/*
* 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 "SkAtomics.h"
#include "SkMalloc.h"
#include "SkMakeUnique.h"
#include "SkStream.h"
#include <atomic>
// Force small chunks to be a page's worth
static const size_t kMinAllocSize = 4096;
struct SkBufferBlock {
SkBufferBlock* fNext; // updated by the writer
size_t fUsed; // updated by the writer
const size_t fCapacity;
SkBufferBlock(size_t capacity) : fNext(nullptr), fUsed(0), fCapacity(capacity) {}
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);
void* buffer = sk_malloc_throw(sizeof(SkBufferBlock) + capacity);
return new (buffer) SkBufferBlock(capacity);
}
// Return number of bytes actually appended. Important that we always completely this block
// before spilling into the next, since the reader uses fCapacity to know how many it can read.
//
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;
}
// Do not call in the reader thread, since the writer may be updating fUsed.
// (The assertion is still true, but TSAN still may complain about its raciness.)
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 std::atomic<int32_t> fRefCnt;
SkBufferBlock fBlock;
SkBufferHead(size_t capacity) : fRefCnt(1), fBlock(capacity) {}
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;
void* buffer = sk_malloc_throw(size);
return new (buffer) SkBufferHead(capacity);
}
void ref() const {
SkAssertResult(fRefCnt.fetch_add(+1, std::memory_order_relaxed));
}
void unref() const {
// A release here acts in place of all releases we "should" have been doing in ref().
int32_t oldRefCnt = fRefCnt.fetch_add(-1, std::memory_order_acq_rel);
SkASSERT(oldRefCnt);
if (1 == oldRefCnt) {
// 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, const SkBufferBlock* tail = nullptr) const {
#ifdef SK_DEBUG
SkASSERT(fRefCnt.load(std::memory_order_relaxed) > 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
}
};
///////////////////////////////////////////////////////////////////////////////////////////////////
// The reader can only access block.fCapacity (which never changes), and cannot access
// block.fUsed, which may be updated by the writer.
//
SkROBuffer::SkROBuffer(const SkBufferHead* head, size_t available, const SkBufferBlock* tail)
: fHead(head), fAvailable(available), fTail(tail)
{
if (head) {
fHead->ref();
SkASSERT(available > 0);
head->validate(available, tail);
} else {
SkASSERT(0 == available);
SkASSERT(!tail);
}
}
SkROBuffer::~SkROBuffer() {
if (fHead) {
fHead->unref();
}
}
SkROBuffer::Iter::Iter(const SkROBuffer* buffer) {
this->reset(buffer);
}
SkROBuffer::Iter::Iter(const sk_sp<SkROBuffer>& buffer) {
this->reset(buffer.get());
}
void SkROBuffer::Iter::reset(const SkROBuffer* buffer) {
fBuffer = buffer;
if (buffer && buffer->fHead) {
fBlock = &buffer->fHead->fBlock;
fRemaining = buffer->fAvailable;
} else {
fBlock = nullptr;
fRemaining = 0;
}
}
const void* SkROBuffer::Iter::data() const {
return fRemaining ? fBlock->startData() : nullptr;
}
size_t SkROBuffer::Iter::size() const {
if (!fBlock) {
return 0;
}
return SkTMin(fBlock->fCapacity, fRemaining);
}
bool SkROBuffer::Iter::next() {
if (fRemaining) {
fRemaining -= this->size();
if (fBuffer->fTail == fBlock) {
// There are more blocks, but fBuffer does not know about them.
SkASSERT(0 == fRemaining);
fBlock = nullptr;
} else {
fBlock = fBlock->fNext;
}
}
return fRemaining != 0;
}
///////////////////////////////////////////////////////////////////////////////////////////////////
SkRWBuffer::SkRWBuffer(size_t initialCapacity) : fHead(nullptr), fTail(nullptr), fTotalUsed(0) {
if (initialCapacity) {
fHead = SkBufferHead::Alloc(initialCapacity);
fTail = &fHead->fBlock;
}
}
SkRWBuffer::~SkRWBuffer() {
this->validate();
if (fHead) {
fHead->unref();
}
}
// It is important that we always completely fill the current block before spilling over to the
// next, since our reader will be using fCapacity (min'd against its total available) to know how
// many bytes to read from a given block.
//
void SkRWBuffer::append(const void* src, size_t length, size_t reserve) {
this->validate();
if (0 == length) {
return;
}
fTotalUsed += length;
if (nullptr == fHead) {
fHead = SkBufferHead::Alloc(length + reserve);
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 + reserve);
fTail->fNext = block;
fTail = block;
written = fTail->append(src, length);
SkASSERT(written == length);
}
this->validate();
}
#ifdef SK_DEBUG
void SkRWBuffer::validate() const {
if (fHead) {
fHead->validate(fTotalUsed, fTail);
} else {
SkASSERT(nullptr == fTail);
SkASSERT(0 == fTotalUsed);
}
}
#endif
///////////////////////////////////////////////////////////////////////////////////////////////////
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(sk_sp<SkROBuffer> buffer) : fBuffer(std::move(buffer)), fIter(fBuffer) {
fGlobalOffset = fLocalOffset = 0;
}
size_t getLength() const override { return fBuffer->size(); }
bool rewind() override {
AUTO_VALIDATE
fIter.reset(fBuffer.get());
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;
}
size_t getPosition() const override {
return fGlobalOffset;
}
bool seek(size_t position) override {
AUTO_VALIDATE
if (position < fGlobalOffset) {
this->rewind();
}
(void)this->skip(position - fGlobalOffset);
return true;
}
bool move(long offset) override{
AUTO_VALIDATE
offset += fGlobalOffset;
if (offset <= 0) {
this->rewind();
} else {
(void)this->seek(SkToSizeT(offset));
}
return true;
}
private:
SkStreamAsset* onDuplicate() const override {
return new SkROBufferStreamAsset(fBuffer);
}
SkStreamAsset* onFork() const override {
auto clone = this->duplicate();
clone->seek(this->getPosition());
return clone.release();
}
sk_sp<SkROBuffer> fBuffer;
SkROBuffer::Iter fIter;
size_t fLocalOffset;
size_t fGlobalOffset;
};
std::unique_ptr<SkStreamAsset> SkRWBuffer::makeStreamSnapshot() const {
return skstd::make_unique<SkROBufferStreamAsset>(this->makeROBufferSnapshot());
}