syncstream

Go to the documentation of this file.

// <syncstream> -*- C++ -*-
 
// Copyright (C) 2020-2025 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
 
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
 
#include <bits/requires_hosted.h> // iostreams
 
#include <bits/c++config.h>
 
#define __glibcxx_want_syncbuf
#include <bits/version.h>
 
#ifdef __cpp_lib_syncbuf // C++ >= 20 && HOSTED && CXX11ABI
#include <sstream>
 
#include <bits/alloc_traits.h>
#include <bits/allocator.h>
#include <bits/functexcept.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 = nullptr;
 
        __mutex(void* __t)  // __t is the underlying sbuf, as hash seed.
        {
          extern mutex& __syncbuf_get_mutex(void*);  // in src/c++20/syncbuf.cc
          if (__t) _M_mtx = &__syncbuf_get_mutex(__t);
        }
 
        void
        swap(__mutex& __other) noexcept
        { std::swap(_M_mtx, __other._M_mtx); }
 
        void
        lock()
        {
          _M_mtx->lock();
        }
 
        void
        unlock()
        {
          _M_mtx->unlock();
        }
#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&&) = 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 // __cpp_lib_syncbuf
 
#endif  /* _GLIBCXX_SYNCSTREAM */