From cc64c96ae6205a76585e99a153c5f2a1fb892454 Mon Sep 17 00:00:00 2001 From: Nicholas Nethercote Date: Wed, 20 May 2015 21:25:55 -0700 Subject: [PATCH] Bug 1170934 (part 1) - Remove PLDHashTable::{Init,Fini}(). r=froydnj. --HG-- extra : rebase_source : 1d1ac910420fbc12c7e2501c74680cce00387c63 --- xpcom/glue/pldhash.cpp | 75 ++++++++++++++++++++---------------------- xpcom/glue/pldhash.h | 14 ++++---- 2 files changed, 43 insertions(+), 46 deletions(-) diff --git a/xpcom/glue/pldhash.cpp b/xpcom/glue/pldhash.cpp index a7c925e15e12..cc212d3b8229 100644 --- a/xpcom/glue/pldhash.cpp +++ b/xpcom/glue/pldhash.cpp @@ -7,6 +7,7 @@ /* * Double hashing implementation. */ +#include #include #include #include @@ -38,7 +39,7 @@ * allowed (and therefore the level is 0 or 1, depending on whether they * incremented it). * - * Only Finish() needs to allow this special value. + * Only the destructor needs to allow this special value. */ #define IMMUTABLE_RECURSION_LEVEL UINT32_MAX @@ -192,15 +193,8 @@ MinLoad(uint32_t aCapacity) return aCapacity >> 2; // == aCapacity * 0.25 } -static inline uint32_t -MinCapacity(uint32_t aLength) -{ - return (aLength * 4 + (3 - 1)) / 3; // == ceil(aLength * 4 / 3) -} - -MOZ_ALWAYS_INLINE void -PLDHashTable::Init(const PLDHashTableOps* aOps, - uint32_t aEntrySize, uint32_t aLength) +static MOZ_ALWAYS_INLINE uint32_t +HashShift(uint32_t aEntrySize, uint32_t aLength) { if (aLength > PL_DHASH_MAX_INITIAL_LENGTH) { MOZ_CRASH("Initial length is too large"); @@ -208,38 +202,39 @@ PLDHashTable::Init(const PLDHashTableOps* aOps, // Compute the smallest capacity allowing |aLength| elements to be inserted // without rehashing. - uint32_t capacity = MinCapacity(aLength); + uint32_t capacity = (aLength * 4 + (3 - 1)) / 3; // == ceil(aLength * 4 / 3) if (capacity < PL_DHASH_MIN_CAPACITY) { capacity = PL_DHASH_MIN_CAPACITY; } + // Round up capacity to next power-of-two. int log2 = CeilingLog2(capacity); - capacity = 1u << log2; MOZ_ASSERT(capacity <= PL_DHASH_MAX_CAPACITY); - mOps = aOps; - mHashShift = PL_DHASH_BITS - log2; - mEntrySize = aEntrySize; - mEntryCount = mRemovedCount = 0; - mGeneration = 0; + uint32_t nbytes; if (!SizeOfEntryStore(capacity, aEntrySize, &nbytes)) { MOZ_CRASH("Initial entry store size is too large"); } - mEntryStore = nullptr; - - METER(memset(&mStats, 0, sizeof(mStats))); - -#ifdef DEBUG - mRecursionLevel = 0; -#endif + // Compute the hashShift value. + return PL_DHASH_BITS - log2; } PLDHashTable::PLDHashTable(const PLDHashTableOps* aOps, uint32_t aEntrySize, uint32_t aLength) + : mOps(aOps) + , mHashShift(HashShift(aEntrySize, aLength)) + , mEntrySize(aEntrySize) + , mEntryCount(0) + , mRemovedCount(0) + , mGeneration(0) + , mEntryStore(nullptr) +#ifdef DEBUG + , mRecursionLevel(0) +#endif { - Init(aOps, aEntrySize, aLength); + METER(memset(&mStats, 0, sizeof(mStats))); } PLDHashTable& @@ -250,12 +245,18 @@ PLDHashTable::operator=(PLDHashTable&& aOther) } // Destruct |this|. - Finish(); + this->~PLDHashTable(); - // Move pieces over. - mOps = Move(aOther.mOps); + // |mOps| and |mEntrySize| are const so we can't assign them. Instead, we + // require that they are equal. The justification for this is that they're + // conceptually part of the type -- indeed, if PLDHashTable was a templated + // type like nsTHashtable, they *would* be part of the type -- so it only + // makes sense to assign in cases where they match. + MOZ_RELEASE_ASSERT(mOps == aOther.mOps); + MOZ_RELEASE_ASSERT(mEntrySize == aOther.mEntrySize); + + // Move non-const pieces over. mHashShift = Move(aOther.mHashShift); - mEntrySize = Move(aOther.mEntrySize); mEntryCount = Move(aOther.mEntryCount); mRemovedCount = Move(aOther.mRemovedCount); mGeneration = Move(aOther.mGeneration); @@ -313,8 +314,7 @@ PLDHashTable::EntryIsFree(PLDHashEntryHdr* aEntry) return aEntry->mKeyHash == 0; } -MOZ_ALWAYS_INLINE void -PLDHashTable::Finish() +PLDHashTable::~PLDHashTable() { if (!mEntryStore) { return; @@ -342,20 +342,15 @@ PLDHashTable::Finish() mEntryStore = nullptr; } -PLDHashTable::~PLDHashTable() -{ - Finish(); -} - void PLDHashTable::ClearAndPrepareForLength(uint32_t aLength) { - // Get these values before the call to Finish() clobbers them. + // Get these values before the destructor clobbers them. const PLDHashTableOps* ops = mOps; uint32_t entrySize = mEntrySize; - Finish(); - Init(ops, entrySize, aLength); + this->~PLDHashTable(); + new (this) PLDHashTable(ops, entrySize, aLength); } void @@ -591,7 +586,7 @@ PLDHashTable::Add(const void* aKey, const mozilla::fallible_t&) // Allocate the entry storage if it hasn't already been allocated. if (!mEntryStore) { uint32_t nbytes; - // We already checked this in Init(), so it must still be true. + // We already checked this in the constructor, so it must still be true. MOZ_RELEASE_ASSERT(SizeOfEntryStore(CapacityFromHashShift(), mEntrySize, &nbytes)); mEntryStore = (char*)malloc(nbytes); diff --git a/xpcom/glue/pldhash.h b/xpcom/glue/pldhash.h index bacabacda26e..30c34854f67b 100644 --- a/xpcom/glue/pldhash.h +++ b/xpcom/glue/pldhash.h @@ -162,9 +162,9 @@ typedef size_t (*PLDHashSizeOfEntryExcludingThisFun)( class PLDHashTable { private: - const PLDHashTableOps* mOps; /* Virtual operations; see below. */ + const PLDHashTableOps* const mOps; /* Virtual operations; see below. */ int16_t mHashShift; /* multiplicative hash shift */ - uint32_t mEntrySize; /* number of bytes in an entry */ + const uint32_t mEntrySize; /* number of bytes in an entry */ uint32_t mEntryCount; /* number of entries in table */ uint32_t mRemovedCount; /* removed entry sentinels in table */ uint32_t mGeneration; /* entry storage generation number */ @@ -214,7 +214,12 @@ public: uint32_t aLength = PL_DHASH_DEFAULT_INITIAL_LENGTH); PLDHashTable(PLDHashTable&& aOther) - : mOps(nullptr) + // These two fields are |const|. Initialize them here because the + // move assignment operator cannot modify them. + : mOps(aOther.mOps) + , mEntrySize(aOther.mEntrySize) + // Initialize these two fields because they are required for a safe call + // to the destructor, which the move assignment operator does. , mEntryStore(nullptr) #ifdef DEBUG , mRecursionLevel(0) @@ -322,9 +327,6 @@ private: PLDHashNumber ComputeKeyHash(const void* aKey); - void Init(const PLDHashTableOps* aOps, uint32_t aEntrySize, uint32_t aLength); - void Finish(); - enum SearchReason { ForSearchOrRemove, ForAdd }; template