bslstl_osyncstream.h

Go to the documentation of this file.

/// @file bslstl_osyncstream.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslstl_osyncstream.h                                               -*-C++-*-
#ifndef INCLUDED_BSLSTL_OSYNCSTREAM
#define INCLUDED_BSLSTL_OSYNCSTREAM
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslstl_osyncstream bslstl_osyncstream
/// @brief  Provide a C++20-compatible `basic_osyncstream` class template.
/// @addtogroup bsl
/// @{
/// @addtogroup bslstl
/// @{
/// @addtogroup bslstl_osyncstream
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslstl_osyncstream-purpose"> Purpose</a>
/// * <a href="#bslstl_osyncstream-classes"> Classes </a>
/// * <a href="#bslstl_osyncstream-description"> Description </a>
///   * <a href="#bslstl_osyncstream-usage"> Usage </a>
///     * <a href="#bslstl_osyncstream-example-1-using-osyncstream"> Example 1: Using osyncstream </a>
///
/// # Purpose {#bslstl_osyncstream-purpose}
/// Provide a C++20-compatible @ref basic_osyncstream  class template.
///
/// # Classes {#bslstl_osyncstream-classes}
///
/// -  bsl::basic_osyncstream: C++20-compatible @ref basic_osyncstream  class.
/// -  bsl::osyncstream: C++20-compatible `osyncstream` class.
/// -  bsl::wosyncstream: C++20-compatible `wosyncstream` class.
///
/// **Canonical header:**  bsl_syncstream.h
///
/// @see  bslstl_syncbuf
///
/// # Description {#bslstl_osyncstream-description}
/// This component is for internal use only.  Please include
/// `<bsl_syncstream.h>` instead.
///
/// This component defines a class template, `bsl::basic_osyncstream`, that is a
/// convenience wrapper for `bsl::basic_syncbuf`.  It provides a mechanism to
/// synchronize threads writing to the same stream, or more precisely, to the
/// same `streambuf`.  It's guaranteed that all output made to the same final
/// destination buffer will be free of data races and will not be interleaved or
/// garbled in any way, as long as every write to that final destination buffer
/// is made through (possibly different) instances of `bsl::basic_syncbuf`.
///
/// Types `bsl::osyncstream` and `bsl::wosyncstream` are aliases for
/// `bsl::basic_osyncstream<char>` and `bsl::basic_osyncstream<wchar_t>`,
/// respectively.
///
/// ## Usage {#bslstl_osyncstream-usage}
///
///
/// This section illustrates intended use of this component.
///
/// In a multi-threaded environment attempts to write from different threads to
/// one `ostream` "may result in a data race", according to the ISO C++
/// Standard.  Concurrent access to the special synchronized iostream objects,
/// like `cout`, `cerr`, etc, does not result in a data race, but output
/// characters from one thread can interleave with the characters from other
/// threads still.  `osyncstream` solves both problems: prevents data races and
/// characters interleaving.
///
/// ### Example 1: Using osyncstream {#bslstl_osyncstream-example-1-using-osyncstream}
///
///
/// The following example demonstrates concurrent printing of a standard STL
/// container of values that can be streamed out.  The elements are separated by
/// comma and the whole sequence is enclosed in curly brackets.  Note that this
/// example requires at least C++11.
/// @code
/// template <class t_CONTAINER>
/// void printContainer(bsl::ostream& stream, const t_CONTAINER& container)
///     // Print elements of the specified 'container' to the specified
///     // 'stream' in a multi-threaded environment without interleaving with
///     // output from another threads.
/// {
///     bsl::osyncstream out(stream);
///     out << '{';
///     bool first = true;
///     for(auto& value : container) {
///         if (first) {
///             first = false;
///         }
///         else {
///             out << ", ";
///         }
///         out << value;
///     }
///     out << '}';
/// } // all output is atomically transferred to 'stream' on 'out' destruction
/// @endcode
/// Now this function can safely be used in a multi-threaded environment:
/// @code
/// int main()
/// {
///     bsl::vector<int>    container1 = {1, 2, 3};
///     bsl::vector<double> container2 = {4.0, 5.0, 6.0, 7.0};
///
///     bsl::thread thread1{[&]{ printContainer(bsl::cout, container1); }};
///     bsl::thread thread2{[&]{ printContainer(bsl::cout, container2); }};
///     thread1.join();
///     thread2.join();
/// }
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslstl
 * @{
 */
/** @addtogroup bslstl_osyncstream
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslstl_syncbuf.h>
 
#include <bsls_keyword.h>
#include <bsls_libraryfeatures.h>
 
#include <ostream>
 
#ifdef BSLS_LIBRARYFEATURES_HAS_CPP11_STREAM_MOVE
#include <utility>  // move
#endif
 
namespace bsl {
 
                            // =======================
                            // class basic_osyncstream
                            // =======================
 
/// This class implements a standard output stream providing an internal
/// buffer to accumulate the written data in order to atomically transmit
/// its entire contents to the wrapped buffer on destruction (or `emit`
/// call).
///
/// See @ref bslstl_osyncstream 
template <class CHAR_TYPE, class CHAR_TRAITS, class ALLOCATOR>
class basic_osyncstream : public std::basic_ostream<CHAR_TYPE, CHAR_TRAITS> {
 
    // PRIVATE TYPES
    typedef std::basic_ostream<CHAR_TYPE, CHAR_TRAITS> Base;
 
  public:
    // TYPES
    typedef CHAR_TYPE                      char_type;
    typedef typename CHAR_TRAITS::int_type int_type;
    typedef typename CHAR_TRAITS::pos_type pos_type;
    typedef typename CHAR_TRAITS::off_type off_type;
    typedef CHAR_TRAITS                    traits_type;
    typedef ALLOCATOR                      allocator_type;
 
    typedef std::basic_streambuf<CHAR_TYPE, CHAR_TRAITS>     streambuf_type;
    typedef basic_syncbuf<CHAR_TYPE, CHAR_TRAITS, ALLOCATOR> syncbuf_type;
 
  private:
    // DATA
    syncbuf_type d_syncbuf;  // wrapped 'syncbuf'
 
  public:
    // CREATORS
 
    /// Create a @ref basic_osycnstream  object that will forward stream output
    /// to the specified `wrapped` buffer.  Optionally specify an
    /// `allocator` used to supply memory.  If `allocator` is not supplied,
    /// a default-constructed object of the (template parameter) `ALLOCATOR`
    /// type is used.  If the `ALLOCATOR` argument is of type
    /// `bsl::allocator` (the default), then `allocator`, if supplied, shall
    /// be convertible to `bslma::Allocator *`.  If the `ALLOCATOR` argument
    /// is of type `bsl::allocator` and `allocator` is not supplied, the
    /// currently installed default allocator will be used to supply memory.
    explicit basic_osyncstream(streambuf_type   *wrapped,
                               const ALLOCATOR&  allocator = ALLOCATOR());
 
    /// Create a @ref basic_osycnstream  object that will forward stream output
    /// to `rdbuf` of the specified `stream`.  Optionally specify an
    /// `allocator` used to supply memory.  If `allocator` is not supplied,
    /// a default-constructed object of the (template parameter) `ALLOCATOR`
    /// type is used.  If the `ALLOCATOR` argument is of type
    /// `bsl::allocator` (the default), then `allocator`, if supplied, shall
    /// be convertible to `bslma::Allocator *`.  If the `ALLOCATOR` argument
    /// is of type `bsl::allocator` and `allocator` is not supplied, the
    /// currently installed default allocator will be used to supply memory.
    explicit basic_osyncstream(
          std::basic_ostream<CHAR_TYPE, CHAR_TRAITS>& stream,
          const ALLOCATOR&                            allocator = ALLOCATOR());
 
     ~basic_osyncstream() = default;
        // Destroy this object.
 
#ifdef BSLS_LIBRARYFEATURES_HAS_CPP11_STREAM_MOVE
    basic_osyncstream(basic_osyncstream&& original) BSLS_KEYWORD_NOEXCEPT;
 
    /// Create a @ref basic_osyncstream  object having the same value as the
    /// specified `original` object by moving the contents of `original` to
    /// the newly-created object.  Optionally specify an `allocator` used
    /// to supply memory.  `original.get_wrapped() == nullptr` after the
    /// call.
    basic_osyncstream(basic_osyncstream&& original,
                      const ALLOCATOR&    allocator) BSLS_KEYWORD_NOEXCEPT;
#endif
 
    // MANIPULATORS
#ifdef BSLS_LIBRARYFEATURES_HAS_CPP11_STREAM_MOVE
    /// Transfer the associated output to the wrapped stream buffer then
    /// assign to this object the value of the specified `original`, and
    /// return a reference providing modifiable access to this object.  The
    /// contents of `original` are move-assigned to this object.
    /// `original.get_wrapped() == nullptr` after the call.
    basic_osyncstream &operator=(basic_osyncstream&& original) = default;
#endif
 
    /// Atomically transfer any characters buffered by this object to the
    /// wrapped stream buffer, so that it appears in the output stream as a
    /// contiguous sequence of characters.  If an error occurs, set the
    /// `badbit` of the `rdstate` to `true`.
    void emit();
 
    // ACCESSORS
 
    /// Return the allocator used to supply memory.
    allocator_type get_allocator() const BSLS_KEYWORD_NOEXCEPT;
 
    /// Return the wrapped buffer.
    streambuf_type *get_wrapped() const BSLS_KEYWORD_NOEXCEPT;
 
    /// Return an address providing modifiable access to the @ref basic_syncbuf 
    /// object that is internally used by this stream object to buffer
    /// unformatted characters.
    syncbuf_type *rdbuf() const BSLS_KEYWORD_NOEXCEPT;
};
 
// STANDARD TYPEDEFS
typedef basic_osyncstream<char>     osyncstream;
typedef basic_osyncstream<wchar_t> wosyncstream;
 
                            // -----------------------
                            // class basic_osyncstream
                            // -----------------------
 
// CREATORS
template <class CHAR, class TRAITS, class ALLOCATOR>
basic_osyncstream<CHAR,TRAITS,ALLOCATOR>::basic_osyncstream(
                                                   streambuf_type   *wrapped,
                                                   const ALLOCATOR&  allocator)
:
#ifndef BSLS_LIBRARYFEATURES_STDCPP_LIBCSTD
  // The Rogue Wave library used by Solaris does not correctly initialize the
  // buffer pointer in the constructor for @ref basic_streambuf . As a result, on
  // Solaris, we need to perform two-phase initialization using the
  // 'basic_osyncstream::init' function instead.
  Base(&d_syncbuf),
#endif
  d_syncbuf(wrapped, allocator)
{
#ifdef BSLS_LIBRARYFEATURES_STDCPP_LIBCSTD
    this->init(&d_syncbuf);
#endif
}
 
template <class CHAR, class TRAITS, class ALLOCATOR>
basic_osyncstream<CHAR,TRAITS,ALLOCATOR>::basic_osyncstream(
                                    std::basic_ostream<CHAR,TRAITS>& stream,
                                    const ALLOCATOR&                 allocator)
:
#ifndef BSLS_LIBRARYFEATURES_STDCPP_LIBCSTD
  Base(&d_syncbuf),
#endif
  d_syncbuf(stream.rdbuf(), allocator)
{
#ifdef BSLS_LIBRARYFEATURES_STDCPP_LIBCSTD
    this->init(&d_syncbuf);
#endif
}
 
#ifdef BSLS_LIBRARYFEATURES_HAS_CPP11_STREAM_MOVE
template <class CHAR, class TRAITS, class ALLOCATOR>
basic_osyncstream<CHAR,TRAITS,ALLOCATOR>::basic_osyncstream(
                            basic_osyncstream&& original) BSLS_KEYWORD_NOEXCEPT
: Base(std::move(original))
, d_syncbuf(std::move(original.d_syncbuf))
{
    this->set_rdbuf(&d_syncbuf);
}
 
template <class CHAR, class TRAITS, class ALLOCATOR>
basic_osyncstream<CHAR,TRAITS,ALLOCATOR>::basic_osyncstream(
                           basic_osyncstream&& original,
                           const ALLOCATOR&    allocator) BSLS_KEYWORD_NOEXCEPT
: Base(std::move(original))
, d_syncbuf(std::move(original.d_syncbuf), allocator)
{
    this->set_rdbuf(&d_syncbuf);
}
#endif
 
// MANIPULATORS
template <class CHAR, class TRAITS, class ALLOCATOR>
void basic_osyncstream<CHAR,TRAITS,ALLOCATOR>::emit()
{
    typename Base::sentry ok(*this);
    if (!ok) {
        this->setstate(ios_base::badbit);
    }
    else {
        if (!d_syncbuf.emit()) {
            this->setstate(ios_base::badbit);
        }
    }
}
 
// ACCESSORS
template <class CHAR, class TRAITS, class ALLOCATOR>
inline
ALLOCATOR basic_osyncstream<CHAR,TRAITS,ALLOCATOR>::get_allocator() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return d_syncbuf.get_allocator();
}
 
template <class CHAR, class TRAITS, class ALLOCATOR>
inline
typename basic_osyncstream<CHAR,TRAITS,ALLOCATOR>::streambuf_type *
basic_osyncstream<CHAR,TRAITS,ALLOCATOR>::get_wrapped() const
                                                          BSLS_KEYWORD_NOEXCEPT
{
    return d_syncbuf.get_wrapped();
}
 
template <class CHAR, class TRAITS, class ALLOCATOR>
inline
typename basic_osyncstream<CHAR,TRAITS,ALLOCATOR>::syncbuf_type *
basic_osyncstream<CHAR,TRAITS,ALLOCATOR>::rdbuf() const BSLS_KEYWORD_NOEXCEPT
{
    return const_cast<syncbuf_type*>(&d_syncbuf);
}
 
}  // close namespace bsl
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2023 Bloomberg Finance L.P.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ----------------------------- END-OF-FILE ----------------------------------
 
/** @} */
/** @} */
/** @} */