Nic*_*ick 16 c++ iostream pipe
我想要做的是创建一种"管道"(如进程之间的管道),但在同一程序中的c ++ iostream之间.我有一个函数需要输入流作为参数,但我的数据来自输出流.那么有没有一种标准的方法将a的输出std::ostream输入到输入std::istream？
Die*_*ühl 17
您可以创建std::streambuf输出到达一个缓冲区的位置,并std::overflow()在缓冲区变满时阻塞.在另一端,你有一个输入缓冲区,underflow()当缓冲区变空时它会阻塞.显然,阅读和写作将分为两个不同的主题.
棘手的业务是如何同步两个缓冲区:流在访问缓冲区时不使用任何同步操作.只有在调用任何虚函数时,您才能拦截操作并处理同步.另一方面,不使用缓冲区效率相当低.我解决这个问题的方法是使用一个相对较小的输出缓冲区(例如256 char秒),并重写sync()使用此函数将字符传输到输入缓冲区.在streambuf将使用一个互斥用于同步和条件变量到框上输出一个完整的输入缓冲器和输入一个空的输入缓冲器.为了支持干净关闭,还应该有一个函数设置一个标志,表示不再有输入,所有进一步的输出操作都应该失败.
创建实际实现表明两个缓冲区是不够的:访问输入和输出缓冲区的线程可能在相应的其他缓冲区阻塞时处于活动状态.因此,需要第三个中间缓冲区.通过对上述计划的这一小改动,下面是一些代码(它使用微小的缓冲区来确保实际的溢出和下溢;对于实际使用,至少输入缓冲区应该更大).
// threadbuf.cpp -*-C++-*-
// ----------------------------------------------------------------------------
// Copyright (C) 2013 Dietmar Kuehl http://www.dietmar-kuehl.de
//
// Permission is hereby granted, free of charge, to any person
// obtaining a copy of this software and associated documentation
// files (the "Software"), to deal in the Software without restriction,
// including without limitation the rights to use, copy, modify,
// merge, publish, distribute, sublicense, and/or sell copies of
// the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.
// ----------------------------------------------------------------------------
#include <algorithm>
#include <condition_variable>
#include <iostream>
#include <mutex>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <thread>
// ----------------------------------------------------------------------------
class threadbuf
: public std::streambuf
{
private:
typedef std::streambuf::traits_type traits_type;
typedef std::string::size_type string_size_t;
std::mutex d_mutex;
std::condition_variable d_condition;
std::string d_out;
std::string d_in;
std::string d_tmp;
char* d_current;
bool d_closed;
public:
threadbuf(string_size_t out_size = 16, string_size_t in_size = 64)
: d_out(std::max(string_size_t(1), out_size), ' ')
, d_in(std::max(string_size_t(1), in_size), ' ')
, d_tmp(std::max(string_size_t(1), in_size), ' ')
, d_current(&this->d_tmp[0])
, d_closed(false)
{
this->setp(&this->d_out[0], &this->d_out[0] + this->d_out.size() - 1);
this->setg(&this->d_in[0], &this->d_in[0], &this->d_in[0]);
}
void close()
{
{
std::unique_lock<std::mutex> lock(this->d_mutex);
this->d_closed = true;
while (this->pbase() != this->pptr()) {
this->internal_sync(lock);
}
}
this->d_condition.notify_all();
}
private:
int_type underflow()
{
if (this->gptr() == this->egptr())
{
std::unique_lock<std::mutex> lock(this->d_mutex);
while (&this->d_tmp[0] == this->d_current && !this->d_closed) {
this->d_condition.wait(lock);
}
if (&this->d_tmp[0] != this->d_current) {
std::streamsize size(this->d_current - &this->d_tmp[0]);
traits_type::copy(this->eback(), &this->d_tmp[0],
this->d_current - &this->d_tmp[0]);
this->setg(this->eback(), this->eback(), this->eback() + size);
this->d_current = &this->d_tmp[0];
this->d_condition.notify_one();
}
}
return this->gptr() == this->egptr()
? traits_type::eof()
: traits_type::to_int_type(*this->gptr());
}
int_type overflow(int_type c)
{
std::unique_lock<std::mutex> lock(this->d_mutex);
if (!traits_type::eq_int_type(c, traits_type::eof())) {
*this->pptr() = traits_type::to_char_type(c);
this->pbump(1);
}
return this->internal_sync(lock)
? traits_type::eof()
: traits_type::not_eof(c);
}
int sync()
{
std::unique_lock<std::mutex> lock(this->d_mutex);
return this->internal_sync(lock);
}
int internal_sync(std::unique_lock<std::mutex>& lock)
{
char* end(&this->d_tmp[0] + this->d_tmp.size());
while (this->d_current == end && !this->d_closed) {
this->d_condition.wait(lock);
}
if (this->d_current != end)
{
std::streamsize size(std::min(end - d_current,
this->pptr() - this->pbase()));
traits_type::copy(d_current, this->pbase(), size);
this->d_current += size;
std::streamsize remain((this->pptr() - this->pbase()) - size);
traits_type::move(this->pbase(), this->pptr(), remain);
this->setp(this->pbase(), this->epptr());
this->pbump(remain);
this->d_condition.notify_one();
return 0;
}
return traits_type::eof();
}
};
// ----------------------------------------------------------------------------
static void writer(std::ostream& out)
{
for (std::string line; std::getline(std::cin, line); )
{
out << "writer: '" << line << "'\n";
}
}
// ----------------------------------------------------------------------------
static void reader(std::istream& in)
{
for (std::string line; std::getline(in, line); )
{
std::cout << "reader: '" << line << "'\n";
}
}
// ----------------------------------------------------------------------------
int main()
{
try
{
threadbuf sbuf;
std::ostream out(&sbuf);
std::istream in(&sbuf);
std::thread write(&::writer, std::ref(out));
std::thread read(&::reader, std::ref(in));
write.join();
sbuf.close();
read.join();
}
catch (std::exception const& ex)
{
std::cerr << "ERROR: " << ex.what() << "\n";
}
}