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gecko-dev/mfbt/HashTable.h

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
//---------------------------------------------------------------------------
// Overview
//---------------------------------------------------------------------------
//
// This file defines HashMap<Key, Value> and HashSet<T>, hash tables that are
// fast and have a nice API.
//
// Both hash tables have two optional template parameters.
//
// - HashPolicy. This defines the operations for hashing and matching keys. The
// default HashPolicy is appropriate when both of the following two
// conditions are true.
//
// - The key type stored in the table (|Key| for |HashMap<Key, Value>|, |T|
// for |HashSet<T>|) is an integer, pointer, UniquePtr, float, or double.
//
// - The type used for lookups (|Lookup|) is the same as the key type. This
// is usually the case, but not always.
//
// There is also a |CStringHasher| policy for |char*| keys. If your keys
// don't match any of the above cases, you must provide your own hash policy;
// see the "Hash Policy" section below.
//
// - AllocPolicy. This defines how allocations are done by the table.
//
// - |MallocAllocPolicy| is the default and is usually appropriate; note that
// operations (such as insertions) that might cause allocations are
// fallible and must be checked for OOM. These checks are enforced by the
// use of MOZ_MUST_USE.
//
// - |InfallibleAllocPolicy| is another possibility; it allows the
// abovementioned OOM checks to be done with MOZ_ALWAYS_TRUE().
//
// Note that entry storage allocation is lazy, and not done until the first
// lookupForAdd(), put(), or putNew() is performed.
//
// See AllocPolicy.h for more details.
//
// Documentation on how to use HashMap and HashSet, including examples, is
// present within those classes. Search for "class HashMap" and "class
// HashSet".
//
// Both HashMap and HashSet are implemented on top of a third class, HashTable.
// You only need to look at HashTable if you want to understand the
// implementation.
//
// How does mozilla::HashTable (this file) compare with PLDHashTable (and its
// subclasses, such as nsTHashtable)?
//
// - mozilla::HashTable is a lot faster, largely because it uses templates
// throughout *and* inlines everything. PLDHashTable inlines operations much
// less aggressively, and also uses "virtual ops" for operations like hashing
// and matching entries that require function calls.
//
// - Correspondingly, mozilla::HashTable use is likely to increase executable
// size much more than PLDHashTable.
//
// - mozilla::HashTable has a nicer API, with a proper HashSet vs. HashMap
// distinction.
//
// - mozilla::HashTable requires more explicit OOM checking. As mentioned
// above, the use of |InfallibleAllocPolicy| can simplify things.
//
// - mozilla::HashTable has a default capacity on creation of 32 and a minimum
// capacity of 4. PLDHashTable has a default capacity on creation of 8 and a
// minimum capacity of 8.
#ifndef mozilla_HashTable_h
#define mozilla_HashTable_h
#include <utility>
#include <type_traits>
#include "mozilla/AllocPolicy.h"
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/Casting.h"
#include "mozilla/HashFunctions.h"
#include "mozilla/MathAlgorithms.h"
#include "mozilla/Maybe.h"
#include "mozilla/MemoryChecking.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/Opaque.h"
#include "mozilla/OperatorNewExtensions.h"
#include "mozilla/PodOperations.h"
#include "mozilla/ReentrancyGuard.h"
#include "mozilla/TypeTraits.h"
#include "mozilla/UniquePtr.h"
#include "mozilla/WrappingOperations.h"
namespace mozilla {
template <class>
struct DefaultHasher;
template <class, class>
class HashMapEntry;
namespace detail {
template <typename T>
class HashTableEntry;
template <class T, class HashPolicy, class AllocPolicy>
class HashTable;
} // namespace detail
// The "generation" of a hash table is an opaque value indicating the state of
// modification of the hash table through its lifetime. If the generation of
// a hash table compares equal at times T1 and T2, then lookups in the hash
// table, pointers to (or into) hash table entries, etc. at time T1 are valid
// at time T2. If the generation compares unequal, these computations are all
// invalid and must be performed again to be used.
//
// Generations are meaningfully comparable only with respect to a single hash
// table. It's always nonsensical to compare the generation of distinct hash
// tables H1 and H2.
using Generation = Opaque<uint64_t>;
//---------------------------------------------------------------------------
// HashMap
//---------------------------------------------------------------------------
// HashMap is a fast hash-based map from keys to values.
//
// Template parameter requirements:
// - Key/Value: movable, destructible, assignable.
// - HashPolicy: see the "Hash Policy" section below.
// - AllocPolicy: see AllocPolicy.h.
//
// Note:
// - HashMap is not reentrant: Key/Value/HashPolicy/AllocPolicy members
// called by HashMap must not call back into the same HashMap object.
//
template <class Key, class Value, class HashPolicy = DefaultHasher<Key>,
class AllocPolicy = MallocAllocPolicy>
class HashMap {
// -- Implementation details -----------------------------------------------
// HashMap is not copyable or assignable.
HashMap(const HashMap& hm) = delete;
HashMap& operator=(const HashMap& hm) = delete;
using TableEntry = HashMapEntry<Key, Value>;
struct MapHashPolicy : HashPolicy {
using Base = HashPolicy;
using KeyType = Key;
static const Key& getKey(TableEntry& aEntry) { return aEntry.key(); }
static void setKey(TableEntry& aEntry, Key& aKey) {
HashPolicy::rekey(aEntry.mutableKey(), aKey);
}
};
using Impl = detail::HashTable<TableEntry, MapHashPolicy, AllocPolicy>;
Impl mImpl;
friend class Impl::Enum;
public:
using Lookup = typename HashPolicy::Lookup;
using Entry = TableEntry;
// -- Initialization -------------------------------------------------------
explicit HashMap(AllocPolicy aAllocPolicy = AllocPolicy(),
uint32_t aLen = Impl::sDefaultLen)
: mImpl(std::move(aAllocPolicy), aLen) {}
explicit HashMap(uint32_t aLen) : mImpl(AllocPolicy(), aLen) {}
// HashMap is movable.
HashMap(HashMap&& aRhs) = default;
HashMap& operator=(HashMap&& aRhs) = default;
// -- Status and sizing ----------------------------------------------------
// The map's current generation.
Generation generation() const { return mImpl.generation(); }
// Is the map empty?
bool empty() const { return mImpl.empty(); }
// Number of keys/values in the map.
uint32_t count() const { return mImpl.count(); }
// Number of key/value slots in the map. Note: resize will happen well before
// count() == capacity().
uint32_t capacity() const { return mImpl.capacity(); }
// The size of the map's entry storage, in bytes. If the keys/values contain
// pointers to other heap blocks, you must iterate over the map and measure
// them separately; hence the "shallow" prefix.
size_t shallowSizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
return mImpl.shallowSizeOfExcludingThis(aMallocSizeOf);
}
size_t shallowSizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const {
return aMallocSizeOf(this) +
mImpl.shallowSizeOfExcludingThis(aMallocSizeOf);
}
// Attempt to minimize the capacity(). If the table is empty, this will free
// the empty storage and upon regrowth it will be given the minimum capacity.
void compact() { mImpl.compact(); }
// Attempt to reserve enough space to fit at least |aLen| elements. Does
// nothing if the map already has sufficient capacity.
MOZ_MUST_USE bool reserve(uint32_t aLen) { return mImpl.reserve(aLen); }
// -- Lookups --------------------------------------------------------------
// Does the map contain a key/value matching |aLookup|?
bool has(const Lookup& aLookup) const {
return mImpl.lookup(aLookup).found();
}
// Return a Ptr indicating whether a key/value matching |aLookup| is
// present in the map. E.g.:
//
// using HM = HashMap<int,char>;
// HM h;
// if (HM::Ptr p = h.lookup(3)) {
// assert(p->key() == 3);
// char val = p->value();
// }
//
using Ptr = typename Impl::Ptr;
MOZ_ALWAYS_INLINE Ptr lookup(const Lookup& aLookup) const {
return mImpl.lookup(aLookup);
}
// Like lookup(), but does not assert if two threads call it at the same
// time. Only use this method when none of the threads will modify the map.
MOZ_ALWAYS_INLINE Ptr readonlyThreadsafeLookup(const Lookup& aLookup) const {
return mImpl.readonlyThreadsafeLookup(aLookup);
}
// -- Insertions -----------------------------------------------------------
// Overwrite existing value with |aValue|, or add it if not present. Returns
// false on OOM.
template <typename KeyInput, typename ValueInput>
MOZ_MUST_USE bool put(KeyInput&& aKey, ValueInput&& aValue) {
AddPtr p = lookupForAdd(aKey);
if (p) {
p->value() = std::forward<ValueInput>(aValue);
return true;
}
return add(p, std::forward<KeyInput>(aKey),
std::forward<ValueInput>(aValue));
}
// Like put(), but slightly faster. Must only be used when the given key is
// not already present. (In debug builds, assertions check this.)
template <typename KeyInput, typename ValueInput>
MOZ_MUST_USE bool putNew(KeyInput&& aKey, ValueInput&& aValue) {
return mImpl.putNew(aKey, std::forward<KeyInput>(aKey),
std::forward<ValueInput>(aValue));
}
// Like putNew(), but should be only used when the table is known to be big
// enough for the insertion, and hashing cannot fail. Typically this is used
// to populate an empty map with known-unique keys after reserving space with
// reserve(), e.g.
//
// using HM = HashMap<int,char>;
// HM h;
// if (!h.reserve(3)) {
// MOZ_CRASH("OOM");
// }
// h.putNewInfallible(1, 'a'); // unique key
// h.putNewInfallible(2, 'b'); // unique key
// h.putNewInfallible(3, 'c'); // unique key
//
template <typename KeyInput, typename ValueInput>
void putNewInfallible(KeyInput&& aKey, ValueInput&& aValue) {
mImpl.putNewInfallible(aKey, std::forward<KeyInput>(aKey),
std::forward<ValueInput>(aValue));
}
// Like |lookup(l)|, but on miss, |p = lookupForAdd(l)| allows efficient
// insertion of Key |k| (where |HashPolicy::match(k,l) == true|) using
// |add(p,k,v)|. After |add(p,k,v)|, |p| points to the new key/value. E.g.:
//
// using HM = HashMap<int,char>;
// HM h;
// HM::AddPtr p = h.lookupForAdd(3);
// if (!p) {
// if (!h.add(p, 3, 'a')) {
// return false;
// }
// }
// assert(p->key() == 3);
// char val = p->value();
//
// N.B. The caller must ensure that no mutating hash table operations occur
// between a pair of lookupForAdd() and add() calls. To avoid looking up the
// key a second time, the caller may use the more efficient relookupOrAdd()
// method. This method reuses part of the hashing computation to more
// efficiently insert the key if it has not been added. For example, a
// mutation-handling version of the previous example:
//
// HM::AddPtr p = h.lookupForAdd(3);
// if (!p) {
// call_that_may_mutate_h();
// if (!h.relookupOrAdd(p, 3, 'a')) {
// return false;
// }
// }
// assert(p->key() == 3);
// char val = p->value();
//
using AddPtr = typename Impl::AddPtr;
MOZ_ALWAYS_INLINE AddPtr lookupForAdd(const Lookup& aLookup) {
return mImpl.lookupForAdd(aLookup);
}
// Add a key/value. Returns false on OOM.
template <typename KeyInput, typename ValueInput>
MOZ_MUST_USE bool add(AddPtr& aPtr, KeyInput&& aKey, ValueInput&& aValue) {
return mImpl.add(aPtr, std::forward<KeyInput>(aKey),
std::forward<ValueInput>(aValue));
}
// See the comment above lookupForAdd() for details.
template <typename KeyInput, typename ValueInput>
MOZ_MUST_USE bool relookupOrAdd(AddPtr& aPtr, KeyInput&& aKey,
ValueInput&& aValue) {
return mImpl.relookupOrAdd(aPtr, aKey, std::forward<KeyInput>(aKey),
std::forward<ValueInput>(aValue));
}
// -- Removal --------------------------------------------------------------
// Lookup and remove the key/value matching |aLookup|, if present.
void remove(const Lookup& aLookup) {
if (Ptr p = lookup(aLookup)) {
remove(p);
}
}
// Remove a previously found key/value (assuming aPtr.found()). The map must
// not have been mutated in the interim.
void remove(Ptr aPtr) { mImpl.remove(aPtr); }
// Remove all keys/values without changing the capacity.
void clear() { mImpl.clear(); }
// Like clear() followed by compact().
void clearAndCompact() { mImpl.clearAndCompact(); }
// -- Rekeying -------------------------------------------------------------
// Infallibly rekey one entry, if necessary. Requires that template
// parameters Key and HashPolicy::Lookup are the same type.
void rekeyIfMoved(const Key& aOldKey, const Key& aNewKey) {
if (aOldKey != aNewKey) {
rekeyAs(aOldKey, aNewKey, aNewKey);
}
}
// Infallibly rekey one entry if present, and return whether that happened.
bool rekeyAs(const Lookup& aOldLookup, const Lookup& aNewLookup,
const Key& aNewKey) {
if (Ptr p = lookup(aOldLookup)) {
mImpl.rekeyAndMaybeRehash(p, aNewLookup, aNewKey);
return true;
}
return false;
}
// -- Iteration ------------------------------------------------------------
// |iter()| returns an Iterator:
//
// HashMap<int, char> h;
// for (auto iter = h.iter(); !iter.done(); iter.next()) {
// char c = iter.get().value();
// }
//
using Iterator = typename Impl::Iterator;
Iterator iter() const { return mImpl.iter(); }
// |modIter()| returns a ModIterator:
//
// HashMap<int, char> h;
// for (auto iter = h.modIter(); !iter.done(); iter.next()) {
// if (iter.get().value() == 'l') {
// iter.remove();
// }
// }
//
// Table resize may occur in ModIterator's destructor.
using ModIterator = typename Impl::ModIterator;
ModIterator modIter() { return mImpl.modIter(); }
// These are similar to Iterator/ModIterator/iter(), but use different
// terminology.
using Range = typename Impl::Range;
using Enum = typename Impl::Enum;
Range all() const { return mImpl.all(); }
};
//---------------------------------------------------------------------------
// HashSet
//---------------------------------------------------------------------------
// HashSet is a fast hash-based set of values.
//
// Template parameter requirements:
// - T: movable, destructible, assignable.
// - HashPolicy: see the "Hash Policy" section below.
// - AllocPolicy: see AllocPolicy.h
//
// Note:
// - HashSet is not reentrant: T/HashPolicy/AllocPolicy members called by
// HashSet must not call back into the same HashSet object.
//
template <class T, class HashPolicy = DefaultHasher<T>,
class AllocPolicy = MallocAllocPolicy>
class HashSet {
// -- Implementation details -----------------------------------------------
// HashSet is not copyable or assignable.
HashSet(const HashSet& hs) = delete;
HashSet& operator=(const HashSet& hs) = delete;
struct SetHashPolicy : HashPolicy {
using Base = HashPolicy;
using KeyType = T;
static const KeyType& getKey(const T& aT) { return aT; }
static void setKey(T& aT, KeyType& aKey) { HashPolicy::rekey(aT, aKey); }
};
using Impl = detail::HashTable<const T, SetHashPolicy, AllocPolicy>;
Impl mImpl;
friend class Impl::Enum;
public:
using Lookup = typename HashPolicy::Lookup;
using Entry = T;
// -- Initialization -------------------------------------------------------
explicit HashSet(AllocPolicy aAllocPolicy = AllocPolicy(),
uint32_t aLen = Impl::sDefaultLen)
: mImpl(std::move(aAllocPolicy), aLen) {}
explicit HashSet(uint32_t aLen) : mImpl(AllocPolicy(), aLen) {}
// HashSet is movable.
HashSet(HashSet&& aRhs) = default;
HashSet& operator=(HashSet&& aRhs) = default;
// -- Status and sizing ----------------------------------------------------
// The set's current generation.
Generation generation() const { return mImpl.generation(); }
// Is the set empty?
bool empty() const { return mImpl.empty(); }
// Number of elements in the set.
uint32_t count() const { return mImpl.count(); }
// Number of element slots in the set. Note: resize will happen well before
// count() == capacity().
uint32_t capacity() const { return mImpl.capacity(); }
// The size of the set's entry storage, in bytes. If the elements contain
// pointers to other heap blocks, you must iterate over the set and measure
// them separately; hence the "shallow" prefix.
size_t shallowSizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
return mImpl.shallowSizeOfExcludingThis(aMallocSizeOf);
}
size_t shallowSizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const {
return aMallocSizeOf(this) +
mImpl.shallowSizeOfExcludingThis(aMallocSizeOf);
}
// Attempt to minimize the capacity(). If the table is empty, this will free
// the empty storage and upon regrowth it will be given the minimum capacity.
void compact() { mImpl.compact(); }
// Attempt to reserve enough space to fit at least |aLen| elements. Does
// nothing if the map already has sufficient capacity.
MOZ_MUST_USE bool reserve(uint32_t aLen) { return mImpl.reserve(aLen); }
// -- Lookups --------------------------------------------------------------
// Does the set contain an element matching |aLookup|?
bool has(const Lookup& aLookup) const {
return mImpl.lookup(aLookup).found();
}
// Return a Ptr indicating whether an element matching |aLookup| is present
// in the set. E.g.:
//
// using HS = HashSet<int>;
// HS h;
// if (HS::Ptr p = h.lookup(3)) {
// assert(*p == 3); // p acts like a pointer to int
// }
//
using Ptr = typename Impl::Ptr;
MOZ_ALWAYS_INLINE Ptr lookup(const Lookup& aLookup) const {
return mImpl.lookup(aLookup);
}
// Like lookup(), but does not assert if two threads call it at the same
// time. Only use this method when none of the threads will modify the set.
MOZ_ALWAYS_INLINE Ptr readonlyThreadsafeLookup(const Lookup& aLookup) const {
return mImpl.readonlyThreadsafeLookup(aLookup);
}
// -- Insertions -----------------------------------------------------------
// Add |aU| if it is not present already. Returns false on OOM.
template <typename U>
MOZ_MUST_USE bool put(U&& aU) {
AddPtr p = lookupForAdd(aU);
return p ? true : add(p, std::forward<U>(aU));
}
// Like put(), but slightly faster. Must only be used when the given element
// is not already present. (In debug builds, assertions check this.)
template <typename U>
MOZ_MUST_USE bool putNew(U&& aU) {
return mImpl.putNew(aU, std::forward<U>(aU));
}
// Like the other putNew(), but for when |Lookup| is different to |T|.
template <typename U>
MOZ_MUST_USE bool putNew(const Lookup& aLookup, U&& aU) {
return mImpl.putNew(aLookup, std::forward<U>(aU));
}
// Like putNew(), but should be only used when the table is known to be big
// enough for the insertion, and hashing cannot fail. Typically this is used
// to populate an empty set with known-unique elements after reserving space
// with reserve(), e.g.
//
// using HS = HashMap<int>;
// HS h;
// if (!h.reserve(3)) {
// MOZ_CRASH("OOM");
// }
// h.putNewInfallible(1); // unique element
// h.putNewInfallible(2); // unique element
// h.putNewInfallible(3); // unique element
//
template <typename U>
void putNewInfallible(const Lookup& aLookup, U&& aU) {
mImpl.putNewInfallible(aLookup, std::forward<U>(aU));
}
// Like |lookup(l)|, but on miss, |p = lookupForAdd(l)| allows efficient
// insertion of T value |t| (where |HashPolicy::match(t,l) == true|) using
// |add(p,t)|. After |add(p,t)|, |p| points to the new element. E.g.:
//
// using HS = HashSet<int>;
// HS h;
// HS::AddPtr p = h.lookupForAdd(3);
// if (!p) {
// if (!h.add(p, 3)) {
// return false;
// }
// }
// assert(*p == 3); // p acts like a pointer to int
//
// N.B. The caller must ensure that no mutating hash table operations occur
// between a pair of lookupForAdd() and add() calls. To avoid looking up the
// key a second time, the caller may use the more efficient relookupOrAdd()
// method. This method reuses part of the hashing computation to more
// efficiently insert the key if it has not been added. For example, a
// mutation-handling version of the previous example:
//
// HS::AddPtr p = h.lookupForAdd(3);
// if (!p) {
// call_that_may_mutate_h();
// if (!h.relookupOrAdd(p, 3, 3)) {
// return false;
// }
// }
// assert(*p == 3);
//
// Note that relookupOrAdd(p,l,t) performs Lookup using |l| and adds the
// entry |t|, where the caller ensures match(l,t).
using AddPtr = typename Impl::AddPtr;
MOZ_ALWAYS_INLINE AddPtr lookupForAdd(const Lookup& aLookup) {
return mImpl.lookupForAdd(aLookup);
}
// Add an element. Returns false on OOM.
template <typename U>
MOZ_MUST_USE bool add(AddPtr& aPtr, U&& aU) {
return mImpl.add(aPtr, std::forward<U>(aU));
}
// See the comment above lookupForAdd() for details.
template <typename U>
MOZ_MUST_USE bool relookupOrAdd(AddPtr& aPtr, const Lookup& aLookup, U&& aU) {
return mImpl.relookupOrAdd(aPtr, aLookup, std::forward<U>(aU));
}
// -- Removal --------------------------------------------------------------
// Lookup and remove the element matching |aLookup|, if present.
void remove(const Lookup& aLookup) {
if (Ptr p = lookup(aLookup)) {
remove(p);
}
}
// Remove a previously found element (assuming aPtr.found()). The set must
// not have been mutated in the interim.
void remove(Ptr aPtr) { mImpl.remove(aPtr); }
// Remove all keys/values without changing the capacity.
void clear() { mImpl.clear(); }
// Like clear() followed by compact().
void clearAndCompact() { mImpl.clearAndCompact(); }
// -- Rekeying -------------------------------------------------------------
// Infallibly rekey one entry, if present. Requires that template parameters
// T and HashPolicy::Lookup are the same type.
void rekeyIfMoved(const Lookup& aOldValue, const T& aNewValue) {
if (aOldValue != aNewValue) {
rekeyAs(aOldValue, aNewValue, aNewValue);
}
}
// Infallibly rekey one entry if present, and return whether that happened.
bool rekeyAs(const Lookup& aOldLookup, const Lookup& aNewLookup,
const T& aNewValue) {
if (Ptr p = lookup(aOldLookup)) {
mImpl.rekeyAndMaybeRehash(p, aNewLookup, aNewValue);
return true;
}
return false;
}
// Infallibly replace the current key at |aPtr| with an equivalent key.
// Specifically, both HashPolicy::hash and HashPolicy::match must return
// identical results for the new and old key when applied against all
// possible matching values.
void replaceKey(Ptr aPtr, const T& aNewValue) {
MOZ_ASSERT(aPtr.found());
MOZ_ASSERT(*aPtr != aNewValue);
MOZ_ASSERT(HashPolicy::hash(*aPtr) == HashPolicy::hash(aNewValue));
MOZ_ASSERT(HashPolicy::match(*aPtr, aNewValue));
const_cast<T&>(*aPtr) = aNewValue;
}
// -- Iteration ------------------------------------------------------------
// |iter()| returns an Iterator:
//
// HashSet<int> h;
// for (auto iter = h.iter(); !iter.done(); iter.next()) {
// int i = iter.get();
// }
//
using Iterator = typename Impl::Iterator;
Iterator iter() const { return mImpl.iter(); }
// |modIter()| returns a ModIterator:
//
// HashSet<int> h;
// for (auto iter = h.modIter(); !iter.done(); iter.next()) {
// if (iter.get() == 42) {
// iter.remove();
// }
// }
//
// Table resize may occur in ModIterator's destructor.
using ModIterator = typename Impl::ModIterator;
ModIterator modIter() { return mImpl.modIter(); }
// These are similar to Iterator/ModIterator/iter(), but use different
// terminology.
using Range = typename Impl::Range;
using Enum = typename Impl::Enum;
Range all() const { return mImpl.all(); }
};
//---------------------------------------------------------------------------
// Hash Policy
//---------------------------------------------------------------------------
// A hash policy |HP| for a hash table with key-type |Key| must provide:
//
// - a type |HP::Lookup| to use to lookup table entries;
//
// - a static member function |HP::hash| that hashes lookup values:
//
// static mozilla::HashNumber hash(const Lookup&);
//
// - a static member function |HP::match| that tests equality of key and
// lookup values:
//
// static bool match(const Key&, const Lookup&);
//
// Normally, Lookup = Key. In general, though, different values and types of
// values can be used to lookup and store. If a Lookup value |l| is not equal
// to the added Key value |k|, the user must ensure that |HP::match(k,l)| is
// true. E.g.:
//
// mozilla::HashSet<Key, HP>::AddPtr p = h.lookup(l);
// if (!p) {
// assert(HP::match(k, l)); // must hold
// h.add(p, k);
// }
// A pointer hashing policy that uses HashGeneric() to create good hashes for
// pointers. Note that we don't shift out the lowest k bits because we don't
// want to assume anything about the alignment of the pointers.
template <typename Key>
struct PointerHasher {
using Lookup = Key;
static HashNumber hash(const Lookup& aLookup) {
size_t word = reinterpret_cast<size_t>(aLookup);
return HashGeneric(word);
}
static bool match(const Key& aKey, const Lookup& aLookup) {
return aKey == aLookup;
}
static void rekey(Key& aKey, const Key& aNewKey) { aKey = aNewKey; }
};
// The default hash policy, which only works with integers.
template <class Key>
struct DefaultHasher {
using Lookup = Key;
static HashNumber hash(const Lookup& aLookup) {
// Just convert the integer to a HashNumber and use that as is. (This
// discards the high 32-bits of 64-bit integers!) ScrambleHashCode() is
// subsequently called on the value to improve the distribution.
return aLookup;
}
static bool match(const Key& aKey, const Lookup& aLookup) {
// Use builtin or overloaded operator==.
return aKey == aLookup;
}
static void rekey(Key& aKey, const Key& aNewKey) { aKey = aNewKey; }
};
// A DefaultHasher specialization for pointers.
template <class T>
struct DefaultHasher<T*> : PointerHasher<T*> {};
// A DefaultHasher specialization for mozilla::UniquePtr.
template <class T, class D>
struct DefaultHasher<UniquePtr<T, D>> {
using Key = UniquePtr<T, D>;
using Lookup = Key;
using PtrHasher = PointerHasher<T*>;
static HashNumber hash(const Lookup& aLookup) {
return PtrHasher::hash(aLookup.get());
}
static bool match(const Key& aKey, const Lookup& aLookup) {
return PtrHasher::match(aKey.get(), aLookup.get());
}
static void rekey(UniquePtr<T, D>& aKey, UniquePtr<T, D>&& aNewKey) {
aKey = std::move(aNewKey);
}
};
// A DefaultHasher specialization for doubles.
template <>
struct DefaultHasher<double> {
using Key = double;
using Lookup = Key;
static HashNumber hash(const Lookup& aLookup) {
// Just xor the high bits with the low bits, and then treat the bits of the
// result as a uint32_t.
static_assert(sizeof(HashNumber) == 4,
"subsequent code assumes a four-byte hash");
uint64_t u = BitwiseCast<uint64_t>(aLookup);
return HashNumber(u ^ (u >> 32));
}
static bool match(const Key& aKey, const Lookup& aLookup) {
return BitwiseCast<uint64_t>(aKey) == BitwiseCast<uint64_t>(aLookup);
}
};
// A DefaultHasher specialization for floats.
template <>
struct DefaultHasher<float> {
using Key = float;
using Lookup = Key;
static HashNumber hash(const Lookup& aLookup) {
// Just use the value as if its bits form an integer. ScrambleHashCode() is
// subsequently called on the value to improve the distribution.
static_assert(sizeof(HashNumber) == 4,
"subsequent code assumes a four-byte hash");
return HashNumber(BitwiseCast<uint32_t>(aLookup));
}
static bool match(const Key& aKey, const Lookup& aLookup) {
return BitwiseCast<uint32_t>(aKey) == BitwiseCast<uint32_t>(aLookup);
}
};
// A hash policy for C strings.
struct CStringHasher {
using Key = const char*;
using Lookup = const char*;
static HashNumber hash(const Lookup& aLookup) { return HashString(aLookup); }
static bool match(const Key& aKey, const Lookup& aLookup) {
return strcmp(aKey, aLookup) == 0;
}
};
//---------------------------------------------------------------------------
// Fallible Hashing Interface
//---------------------------------------------------------------------------
// Most of the time generating a hash code is infallible so this class provides
// default methods that always succeed. Specialize this class for your own hash
// policy to provide fallible hashing.
//
// This is used by MovableCellHasher to handle the fact that generating a unique
// ID for cell pointer may fail due to OOM.
template <typename HashPolicy>
struct FallibleHashMethods {
// Return true if a hashcode is already available for its argument. Once
// this returns true for a specific argument it must continue to do so.
template <typename Lookup>
static bool hasHash(Lookup&& aLookup) {
return true;
}
// Fallible method to ensure a hashcode exists for its argument and create
// one if not. Returns false on error, e.g. out of memory.
template <typename Lookup>
static bool ensureHash(Lookup&& aLookup) {
return true;
}
};
template <typename HashPolicy, typename Lookup>
static bool HasHash(Lookup&& aLookup) {
return FallibleHashMethods<typename HashPolicy::Base>::hasHash(
std::forward<Lookup>(aLookup));
}
template <typename HashPolicy, typename Lookup>
static bool EnsureHash(Lookup&& aLookup) {
return FallibleHashMethods<typename HashPolicy::Base>::ensureHash(
std::forward<Lookup>(aLookup));
}
//---------------------------------------------------------------------------
// Implementation Details (HashMapEntry, HashTableEntry, HashTable)
//---------------------------------------------------------------------------
// Both HashMap and HashSet are implemented by a single HashTable that is even
// more heavily parameterized than the other two. This leaves HashTable gnarly
// and extremely coupled to HashMap and HashSet; thus code should not use
// HashTable directly.
template <class Key, class Value>
class HashMapEntry {
Key key_;
Value value_;
template <class, class, class>
friend class detail::HashTable;
template <class>
friend class detail::HashTableEntry;
template <class, class, class, class>
friend class HashMap;
public:
template <typename KeyInput, typename ValueInput>
HashMapEntry(KeyInput&& aKey, ValueInput&& aValue)
: key_(std::forward<KeyInput>(aKey)),
value_(std::forward<ValueInput>(aValue)) {}
HashMapEntry(HashMapEntry&& aRhs) = default;
HashMapEntry& operator=(HashMapEntry&& aRhs) = default;
using KeyType = Key;
using ValueType = Value;
const Key& key() const { return key_; }
// Use this method with caution! If the key is changed such that its hash
// value also changes, the map will be left in an invalid state.
Key& mutableKey() { return key_; }
const Value& value() const { return value_; }
Value& value() { return value_; }
private:
HashMapEntry(const HashMapEntry&) = delete;
void operator=(const HashMapEntry&) = delete;
};
template <typename K, typename V>
struct IsPod<HashMapEntry<K, V>>
: std::integral_constant<bool, IsPod<K>::value && IsPod<V>::value> {};
namespace detail {
template <class T, class HashPolicy, class AllocPolicy>
class HashTable;
template <typename T>
class EntrySlot;
template <typename T>
class HashTableEntry {
private:
using NonConstT = std::remove_const_t<T>;
// Instead of having a hash table entry store that looks like this:
//
// +--------+--------+--------+--------+
// | entry0 | entry1 | .... | entryN |
// +--------+--------+--------+--------+
//
// where the entries contained their cached hash code, we're going to lay out
// the entry store thusly:
//
// +-------+-------+-------+-------+--------+--------+--------+--------+
// | hash0 | hash1 | ... | hashN | entry0 | entry1 | .... | entryN |
// +-------+-------+-------+-------+--------+--------+--------+--------+
//
// with all the cached hashes prior to the actual entries themselves.
//
// We do this because implementing the first strategy requires us to make
// HashTableEntry look roughly like:
//
// template <typename T>
// class HashTableEntry {
// HashNumber mKeyHash;
// T mValue;
// };
//
// The problem with this setup is that, depending on the layout of `T`, there
// may be platform ABI-mandated padding between `mKeyHash` and the first
// member of `T`. This ABI-mandated padding is wasted space, and can be
// surprisingly common, e.g. when `T` is a single pointer on 64-bit platforms.
// In such cases, we're throwing away a quarter of our entry store on padding,
// which is undesirable.
//
// The second layout above, namely:
//
// +-------+-------+-------+-------+--------+--------+--------+--------+
// | hash0 | hash1 | ... | hashN | entry0 | entry1 | .... | entryN |
// +-------+-------+-------+-------+--------+--------+--------+--------+
//
// means there is no wasted space between the hashes themselves, and no wasted
// space between the entries themselves. However, we would also like there to
// be no gap between the last hash and the first entry. The memory allocator
// guarantees the alignment of the start of the hashes. The use of a
// power-of-two capacity of at least 4 guarantees that the alignment of the
// *end* of the hash array is no less than the alignment of the start.
// Finally, the static_asserts here guarantee that the entries themselves
// don't need to be any more aligned than the alignment of the entry store
// itself.
//
// This assertion is safe for 32-bit builds because on both Windows and Linux
// (including Android), the minimum alignment for allocations larger than 8
// bytes is 8 bytes, and the actual data for entries in our entry store is
// guaranteed to have that alignment as well, thanks to the power-of-two
// number of cached hash values stored prior to the entry data.
// The allocation policy must allocate a table with at least this much
// alignment.
static constexpr size_t kMinimumAlignment = 8;
static_assert(alignof(HashNumber) <= kMinimumAlignment,
"[N*2 hashes, N*2 T values] allocation's alignment must be "
"enough to align each hash");
static_assert(alignof(NonConstT) <= 2 * sizeof(HashNumber),
"subsequent N*2 T values must not require more than an even "
"number of HashNumbers provides");
static const HashNumber sFreeKey = 0;
static const HashNumber sRemovedKey = 1;
static const HashNumber sCollisionBit = 1;
alignas(NonConstT) unsigned char mValueData[sizeof(NonConstT)];
private:
template <class, class, class>
friend class HashTable;
template <typename>
friend class EntrySlot;
// Some versions of GCC treat it as a -Wstrict-aliasing violation (ergo a
// -Werror compile error) to reinterpret_cast<> |mValueData| to |T*|, even
// through |void*|. Placing the latter cast in these separate functions
// breaks the chain such that affected GCC versions no longer warn/error.
void* rawValuePtr() { return mValueData; }
static bool isLiveHash(HashNumber hash) { return hash > sRemovedKey; }
HashTableEntry(const HashTableEntry&) = delete;
void operator=(const HashTableEntry&) = delete;
NonConstT* valuePtr() { return reinterpret_cast<NonConstT*>(rawValuePtr()); }
void destroyStoredT() {
NonConstT* ptr = valuePtr();
ptr->~T();
MOZ_MAKE_MEM_UNDEFINED(ptr, sizeof(*ptr));
}
public:
HashTableEntry() = default;
~HashTableEntry() { MOZ_MAKE_MEM_UNDEFINED(this, sizeof(*this)); }
void destroy() { destroyStoredT(); }
void swap(HashTableEntry* aOther, bool aIsLive) {
// This allows types to use Argument-Dependent-Lookup, and thus use a custom
// std::swap, which is needed by types like JS::Heap and such.
using std::swap;
if (this == aOther) {
return;
}
if (aIsLive) {
swap(*valuePtr(), *aOther->valuePtr());
} else {
*aOther->valuePtr() = std::move(*valuePtr());
destroy();
}
}
T& get() { return *valuePtr(); }
NonConstT& getMutable() { return *valuePtr(); }
};
// A slot represents a cached hash value and its associated entry stored
// in the hash table. These two things are not stored in contiguous memory.
template <class T>
class EntrySlot {
using NonConstT = std::remove_const_t<T>;
using Entry = HashTableEntry<T>;
Entry* mEntry;
HashNumber* mKeyHash;
template <class, class, class>
friend class HashTable;
EntrySlot(Entry* aEntry, HashNumber* aKeyHash)
: mEntry(aEntry), mKeyHash(aKeyHash) {}
public:
static bool isLiveHash(HashNumber hash) { return hash > Entry::sRemovedKey; }
EntrySlot(const EntrySlot&) = default;
EntrySlot(EntrySlot&& aOther) = default;
EntrySlot& operator=(const EntrySlot&) = default;
EntrySlot& operator=(EntrySlot&&) = default;
bool operator==(const EntrySlot& aRhs) const { return mEntry == aRhs.mEntry; }
bool operator<(const EntrySlot& aRhs) const { return mEntry < aRhs.mEntry; }
EntrySlot& operator++() {
++mEntry;
++mKeyHash;
return *this;
}
void destroy() { mEntry->destroy(); }
void swap(EntrySlot& aOther) {
mEntry->swap(aOther.mEntry, aOther.isLive());
std::swap(*mKeyHash, *aOther.mKeyHash);
}
T& get() const { return mEntry->get(); }
NonConstT& getMutable() { return mEntry->getMutable(); }
bool isFree() const { return *mKeyHash == Entry::sFreeKey; }
void clearLive() {
MOZ_ASSERT(isLive());
*mKeyHash = Entry::sFreeKey;
mEntry->destroyStoredT();
}
void clear() {
if (isLive()) {
mEntry->destroyStoredT();
}
MOZ_MAKE_MEM_UNDEFINED(mEntry, sizeof(*mEntry));
*mKeyHash = Entry::sFreeKey;
}
bool isRemoved() const { return *mKeyHash == Entry::sRemovedKey; }
void removeLive() {
MOZ_ASSERT(isLive());
*mKeyHash = Entry::sRemovedKey;
mEntry->destroyStoredT();
}
bool isLive() const { return isLiveHash(*mKeyHash); }
void setCollision() {
MOZ_ASSERT(isLive());
*mKeyHash |= Entry::sCollisionBit;
}
void unsetCollision() { *mKeyHash &= ~Entry::sCollisionBit; }
bool hasCollision() const { return *mKeyHash & Entry::sCollisionBit; }
bool matchHash(HashNumber hn) {
return (*mKeyHash & ~Entry::sCollisionBit) == hn;
}
HashNumber getKeyHash() const { return *mKeyHash & ~Entry::sCollisionBit; }
template <typename... Args>
void setLive(HashNumber aHashNumber, Args&&... aArgs) {
MOZ_ASSERT(!isLive());
*mKeyHash = aHashNumber;
new (KnownNotNull, mEntry->valuePtr()) T(std::forward<Args>(aArgs)...);
MOZ_ASSERT(isLive());
}
Entry* toEntry() const { return mEntry; }
};
template <class T, class HashPolicy, class AllocPolicy>
class HashTable : private AllocPolicy {
friend class mozilla::ReentrancyGuard;
using NonConstT = std::remove_const_t<T>;
using Key = typename HashPolicy::KeyType;
using Lookup = typename HashPolicy::Lookup;
public:
using Entry = HashTableEntry<T>;
using Slot = EntrySlot<T>;
template <typename F>
static void forEachSlot(char* aTable, uint32_t aCapacity, F&& f) {
auto hashes = reinterpret_cast<HashNumber*>(aTable);
auto entries = reinterpret_cast<Entry*>(&hashes[aCapacity]);
Slot slot(entries, hashes);
for (size_t i = 0; i < size_t(aCapacity); ++i) {
f(slot);
++slot;
}
}
// A nullable pointer to a hash table element. A Ptr |p| can be tested
// either explicitly |if (p.found()) p->...| or using boolean conversion
// |if (p) p->...|. Ptr objects must not be used after any mutating hash
// table operations unless |generation()| is tested.
class Ptr {
friend class HashTable;
Slot mSlot;
#ifdef DEBUG
const HashTable* mTable;
Generation mGeneration;
#endif
protected:
Ptr(Slot aSlot, const HashTable& aTable)
: mSlot(aSlot)
#ifdef DEBUG
,
mTable(&aTable),
mGeneration(aTable.generation())
#endif
{
}
// This constructor is used only by AddPtr() within lookupForAdd().
explicit Ptr(const HashTable& aTable)
: mSlot(nullptr, nullptr)
#ifdef DEBUG
,
mTable(&aTable),
mGeneration(aTable.generation())
#endif
{
}
bool isValid() const { return !!mSlot.toEntry(); }
public:
Ptr()
: mSlot(nullptr, nullptr)
#ifdef DEBUG
,
mTable(nullptr),
mGeneration(0)
#endif
{
}
bool found() const {
if (!isValid()) {
return false;
}
#ifdef DEBUG
MOZ_ASSERT(mGeneration == mTable->generation());
#endif
return mSlot.isLive();
}
explicit operator bool() const { return found(); }
bool operator==(const Ptr& aRhs) const {
MOZ_ASSERT(found() && aRhs.found());
return mSlot == aRhs.mSlot;
}
bool operator!=(const Ptr& aRhs) const {
#ifdef DEBUG
MOZ_ASSERT(mGeneration == mTable->generation());
#endif
return !(*this == aRhs);
}
T& operator*() const {
#ifdef DEBUG
MOZ_ASSERT(found());
MOZ_ASSERT(mGeneration == mTable->generation());
#endif
return mSlot.get();
}
T* operator->() const {
#ifdef DEBUG
MOZ_ASSERT(found());
MOZ_ASSERT(mGeneration == mTable->generation());
#endif
return &mSlot.get();
}
};
// A Ptr that can be used to add a key after a failed lookup.
class AddPtr : public Ptr {
friend class HashTable;
HashNumber mKeyHash;
#ifdef DEBUG
uint64_t mMutationCount;
#endif
AddPtr(Slot aSlot, const HashTable& aTable, HashNumber aHashNumber)
: Ptr(aSlot, aTable),
mKeyHash(aHashNumber)
#ifdef DEBUG
,
mMutationCount(aTable.mMutationCount)
#endif
{
}
// This constructor is used when lookupForAdd() is performed on a table
// lacking entry storage; it leaves mSlot null but initializes everything
// else.
AddPtr(const HashTable& aTable, HashNumber aHashNumber)
: Ptr(aTable),
mKeyHash(aHashNumber)
#ifdef DEBUG
,
mMutationCount(aTable.mMutationCount)
#endif
{
MOZ_ASSERT(isLive());
}
bool isLive() const { return isLiveHash(mKeyHash); }
public:
AddPtr() : mKeyHash(0) {}
};
// A hash table iterator that (mostly) doesn't allow table modifications.
// As with Ptr/AddPtr, Iterator objects must not be used after any mutating
// hash table operation unless the |generation()| is tested.
class Iterator {
void moveToNextLiveEntry() {
while (++mCur < mEnd && !mCur.isLive()) {
continue;
}
}
protected:
friend class HashTable;
explicit Iterator(const HashTable& aTable)
: mCur(aTable.slotForIndex(0)),
mEnd(aTable.slotForIndex(aTable.capacity()))
#ifdef DEBUG
,
mTable(aTable),
mMutationCount(aTable.mMutationCount),
mGeneration(aTable.generation()),
mValidEntry(true)
#endif
{
if (!done() && !mCur.isLive()) {
moveToNextLiveEntry();
}
}
Slot mCur;
Slot mEnd;
#ifdef DEBUG
const HashTable& mTable;
uint64_t mMutationCount;
Generation mGeneration;
bool mValidEntry;
#endif
public:
bool done() const {
MOZ_ASSERT(mGeneration == mTable.generation());
MOZ_ASSERT(mMutationCount == mTable.mMutationCount);
return mCur == mEnd;
}
T& get() const {
MOZ_ASSERT(!done());
MOZ_ASSERT(mValidEntry);
MOZ_ASSERT(mGeneration == mTable.generation());
MOZ_ASSERT(mMutationCount == mTable.mMutationCount);
return mCur.get();
}
void next() {
MOZ_ASSERT(!done());
MOZ_ASSERT(mGeneration == mTable.generation());
MOZ_ASSERT(mMutationCount == mTable.mMutationCount);
moveToNextLiveEntry();
#ifdef DEBUG
mValidEntry = true;
#endif
}
};
// A hash table iterator that permits modification, removal and rekeying.
// Since rehashing when elements were removed during enumeration would be
// bad, it is postponed until the ModIterator is destructed. Since the
// ModIterator's destructor touches the hash table, the user must ensure
// that the hash table is still alive when the destructor runs.
class ModIterator : public Iterator {
friend class HashTable;
HashTable& mTable;
bool mRekeyed;
bool mRemoved;
// ModIterator is movable but not copyable.
ModIterator(const ModIterator&) = delete;
void operator=(const ModIterator&) = delete;
protected:
explicit ModIterator(HashTable& aTable)
: Iterator(aTable), mTable(aTable), mRekeyed(false), mRemoved(false) {}
public:
MOZ_IMPLICIT ModIterator(ModIterator&& aOther)
: Iterator(aOther),
mTable(aOther.mTable),
mRekeyed(aOther.mRekeyed),
mRemoved(aOther.mRemoved) {
aOther.mRekeyed = false;
aOther.mRemoved = false;
}
// Removes the current element from the table, leaving |get()|
// invalid until the next call to |next()|.
void remove() {
mTable.remove(this->mCur);
mRemoved = true;
#ifdef DEBUG
this->mValidEntry = false;
this->mMutationCount = mTable.mMutationCount;
#endif
}
NonConstT& getMutable() {
MOZ_ASSERT(!this->done());
MOZ_ASSERT(this->mValidEntry);
MOZ_ASSERT(this->mGeneration == this->Iterator::mTable.generation());
MOZ_ASSERT(this->mMutationCount == this->Iterator::mTable.mMutationCount);
return this->mCur.getMutable();
}
// Removes the current element and re-inserts it into the table with
// a new key at the new Lookup position. |get()| is invalid after
// this operation until the next call to |next()|.
void rekey(const Lookup& l, const Key& k) {
MOZ_ASSERT(&k != &HashPolicy::getKey(this->mCur.get()));
Ptr p(this->mCur, mTable);
mTable.rekeyWithoutRehash(p, l, k);
mRekeyed = true;
#ifdef DEBUG
this->mValidEntry = false;
this->mMutationCount = mTable.mMutationCount;
#endif
}
void rekey(const Key& k) { rekey(k, k); }
// Potentially rehashes the table.
~ModIterator() {
if (mRekeyed) {
mTable.mGen++;
mTable.infallibleRehashIfOverloaded();
}
if (mRemoved) {
mTable.compact();
}
}
};
// Range is similar to Iterator, but uses different terminology.
class Range {
friend class HashTable;
Iterator mIter;
protected:
explicit Range(const HashTable& table) : mIter(table) {}
public:
bool empty() const { return mIter.done(); }
T& front() const { return mIter.get(); }
void popFront() { return mIter.next(); }
};
// Enum is similar to ModIterator, but uses different terminology.
class Enum {
ModIterator mIter;
// Enum is movable but not copyable.
Enum(const Enum&) = delete;
void operator=(const Enum&) = delete;
public:
template <class Map>
explicit Enum(Map& map) : mIter(map.mImpl) {}
MOZ_IMPLICIT Enum(Enum&& other) : mIter(std::move(other.mIter)) {}
bool empty() const { return mIter.done(); }
T& front() const { return mIter.get(); }
void popFront() { return mIter.next(); }
void removeFront() { mIter.remove(); }
NonConstT& mutableFront() { return mIter.getMutable(); }
void rekeyFront(const Lookup& aLookup, const Key& aKey) {
mIter.rekey(aLookup, aKey);
}
void rekeyFront(const Key& aKey) { mIter.rekey(aKey); }
};
// HashTable is movable
HashTable(HashTable&& aRhs) : AllocPolicy(std::move(aRhs)) { moveFrom(aRhs); }
HashTable& operator=(HashTable&& aRhs) {
MOZ_ASSERT(this != &aRhs, "self-move assignment is prohibited");
if (mTable) {
destroyTable(*this, mTable, capacity());
}
AllocPolicy::operator=(std::move(aRhs));
moveFrom(aRhs);
return *this;
}
private:
void moveFrom(HashTable& aRhs) {
mGen = aRhs.mGen;
mHashShift = aRhs.mHashShift;
mTable = aRhs.mTable;
mEntryCount = aRhs.mEntryCount;
mRemovedCount = aRhs.mRemovedCount;
#ifdef DEBUG
mMutationCount = aRhs.mMutationCount;
mEntered = aRhs.mEntered;
#endif
aRhs.mTable = nullptr;
aRhs.clearAndCompact();
}
// HashTable is not copyable or assignable
HashTable(const HashTable&) = delete;
void operator=(const HashTable&) = delete;
static const uint32_t CAP_BITS = 30;
public:
uint64_t mGen : 56; // entry storage generation number
uint64_t mHashShift : 8; // multiplicative hash shift
char* mTable; // entry storage
uint32_t mEntryCount; // number of entries in mTable
uint32_t mRemovedCount; // removed entry sentinels in mTable
#ifdef DEBUG
uint64_t mMutationCount;
mutable bool mEntered;
#endif
// The default initial capacity is 32 (enough to hold 16 elements), but it
// can be as low as 4.
static const uint32_t sDefaultLen = 16;
static const uint32_t sMinCapacity = 4;
// See the comments in HashTableEntry about this value.
static_assert(sMinCapacity >= 4, "too-small sMinCapacity breaks assumptions");
static const uint32_t sMaxInit = 1u << (CAP_BITS - 1);
static const uint32_t sMaxCapacity = 1u << CAP_BITS;
// Hash-table alpha is conceptually a fraction, but to avoid floating-point
// math we implement it as a ratio of integers.
static const uint8_t sAlphaDenominator = 4;
static const uint8_t sMinAlphaNumerator = 1; // min alpha: 1/4
static const uint8_t sMaxAlphaNumerator = 3; // max alpha: 3/4
static const HashNumber sFreeKey = Entry::sFreeKey;
static const HashNumber sRemovedKey = Entry::sRemovedKey;
static const HashNumber sCollisionBit = Entry::sCollisionBit;
static uint32_t bestCapacity(uint32_t aLen) {
static_assert(
(sMaxInit * sAlphaDenominator) / sAlphaDenominator == sMaxInit,
"multiplication in numerator below could overflow");
static_assert(
sMaxInit * sAlphaDenominator <= UINT32_MAX - sMaxAlphaNumerator,
"numerator calculation below could potentially overflow");
// Callers should ensure this is true.
MOZ_ASSERT(aLen <= sMaxInit);
// Compute the smallest capacity allowing |aLen| elements to be
// inserted without rehashing: ceil(aLen / max-alpha). (Ceiling
// integral division: <http://stackoverflow.com/a/2745086>.)
uint32_t capacity = (aLen * sAlphaDenominator + sMaxAlphaNumerator - 1) /
sMaxAlphaNumerator;
capacity = (capacity < sMinCapacity) ? sMinCapacity : RoundUpPow2(capacity);
MOZ_ASSERT(capacity >= aLen);
MOZ_ASSERT(capacity <= sMaxCapacity);
return capacity;
}
static uint32_t hashShift(uint32_t aLen) {
// Reject all lengths whose initial computed capacity would exceed
// sMaxCapacity. Round that maximum aLen down to the nearest power of two
// for speedier code.
if (MOZ_UNLIKELY(aLen > sMaxInit)) {
MOZ_CRASH("initial length is too large");
}
return kHashNumberBits - mozilla::CeilingLog2(bestCapacity(aLen));
}
static bool isLiveHash(HashNumber aHash) { return Entry::isLiveHash(aHash); }
static HashNumber prepareHash(const Lookup& aLookup) {
HashNumber keyHash = ScrambleHashCode(HashPolicy::hash(aLookup));
// Avoid reserved hash codes.
if (!isLiveHash(keyHash)) {
keyHash -= (sRemovedKey + 1);
}
return keyHash & ~sCollisionBit;
}
enum FailureBehavior { DontReportFailure = false, ReportFailure = true };
// Fake a struct that we're going to alloc. See the comments in
// HashTableEntry about how the table is laid out, and why it's safe.
struct FakeSlot {
unsigned char c[sizeof(HashNumber) + sizeof(typename Entry::NonConstT)];
};
static char* createTable(AllocPolicy& aAllocPolicy, uint32_t aCapacity,
FailureBehavior aReportFailure = ReportFailure) {
FakeSlot* fake =
aReportFailure
? aAllocPolicy.template pod_malloc<FakeSlot>(aCapacity)
: aAllocPolicy.template maybe_pod_malloc<FakeSlot>(aCapacity);
MOZ_ASSERT((reinterpret_cast<uintptr_t>(fake) % Entry::kMinimumAlignment) ==
0);
char* table = reinterpret_cast<char*>(fake);
if (table) {
forEachSlot(table, aCapacity, [&](Slot& slot) {
*slot.mKeyHash = sFreeKey;
new (KnownNotNull, slot.toEntry()) Entry();
});
}
return table;
}
static void destroyTable(AllocPolicy& aAllocPolicy, char* aOldTable,
uint32_t aCapacity) {
forEachSlot(aOldTable, aCapacity, [&](const Slot& slot) {
if (slot.isLive()) {
slot.toEntry()->destroyStoredT();
}
});
freeTable(aAllocPolicy, aOldTable, aCapacity);
}
static void freeTable(AllocPolicy& aAllocPolicy, char* aOldTable,
uint32_t aCapacity) {
FakeSlot* fake = reinterpret_cast<FakeSlot*>(aOldTable);
aAllocPolicy.free_(fake, aCapacity);
}
public:
HashTable(AllocPolicy aAllocPolicy, uint32_t aLen)
: AllocPolicy(std::move(aAllocPolicy)),
mGen(0),
mHashShift(hashShift(aLen)),
mTable(nullptr),
mEntryCount(0),
mRemovedCount(0)
#ifdef DEBUG
,
mMutationCount(0),
mEntered(false)
#endif
{
}
explicit HashTable(AllocPolicy aAllocPolicy)
: HashTable(aAllocPolicy, sDefaultLen) {}
~HashTable() {
if (mTable) {
destroyTable(*this, mTable, capacity());
}
}
private:
HashNumber hash1(HashNumber aHash0) const { return aHash0 >> mHashShift; }
struct DoubleHash {
HashNumber mHash2;
HashNumber mSizeMask;
};
DoubleHash hash2(HashNumber aCurKeyHash) const {
uint32_t sizeLog2 = kHashNumberBits - mHashShift;
DoubleHash dh = {((aCurKeyHash << sizeLog2) >> mHashShift) | 1,
(HashNumber(1) << sizeLog2) - 1};
return dh;
}
static HashNumber applyDoubleHash(HashNumber aHash1,
const DoubleHash& aDoubleHash) {
return WrappingSubtract(aHash1, aDoubleHash.mHash2) & aDoubleHash.mSizeMask;
}
static MOZ_ALWAYS_INLINE bool match(T& aEntry, const Lookup& aLookup) {
return HashPolicy::match(HashPolicy::getKey(aEntry), aLookup);
}
enum LookupReason { ForNonAdd, ForAdd };
Slot slotForIndex(HashNumber aIndex) const {
auto hashes = reinterpret_cast<HashNumber*>(mTable);
auto entries = reinterpret_cast<Entry*>(&hashes[capacity()]);
return Slot(&entries[aIndex], &hashes[aIndex]);
}
// Warning: in order for readonlyThreadsafeLookup() to be safe this
// function must not modify the table in any way when Reason==ForNonAdd.
template <LookupReason Reason>
MOZ_ALWAYS_INLINE Slot lookup(const Lookup& aLookup,
HashNumber aKeyHash) const {
MOZ_ASSERT(isLiveHash(aKeyHash));
MOZ_ASSERT(!(aKeyHash & sCollisionBit));
MOZ_ASSERT(mTable);
// Compute the primary hash address.
HashNumber h1 = hash1(aKeyHash);
Slot slot = slotForIndex(h1);
// Miss: return space for a new entry.
if (slot.isFree()) {
return slot;
}
// Hit: return entry.
if (slot.matchHash(aKeyHash) && match(slot.get(), aLookup)) {
return slot;
}
// Collision: double hash.
DoubleHash dh = hash2(aKeyHash);
// Save the first removed entry pointer so we can recycle later.
Maybe<Slot> firstRemoved;
while (true) {
if (Reason == ForAdd && !firstRemoved) {
if (MOZ_UNLIKELY(slot.isRemoved())) {
firstRemoved.emplace(slot);
} else {
slot.setCollision();
}
}
h1 = applyDoubleHash(h1, dh);
slot = slotForIndex(h1);
if (slot.isFree()) {
return firstRemoved.refOr(slot);
}
if (slot.matchHash(aKeyHash) && match(slot.get(), aLookup)) {
return slot;
}
}
}
// This is a copy of lookup() hardcoded to the assumptions:
// 1. the lookup is for an add;
// 2. the key, whose |keyHash| has been passed, is not in the table.
Slot findNonLiveSlot(HashNumber aKeyHash) {
MOZ_ASSERT(!(aKeyHash & sCollisionBit));
MOZ_ASSERT(mTable);
// We assume 'aKeyHash' has already been distributed.
// Compute the primary hash address.
HashNumber h1 = hash1(aKeyHash);
Slot slot = slotForIndex(h1);
// Miss: return space for a new entry.
if (!slot.isLive()) {
return slot;
}
// Collision: double hash.
DoubleHash dh = hash2(aKeyHash);
while (true) {
slot.setCollision();
h1 = applyDoubleHash(h1, dh);
slot = slotForIndex(h1);
if (!slot.isLive()) {
return slot;
}
}
}
enum RebuildStatus { NotOverloaded, Rehashed, RehashFailed };
RebuildStatus changeTableSize(
uint32_t newCapacity, FailureBehavior aReportFailure = ReportFailure) {
MOZ_ASSERT(IsPowerOfTwo(newCapacity));
MOZ_ASSERT(!!mTable == !!capacity());
// Look, but don't touch, until we succeed in getting new entry store.
char* oldTable = mTable;
uint32_t oldCapacity = capacity();
uint32_t newLog2 = mozilla::CeilingLog2(newCapacity);
if (MOZ_UNLIKELY(newCapacity > sMaxCapacity)) {
if (aReportFailure) {
this->reportAllocOverflow();
}
return RehashFailed;
}
char* newTable = createTable(*this, newCapacity, aReportFailure);
if (!newTable) {
return RehashFailed;
}
// We can't fail from here on, so update table parameters.
mHashShift = kHashNumberBits - newLog2;
mRemovedCount = 0;
mGen++;
mTable = newTable;
// Copy only live entries, leaving removed ones behind.
forEachSlot(oldTable, oldCapacity, [&](Slot& slot) {
if (slot.isLive()) {
HashNumber hn = slot.getKeyHash();
findNonLiveSlot(hn).setLive(
hn, std::move(const_cast<typename Entry::NonConstT&>(slot.get())));
}
slot.clear();
});
// All entries have been destroyed, no need to destroyTable.
freeTable(*this, oldTable, oldCapacity);
return Rehashed;
}
RebuildStatus rehashIfOverloaded(
FailureBehavior aReportFailure = ReportFailure) {
static_assert(sMaxCapacity <= UINT32_MAX / sMaxAlphaNumerator,
"multiplication below could overflow");
// Note: if capacity() is zero, this will always succeed, which is
// what we want.
bool overloaded = mEntryCount + mRemovedCount >=
capacity() * sMaxAlphaNumerator / sAlphaDenominator;
if (!overloaded) {
return NotOverloaded;
}
// Succeed if a quarter or more of all entries are removed. Note that this
// always succeeds if capacity() == 0 (i.e. entry storage has not been
// allocated), which is what we want, because it means changeTableSize()
// will allocate the requested capacity rather than doubling it.
bool manyRemoved = mRemovedCount >= (capacity() >> 2);
uint32_t newCapacity = manyRemoved ? rawCapacity() : rawCapacity() * 2;
return changeTableSize(newCapacity, aReportFailure);
}
void infallibleRehashIfOverloaded() {
if (rehashIfOverloaded(DontReportFailure) == RehashFailed) {
rehashTableInPlace();
}
}
void remove(Slot& aSlot) {
MOZ_ASSERT(mTable);
if (aSlot.hasCollision()) {
aSlot.removeLive();
mRemovedCount++;
} else {
aSlot.clearLive();
}
mEntryCount--;
#ifdef DEBUG
mMutationCount++;
#endif
}
void shrinkIfUnderloaded() {
static_assert(sMaxCapacity <= UINT32_MAX / sMinAlphaNumerator,
"multiplication below could overflow");
bool underloaded =
capacity() > sMinCapacity &&
mEntryCount <= capacity() * sMinAlphaNumerator / sAlphaDenominator;
if (underloaded) {
(void)changeTableSize(capacity() / 2, DontReportFailure);
}
}
// This is identical to changeTableSize(currentSize), but without requiring
// a second table. We do this by recycling the collision bits to tell us if
// the element is already inserted or still waiting to be inserted. Since
// already-inserted elements win any conflicts, we get the same table as we
// would have gotten through random insertion order.
void rehashTableInPlace() {
mRemovedCount = 0;
mGen++;
forEachSlot(mTable, capacity(), [&](Slot& slot) { slot.unsetCollision(); });
for (uint32_t i = 0; i < capacity();) {
Slot src = slotForIndex(i);
if (!src.isLive() || src.hasCollision()) {
++i;
continue;
}
HashNumber keyHash = src.getKeyHash();
HashNumber h1 = hash1(keyHash);
DoubleHash dh = hash2(keyHash);
Slot tgt = slotForIndex(h1);
while (true) {
if (!tgt.hasCollision()) {
src.swap(tgt);
tgt.setCollision();
break;
}
h1 = applyDoubleHash(h1, dh);
tgt = slotForIndex(h1);
}
}
// TODO: this algorithm leaves collision bits on *all* elements, even if
// they are on no collision path. We have the option of setting the
// collision bits correctly on a subsequent pass or skipping the rehash
// unless we are totally filled with tombstones: benchmark to find out
// which approach is best.
}
// Note: |aLookup| may be a reference to a piece of |u|, so this function
// must take care not to use |aLookup| after moving |u|.
//
// Prefer to use putNewInfallible; this function does not check
// invariants.
template <typename... Args>
void putNewInfallibleInternal(const Lookup& aLookup, Args&&... aArgs) {
MOZ_ASSERT(mTable);
HashNumber keyHash = prepareHash(aLookup);
Slot slot = findNonLiveSlot(keyHash);
if (slot.isRemoved()) {
mRemovedCount--;
keyHash |= sCollisionBit;
}
slot.setLive(keyHash, std::forward<Args>(aArgs)...);
mEntryCount++;
#ifdef DEBUG
mMutationCount++;
#endif
}
public:
void clear() {
forEachSlot(mTable, capacity(), [&](Slot& slot) { slot.clear(); });
mRemovedCount = 0;
mEntryCount = 0;
#ifdef DEBUG
mMutationCount++;
#endif
}
// Resize the table down to the smallest capacity that doesn't overload the
// table. Since we call shrinkIfUnderloaded() on every remove, you only need
// to call this after a bulk removal of items done without calling remove().
void compact() {
if (empty()) {
// Free the entry storage.
freeTable(*this, mTable, capacity());
mGen++;
mHashShift = hashShift(0); // gives minimum capacity on regrowth
mTable = nullptr;
mRemovedCount = 0;
return;
}
uint32_t bestCapacity = this->bestCapacity(mEntryCount);
MOZ_ASSERT(bestCapacity <= capacity());
if (bestCapacity < capacity()) {
(void)changeTableSize(bestCapacity, DontReportFailure);
}
}
void clearAndCompact() {
clear();
compact();
}
MOZ_MUST_USE bool reserve(uint32_t aLen) {
if (aLen == 0) {
return true;
}
if (MOZ_UNLIKELY(aLen > sMaxInit)) {
return false;
}
uint32_t bestCapacity = this->bestCapacity(aLen);
if (bestCapacity <= capacity()) {
return true; // Capacity is already sufficient.
}
RebuildStatus status = changeTableSize(bestCapacity, ReportFailure);
MOZ_ASSERT(status != NotOverloaded);
return status != RehashFailed;
}
Iterator iter() const { return Iterator(*this); }
ModIterator modIter() { return ModIterator(*this); }
Range all() const { return Range(*this); }
bool empty() const { return mEntryCount == 0; }
uint32_t count() const { return mEntryCount; }
uint32_t rawCapacity() const { return 1u << (kHashNumberBits - mHashShift); }
uint32_t capacity() const { return mTable ? rawCapacity() : 0; }
Generation generation() const { return Generation(mGen); }
size_t shallowSizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
return aMallocSizeOf(mTable);
}
size_t shallowSizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const {
return aMallocSizeOf(this) + shallowSizeOfExcludingThis(aMallocSizeOf);
}
MOZ_ALWAYS_INLINE Ptr readonlyThreadsafeLookup(const Lookup& aLookup) const {
if (empty() || !HasHash<HashPolicy>(aLookup)) {
return Ptr();
}
HashNumber keyHash = prepareHash(aLookup);
return Ptr(lookup<ForNonAdd>(aLookup, keyHash), *this);
}
MOZ_ALWAYS_INLINE Ptr lookup(const Lookup& aLookup) const {
ReentrancyGuard g(*this);
return readonlyThreadsafeLookup(aLookup);
}
MOZ_ALWAYS_INLINE AddPtr lookupForAdd(const Lookup& aLookup) {
ReentrancyGuard g(*this);
if (!EnsureHash<HashPolicy>(aLookup)) {
return AddPtr();
}
HashNumber keyHash = prepareHash(aLookup);
if (!mTable) {
return AddPtr(*this, keyHash);
}
// Directly call the constructor in the return statement to avoid
// excess copying when building with Visual Studio 2017.
// See bug 1385181.
return AddPtr(lookup<ForAdd>(aLookup, keyHash), *this, keyHash);
}
template <typename... Args>
MOZ_MUST_USE bool add(AddPtr& aPtr, Args&&... aArgs) {
ReentrancyGuard g(*this);
MOZ_ASSERT_IF(aPtr.isValid(), mTable);
MOZ_ASSERT_IF(aPtr.isValid(), aPtr.mTable == this);
MOZ_ASSERT(!aPtr.found());
MOZ_ASSERT(!(aPtr.mKeyHash & sCollisionBit));
// Check for error from ensureHash() here.
if (!aPtr.isLive()) {
return false;
}
MOZ_ASSERT(aPtr.mGeneration == generation());
#ifdef DEBUG
MOZ_ASSERT(aPtr.mMutationCount == mMutationCount);
#endif
if (!aPtr.isValid()) {
MOZ_ASSERT(!mTable && mEntryCount == 0);
uint32_t newCapacity = rawCapacity();
RebuildStatus status = changeTableSize(newCapacity, ReportFailure);
MOZ_ASSERT(status != NotOverloaded);
if (status == RehashFailed) {
return false;
}
aPtr.mSlot = findNonLiveSlot(aPtr.mKeyHash);
} else if (aPtr.mSlot.isRemoved()) {
// Changing an entry from removed to live does not affect whether we are
// overloaded and can be handled separately.
if (!this->checkSimulatedOOM()) {
return false;
}
mRemovedCount--;
aPtr.mKeyHash |= sCollisionBit;
} else {
// Preserve the validity of |aPtr.mSlot|.
RebuildStatus status = rehashIfOverloaded();
if (status == RehashFailed) {
return false;
}
if (status == NotOverloaded && !this->checkSimulatedOOM()) {
return false;
}
if (status == Rehashed) {
aPtr.mSlot = findNonLiveSlot(aPtr.mKeyHash);
}
}
aPtr.mSlot.setLive(aPtr.mKeyHash, std::forward<Args>(aArgs)...);
mEntryCount++;
#ifdef DEBUG
mMutationCount++;
aPtr.mGeneration = generation();
aPtr.mMutationCount = mMutationCount;
#endif
return true;
}
// Note: |aLookup| may be a reference to a piece of |u|, so this function
// must take care not to use |aLookup| after moving |u|.
template <typename... Args>
void putNewInfallible(const Lookup& aLookup, Args&&... aArgs) {
MOZ_ASSERT(!lookup(aLookup).found());
ReentrancyGuard g(*this);
putNewInfallibleInternal(aLookup, std::forward<Args>(aArgs)...);
}
// Note: |aLookup| may be alias arguments in |aArgs|, so this function must
// take care not to use |aLookup| after moving |aArgs|.
template <typename... Args>
MOZ_MUST_USE bool putNew(const Lookup& aLookup, Args&&... aArgs) {
if (!this->checkSimulatedOOM()) {
return false;
}
if (!EnsureHash<HashPolicy>(aLookup)) {
return false;
}
if (rehashIfOverloaded() == RehashFailed) {
return false;
}
putNewInfallible(aLookup, std::forward<Args>(aArgs)...);
return true;
}
// Note: |aLookup| may be a reference to a piece of |u|, so this function
// must take care not to use |aLookup| after moving |u|.
template <typename... Args>
MOZ_MUST_USE bool relookupOrAdd(AddPtr& aPtr, const Lookup& aLookup,
Args&&... aArgs) {
// Check for error from ensureHash() here.
if (!aPtr.isLive()) {
return false;
}
#ifdef DEBUG
aPtr.mGeneration = generation();
aPtr.mMutationCount = mMutationCount;
#endif
if (mTable) {
ReentrancyGuard g(*this);
// Check that aLookup has not been destroyed.
MOZ_ASSERT(prepareHash(aLookup) == aPtr.mKeyHash);
aPtr.mSlot = lookup<ForAdd>(aLookup, aPtr.mKeyHash);
if (aPtr.found()) {
return true;
}
} else {
// Clear aPtr so it's invalid; add() will allocate storage and redo the
// lookup.
aPtr.mSlot = Slot(nullptr, nullptr);
}
return add(aPtr, std::forward<Args>(aArgs)...);
}
void remove(Ptr aPtr) {
MOZ_ASSERT(mTable);
ReentrancyGuard g(*this);
MOZ_ASSERT(aPtr.found());
MOZ_ASSERT(aPtr.mGeneration == generation());
remove(aPtr.mSlot);
shrinkIfUnderloaded();
}
void rekeyWithoutRehash(Ptr aPtr, const Lookup& aLookup, const Key& aKey) {
MOZ_ASSERT(mTable);
ReentrancyGuard g(*this);
MOZ_ASSERT(aPtr.found());
MOZ_ASSERT(aPtr.mGeneration == generation());
typename HashTableEntry<T>::NonConstT t(std::move(*aPtr));
HashPolicy::setKey(t, const_cast<Key&>(aKey));
remove(aPtr.mSlot);
putNewInfallibleInternal(aLookup, std::move(t));
}
void rekeyAndMaybeRehash(Ptr aPtr, const Lookup& aLookup, const Key& aKey) {
rekeyWithoutRehash(aPtr, aLookup, aKey);
infallibleRehashIfOverloaded();
}
};
} // namespace detail
} // namespace mozilla
#endif /* mozilla_HashTable_h */
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