/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- * vim: set ts=8 sts=4 et sw=4 tw=99: * 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/. */ #ifndef js_HashTable_h #define js_HashTable_h #include "mozilla/Alignment.h" #include "mozilla/Assertions.h" #include "mozilla/Attributes.h" #include "mozilla/Casting.h" #include "mozilla/MemoryReporting.h" #include "mozilla/Move.h" #include "mozilla/PodOperations.h" #include "mozilla/ReentrancyGuard.h" #include "mozilla/TemplateLib.h" #include "mozilla/TypeTraits.h" #include "js/Utility.h" namespace js { class TempAllocPolicy; template struct DefaultHasher; template class HashMapEntry; namespace detail { template class HashTableEntry; template class HashTable; } /*****************************************************************************/ // A JS-friendly, STL-like container providing a hash-based map from keys to // values. In particular, HashMap calls constructors and destructors of all // objects added so non-PODs may be used safely. // // Key/Value requirements: // - movable, destructible, assignable // HashPolicy requirements: // - see Hash Policy section below // AllocPolicy: // - see jsalloc.h // // Note: // - HashMap is not reentrant: Key/Value/HashPolicy/AllocPolicy members // called by HashMap must not call back into the same HashMap object. // - Due to the lack of exception handling, the user must call |init()|. template , class AllocPolicy = TempAllocPolicy> class HashMap { typedef HashMapEntry TableEntry; struct MapHashPolicy : HashPolicy { typedef Key KeyType; static const Key &getKey(TableEntry &e) { return e.key(); } static void setKey(TableEntry &e, Key &k) { HashPolicy::rekey(e.mutableKey(), k); } }; typedef detail::HashTable Impl; Impl impl; public: typedef typename HashPolicy::Lookup Lookup; typedef TableEntry Entry; // HashMap construction is fallible (due to OOM); thus the user must call // init after constructing a HashMap and check the return value. explicit HashMap(AllocPolicy a = AllocPolicy()) : impl(a) {} bool init(uint32_t len = 16) { return impl.init(len); } bool initialized() const { return impl.initialized(); } // Return whether the given lookup value is present in the map. E.g.: // // typedef HashMap HM; // HM h; // if (HM::Ptr p = h.lookup(3)) { // const HM::Entry &e = *p; // p acts like a pointer to Entry // assert(p->key == 3); // Entry contains the key // char val = p->value; // and value // } // // Also see the definition of Ptr in HashTable above (with T = Entry). typedef typename Impl::Ptr Ptr; Ptr lookup(const Lookup &l) const { return impl.lookup(l); } // Like lookup, but does not assert if two threads call lookup at the same // time. Only use this method when none of the threads will modify the map. Ptr readonlyThreadsafeLookup(const Lookup &l) const { return impl.readonlyThreadsafeLookup(l); } // Assuming |p.found()|, remove |*p|. void remove(Ptr p) { impl.remove(p); } // 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 Entry. E.g.: // // typedef HashMap HM; // HM h; // HM::AddPtr p = h.lookupForAdd(3); // if (!p) { // if (!h.add(p, 3, 'a')) // return false; // } // const HM::Entry &e = *p; // p acts like a pointer to Entry // assert(p->key == 3); // Entry contains the key // char val = p->value; // and value // // Also see the definition of AddPtr in HashTable above (with T = Entry). // // 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; // } // const HM::Entry &e = *p; // assert(p->key == 3); // char val = p->value; typedef typename Impl::AddPtr AddPtr; AddPtr lookupForAdd(const Lookup &l) const { return impl.lookupForAdd(l); } template bool add(AddPtr &p, KeyInput &&k, ValueInput &&v) { Entry e(mozilla::Forward(k), mozilla::Forward(v)); return impl.add(p, mozilla::Move(e)); } template bool add(AddPtr &p, KeyInput &&k) { Entry e(mozilla::Forward(k), Value()); return impl.add(p, mozilla::Move(e)); } template bool relookupOrAdd(AddPtr &p, KeyInput &&k, ValueInput &&v) { Entry e(mozilla::Forward(k), mozilla::Forward(v)); return impl.relookupOrAdd(p, e.key(), mozilla::Move(e)); } // |all()| returns a Range containing |count()| elements. E.g.: // // typedef HashMap HM; // HM h; // for (HM::Range r = h.all(); !r.empty(); r.popFront()) // char c = r.front().value(); // // Also see the definition of Range in HashTable above (with T = Entry). typedef typename Impl::Range Range; Range all() const { return impl.all(); } // Typedef for the enumeration class. An Enum may be used to examine and // remove table entries: // // typedef HashMap HM; // HM s; // for (HM::Enum e(s); !e.empty(); e.popFront()) // if (e.front().value() == 'l') // e.removeFront(); // // Table resize may occur in Enum's destructor. Also see the definition of // Enum in HashTable above (with T = Entry). typedef typename Impl::Enum Enum; // Remove all entries. This does not shrink the table. For that consider // using the finish() method. void clear() { impl.clear(); } // Remove all the entries and release all internal buffers. The map must // be initialized again before any use. void finish() { impl.finish(); } // Does the table contain any entries? bool empty() const { return impl.empty(); } // Number of live elements in the map. uint32_t count() const { return impl.count(); } // Total number of allocation in the dynamic table. Note: resize will // happen well before count() == capacity(). size_t capacity() const { return impl.capacity(); } // Don't just call |impl.sizeOfExcludingThis()| because there's no // guarantee that |impl| is the first field in HashMap. size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const { return impl.sizeOfExcludingThis(mallocSizeOf); } size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const { return mallocSizeOf(this) + impl.sizeOfExcludingThis(mallocSizeOf); } // If |generation()| is the same before and after a HashMap operation, // pointers into the table remain valid. uint32_t generation() const { return impl.generation(); } /************************************************** Shorthand operations */ bool has(const Lookup &l) const { return impl.lookup(l).found(); } // Overwrite existing value with v. Return false on oom. template bool put(KeyInput &&k, ValueInput &&v) { AddPtr p = lookupForAdd(k); if (p) { p->value() = mozilla::Forward(v); return true; } return add(p, mozilla::Forward(k), mozilla::Forward(v)); } // Like put, but assert that the given key is not already present. template bool putNew(KeyInput &&k, ValueInput &&v) { Entry e(mozilla::Forward(k), mozilla::Forward(v)); return impl.putNew(e.key(), mozilla::Move(e)); } // Add (k,defaultValue) if |k| is not found. Return a false-y Ptr on oom. Ptr lookupWithDefault(const Key &k, const Value &defaultValue) { AddPtr p = lookupForAdd(k); if (p) return p; (void)add(p, k, defaultValue); // p is left false-y on oom. return p; } // Remove if present. void remove(const Lookup &l) { if (Ptr p = lookup(l)) remove(p); } // Infallibly rekey one entry, if necessary. // Requires template parameters Key and HashPolicy::Lookup to be the same type. void rekeyIfMoved(const Key &old_key, const Key &new_key) { if (old_key != new_key) rekeyAs(old_key, new_key, new_key); } // Infallibly rekey one entry if present, and return whether that happened. bool rekeyAs(const Lookup &old_lookup, const Lookup &new_lookup, const Key &new_key) { if (Ptr p = lookup(old_lookup)) { impl.rekeyAndMaybeRehash(p, new_lookup, new_key); return true; } return false; } // HashMap is movable HashMap(HashMap &&rhs) : impl(mozilla::Move(rhs.impl)) {} void operator=(HashMap &&rhs) { MOZ_ASSERT(this != &rhs, "self-move assignment is prohibited"); impl = mozilla::Move(rhs.impl); } private: // HashMap is not copyable or assignable HashMap(const HashMap &hm) = delete; HashMap &operator=(const HashMap &hm) = delete; friend class Impl::Enum; }; /*****************************************************************************/ // A JS-friendly, STL-like container providing a hash-based set of values. In // particular, HashSet calls constructors and destructors of all objects added // so non-PODs may be used safely. // // T requirements: // - movable, destructible, assignable // HashPolicy requirements: // - see Hash Policy section below // AllocPolicy: // - see jsalloc.h // // Note: // - HashSet is not reentrant: T/HashPolicy/AllocPolicy members called by // HashSet must not call back into the same HashSet object. // - Due to the lack of exception handling, the user must call |init()|. template , class AllocPolicy = TempAllocPolicy> class HashSet { struct SetOps : HashPolicy { typedef T KeyType; static const KeyType &getKey(const T &t) { return t; } static void setKey(T &t, KeyType &k) { HashPolicy::rekey(t, k); } }; typedef detail::HashTable Impl; Impl impl; public: typedef typename HashPolicy::Lookup Lookup; typedef T Entry; // HashSet construction is fallible (due to OOM); thus the user must call // init after constructing a HashSet and check the return value. explicit HashSet(AllocPolicy a = AllocPolicy()) : impl(a) {} bool init(uint32_t len = 16) { return impl.init(len); } bool initialized() const { return impl.initialized(); } // Return whether the given lookup value is present in the map. E.g.: // // typedef HashSet HS; // HS h; // if (HS::Ptr p = h.lookup(3)) { // assert(*p == 3); // p acts like a pointer to int // } // // Also see the definition of Ptr in HashTable above. typedef typename Impl::Ptr Ptr; Ptr lookup(const Lookup &l) const { return impl.lookup(l); } // Like lookup, but does not assert if two threads call lookup at the same // time. Only use this method when none of the threads will modify the map. Ptr readonlyThreadsafeLookup(const Lookup &l) const { return impl.readonlyThreadsafeLookup(l); } // Assuming |p.found()|, remove |*p|. void remove(Ptr p) { impl.remove(p); } // 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.: // // typedef HashSet HS; // 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 // // Also see the definition of AddPtr in HashTable above. // // 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). typedef typename Impl::AddPtr AddPtr; AddPtr lookupForAdd(const Lookup &l) const { return impl.lookupForAdd(l); } template bool add(AddPtr &p, U &&u) { return impl.add(p, mozilla::Forward(u)); } template bool relookupOrAdd(AddPtr &p, const Lookup &l, U &&u) { return impl.relookupOrAdd(p, l, mozilla::Forward(u)); } // |all()| returns a Range containing |count()| elements: // // typedef HashSet HS; // HS h; // for (HS::Range r = h.all(); !r.empty(); r.popFront()) // int i = r.front(); // // Also see the definition of Range in HashTable above. typedef typename Impl::Range Range; Range all() const { return impl.all(); } // Typedef for the enumeration class. An Enum may be used to examine and // remove table entries: // // typedef HashSet HS; // HS s; // for (HS::Enum e(s); !e.empty(); e.popFront()) // if (e.front() == 42) // e.removeFront(); // // Table resize may occur in Enum's destructor. Also see the definition of // Enum in HashTable above. typedef typename Impl::Enum Enum; // Remove all entries. This does not shrink the table. For that consider // using the finish() method. void clear() { impl.clear(); } // Remove all the entries and release all internal buffers. The set must // be initialized again before any use. void finish() { impl.finish(); } // Does the table contain any entries? bool empty() const { return impl.empty(); } // Number of live elements in the map. uint32_t count() const { return impl.count(); } // Total number of allocation in the dynamic table. Note: resize will // happen well before count() == capacity(). size_t capacity() const { return impl.capacity(); } // Don't just call |impl.sizeOfExcludingThis()| because there's no // guarantee that |impl| is the first field in HashSet. size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const { return impl.sizeOfExcludingThis(mallocSizeOf); } size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const { return mallocSizeOf(this) + impl.sizeOfExcludingThis(mallocSizeOf); } // If |generation()| is the same before and after a HashSet operation, // pointers into the table remain valid. uint32_t generation() const { return impl.generation(); } /************************************************** Shorthand operations */ bool has(const Lookup &l) const { return impl.lookup(l).found(); } // Add |u| if it is not present already. Return false on oom. template bool put(U &&u) { AddPtr p = lookupForAdd(u); return p ? true : add(p, mozilla::Forward(u)); } // Like put, but assert that the given key is not already present. template bool putNew(U &&u) { return impl.putNew(u, mozilla::Forward(u)); } template bool putNew(const Lookup &l, U &&u) { return impl.putNew(l, mozilla::Forward(u)); } void remove(const Lookup &l) { if (Ptr p = lookup(l)) remove(p); } // Infallibly rekey one entry, if present. // Requires template parameters T and HashPolicy::Lookup to be the same type. void rekeyIfMoved(const Lookup &old_value, const T &new_value) { if (old_value != new_value) rekeyAs(old_value, new_value, new_value); } // Infallibly rekey one entry if present, and return whether that happened. bool rekeyAs(const Lookup &old_lookup, const Lookup &new_lookup, const T &new_value) { if (Ptr p = lookup(old_lookup)) { impl.rekeyAndMaybeRehash(p, new_lookup, new_value); return true; } return false; } // Infallibly rekey one entry with a new key that is equivalent. void rekeyInPlace(Ptr p, const T &new_value) { MOZ_ASSERT(HashPolicy::match(*p, new_value)); impl.rekeyInPlace(p, new_value); } // HashSet is movable HashSet(HashSet &&rhs) : impl(mozilla::Move(rhs.impl)) {} void operator=(HashSet &&rhs) { MOZ_ASSERT(this != &rhs, "self-move assignment is prohibited"); impl = mozilla::Move(rhs.impl); } private: // HashSet is not copyable or assignable HashSet(const HashSet &hs) = delete; HashSet &operator=(const HashSet &hs) = delete; friend class Impl::Enum; }; /*****************************************************************************/ // Hash Policy // // A hash policy P for a hash table with key-type Key must provide: // - a type |P::Lookup| to use to lookup table entries; // - a static member function |P::hash| with signature // // static js::HashNumber hash(Lookup) // // to use to hash the lookup type; and // - a static member function |P::match| with signature // // static bool match(Key, Lookup) // // to use to test equality of key and lookup values. // // 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 != to the // added Key value |k|, the user must ensure that |P::match(k,l)|. E.g.: // // js::HashSet::AddPtr p = h.lookup(l); // if (!p) { // assert(P::match(k, l)); // must hold // h.add(p, k); // } // Pointer hashing policy that strips the lowest zeroBits when calculating the // hash to improve key distribution. template struct PointerHasher { typedef Key Lookup; static HashNumber hash(const Lookup &l) { MOZ_ASSERT(!JS::IsPoisonedPtr(l)); size_t word = reinterpret_cast(l) >> zeroBits; static_assert(sizeof(HashNumber) == 4, "subsequent code assumes a four-byte hash"); #if JS_BITS_PER_WORD == 32 return HashNumber(word); #else static_assert(sizeof(word) == 8, "unexpected word size, new hashing strategy required to " "properly incorporate all bits"); return HashNumber((word >> 32) ^ word); #endif } static bool match(const Key &k, const Lookup &l) { MOZ_ASSERT(!JS::IsPoisonedPtr(k)); MOZ_ASSERT(!JS::IsPoisonedPtr(l)); return k == l; } static void rekey(Key &k, const Key& newKey) { k = newKey; } }; // Default hash policy: just use the 'lookup' value. This of course only // works if the lookup value is integral. HashTable applies ScrambleHashCode to // the result of the 'hash' which means that it is 'ok' if the lookup value is // not well distributed over the HashNumber domain. template struct DefaultHasher { typedef Key Lookup; static HashNumber hash(const Lookup &l) { // Hash if can implicitly cast to hash number type. return l; } static bool match(const Key &k, const Lookup &l) { // Use builtin or overloaded operator==. return k == l; } static void rekey(Key &k, const Key& newKey) { k = newKey; } }; // Specialize hashing policy for pointer types. It assumes that the type is // at least word-aligned. For types with smaller size use PointerHasher. template struct DefaultHasher : PointerHasher::value> {}; // For doubles, we can xor the two uint32s. template <> struct DefaultHasher { typedef double Lookup; static HashNumber hash(double d) { static_assert(sizeof(HashNumber) == 4, "subsequent code assumes a four-byte hash"); uint64_t u = mozilla::BitwiseCast(d); return HashNumber(u ^ (u >> 32)); } static bool match(double lhs, double rhs) { return mozilla::BitwiseCast(lhs) == mozilla::BitwiseCast(rhs); } }; template <> struct DefaultHasher { typedef float Lookup; static HashNumber hash(float f) { static_assert(sizeof(HashNumber) == 4, "subsequent code assumes a four-byte hash"); return HashNumber(mozilla::BitwiseCast(f)); } static bool match(float lhs, float rhs) { return mozilla::BitwiseCast(lhs) == mozilla::BitwiseCast(rhs); } }; /*****************************************************************************/ // 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 HashMapEntry { Key key_; Value value_; template friend class detail::HashTable; template friend class detail::HashTableEntry; template friend class HashMap; Key & mutableKey() { return key_; } public: template HashMapEntry(KeyInput &&k, ValueInput &&v) : key_(mozilla::Forward(k)), value_(mozilla::Forward(v)) {} HashMapEntry(HashMapEntry &&rhs) : key_(mozilla::Move(rhs.key_)), value_(mozilla::Move(rhs.value_)) {} typedef Key KeyType; typedef Value ValueType; const Key & key() const { return key_; } const Value & value() const { return value_; } Value & value() { return value_; } private: HashMapEntry(const HashMapEntry &) = delete; void operator=(const HashMapEntry &) = delete; }; } // namespace js namespace mozilla { template struct IsPod > : IsPod {}; template struct IsPod > : IntegralConstant::value && IsPod::value> {}; } // namespace mozilla namespace js { namespace detail { template class HashTable; template class HashTableEntry { template friend class HashTable; typedef typename mozilla::RemoveConst::Type NonConstT; HashNumber keyHash; mozilla::AlignedStorage2 mem; static const HashNumber sFreeKey = 0; static const HashNumber sRemovedKey = 1; static const HashNumber sCollisionBit = 1; static bool isLiveHash(HashNumber hash) { return hash > sRemovedKey; } HashTableEntry(const HashTableEntry &) = delete; void operator=(const HashTableEntry &) = delete; ~HashTableEntry() = delete; public: // NB: HashTableEntry is treated as a POD: no constructor or destructor calls. void destroyIfLive() { if (isLive()) mem.addr()->~T(); } void destroy() { MOZ_ASSERT(isLive()); mem.addr()->~T(); } void swap(HashTableEntry *other) { mozilla::Swap(keyHash, other->keyHash); mozilla::Swap(mem, other->mem); } T &get() { MOZ_ASSERT(isLive()); return *mem.addr(); } bool isFree() const { return keyHash == sFreeKey; } void clearLive() { MOZ_ASSERT(isLive()); keyHash = sFreeKey; mem.addr()->~T(); } void clear() { if (isLive()) mem.addr()->~T(); keyHash = sFreeKey; } bool isRemoved() const { return keyHash == sRemovedKey; } void removeLive() { MOZ_ASSERT(isLive()); keyHash = sRemovedKey; mem.addr()->~T(); } bool isLive() const { return isLiveHash(keyHash); } void setCollision() { MOZ_ASSERT(isLive()); keyHash |= sCollisionBit; } void setCollision(HashNumber bit) { MOZ_ASSERT(isLive()); keyHash |= bit; } void unsetCollision() { keyHash &= ~sCollisionBit; } bool hasCollision() const { return keyHash & sCollisionBit; } bool matchHash(HashNumber hn) { return (keyHash & ~sCollisionBit) == hn; } HashNumber getKeyHash() const { return keyHash & ~sCollisionBit; } template void setLive(HashNumber hn, U &&u) { MOZ_ASSERT(!isLive()); keyHash = hn; new(mem.addr()) T(mozilla::Forward(u)); MOZ_ASSERT(isLive()); } }; template class HashTable : private AllocPolicy { friend class mozilla::ReentrancyGuard; typedef typename mozilla::RemoveConst::Type NonConstT; typedef typename HashPolicy::KeyType Key; typedef typename HashPolicy::Lookup Lookup; public: typedef HashTableEntry Entry; // 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; Entry *entry_; #ifdef JS_DEBUG const HashTable *table_; uint32_t generation; #endif protected: Ptr(Entry &entry, const HashTable &tableArg) : entry_(&entry) #ifdef JS_DEBUG , table_(&tableArg) , generation(tableArg.generation()) #endif {} public: // Leaves Ptr uninitialized. Ptr() { #ifdef JS_DEBUG entry_ = (Entry *)0xbad; #endif } bool found() const { #ifdef JS_DEBUG MOZ_ASSERT(generation == table_->generation()); #endif return entry_->isLive(); } explicit operator bool() const { return found(); } bool operator==(const Ptr &rhs) const { MOZ_ASSERT(found() && rhs.found()); return entry_ == rhs.entry_; } bool operator!=(const Ptr &rhs) const { #ifdef JS_DEBUG MOZ_ASSERT(generation == table_->generation()); #endif return !(*this == rhs); } T &operator*() const { #ifdef JS_DEBUG MOZ_ASSERT(generation == table_->generation()); #endif return entry_->get(); } T *operator->() const { #ifdef JS_DEBUG MOZ_ASSERT(generation == table_->generation()); #endif return &entry_->get(); } }; // A Ptr that can be used to add a key after a failed lookup. class AddPtr : public Ptr { friend class HashTable; HashNumber keyHash; #ifdef JS_DEBUG uint64_t mutationCount; #endif AddPtr(Entry &entry, const HashTable &tableArg, HashNumber hn) : Ptr(entry, tableArg) , keyHash(hn) #ifdef JS_DEBUG , mutationCount(tableArg.mutationCount) #endif {} public: // Leaves AddPtr uninitialized. AddPtr() {} }; // A collection of hash table entries. The collection is enumerated by // calling |front()| followed by |popFront()| as long as |!empty()|. As // with Ptr/AddPtr, Range objects must not be used after any mutating hash // table operation unless the |generation()| is tested. class Range { protected: friend class HashTable; Range(const HashTable &tableArg, Entry *c, Entry *e) : cur(c) , end(e) #ifdef JS_DEBUG , table_(&tableArg) , mutationCount(tableArg.mutationCount) , generation(tableArg.generation()) , validEntry(true) #endif { while (cur < end && !cur->isLive()) ++cur; } Entry *cur, *end; #ifdef JS_DEBUG const HashTable *table_; uint64_t mutationCount; uint32_t generation; bool validEntry; #endif public: Range() : cur(nullptr) , end(nullptr) #ifdef JS_DEBUG , table_(nullptr) , mutationCount(0) , generation(0) , validEntry(false) #endif {} bool empty() const { #ifdef JS_DEBUG MOZ_ASSERT(generation == table_->generation()); MOZ_ASSERT(mutationCount == table_->mutationCount); #endif return cur == end; } T &front() const { MOZ_ASSERT(!empty()); #ifdef JS_DEBUG MOZ_ASSERT(validEntry); MOZ_ASSERT(generation == table_->generation()); MOZ_ASSERT(mutationCount == table_->mutationCount); #endif return cur->get(); } void popFront() { MOZ_ASSERT(!empty()); #ifdef JS_DEBUG MOZ_ASSERT(generation == table_->generation()); MOZ_ASSERT(mutationCount == table_->mutationCount); #endif while (++cur < end && !cur->isLive()) continue; #ifdef JS_DEBUG validEntry = true; #endif } }; // A Range whose lifetime delimits a mutating enumeration of a hash table. // Since rehashing when elements were removed during enumeration would be // bad, it is postponed until the Enum is destructed. Since the Enum's // destructor touches the hash table, the user must ensure that the hash // table is still alive when the destructor runs. class Enum : public Range { friend class HashTable; HashTable &table_; bool rekeyed; bool removed; /* Not copyable. */ Enum(const Enum &) = delete; void operator=(const Enum &) = delete; public: template explicit Enum(Map &map) : Range(map.all()), table_(map.impl), rekeyed(false), removed(false) {} // Removes the |front()| element from the table, leaving |front()| // invalid until the next call to |popFront()|. For example: // // HashSet s; // for (HashSet::Enum e(s); !e.empty(); e.popFront()) // if (e.front() == 42) // e.removeFront(); void removeFront() { table_.remove(*this->cur); removed = true; #ifdef JS_DEBUG this->validEntry = false; this->mutationCount = table_.mutationCount; #endif } // Removes the |front()| element and re-inserts it into the table with // a new key at the new Lookup position. |front()| is invalid after // this operation until the next call to |popFront()|. void rekeyFront(const Lookup &l, const Key &k) { MOZ_ASSERT(&k != &HashPolicy::getKey(this->cur->get())); Ptr p(*this->cur, table_); table_.rekeyWithoutRehash(p, l, k); rekeyed = true; #ifdef JS_DEBUG this->validEntry = false; this->mutationCount = table_.mutationCount; #endif } void rekeyFront(const Key &k) { rekeyFront(k, k); } // Potentially rehashes the table. ~Enum() { if (rekeyed) { table_.gen++; table_.checkOverRemoved(); } if (removed) table_.compactIfUnderloaded(); } }; // HashTable is movable HashTable(HashTable &&rhs) : AllocPolicy(rhs) { mozilla::PodAssign(this, &rhs); rhs.table = nullptr; } void operator=(HashTable &&rhs) { MOZ_ASSERT(this != &rhs, "self-move assignment is prohibited"); if (table) destroyTable(*this, table, capacity()); mozilla::PodAssign(this, &rhs); rhs.table = nullptr; } private: // HashTable is not copyable or assignable HashTable(const HashTable &) = delete; void operator=(const HashTable &) = delete; private: static const size_t CAP_BITS = 24; public: Entry *table; // entry storage uint32_t gen; // entry storage generation number uint32_t entryCount; // number of entries in table uint32_t removedCount:CAP_BITS; // removed entry sentinels in table uint32_t hashShift:8; // multiplicative hash shift #ifdef JS_DEBUG uint64_t mutationCount; mutable bool mEntered; mutable struct Stats { uint32_t searches; // total number of table searches uint32_t steps; // hash chain links traversed uint32_t hits; // searches that found key uint32_t misses; // searches that didn't find key uint32_t addOverRemoved; // adds that recycled a removed entry uint32_t removes; // calls to remove uint32_t removeFrees; // calls to remove that freed the entry uint32_t grows; // table expansions uint32_t shrinks; // table contractions uint32_t compresses; // table compressions uint32_t rehashes; // tombstone decontaminations } stats; # define METER(x) x #else # define METER(x) #endif // The default initial capacity is 32 (enough to hold 16 elements), but it // can be as low as 4. static const unsigned sMinCapacityLog2 = 2; static const unsigned sMinCapacity = 1 << sMinCapacityLog2; static const unsigned sMaxInit = JS_BIT(CAP_BITS - 1); static const unsigned sMaxCapacity = JS_BIT(CAP_BITS); static const unsigned sHashBits = mozilla::tl::BitSize::value; // 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; void setTableSizeLog2(unsigned sizeLog2) { hashShift = sHashBits - sizeLog2; } static bool isLiveHash(HashNumber hash) { return Entry::isLiveHash(hash); } static HashNumber prepareHash(const Lookup& l) { HashNumber keyHash = ScrambleHashCode(HashPolicy::hash(l)); // Avoid reserved hash codes. if (!isLiveHash(keyHash)) keyHash -= (sRemovedKey + 1); return keyHash & ~sCollisionBit; } static Entry *createTable(AllocPolicy &alloc, uint32_t capacity) { static_assert(sFreeKey == 0, "newly-calloc'd tables have to be considered empty"); static_assert(sMaxCapacity <= SIZE_MAX / sizeof(Entry), "would overflow allocating max number of entries"); return alloc.template pod_calloc(capacity); } static void destroyTable(AllocPolicy &alloc, Entry *oldTable, uint32_t capacity) { for (Entry *e = oldTable, *end = e + capacity; e < end; ++e) e->destroyIfLive(); alloc.free_(oldTable); } public: explicit HashTable(AllocPolicy ap) : AllocPolicy(ap) , table(nullptr) , gen(0) , entryCount(0) , removedCount(0) , hashShift(sHashBits) #ifdef JS_DEBUG , mutationCount(0) , mEntered(false) #endif {} MOZ_WARN_UNUSED_RESULT bool init(uint32_t length) { MOZ_ASSERT(!initialized()); // Reject all lengths whose initial computed capacity would exceed // sMaxCapacity. Round that maximum length down to the nearest power // of two for speedier code. if (MOZ_UNLIKELY(length > sMaxInit)) { this->reportAllocOverflow(); return false; } 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"); // Compute the smallest capacity allowing |length| elements to be // inserted without rehashing: ceil(length / max-alpha). (Ceiling // integral division: .) uint32_t newCapacity = (length * sAlphaDenominator + sMaxAlphaNumerator - 1) / sMaxAlphaNumerator; if (newCapacity < sMinCapacity) newCapacity = sMinCapacity; // FIXME: use JS_CEILING_LOG2 when PGO stops crashing (bug 543034). uint32_t roundUp = sMinCapacity, roundUpLog2 = sMinCapacityLog2; while (roundUp < newCapacity) { roundUp <<= 1; ++roundUpLog2; } newCapacity = roundUp; MOZ_ASSERT(newCapacity >= length); MOZ_ASSERT(newCapacity <= sMaxCapacity); table = createTable(*this, newCapacity); if (!table) return false; setTableSizeLog2(roundUpLog2); METER(memset(&stats, 0, sizeof(stats))); return true; } bool initialized() const { return !!table; } ~HashTable() { if (table) destroyTable(*this, table, capacity()); } private: HashNumber hash1(HashNumber hash0) const { return hash0 >> hashShift; } struct DoubleHash { HashNumber h2; HashNumber sizeMask; }; DoubleHash hash2(HashNumber curKeyHash) const { unsigned sizeLog2 = sHashBits - hashShift; DoubleHash dh = { ((curKeyHash << sizeLog2) >> hashShift) | 1, (HashNumber(1) << sizeLog2) - 1 }; return dh; } static HashNumber applyDoubleHash(HashNumber h1, const DoubleHash &dh) { return (h1 - dh.h2) & dh.sizeMask; } bool overloaded() { static_assert(sMaxCapacity <= UINT32_MAX / sMaxAlphaNumerator, "multiplication below could overflow"); return entryCount + removedCount >= capacity() * sMaxAlphaNumerator / sAlphaDenominator; } // Would the table be underloaded if it had the given capacity and entryCount? static bool wouldBeUnderloaded(uint32_t capacity, uint32_t entryCount) { static_assert(sMaxCapacity <= UINT32_MAX / sMinAlphaNumerator, "multiplication below could overflow"); return capacity > sMinCapacity && entryCount <= capacity * sMinAlphaNumerator / sAlphaDenominator; } bool underloaded() { return wouldBeUnderloaded(capacity(), entryCount); } static bool match(Entry &e, const Lookup &l) { return HashPolicy::match(HashPolicy::getKey(e.get()), l); } Entry &lookup(const Lookup &l, HashNumber keyHash, unsigned collisionBit) const { MOZ_ASSERT(isLiveHash(keyHash)); MOZ_ASSERT(!(keyHash & sCollisionBit)); MOZ_ASSERT(collisionBit == 0 || collisionBit == sCollisionBit); MOZ_ASSERT(table); METER(stats.searches++); // Compute the primary hash address. HashNumber h1 = hash1(keyHash); Entry *entry = &table[h1]; // Miss: return space for a new entry. if (entry->isFree()) { METER(stats.misses++); return *entry; } // Hit: return entry. if (entry->matchHash(keyHash) && match(*entry, l)) { METER(stats.hits++); return *entry; } // Collision: double hash. DoubleHash dh = hash2(keyHash); // Save the first removed entry pointer so we can recycle later. Entry *firstRemoved = nullptr; while(true) { if (MOZ_UNLIKELY(entry->isRemoved())) { if (!firstRemoved) firstRemoved = entry; } else { entry->setCollision(collisionBit); } METER(stats.steps++); h1 = applyDoubleHash(h1, dh); entry = &table[h1]; if (entry->isFree()) { METER(stats.misses++); return firstRemoved ? *firstRemoved : *entry; } if (entry->matchHash(keyHash) && match(*entry, l)) { METER(stats.hits++); return *entry; } } } // This is a copy of lookup hardcoded to the assumptions: // 1. the lookup is a lookupForAdd // 2. the key, whose |keyHash| has been passed is not in the table, // 3. no entries have been removed from the table. // This specialized search avoids the need for recovering lookup values // from entries, which allows more flexible Lookup/Key types. Entry &findFreeEntry(HashNumber keyHash) { MOZ_ASSERT(!(keyHash & sCollisionBit)); MOZ_ASSERT(table); METER(stats.searches++); // We assume 'keyHash' has already been distributed. // Compute the primary hash address. HashNumber h1 = hash1(keyHash); Entry *entry = &table[h1]; // Miss: return space for a new entry. if (!entry->isLive()) { METER(stats.misses++); return *entry; } // Collision: double hash. DoubleHash dh = hash2(keyHash); while(true) { MOZ_ASSERT(!entry->isRemoved()); entry->setCollision(); METER(stats.steps++); h1 = applyDoubleHash(h1, dh); entry = &table[h1]; if (!entry->isLive()) { METER(stats.misses++); return *entry; } } } enum RebuildStatus { NotOverloaded, Rehashed, RehashFailed }; RebuildStatus changeTableSize(int deltaLog2) { // Look, but don't touch, until we succeed in getting new entry store. Entry *oldTable = table; uint32_t oldCap = capacity(); uint32_t newLog2 = sHashBits - hashShift + deltaLog2; uint32_t newCapacity = JS_BIT(newLog2); if (MOZ_UNLIKELY(newCapacity > sMaxCapacity)) { this->reportAllocOverflow(); return RehashFailed; } Entry *newTable = createTable(*this, newCapacity); if (!newTable) return RehashFailed; // We can't fail from here on, so update table parameters. setTableSizeLog2(newLog2); removedCount = 0; gen++; table = newTable; // Copy only live entries, leaving removed ones behind. for (Entry *src = oldTable, *end = src + oldCap; src < end; ++src) { if (src->isLive()) { HashNumber hn = src->getKeyHash(); findFreeEntry(hn).setLive(hn, mozilla::Move(src->get())); src->destroy(); } } // All entries have been destroyed, no need to destroyTable. this->free_(oldTable); return Rehashed; } RebuildStatus checkOverloaded() { if (!overloaded()) return NotOverloaded; // Compress if a quarter or more of all entries are removed. int deltaLog2; if (removedCount >= (capacity() >> 2)) { METER(stats.compresses++); deltaLog2 = 0; } else { METER(stats.grows++); deltaLog2 = 1; } return changeTableSize(deltaLog2); } // Infallibly rehash the table if we are overloaded with removals. void checkOverRemoved() { if (overloaded()) { if (checkOverloaded() == RehashFailed) rehashTableInPlace(); } } void remove(Entry &e) { MOZ_ASSERT(table); METER(stats.removes++); if (e.hasCollision()) { e.removeLive(); removedCount++; } else { METER(stats.removeFrees++); e.clearLive(); } entryCount--; #ifdef JS_DEBUG mutationCount++; #endif } void checkUnderloaded() { if (underloaded()) { METER(stats.shrinks++); (void) changeTableSize(-1); } } // Resize the table down to the largest capacity which doesn't underload the // table. Since we call checkUnderloaded() on every remove, you only need // to call this after a bulk removal of items done without calling remove(). void compactIfUnderloaded() { int32_t resizeLog2 = 0; uint32_t newCapacity = capacity(); while (wouldBeUnderloaded(newCapacity, entryCount)) { newCapacity = newCapacity >> 1; resizeLog2--; } if (resizeLog2 != 0) { changeTableSize(resizeLog2); } } // 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() { METER(stats.rehashes++); removedCount = 0; for (size_t i = 0; i < capacity(); ++i) table[i].unsetCollision(); for (size_t i = 0; i < capacity();) { Entry *src = &table[i]; if (!src->isLive() || src->hasCollision()) { ++i; continue; } HashNumber keyHash = src->getKeyHash(); HashNumber h1 = hash1(keyHash); DoubleHash dh = hash2(keyHash); Entry *tgt = &table[h1]; while (true) { if (!tgt->hasCollision()) { src->swap(tgt); tgt->setCollision(); break; } h1 = applyDoubleHash(h1, dh); tgt = &table[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. } public: void clear() { if (mozilla::IsPod::value) { memset(table, 0, sizeof(*table) * capacity()); } else { uint32_t tableCapacity = capacity(); for (Entry *e = table, *end = table + tableCapacity; e < end; ++e) e->clear(); } removedCount = 0; entryCount = 0; #ifdef JS_DEBUG mutationCount++; #endif } void finish() { #ifdef JS_DEBUG MOZ_ASSERT(!mEntered); #endif if (!table) return; destroyTable(*this, table, capacity()); table = nullptr; gen++; entryCount = 0; removedCount = 0; #ifdef JS_DEBUG mutationCount++; #endif } Range all() const { MOZ_ASSERT(table); return Range(*this, table, table + capacity()); } bool empty() const { MOZ_ASSERT(table); return !entryCount; } uint32_t count() const { MOZ_ASSERT(table); return entryCount; } uint32_t capacity() const { MOZ_ASSERT(table); return JS_BIT(sHashBits - hashShift); } uint32_t generation() const { MOZ_ASSERT(table); return gen; } size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const { return mallocSizeOf(table); } size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const { return mallocSizeOf(this) + sizeOfExcludingThis(mallocSizeOf); } Ptr lookup(const Lookup &l) const { mozilla::ReentrancyGuard g(*this); HashNumber keyHash = prepareHash(l); return Ptr(lookup(l, keyHash, 0), *this); } Ptr readonlyThreadsafeLookup(const Lookup &l) const { HashNumber keyHash = prepareHash(l); return Ptr(lookup(l, keyHash, 0), *this); } AddPtr lookupForAdd(const Lookup &l) const { mozilla::ReentrancyGuard g(*this); HashNumber keyHash = prepareHash(l); Entry &entry = lookup(l, keyHash, sCollisionBit); AddPtr p(entry, *this, keyHash); return p; } template bool add(AddPtr &p, U &&u) { mozilla::ReentrancyGuard g(*this); MOZ_ASSERT(table); MOZ_ASSERT(!p.found()); MOZ_ASSERT(!(p.keyHash & sCollisionBit)); // Changing an entry from removed to live does not affect whether we // are overloaded and can be handled separately. if (p.entry_->isRemoved()) { METER(stats.addOverRemoved++); removedCount--; p.keyHash |= sCollisionBit; } else { // Preserve the validity of |p.entry_|. RebuildStatus status = checkOverloaded(); if (status == RehashFailed) return false; if (status == Rehashed) p.entry_ = &findFreeEntry(p.keyHash); } p.entry_->setLive(p.keyHash, mozilla::Forward(u)); entryCount++; #ifdef JS_DEBUG mutationCount++; p.generation = generation(); p.mutationCount = mutationCount; #endif return true; } // Note: |l| may be a reference to a piece of |u|, so this function // must take care not to use |l| after moving |u|. template void putNewInfallible(const Lookup &l, U &&u) { MOZ_ASSERT(table); HashNumber keyHash = prepareHash(l); Entry *entry = &findFreeEntry(keyHash); if (entry->isRemoved()) { METER(stats.addOverRemoved++); removedCount--; keyHash |= sCollisionBit; } entry->setLive(keyHash, mozilla::Forward(u)); entryCount++; #ifdef JS_DEBUG mutationCount++; #endif } // Note: |l| may be a reference to a piece of |u|, so this function // must take care not to use |l| after moving |u|. template bool putNew(const Lookup &l, U &&u) { if (checkOverloaded() == RehashFailed) return false; putNewInfallible(l, mozilla::Forward(u)); return true; } // Note: |l| may be a reference to a piece of |u|, so this function // must take care not to use |l| after moving |u|. template bool relookupOrAdd(AddPtr& p, const Lookup &l, U &&u) { #ifdef JS_DEBUG p.generation = generation(); p.mutationCount = mutationCount; #endif { mozilla::ReentrancyGuard g(*this); MOZ_ASSERT(prepareHash(l) == p.keyHash); // l has not been destroyed p.entry_ = &lookup(l, p.keyHash, sCollisionBit); } return p.found() || add(p, mozilla::Forward(u)); } void remove(Ptr p) { MOZ_ASSERT(table); mozilla::ReentrancyGuard g(*this); MOZ_ASSERT(p.found()); remove(*p.entry_); checkUnderloaded(); } void rekeyWithoutRehash(Ptr p, const Lookup &l, const Key &k) { MOZ_ASSERT(table); mozilla::ReentrancyGuard g(*this); MOZ_ASSERT(p.found()); typename HashTableEntry::NonConstT t(mozilla::Move(*p)); HashPolicy::setKey(t, const_cast(k)); remove(*p.entry_); putNewInfallible(l, mozilla::Move(t)); } void rekeyAndMaybeRehash(Ptr p, const Lookup &l, const Key &k) { rekeyWithoutRehash(p, l, k); checkOverRemoved(); } void rekeyInPlace(Ptr p, const Key &k) { MOZ_ASSERT(table); mozilla::ReentrancyGuard g(*this); MOZ_ASSERT(p.found()); HashPolicy::rekey(const_cast(*p), const_cast(k)); } #undef METER }; } // namespace detail } // namespace js #endif /* js_HashTable_h */