src/gpu/GrBlockAllocator.cpp - skia - Git at Google

 /*
  * Copyright 2020 Google LLC
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */

 #include "src/gpu/GrBlockAllocator.h"

 #ifdef SK_DEBUG
 #include <vector>
 #endif

 GrBlockAllocator::GrBlockAllocator(GrowthPolicy policy, size_t blockIncrementBytes,
                                    size_t additionalPreallocBytes)
         : fTail(&fHead)
         // Round up to the nearest max-aligned value, and then divide so that fBlockSizeIncrement
         // can effectively fit higher byte counts in its 16 bits of storage
         , fBlockIncrement(SkTo<uint16_t>(GrAlignTo(blockIncrementBytes, kBlockIncrementUnits)
                                                 / kBlockIncrementUnits))
         , fGrowthPolicy(static_cast<uint64_t>(policy))
         , fN0((policy == GrowthPolicy::kLinear || policy == GrowthPolicy::kExponential) ? 1 : 0)
         , fN1(1)
         // The head block always fills remaiing space from GrBlockAllocator's size, because it's
         // inline, but can take over the specified number of bytes immediately after it.
         , fHead(nullptr, additionalPreallocBytes + BaseHeadBlockSize()) {
     SkASSERT(fBlockIncrement >= 1);
     SkASSERT(additionalPreallocBytes <= kMaxAllocationSize);
 }

 GrBlockAllocator::Block::Block(Block* prev, int allocationSize)
          : fNext(nullptr)
          , fPrev(prev)
          , fSize(allocationSize)
          , fCursor(kDataStart)
          , fMetadata(0) {
     SkASSERT(allocationSize >= (int) sizeof(Block));
     SkDEBUGCODE(fSentinel = kAssignedMarker;)
 }

 GrBlockAllocator::Block::~Block() {
     SkASSERT(fSentinel == kAssignedMarker);
     SkDEBUGCODE(fSentinel = kFreedMarker;) // FWIW
 }

 size_t GrBlockAllocator::totalSize() const {
     // Use size_t since the sum across all blocks could exceed 'int', even though each block won't
     size_t size = offsetof(GrBlockAllocator, fHead);
     for (const Block* b : this->blocks()) {
         size += b->fSize;
     }
     SkASSERT(size >= this->preallocSize());
     return size;
 }

 size_t GrBlockAllocator::totalUsableSpace() const {
     size_t size = 0;
     for (const Block* b : this->blocks()) {
         size += (b->fSize - kDataStart);
     }
     SkASSERT(size >= this->preallocUsableSpace());
     return size;
 }

 size_t GrBlockAllocator::totalSpaceInUse() const {
     size_t size = 0;
     for (const Block* b : this->blocks()) {
         size += (b->fCursor - kDataStart);
     }
     SkASSERT(size <= this->totalUsableSpace());
     return size;
 }

 GrBlockAllocator::Block* GrBlockAllocator::findOwningBlock(const void* p) {
     // When in doubt, search in reverse to find an overlapping block.
     uintptr_t ptr = reinterpret_cast<uintptr_t>(p);
     for (Block* b : this->rblocks()) {
         uintptr_t lowerBound = reinterpret_cast<uintptr_t>(b) + kDataStart;
         uintptr_t upperBound = reinterpret_cast<uintptr_t>(b) + b->fSize;
         if (lowerBound <= ptr && ptr < upperBound) {
             SkASSERT(b->fSentinel == kAssignedMarker);
             return b;
         }
     }
     return nullptr;
 }

 void GrBlockAllocator::releaseBlock(Block* block) {
     if (block->fPrev) {
         // Unlink block from the double-linked list of blocks
         SkASSERT(block != &fHead);
         block->fPrev->fNext = block->fNext;
         if (block->fNext) {
             SkASSERT(fTail != block);
             block->fNext->fPrev = block->fPrev;
         } else {
             SkASSERT(fTail == block);
             fTail = block->fPrev;
         }

         delete block;
     } else {
         // Reset the cursor of the head block so that it can be reused
         SkASSERT(block == &fHead);
         block->fCursor = kDataStart;
         block->fMetadata = 0;
         // Unlike in reset(), we don't set the head's next block to null because there are
         // potentially heap-allocated blocks that are still connected to it.
     }

     // Decrement growth policy (opposite of addBlock()'s increment operations)
     GrowthPolicy gp = static_cast<GrowthPolicy>(fGrowthPolicy);
     if (fN0 > 0 && (fN1 > 1 || gp == GrowthPolicy::kFibonacci)) {
         SkASSERT(gp != GrowthPolicy::kFixed); // fixed never needs undoing, fN0 always is 0
         if (gp == GrowthPolicy::kLinear) {
             fN1 = fN1 - fN0;
         } else if (gp == GrowthPolicy::kFibonacci) {
             // Subtract n0 from n1 to get the prior 2 terms in the fibonacci sequence
             int temp = fN1 - fN0; // yields prior fN0
             fN1 = fN1 - temp;     // yields prior fN1
             fN0 = temp;
         } else {
             SkASSERT(gp == GrowthPolicy::kExponential);
             // Divide by 2 to undo the 2N update from addBlock
             fN1 = fN1 >> 1;
             fN0 = fN1;
         }
     }

     SkASSERT(fN1 >= 1 && fN0 >= 0);
 }

 void GrBlockAllocator::reset() {
     // We can't use the RBlocks for-range since we're destroying the linked list as we go
     Block* toFree = fTail;
     while(toFree) {
         Block* prev = toFree->fPrev;
         if (prev) {
             SkASSERT(toFree != &fHead);
             delete toFree;
         } else {
             SkASSERT(toFree == &fHead);
             fTail = toFree;
             // the head block's prev is already null, it's next block was deleted last iteration
             fTail->fNext = nullptr;
             fTail->fCursor = kDataStart;
             fTail->fMetadata = 0;
         }

         toFree = prev;
     }

     GrowthPolicy gp = static_cast<GrowthPolicy>(fGrowthPolicy);
     fN0 = (gp == GrowthPolicy::kLinear || gp == GrowthPolicy::kExponential) ? 1 : 0;
     fN1 = 1;
 }

 void GrBlockAllocator::addBlock(int minimumSize, int maxSize) {
     SkASSERT(minimumSize > (int) sizeof(Block) && minimumSize <= maxSize);

     // Max positive value for uint:23 storage (decltype(fN0) picks up uint64_t, not uint:23).
     static constexpr int kMaxN = (1 << 23) - 1;
     static_assert(2 * kMaxN <= std::numeric_limits<int32_t>::max()); // Growth policy won't overflow

     // Calculate the 'next' size per growth policy sequence
     GrowthPolicy gp = static_cast<GrowthPolicy>(fGrowthPolicy);
     int nextN1 = fN0 + fN1;
     int nextN0;
     if (gp == GrowthPolicy::kFixed || gp == GrowthPolicy::kLinear) {
         nextN0 = fN0;
     } else if (gp == GrowthPolicy::kFibonacci) {
         nextN0 = fN1;
     } else {
         SkASSERT(gp == GrowthPolicy::kExponential);
         nextN0 = nextN1;
     }
     fN0 = std::min(kMaxN, nextN0);
     fN1 = std::min(kMaxN, nextN1);

     // However, must guard against overflow here, since all the size-based asserts prevented
     // alignment/addition overflows, while multiplication requires 2x bits instead of x+1.
     int sizeIncrement = fBlockIncrement * kBlockIncrementUnits;
     int allocSize;
     if (maxSize / sizeIncrement < nextN1) {
         // The growth policy would overflow, so use the max. We've already confirmed that maxSize
         // will be sufficient for the requested minimumSize
         allocSize = maxSize;
     } else {
         allocSize = std::max(minimumSize, sizeIncrement * nextN1);
         // Then round to a nice boundary since the block isn't maxing out:
         //   if allocSize > 32K, aligns on 4K boundary otherwise aligns on max_align_t, to play
         //   nicely with jeMalloc (from SkArenaAlloc).
         int mask = allocSize > (1 << 15) ? ((1 << 12) - 1) : (kBlockIncrementUnits - 1);
         allocSize = std::min((allocSize + mask) & ~mask, maxSize);
     }

     // Create new block and append to the linked list of blocks in this allocator
     void* mem = operator new(allocSize);
     fTail->fNext = new (mem) Block(fTail, allocSize);
     fTail = fTail->fNext;
 }

 #ifdef SK_DEBUG
 void GrBlockAllocator::validate() const {
     std::vector<const Block*> blocks;
     const Block* prev = nullptr;
     for (const Block* block : this->blocks()) {
         blocks.push_back(block);

         SkASSERT(kAssignedMarker == block->fSentinel);
         SkASSERT(prev == block->fPrev);
         if (prev) {
             SkASSERT(prev->fNext == block);
         }

         SkASSERT(block->fSize >= (int) sizeof(Block));
         SkASSERT(block->fCursor >= kDataStart);
         SkASSERT(block->fCursor <= block->fSize);

         prev = block;
     }
     SkASSERT(prev == fTail);
     SkASSERT(blocks.size() > 0);
     SkASSERT(blocks[0] == &fHead);

     // Confirm reverse iteration matches forward iteration
     size_t j = blocks.size();
     for (const Block* b : this->rblocks()) {
         SkASSERT(b == blocks[j - 1]);
         j--;
     }
     SkASSERT(j == 0);
 }
 #endif
	/*
	* Copyright 2020 Google LLC
	*
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*/

	#include "src/gpu/GrBlockAllocator.h"

	#ifdef SK_DEBUG
	#include <vector>
	#endif

	GrBlockAllocator::GrBlockAllocator(GrowthPolicy policy, size_t blockIncrementBytes,
	size_t additionalPreallocBytes)
	: fTail(&fHead)
	// Round up to the nearest max-aligned value, and then divide so that fBlockSizeIncrement
	// can effectively fit higher byte counts in its 16 bits of storage
	, fBlockIncrement(SkTo<uint16_t>(GrAlignTo(blockIncrementBytes, kBlockIncrementUnits)
	/ kBlockIncrementUnits))
	, fGrowthPolicy(static_cast<uint64_t>(policy))
	, fN0((policy == GrowthPolicy::kLinear \|\| policy == GrowthPolicy::kExponential) ? 1 : 0)
	, fN1(1)
	// The head block always fills remaiing space from GrBlockAllocator's size, because it's
	// inline, but can take over the specified number of bytes immediately after it.
	, fHead(nullptr, additionalPreallocBytes + BaseHeadBlockSize()) {
	SkASSERT(fBlockIncrement >= 1);
	SkASSERT(additionalPreallocBytes <= kMaxAllocationSize);
	}

	GrBlockAllocator::Block::Block(Block* prev, int allocationSize)
	: fNext(nullptr)
	, fPrev(prev)
	, fSize(allocationSize)
	, fCursor(kDataStart)
	, fMetadata(0) {
	SkASSERT(allocationSize >= (int) sizeof(Block));
	SkDEBUGCODE(fSentinel = kAssignedMarker;)
	}

	GrBlockAllocator::Block::~Block() {
	SkASSERT(fSentinel == kAssignedMarker);
	SkDEBUGCODE(fSentinel = kFreedMarker;) // FWIW
	}

	size_t GrBlockAllocator::totalSize() const {
	// Use size_t since the sum across all blocks could exceed 'int', even though each block won't
	size_t size = offsetof(GrBlockAllocator, fHead);
	for (const Block* b : this->blocks()) {
	size += b->fSize;
	}
	SkASSERT(size >= this->preallocSize());
	return size;
	}

	size_t GrBlockAllocator::totalUsableSpace() const {
	size_t size = 0;
	for (const Block* b : this->blocks()) {
	size += (b->fSize - kDataStart);
	}
	SkASSERT(size >= this->preallocUsableSpace());
	return size;
	}

	size_t GrBlockAllocator::totalSpaceInUse() const {
	size_t size = 0;
	for (const Block* b : this->blocks()) {
	size += (b->fCursor - kDataStart);
	}
	SkASSERT(size <= this->totalUsableSpace());
	return size;
	}

	GrBlockAllocator::Block* GrBlockAllocator::findOwningBlock(const void* p) {
	// When in doubt, search in reverse to find an overlapping block.
	uintptr_t ptr = reinterpret_cast<uintptr_t>(p);
	for (Block* b : this->rblocks()) {
	uintptr_t lowerBound = reinterpret_cast<uintptr_t>(b) + kDataStart;
	uintptr_t upperBound = reinterpret_cast<uintptr_t>(b) + b->fSize;
	if (lowerBound <= ptr && ptr < upperBound) {
	SkASSERT(b->fSentinel == kAssignedMarker);
	return b;
	}
	}
	return nullptr;
	}

	void GrBlockAllocator::releaseBlock(Block* block) {
	if (block->fPrev) {
	// Unlink block from the double-linked list of blocks
	SkASSERT(block != &fHead);
	block->fPrev->fNext = block->fNext;
	if (block->fNext) {
	SkASSERT(fTail != block);
	block->fNext->fPrev = block->fPrev;
	} else {
	SkASSERT(fTail == block);
	fTail = block->fPrev;
	}

	delete block;
	} else {
	// Reset the cursor of the head block so that it can be reused
	SkASSERT(block == &fHead);
	block->fCursor = kDataStart;
	block->fMetadata = 0;
	// Unlike in reset(), we don't set the head's next block to null because there are
	// potentially heap-allocated blocks that are still connected to it.
	}

	// Decrement growth policy (opposite of addBlock()'s increment operations)
	GrowthPolicy gp = static_cast<GrowthPolicy>(fGrowthPolicy);
	if (fN0 > 0 && (fN1 > 1 \|\| gp == GrowthPolicy::kFibonacci)) {
	SkASSERT(gp != GrowthPolicy::kFixed); // fixed never needs undoing, fN0 always is 0
	if (gp == GrowthPolicy::kLinear) {
	fN1 = fN1 - fN0;
	} else if (gp == GrowthPolicy::kFibonacci) {
	// Subtract n0 from n1 to get the prior 2 terms in the fibonacci sequence
	int temp = fN1 - fN0; // yields prior fN0
	fN1 = fN1 - temp; // yields prior fN1
	fN0 = temp;
	} else {
	SkASSERT(gp == GrowthPolicy::kExponential);
	// Divide by 2 to undo the 2N update from addBlock
	fN1 = fN1 >> 1;
	fN0 = fN1;
	}
	}

	SkASSERT(fN1 >= 1 && fN0 >= 0);
	}

	void GrBlockAllocator::reset() {
	// We can't use the RBlocks for-range since we're destroying the linked list as we go
	Block* toFree = fTail;
	while(toFree) {
	Block* prev = toFree->fPrev;
	if (prev) {
	SkASSERT(toFree != &fHead);
	delete toFree;
	} else {
	SkASSERT(toFree == &fHead);
	fTail = toFree;
	// the head block's prev is already null, it's next block was deleted last iteration
	fTail->fNext = nullptr;
	fTail->fCursor = kDataStart;
	fTail->fMetadata = 0;
	}

	toFree = prev;
	}

	GrowthPolicy gp = static_cast<GrowthPolicy>(fGrowthPolicy);
	fN0 = (gp == GrowthPolicy::kLinear \|\| gp == GrowthPolicy::kExponential) ? 1 : 0;
	fN1 = 1;
	}

	void GrBlockAllocator::addBlock(int minimumSize, int maxSize) {
	SkASSERT(minimumSize > (int) sizeof(Block) && minimumSize <= maxSize);

	// Max positive value for uint:23 storage (decltype(fN0) picks up uint64_t, not uint:23).
	static constexpr int kMaxN = (1 << 23) - 1;
	static_assert(2 * kMaxN <= std::numeric_limits<int32_t>::max()); // Growth policy won't overflow

	// Calculate the 'next' size per growth policy sequence
	GrowthPolicy gp = static_cast<GrowthPolicy>(fGrowthPolicy);
	int nextN1 = fN0 + fN1;
	int nextN0;
	if (gp == GrowthPolicy::kFixed \|\| gp == GrowthPolicy::kLinear) {
	nextN0 = fN0;
	} else if (gp == GrowthPolicy::kFibonacci) {
	nextN0 = fN1;
	} else {
	SkASSERT(gp == GrowthPolicy::kExponential);
	nextN0 = nextN1;
	}
	fN0 = std::min(kMaxN, nextN0);
	fN1 = std::min(kMaxN, nextN1);

	// However, must guard against overflow here, since all the size-based asserts prevented
	// alignment/addition overflows, while multiplication requires 2x bits instead of x+1.
	int sizeIncrement = fBlockIncrement * kBlockIncrementUnits;
	int allocSize;
	if (maxSize / sizeIncrement < nextN1) {
	// The growth policy would overflow, so use the max. We've already confirmed that maxSize
	// will be sufficient for the requested minimumSize
	allocSize = maxSize;
	} else {
	allocSize = std::max(minimumSize, sizeIncrement * nextN1);
	// Then round to a nice boundary since the block isn't maxing out:
	// if allocSize > 32K, aligns on 4K boundary otherwise aligns on max_align_t, to play
	// nicely with jeMalloc (from SkArenaAlloc).
	int mask = allocSize > (1 << 15) ? ((1 << 12) - 1) : (kBlockIncrementUnits - 1);
	allocSize = std::min((allocSize + mask) & ~mask, maxSize);
	}

	// Create new block and append to the linked list of blocks in this allocator
	void* mem = operator new(allocSize);
	fTail->fNext = new (mem) Block(fTail, allocSize);
	fTail = fTail->fNext;
	}

	#ifdef SK_DEBUG
	void GrBlockAllocator::validate() const {
	std::vector<const Block*> blocks;
	const Block* prev = nullptr;
	for (const Block* block : this->blocks()) {
	blocks.push_back(block);

	SkASSERT(kAssignedMarker == block->fSentinel);
	SkASSERT(prev == block->fPrev);
	if (prev) {
	SkASSERT(prev->fNext == block);
	}

	SkASSERT(block->fSize >= (int) sizeof(Block));
	SkASSERT(block->fCursor >= kDataStart);
	SkASSERT(block->fCursor <= block->fSize);

	prev = block;
	}
	SkASSERT(prev == fTail);
	SkASSERT(blocks.size() > 0);
	SkASSERT(blocks[0] == &fHead);

	// Confirm reverse iteration matches forward iteration
	size_t j = blocks.size();
	for (const Block* b : this->rblocks()) {
	SkASSERT(b == blocks[j - 1]);
	j--;
	}
	SkASSERT(j == 0);
	}
	#endif