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Editing: syncstream

// <syncstream> -*- C++ -*-

// Copyright (C) 2020-2021 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file include/syncstream
 *  This is a Standard C++ Library header.
 */

#ifndef _GLIBCXX_SYNCSTREAM
#define _GLIBCXX_SYNCSTREAM 1

#if __cplusplus > 201703L

#include <bits/c++config.h>
#if _GLIBCXX_USE_CXX11_ABI

#define __cpp_lib_syncbuf 201803L

#pragma GCC system_header

#include <sstream>

#include <bits/alloc_traits.h>
#include <bits/allocator.h>
#include <bits/functexcept.h>
#include <bits/functional_hash.h>
#include <bits/std_mutex.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

template<typename _CharT, typename _Traits, typename _Alloc>
    class basic_syncbuf : public __syncbuf_base<_CharT, _Traits>
    {
    public:
      using char_type = _CharT;
      using int_type = typename _Traits::int_type;
      using pos_type = typename _Traits::pos_type;
      using off_type = typename _Traits::off_type;
      using traits_type = _Traits;
      using allocator_type = _Alloc;
      using streambuf_type = basic_streambuf<_CharT, _Traits>;

basic_syncbuf()
      : basic_syncbuf(nullptr, allocator_type{})
      { }

explicit
      basic_syncbuf(streambuf_type* __obuf)
      : basic_syncbuf(__obuf, allocator_type{})
      { }

basic_syncbuf(streambuf_type* __obuf, const allocator_type& __alloc)
      : __syncbuf_base<_CharT, _Traits>(__obuf)
      , _M_impl(__alloc)
      , _M_mtx(__obuf)
      { }

basic_syncbuf(basic_syncbuf&& __other)
      : __syncbuf_base<_CharT, _Traits>(__other._M_wrapped)
      , _M_impl(std::move(__other._M_impl))
      , _M_mtx(std::move(__other._M_mtx))
      {
	this->_M_emit_on_sync = __other._M_emit_on_sync;
	this->_M_needs_sync = __other._M_needs_sync;
	__other._M_wrapped = nullptr;
      }

~basic_syncbuf()
      {
	__try
	  {
	    emit();
	  }
	__catch (...)
	  { }
      }

basic_syncbuf&
      operator=(basic_syncbuf&& __other)
      {
	emit();

_M_impl = std::move(__other._M_impl);
	this->_M_emit_on_sync = __other._M_emit_on_sync;
	this->_M_needs_sync = __other._M_needs_sync;
	this->_M_wrapped = __other._M_wrapped;
	__other._M_wrapped = nullptr;
	_M_mtx = std::move(__other._M_mtx);

return *this;
      }

void
      swap(basic_syncbuf& __other)
      {
	using _ATr = allocator_traits<_Alloc>;
	if constexpr (!_ATr::propagate_on_container_swap::value)
	  __glibcxx_assert(get_allocator() == __other.get_allocator());

std::swap(_M_impl, __other._M_impl);
	std::swap(this->_M_emit_on_sync, __other._M_emit_on_sync);
	std::swap(this->_M_needs_sync, __other._M_needs_sync);
	std::swap(this->_M_wrapped, __other._M_wrapped);
	std::swap(_M_mtx, __other._M_mtx);
      }

bool
      emit()
      {
	if (!this->_M_wrapped)
	  return false;

auto __s = std::move(_M_impl).str();

const lock_guard<__mutex> __l(_M_mtx);
	if (auto __size = __s.size())
	  {
	    auto __n = this->_M_wrapped->sputn(__s.data(), __size);
	    if (__n != __size)
	      {
		__s.erase(0, __n);
		_M_impl.str(std::move(__s));
		return false;
	      }
	  }

if (this->_M_needs_sync)
	  {
	    this->_M_needs_sync = false;
	    if (this->_M_wrapped->pubsync() != 0)
	      return false;
	  }
	return true;
      }

streambuf_type*
      get_wrapped() const noexcept
      { return this->_M_wrapped; }

allocator_type
      get_allocator() const noexcept
      { return _M_impl.get_allocator(); }

void
      set_emit_on_sync(bool __b) noexcept
      { this->_M_emit_on_sync = __b; }

protected:
      int
      sync() override
      {
	this->_M_needs_sync = true;
	if (this->_M_emit_on_sync && !emit())
	  return -1;
	return 0;
      }

int_type
      overflow(int_type __c) override
      {
	int_type __eof = traits_type::eof();
	if (__builtin_expect(!traits_type::eq_int_type(__c, __eof), true))
	  return _M_impl.sputc(__c);
	return __eof;
      }

streamsize
      xsputn(const char_type* __s, streamsize __n) override
      { return _M_impl.sputn(__s, __n); }

private:
      basic_stringbuf<char_type, traits_type, allocator_type> _M_impl;

struct __mutex
      {
#if _GLIBCXX_HAS_GTHREADS
	mutex* _M_mtx;

__mutex(void* __t)
	  : _M_mtx(__t ? &_S_get_mutex(__t) : nullptr)
	{ }

void
	swap(__mutex& __other) noexcept
	{ std::swap(_M_mtx, __other._M_mtx); }

void
	lock()
	{
	  _M_mtx->lock();
	}

void
	unlock()
	{
	  _M_mtx->unlock();
	}

// FIXME: This should be put in the .so
	static mutex&
	_S_get_mutex(void* __t)
	{
	  const unsigned char __mask = 0xf;
	  static mutex __m[__mask + 1];

auto __key = _Hash_impl::hash(__t) & __mask;
	  return __m[__key];
	}
#else
	__mutex(void*) { }
	void swap(__mutex&&) noexcept { }
	void lock() { }
	void unlock() { }
#endif
	__mutex(__mutex&&) = default;
	__mutex& operator=(__mutex&&) = default;
      };
      __mutex _M_mtx;
    };

template <typename _CharT, typename _Traits, typename _Alloc>
    class basic_osyncstream : public basic_ostream<_CharT, _Traits>
    {
      using __ostream_type = basic_ostream<_CharT, _Traits>;

public:
      // Types:
      using char_type = _CharT;
      using traits_type = _Traits;
      using allocator_type = _Alloc;
      using int_type = typename traits_type::int_type;
      using pos_type = typename traits_type::pos_type;
      using off_type = typename traits_type::off_type;
      using syncbuf_type = basic_syncbuf<_CharT, _Traits, _Alloc>;
      using streambuf_type = typename syncbuf_type::streambuf_type;

private:
      syncbuf_type _M_syncbuf;

public:
      basic_osyncstream(streambuf_type* __buf, const allocator_type& __a)
	: _M_syncbuf(__buf, __a)
      { this->init(std::__addressof(_M_syncbuf)); }

explicit basic_osyncstream(streambuf_type* __buf)
	: _M_syncbuf(__buf)
      { this->init(std::__addressof(_M_syncbuf)); }

basic_osyncstream(basic_ostream<char_type, traits_type>& __os,
		        const allocator_type& __a)
	: basic_osyncstream(__os.rdbuf(), __a)
      { this->init(std::__addressof(_M_syncbuf)); }

explicit basic_osyncstream(basic_ostream<char_type, traits_type>& __os)
	: basic_osyncstream(__os.rdbuf())
      { this->init(std::__addressof(_M_syncbuf)); }

basic_osyncstream(basic_osyncstream&& __rhs) noexcept
	: __ostream_type(std::move(__rhs)),
	_M_syncbuf(std::move(__rhs._M_syncbuf))
      { __ostream_type::set_rdbuf(std::__addressof(_M_syncbuf)); }

~basic_osyncstream() = default;

basic_osyncstream& operator=(basic_osyncstream&&) noexcept = default;

syncbuf_type* rdbuf() const noexcept
      { return const_cast<syncbuf_type*>(&_M_syncbuf); }

streambuf_type* get_wrapped() const noexcept
      { return _M_syncbuf.get_wrapped(); }

void emit()
      {
	if (!_M_syncbuf.emit())
	  this->setstate(ios_base::failbit);
      }
    };

template <class _CharT, class _Traits, class _Allocator>
    inline void
    swap(basic_syncbuf<_CharT, _Traits, _Allocator>& __x,
	 basic_syncbuf<_CharT, _Traits, _Allocator>& __y) noexcept
    { __x.swap(__y); }

using syncbuf = basic_syncbuf<char>;
  using wsyncbuf = basic_syncbuf<wchar_t>;

using osyncstream = basic_osyncstream<char>;
  using wosyncstream = basic_osyncstream<wchar_t>;
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // _GLIBCXX_USE_CXX11_ABI
#endif // C++2a
#endif	/* _GLIBCXX_SYNCSTREAM */

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