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Fix basic_streambuf:
prepare() is rewritten to operate more simply; the state of the container is always consistent even between internal operations.
This commit is contained in:
Vinnie Falco
@@ -19,65 +19,65 @@ namespace beast {
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/* These diagrams illustrate the layout and state variables.
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Input and output contained entirely in one element:
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1 Input and output contained entirely in one element:
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0 out_
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|<-------------+------------------------------------------->|
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in_pos_ out_pos_ out_end_
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in_pos_ out_pos_ out_end_
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Output contained in first and second elements:
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2 Output contained in first and second elements:
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out_
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|<------+----------+------->| |<----------+-------------->|
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in_pos_ out_pos_ out_end_
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in_pos_ out_pos_ out_end_
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Output contained in the second element:
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3 Output contained in the second element:
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out_
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|<------------+------------>| |<----+-------------------->|
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in_pos_ out_pos_ out_end_
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Output contained in second and third elements:
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4 Output contained in second and third elements:
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out_
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|<-----+-------->| |<-------+------>| |<--------------->|
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in_pos_ out_pos_ out_end_
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in_pos_ out_pos_ out_end_
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Input sequence is empty:
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5 Input sequence is empty:
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out_
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|<------+------------------>| |<-----------+------------->|
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out_pos_ out_end_
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in_pos_
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out_pos_ out_end_
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in_pos_
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Output sequence is empty:
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6 Output sequence is empty:
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out_
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|<------+------------------>| |<------+------------------>|
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in_pos_ out_pos_
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out_end_
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in_pos_ out_pos_
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out_end_
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The end of output can point to the end of an element.
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7 The end of output can point to the end of an element.
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But out_pos_ should never point to the end:
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out_
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|<------+------------------>| |<------+------------------>|
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in_pos_ out_pos_ out_end_
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in_pos_ out_pos_ out_end_
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When the input sequence entirely fills the last element and
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8 When the input sequence entirely fills the last element and
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the output sequence is empty, out_ will point to the end of
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the list of buffers, and out_pos_ and out_end_ will be 0:
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|<------+------------------>| out_ == list_.end()
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in_pos_ out_pos_ == 0
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in_pos_ out_pos_ == 0
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out_end_ == 0
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*/
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@@ -478,74 +478,77 @@ auto
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basic_streambuf<Allocator>::prepare(size_type n) ->
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mutable_buffers_type
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{
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iterator pos = out_;
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if(pos != list_.end())
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list_type reuse;
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if(out_ != list_.end())
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{
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auto const avail = pos->size() - out_pos_;
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if(out_ != list_.iterator_to(list_.back()))
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{
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out_end_ = out_->size();
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reuse.splice(reuse.end(), list_,
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std::next(out_), list_.end());
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debug_check();
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}
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auto const avail = out_->size() - out_pos_;
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if(n > avail)
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{
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out_end_ = out_->size();
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n -= avail;
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out_end_ = pos->size();
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while(++pos != list_.end())
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{
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if(n < pos->size())
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{
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out_end_ = n;
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n = 0;
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++pos;
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break;
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}
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n -= pos->size();
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}
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}
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else
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{
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++pos;
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out_end_ = out_pos_ + n;
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n = 0;
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}
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debug_check();
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}
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if(n > 0)
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while(n > 0 && ! reuse.empty())
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{
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assert(pos == list_.end());
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for(;;)
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auto& e = reuse.front();
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reuse.erase(reuse.iterator_to(e));
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list_.push_back(e);
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if(n > e.size())
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{
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auto const size = std::max(alloc_size_, n);
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auto& e = *reinterpret_cast<element*>(
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alloc_traits::allocate(this->member(),
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size + sizeof(element)));
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alloc_traits::construct(this->member(), &e, size);
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list_.push_back(e);
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if(out_ == list_.end())
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{
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out_ = list_.iterator_to(e);
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debug_check();
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}
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if(n <= size)
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{
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out_end_ = n;
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debug_check();
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break;
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}
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n -= size;
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debug_check();
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out_end_ = e.size();
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n -= e.size();
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}
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}
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else
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{
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while(pos != list_.end())
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else
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{
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auto& e = *pos++;
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list_.erase(list_.iterator_to(e));
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auto const len = e.size() + sizeof(e);
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alloc_traits::destroy(this->member(), &e);
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alloc_traits::deallocate(this->member(),
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reinterpret_cast<std::uint8_t*>(&e), len);
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out_end_ = n;
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n = 0;
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}
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debug_check();
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}
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while(n > 0)
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{
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auto const size = std::max(alloc_size_, n);
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auto& e = *reinterpret_cast<element*>(
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alloc_traits::allocate(this->member(),
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sizeof(element) + size));
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alloc_traits::construct(this->member(), &e, size);
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list_.push_back(e);
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if(out_ == list_.end())
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out_ = list_.iterator_to(e);
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if(n > e.size())
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{
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out_end_ = e.size();
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n -= e.size();
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}
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else
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{
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out_end_ = n;
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n = 0;
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}
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debug_check();
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}
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for(auto it = reuse.begin(); it != reuse.end();)
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{
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auto& e = *it++;
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reuse.erase(list_.iterator_to(e));
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auto const len = e.size() + sizeof(e);
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alloc_traits::destroy(this->member(), &e);
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alloc_traits::deallocate(this->member(),
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reinterpret_cast<std::uint8_t*>(&e), len);
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}
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return mutable_buffers_type(*this);
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}
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@@ -557,8 +560,9 @@ basic_streambuf<Allocator>::commit(size_type n)
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return;
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if(out_ == list_.end())
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return;
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auto const last = std::prev(list_.end());
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while(out_ != last)
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auto const back =
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list_.iterator_to(list_.back());
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while(out_ != back)
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{
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auto const avail =
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out_->size() - out_pos_;
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@@ -603,12 +607,11 @@ basic_streambuf<Allocator>::consume(size_type n)
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if(list_.empty())
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return;
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auto pos = list_.begin();
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for(;;)
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{
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if(pos != out_)
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if(list_.begin() != out_)
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{
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auto const avail = pos->size() - in_pos_;
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auto const avail = list_.front().size() - in_pos_;
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if(n < avail)
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{
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in_size_ -= n;
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@@ -619,14 +622,13 @@ basic_streambuf<Allocator>::consume(size_type n)
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n -= avail;
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in_size_ -= avail;
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in_pos_ = 0;
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debug_check();
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element& e = *pos++;
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auto& e = list_.front();
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list_.erase(list_.iterator_to(e));
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auto const len = e.size() + sizeof(e);
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alloc_traits::destroy(this->member(), &e);
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alloc_traits::deallocate(this->member(),
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reinterpret_cast<std::uint8_t*>(&e), len);
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debug_check();
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}
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else
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{
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@@ -638,15 +640,15 @@ basic_streambuf<Allocator>::consume(size_type n)
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}
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else
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{
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in_size_ -= avail;
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if(out_pos_ != out_end_||
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out_ != list_.iterator_to(list_.back()))
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in_size_ = 0;
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if(out_ != list_.iterator_to(list_.back()) ||
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out_pos_ != out_end_)
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{
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in_pos_ = out_pos_;
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}
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else
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{
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// Use the whole buffer now.
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// Input and output sequences are empty, reuse buffer.
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// Alternatively we could deallocate it.
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in_pos_ = 0;
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out_pos_ = 0;
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@@ -759,6 +761,8 @@ void
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basic_streambuf<Allocator>::debug_check() const
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{
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#ifndef NDEBUG
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using boost::asio::buffer_size;
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assert(buffer_size(data()) == in_size_);
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if(list_.empty())
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{
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assert(in_pos_ == 0);
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