ConcurrentCollection_SyncRoot_NotSupported);
return default(object);
}
}
#endregion
///
/// Replaces the bucket table with a larger one. To prevent multiple threads from resizing the
/// table as a result of a race condition, the Tables instance that holds the table of buckets deemed too
/// small is passed in as an argument to GrowTable(). GrowTable() obtains a lock, and then checks
/// the Tables instance has been replaced in the meantime or not.
/// The will be used to ensure that we don't do two subsequent resizes
/// because of a collision
///
private void GrowTable(Tables tables, IEqualityComparer newComparer, bool regenerateHashKeys, int rehashCount)
{
int locksAcquired = 0;
try
{
// The thread that first obtains m_locks[0] will be the one doing the resize operation
AcquireLocks(0, 1, ref locksAcquired);
if (regenerateHashKeys && rehashCount == m_keyRehashCount)
{
// This method is called with regenerateHashKeys==true when we detected
// more than HashHelpers.HashCollisionThreshold collisions when adding a new element.
// In that case we are in the process of switching to another (randomized) comparer
// and we have to re-hash all the keys in the table.
// We are only going to do this if we did not just rehash the entire table while waiting for the lock
tables = m_tables;
}
else
{
// If we don't require a regeneration of hash keys we want to make sure we don't do work when
// we don't have to
if (tables != m_tables)
{
// We assume that since the table reference is different, it was already resized (or the budget
// was adjusted). If we ever decide to do table shrinking, or replace the table for other reasons,
// we will have to revisit this logic.
return;
}
// Compute the (approx.) total size. Use an Int64 accumulation variable to avoid an overflow.
long approxCount = 0;
for (int i = 0; i < tables.m_countPerLock.Length; i++)
{
approxCount += tables.m_countPerLock[i];
}
//
// If the bucket array is too empty, double the budget instead of resizing the table
//
if (approxCount < tables.m_buckets.Length / 4)
{
m_budget = 2 * m_budget;
if (m_budget < 0)
{
m_budget = int.MaxValue;
}
return;
}
}
// Compute the new table size. We find the smallest integer larger than twice the previous table size, and not divisible by
// 2,3,5 or 7. We can consider a different table-sizing policy in the future.
int newLength = 0;
bool maximizeTableSize = false;
try
{
checked
{
// Double the size of the buckets table and add one, so that we have an odd integer.
newLength = tables.m_buckets.Length * 2 + 1;
// Now, we only need to check odd integers, and find the first that is not divisible
// by 3, 5 or 7.
while (newLength % 3 == 0 || newLength % 5 == 0 || newLength % 7 == 0)
{
newLength += 2;
}
Assert(newLength % 2 != 0);
if (newLength > Array.MaxArrayLength)
{
maximizeTableSize = true;
}
}
}
catch (OverflowException)
{
maximizeTableSize = true;
}
if (maximizeTableSize)
{
newLength = Array.MaxArrayLength;
// We want to make sure that GrowTable will not be called again, since table is at the maximum size.
// To achieve that, we set the budget to int.MaxValue.
//
// (There is one special case that would allow GrowTable() to be called in the future:
// calling Clear() on the ConcurrentDictionary will shrink the table and lower the budget.)
m_budget = int.MaxValue;
}
// Now acquire all other locks for the table
AcquireLocks(1, tables.m_locks.Length, ref locksAcquired);
object[] newLocks = tables.m_locks;
// Add more locks
if (m_growLockArray && tables.m_locks.Length < MAX_LOCK_NUMBER)
{
newLocks = new object[tables.m_locks.Length * 2];
Array.Copy(tables.m_locks, newLocks, tables.m_locks.Length);
for (int i = tables.m_locks.Length; i < newLocks.Length; i++)
{
newLocks[i] = new object();
}
}
Node[] newBuckets = new Node[newLength];
int[] newCountPerLock = new int[newLocks.Length];
// Copy all data into a new table, creating new nodes for all elements
for (int i = 0; i < tables.m_buckets.Length; i++)
{
Node current = tables.m_buckets[i];
while (current != null)
{
Node next = current.m_next;
int newBucketNo, newLockNo;
int nodeHashCode = current.m_hashcode;
if (regenerateHashKeys)
{
// Recompute the hash from the key
nodeHashCode = newComparer.GetHashCode(current.m_key);
}
GetBucketAndLockNo(nodeHashCode, out newBucketNo, out newLockNo, newBuckets.Length, newLocks.Length);
newBuckets[newBucketNo] = new Node(current.m_key, current.m_value, nodeHashCode, newBuckets[newBucketNo]);
checked
{
newCountPerLock[newLockNo]++;
}
current = next;
}
}
// If this resize regenerated the hashkeys, increment the count
if (regenerateHashKeys)
{
// We use unchecked here because we don't want to throw an exception if
// an overflow happens
unchecked
{
m_keyRehashCount++;
}
}
// Adjust the budget
m_budget = Math.Max(1, newBuckets.Length / newLocks.Length);
// Replace tables with the new versions
m_tables = new Tables(newBuckets, newLocks, newCountPerLock, newComparer);
}
finally
{
// Release all locks that we took earlier
ReleaseLocks(0, locksAcquired);
}
}
///
/// Computes the bucket and lock number for a particular key.
///
private void GetBucketAndLockNo(
int hashcode, out int bucketNo, out int lockNo, int bucketCount, int lockCount)
{
bucketNo = (hashcode & 0x7fffffff) % bucketCount;
lockNo = bucketNo % lockCount;
Assert(bucketNo >= 0 && bucketNo < bucketCount);
Assert(lockNo >= 0 && lockNo < lockCount);
}
///
/// The number of concurrent writes for which to optimize by default.
///
private static int DefaultConcurrencyLevel
{
get { return DEFAULT_CONCURRENCY_MULTIPLIER * PlatformHelper.ProcessorCount; }
}
///
/// Acquires all locks for this hash table, and increments locksAcquired by the number
/// of locks that were successfully acquired. The locks are acquired in an increasing
/// order.
///
private void AcquireAllLocks(ref int locksAcquired)
{
// First, acquire lock 0
AcquireLocks(0, 1, ref locksAcquired);
// Now that we have lock 0, the m_locks array will not change (i.e., grow),
// and so we can safely read m_locks.Length.
AcquireLocks(1, m_tables.m_locks.Length, ref locksAcquired);
Assert(locksAcquired == m_tables.m_locks.Length);
}
///
/// Acquires a contiguous range of locks for this hash table, and increments locksAcquired
/// by the number of locks that were successfully acquired. The locks are acquired in an
/// increasing order.
///
private void AcquireLocks(int fromInclusive, int toExclusive, ref int locksAcquired)
{
Assert(fromInclusive <= toExclusive);
object[] locks = m_tables.m_locks;
for (int i = fromInclusive; i < toExclusive; i++)
{
bool lockTaken = false;
try
{
Monitor.Enter(locks[i], ref lockTaken);
}
finally
{
if (lockTaken)
{
locksAcquired++;
}
}
}
}
///
/// Releases a contiguous range of locks.
///
[SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "Reviewed for thread safety")]
private void ReleaseLocks(int fromInclusive, int toExclusive)
{
Assert(fromInclusive <= toExclusive);
for (int i = fromInclusive; i < toExclusive; i++)
{
Monitor.Exit(m_tables.m_locks[i]);
}
}
///
/// Gets a collection containing the keys in the dictionary.
///
[SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "ConcurrencyCop just doesn't know about these locks")]
private ReadOnlyCollection GetKeys()
{
int locksAcquired = 0;
try
{
AcquireAllLocks(ref locksAcquired);
List keys = new List();
for (int i = 0; i < m_tables.m_buckets.Length; i++)
{
Node current = m_tables.m_buckets[i];
while (current != null)
{
keys.Add(current.m_key);
current = current.m_next;
}
}
return new ReadOnlyCollection(keys);
}
finally
{
ReleaseLocks(0, locksAcquired);
}
}
///
/// Gets a collection containing the values in the dictionary.
///
[SuppressMessage("Microsoft.Concurrency", "CA8001", Justification = "ConcurrencyCop just doesn't know about these locks")]
private ReadOnlyCollection GetValues()
{
int locksAcquired = 0;
try
{
AcquireAllLocks(ref locksAcquired);
List values = new List();
for (int i = 0; i < m_tables.m_buckets.Length; i++)
{
Node current = m_tables.m_buckets[i];
while (current != null)
{
values.Add(current.m_value);
current = current.m_next;
}
}
return new ReadOnlyCollection(values);
}
finally
{
ReleaseLocks(0, locksAcquired);
}
}
///
/// A helper method for asserts.
///
[Conditional("DEBUG")]
private void Assert(bool condition)
{
Debug.Assert(condition);
}
///
/// A node in a singly-linked list representing a particular hash table bucket.
///
private class Node
{
internal TKey m_key;
internal TValue m_value;
internal volatile Node m_next;
internal int m_hashcode;
internal Node(TKey key, TValue value, int hashcode, Node next)
{
m_key = key;
m_value = value;
m_next = next;
m_hashcode = hashcode;
}
}
///
/// A private class to represent enumeration over the dictionary that implements the
/// IDictionaryEnumerator interface.
///
private class DictionaryEnumerator : IDictionaryEnumerator
{
IEnumerator> m_enumerator; // Enumerator over the dictionary.
internal DictionaryEnumerator(ConcurrentDictionary dictionary)
{
m_enumerator = dictionary.GetEnumerator();
}
public DictionaryEntry Entry
{
get { return new DictionaryEntry(m_enumerator.Current.Key, m_enumerator.Current.Value); }
}
public object Key
{
get { return m_enumerator.Current.Key; }
}
public object Value
{
get { return m_enumerator.Current.Value; }
}
public object Current
{
get { return this.Entry; }
}
public bool MoveNext()
{
return m_enumerator.MoveNext();
}
public void Reset()
{
m_enumerator.Reset();
}
}
}
}