src/core/SkRWBuffer.cpp - skia - Git at Google

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */

 #include "SkRWBuffer.h"
 #include "SkStream.h"

 // Force small chunks to be a page's worth
 static const size_t kMinAllocSize = 4096;

 struct SkBufferBlock {
     SkBufferBlock*  fNext;
     size_t          fUsed;
     size_t          fCapacity;

     const void* startData() const { return this + 1; };

     size_t avail() const { return fCapacity - fUsed; }
     void* availData() { return (char*)this->startData() + fUsed; }

     static SkBufferBlock* Alloc(size_t length) {
         size_t capacity = LengthToCapacity(length);
         SkBufferBlock* block = (SkBufferBlock*)sk_malloc_throw(sizeof(SkBufferBlock) + capacity);
         block->fNext = NULL;
         block->fUsed = 0;
         block->fCapacity = capacity;
         return block;
     }

     // Return number of bytes actually appended
     size_t append(const void* src, size_t length) {
         this->validate();
         size_t amount = SkTMin(this->avail(), length);
         memcpy(this->availData(), src, amount);
         fUsed += amount;
         this->validate();
         return amount;
     }

     void validate() const {
 #ifdef SK_DEBUG
         SkASSERT(fCapacity > 0);
         SkASSERT(fUsed <= fCapacity);
 #endif
     }

 private:
     static size_t LengthToCapacity(size_t length) {
         const size_t minSize = kMinAllocSize - sizeof(SkBufferBlock);
         return SkTMax(length, minSize);
     }
 };

 struct SkBufferHead {
     mutable int32_t fRefCnt;
     SkBufferBlock   fBlock;

     static size_t LengthToCapacity(size_t length) {
         const size_t minSize = kMinAllocSize - sizeof(SkBufferHead);
         return SkTMax(length, minSize);
     }

     static SkBufferHead* Alloc(size_t length) {
         size_t capacity = LengthToCapacity(length);
         size_t size = sizeof(SkBufferHead) + capacity;
         SkBufferHead* head = (SkBufferHead*)sk_malloc_throw(size);
         head->fRefCnt = 1;
         head->fBlock.fNext = NULL;
         head->fBlock.fUsed = 0;
         head->fBlock.fCapacity = capacity;
         return head;
     }

     void ref() const {
         SkASSERT(fRefCnt > 0);
         sk_atomic_inc(&fRefCnt);
     }

     void unref() const {
         SkASSERT(fRefCnt > 0);
         // A release here acts in place of all releases we "should" have been doing in ref().
         if (1 == sk_atomic_fetch_add(&fRefCnt, -1, sk_memory_order_acq_rel)) {
             // Like unique(), the acquire is only needed on success.
             SkBufferBlock* block = fBlock.fNext;
             sk_free((void*)this);
             while (block) {
                 SkBufferBlock* next = block->fNext;
                 sk_free(block);
                 block = next;
             }
         }
     }

     void validate(size_t minUsed, SkBufferBlock* tail = NULL) const {
 #ifdef SK_DEBUG
         SkASSERT(fRefCnt > 0);
         size_t totalUsed = 0;
         const SkBufferBlock* block = &fBlock;
         const SkBufferBlock* lastBlock = block;
         while (block) {
             block->validate();
             totalUsed += block->fUsed;
             lastBlock = block;
             block = block->fNext;
         }
         SkASSERT(minUsed <= totalUsed);
         if (tail) {
             SkASSERT(tail == lastBlock);
         }
 #endif
     }
 };

 SkROBuffer::SkROBuffer(const SkBufferHead* head, size_t used) : fHead(head), fUsed(used) {
     if (head) {
         fHead->ref();
         SkASSERT(used > 0);
         head->validate(used);
     } else {
         SkASSERT(0 == used);
     }
 }

 SkROBuffer::~SkROBuffer() {
     if (fHead) {
         fHead->validate(fUsed);
         fHead->unref();
     }
 }

 SkROBuffer::Iter::Iter(const SkROBuffer* buffer) {
     this->reset(buffer);
 }

 void SkROBuffer::Iter::reset(const SkROBuffer* buffer) {
     if (buffer) {
         fBlock = &buffer->fHead->fBlock;
         fRemaining = buffer->fUsed;
     } else {
         fBlock = NULL;
         fRemaining = 0;
     }
 }

 const void* SkROBuffer::Iter::data() const {
     return fRemaining ? fBlock->startData() : NULL;
 }

 size_t SkROBuffer::Iter::size() const {
     return SkTMin(fBlock->fUsed, fRemaining);
 }

 bool SkROBuffer::Iter::next() {
     if (fRemaining) {
         fRemaining -= this->size();
         fBlock = fBlock->fNext;
     }
     return fRemaining != 0;
 }

 SkRWBuffer::SkRWBuffer(size_t initialCapacity) : fHead(NULL), fTail(NULL), fTotalUsed(0) {}

 SkRWBuffer::~SkRWBuffer() {
     this->validate();
     fHead->unref();
 }

 void SkRWBuffer::append(const void* src, size_t length) {
     this->validate();
     if (0 == length) {
         return;
     }

     fTotalUsed += length;

     if (NULL == fHead) {
         fHead = SkBufferHead::Alloc(length);
         fTail = &fHead->fBlock;
     }

     size_t written = fTail->append(src, length);
     SkASSERT(written <= length);
     src = (const char*)src + written;
     length -= written;

     if (length) {
         SkBufferBlock* block = SkBufferBlock::Alloc(length);
         fTail->fNext = block;
         fTail = block;
         written = fTail->append(src, length);
         SkASSERT(written == length);
     }
     this->validate();
 }

 void* SkRWBuffer::append(size_t length) {
     this->validate();
     if (0 == length) {
         return NULL;
     }

     fTotalUsed += length;

     if (NULL == fHead) {
         fHead = SkBufferHead::Alloc(length);
         fTail = &fHead->fBlock;
     } else if (fTail->avail() < length) {
         SkBufferBlock* block = SkBufferBlock::Alloc(length);
         fTail->fNext = block;
         fTail = block;
     }

     fTail->fUsed += length;
     this->validate();
     return (char*)fTail->availData() - length;
 }

 #ifdef SK_DEBUG
 void SkRWBuffer::validate() const {
     if (fHead) {
         fHead->validate(fTotalUsed, fTail);
     } else {
         SkASSERT(NULL == fTail);
         SkASSERT(0 == fTotalUsed);
     }
 }
 #endif

 SkROBuffer* SkRWBuffer::newRBufferSnapshot() const {
     return SkNEW_ARGS(SkROBuffer, (fHead, fTotalUsed));
 }

 ///////////////////////////////////////////////////////////////////////////////////////////////////

 class SkROBufferStreamAsset : public SkStreamAsset {
     void validate() const {
 #ifdef SK_DEBUG
         SkASSERT(fGlobalOffset <= fBuffer->size());
         SkASSERT(fLocalOffset <= fIter.size());
         SkASSERT(fLocalOffset <= fGlobalOffset);
 #endif
     }

 #ifdef SK_DEBUG
     class AutoValidate {
         SkROBufferStreamAsset* fStream;
     public:
         AutoValidate(SkROBufferStreamAsset* stream) : fStream(stream) { stream->validate(); }
         ~AutoValidate() { fStream->validate(); }
     };
     #define AUTO_VALIDATE   AutoValidate av(this);
 #else
     #define AUTO_VALIDATE
 #endif

 public:
     SkROBufferStreamAsset(const SkROBuffer* buffer) : fBuffer(SkRef(buffer)), fIter(buffer) {
         fGlobalOffset = fLocalOffset = 0;
     }

     virtual ~SkROBufferStreamAsset() { fBuffer->unref(); }

     size_t getLength() const override { return fBuffer->size(); }

     bool rewind() override {
         AUTO_VALIDATE
         fIter.reset(fBuffer);
         fGlobalOffset = fLocalOffset = 0;
         return true;
     }

     size_t read(void* dst, size_t request) override {
         AUTO_VALIDATE
         size_t bytesRead = 0;
         for (;;) {
             size_t size = fIter.size();
             SkASSERT(fLocalOffset <= size);
             size_t avail = SkTMin(size - fLocalOffset, request - bytesRead);
             if (dst) {
                 memcpy(dst, (const char*)fIter.data() + fLocalOffset, avail);
                 dst = (char*)dst + avail;
             }
             bytesRead += avail;
             fLocalOffset += avail;
             SkASSERT(bytesRead <= request);
             if (bytesRead == request) {
                 break;
             }
             // If we get here, we've exhausted the current iter
             SkASSERT(fLocalOffset == size);
             fLocalOffset = 0;
             if (!fIter.next()) {
                 break;   // ran out of data
             }
         }
         fGlobalOffset += bytesRead;
         SkASSERT(fGlobalOffset <= fBuffer->size());
         return bytesRead;
     }

     bool isAtEnd() const override {
         return fBuffer->size() == fGlobalOffset;
     }

     SkStreamAsset* duplicate() const override {
         return SkNEW_ARGS(SkROBufferStreamAsset, (fBuffer));
     }

     size_t getPosition() const {
         return fGlobalOffset;
     }

     bool seek(size_t position) {
         AUTO_VALIDATE
         if (position < fGlobalOffset) {
             this->rewind();
         }
         (void)this->skip(position - fGlobalOffset);
         return true;
     }

     bool move(long offset) {
         AUTO_VALIDATE
         offset += fGlobalOffset;
         if (offset <= 0) {
             this->rewind();
         } else {
             (void)this->seek(SkToSizeT(offset));
         }
         return true;
     }

     SkStreamAsset* fork() const override {
         SkStreamAsset* clone = this->duplicate();
         clone->seek(this->getPosition());
         return clone;
     }


 private:
     const SkROBuffer*   fBuffer;
     SkROBuffer::Iter    fIter;
     size_t              fLocalOffset;
     size_t              fGlobalOffset;
 };

 SkStreamAsset* SkRWBuffer::newStreamSnapshot() const {
     SkAutoTUnref<SkROBuffer> buffer(this->newRBufferSnapshot());
     return SkNEW_ARGS(SkROBufferStreamAsset, (buffer));
 }
	/*
	* Copyright 2015 Google Inc.
	*
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*/

	#include "SkRWBuffer.h"
	#include "SkStream.h"

	// Force small chunks to be a page's worth
	static const size_t kMinAllocSize = 4096;

	struct SkBufferBlock {
	SkBufferBlock* fNext;
	size_t fUsed;
	size_t fCapacity;

	const void* startData() const { return this + 1; };

	size_t avail() const { return fCapacity - fUsed; }
	void* availData() { return (char*)this->startData() + fUsed; }

	static SkBufferBlock* Alloc(size_t length) {
	size_t capacity = LengthToCapacity(length);
	SkBufferBlock* block = (SkBufferBlock*)sk_malloc_throw(sizeof(SkBufferBlock) + capacity);
	block->fNext = NULL;
	block->fUsed = 0;
	block->fCapacity = capacity;
	return block;
	}

	// Return number of bytes actually appended
	size_t append(const void* src, size_t length) {
	this->validate();
	size_t amount = SkTMin(this->avail(), length);
	memcpy(this->availData(), src, amount);
	fUsed += amount;
	this->validate();
	return amount;
	}

	void validate() const {
	#ifdef SK_DEBUG
	SkASSERT(fCapacity > 0);
	SkASSERT(fUsed <= fCapacity);
	#endif
	}

	private:
	static size_t LengthToCapacity(size_t length) {
	const size_t minSize = kMinAllocSize - sizeof(SkBufferBlock);
	return SkTMax(length, minSize);
	}
	};

	struct SkBufferHead {
	mutable int32_t fRefCnt;
	SkBufferBlock fBlock;

	static size_t LengthToCapacity(size_t length) {
	const size_t minSize = kMinAllocSize - sizeof(SkBufferHead);
	return SkTMax(length, minSize);
	}

	static SkBufferHead* Alloc(size_t length) {
	size_t capacity = LengthToCapacity(length);
	size_t size = sizeof(SkBufferHead) + capacity;
	SkBufferHead* head = (SkBufferHead*)sk_malloc_throw(size);
	head->fRefCnt = 1;
	head->fBlock.fNext = NULL;
	head->fBlock.fUsed = 0;
	head->fBlock.fCapacity = capacity;
	return head;
	}

	void ref() const {
	SkASSERT(fRefCnt > 0);
	sk_atomic_inc(&fRefCnt);
	}

	void unref() const {
	SkASSERT(fRefCnt > 0);
	// A release here acts in place of all releases we "should" have been doing in ref().
	if (1 == sk_atomic_fetch_add(&fRefCnt, -1, sk_memory_order_acq_rel)) {
	// Like unique(), the acquire is only needed on success.
	SkBufferBlock* block = fBlock.fNext;
	sk_free((void*)this);
	while (block) {
	SkBufferBlock* next = block->fNext;
	sk_free(block);
	block = next;
	}
	}
	}

	void validate(size_t minUsed, SkBufferBlock* tail = NULL) const {
	#ifdef SK_DEBUG
	SkASSERT(fRefCnt > 0);
	size_t totalUsed = 0;
	const SkBufferBlock* block = &fBlock;
	const SkBufferBlock* lastBlock = block;
	while (block) {
	block->validate();
	totalUsed += block->fUsed;
	lastBlock = block;
	block = block->fNext;
	}
	SkASSERT(minUsed <= totalUsed);
	if (tail) {
	SkASSERT(tail == lastBlock);
	}
	#endif
	}
	};

	SkROBuffer::SkROBuffer(const SkBufferHead* head, size_t used) : fHead(head), fUsed(used) {
	if (head) {
	fHead->ref();
	SkASSERT(used > 0);
	head->validate(used);
	} else {
	SkASSERT(0 == used);
	}
	}

	SkROBuffer::~SkROBuffer() {
	if (fHead) {
	fHead->validate(fUsed);
	fHead->unref();
	}
	}

	SkROBuffer::Iter::Iter(const SkROBuffer* buffer) {
	this->reset(buffer);
	}

	void SkROBuffer::Iter::reset(const SkROBuffer* buffer) {
	if (buffer) {
	fBlock = &buffer->fHead->fBlock;
	fRemaining = buffer->fUsed;
	} else {
	fBlock = NULL;
	fRemaining = 0;
	}
	}

	const void* SkROBuffer::Iter::data() const {
	return fRemaining ? fBlock->startData() : NULL;
	}

	size_t SkROBuffer::Iter::size() const {
	return SkTMin(fBlock->fUsed, fRemaining);
	}

	bool SkROBuffer::Iter::next() {
	if (fRemaining) {
	fRemaining -= this->size();
	fBlock = fBlock->fNext;
	}
	return fRemaining != 0;
	}

	SkRWBuffer::SkRWBuffer(size_t initialCapacity) : fHead(NULL), fTail(NULL), fTotalUsed(0) {}

	SkRWBuffer::~SkRWBuffer() {
	this->validate();
	fHead->unref();
	}

	void SkRWBuffer::append(const void* src, size_t length) {
	this->validate();
	if (0 == length) {
	return;
	}

	fTotalUsed += length;

	if (NULL == fHead) {
	fHead = SkBufferHead::Alloc(length);
	fTail = &fHead->fBlock;
	}

	size_t written = fTail->append(src, length);
	SkASSERT(written <= length);
	src = (const char*)src + written;
	length -= written;

	if (length) {
	SkBufferBlock* block = SkBufferBlock::Alloc(length);
	fTail->fNext = block;
	fTail = block;
	written = fTail->append(src, length);
	SkASSERT(written == length);
	}
	this->validate();
	}

	void* SkRWBuffer::append(size_t length) {
	this->validate();
	if (0 == length) {
	return NULL;
	}

	fTotalUsed += length;

	if (NULL == fHead) {
	fHead = SkBufferHead::Alloc(length);
	fTail = &fHead->fBlock;
	} else if (fTail->avail() < length) {
	SkBufferBlock* block = SkBufferBlock::Alloc(length);
	fTail->fNext = block;
	fTail = block;
	}

	fTail->fUsed += length;
	this->validate();
	return (char*)fTail->availData() - length;
	}

	#ifdef SK_DEBUG
	void SkRWBuffer::validate() const {
	if (fHead) {
	fHead->validate(fTotalUsed, fTail);
	} else {
	SkASSERT(NULL == fTail);
	SkASSERT(0 == fTotalUsed);
	}
	}
	#endif

	SkROBuffer* SkRWBuffer::newRBufferSnapshot() const {
	return SkNEW_ARGS(SkROBuffer, (fHead, fTotalUsed));
	}

	///////////////////////////////////////////////////////////////////////////////////////////////////

	class SkROBufferStreamAsset : public SkStreamAsset {
	void validate() const {
	#ifdef SK_DEBUG
	SkASSERT(fGlobalOffset <= fBuffer->size());
	SkASSERT(fLocalOffset <= fIter.size());
	SkASSERT(fLocalOffset <= fGlobalOffset);
	#endif
	}

	#ifdef SK_DEBUG
	class AutoValidate {
	SkROBufferStreamAsset* fStream;
	public:
	AutoValidate(SkROBufferStreamAsset* stream) : fStream(stream) { stream->validate(); }
	~AutoValidate() { fStream->validate(); }
	};
	#define AUTO_VALIDATE AutoValidate av(this);
	#else
	#define AUTO_VALIDATE
	#endif

	public:
	SkROBufferStreamAsset(const SkROBuffer* buffer) : fBuffer(SkRef(buffer)), fIter(buffer) {
	fGlobalOffset = fLocalOffset = 0;
	}

	virtual ~SkROBufferStreamAsset() { fBuffer->unref(); }

	size_t getLength() const override { return fBuffer->size(); }

	bool rewind() override {
	AUTO_VALIDATE
	fIter.reset(fBuffer);
	fGlobalOffset = fLocalOffset = 0;
	return true;
	}

	size_t read(void* dst, size_t request) override {
	AUTO_VALIDATE
	size_t bytesRead = 0;
	for (;;) {
	size_t size = fIter.size();
	SkASSERT(fLocalOffset <= size);
	size_t avail = SkTMin(size - fLocalOffset, request - bytesRead);
	if (dst) {
	memcpy(dst, (const char*)fIter.data() + fLocalOffset, avail);
	dst = (char*)dst + avail;
	}
	bytesRead += avail;
	fLocalOffset += avail;
	SkASSERT(bytesRead <= request);
	if (bytesRead == request) {
	break;
	}
	// If we get here, we've exhausted the current iter
	SkASSERT(fLocalOffset == size);
	fLocalOffset = 0;
	if (!fIter.next()) {
	break; // ran out of data
	}
	}
	fGlobalOffset += bytesRead;
	SkASSERT(fGlobalOffset <= fBuffer->size());
	return bytesRead;
	}

	bool isAtEnd() const override {
	return fBuffer->size() == fGlobalOffset;
	}

	SkStreamAsset* duplicate() const override {
	return SkNEW_ARGS(SkROBufferStreamAsset, (fBuffer));
	}

	size_t getPosition() const {
	return fGlobalOffset;
	}

	bool seek(size_t position) {
	AUTO_VALIDATE
	if (position < fGlobalOffset) {
	this->rewind();
	}
	(void)this->skip(position - fGlobalOffset);
	return true;
	}

	bool move(long offset) {
	AUTO_VALIDATE
	offset += fGlobalOffset;
	if (offset <= 0) {
	this->rewind();
	} else {
	(void)this->seek(SkToSizeT(offset));
	}
	return true;
	}

	SkStreamAsset* fork() const override {
	SkStreamAsset* clone = this->duplicate();
	clone->seek(this->getPosition());
	return clone;
	}


	private:
	const SkROBuffer* fBuffer;
	SkROBuffer::Iter fIter;
	size_t fLocalOffset;
	size_t fGlobalOffset;
	};

	SkStreamAsset* SkRWBuffer::newStreamSnapshot() const {
	SkAutoTUnref<SkROBuffer> buffer(this->newRBufferSnapshot());
	return SkNEW_ARGS(SkROBufferStreamAsset, (buffer));
	}