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// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
// vim: ts=8 sw=2 smarttab
/*
* Ceph - scalable distributed file system
*
* Copyright (C) 2018 Red Hat, Inc.
*
* This is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License version 2.1, as published by the Free Software
* Foundation. See file COPYING.
*
*/
#ifndef COMMON_STACKSTRINGSTREAM_H
#define COMMON_STACKSTRINGSTREAM_H
#include <boost/container/small_vector.hpp>
#include <algorithm>
#include <iostream>
#include <memory>
#include <ostream>
#include <sstream>
#include <string_view>
#include <vector>
#include "include/inline_memory.h"
template<std::size_t SIZE>
class StackStringBuf : public std::basic_streambuf<char>
{
public:
StackStringBuf()
: vec{SIZE, boost::container::default_init_t{}}
{
setp(vec.data(), vec.data() + vec.size());
}
StackStringBuf(const StackStringBuf&) = delete;
StackStringBuf& operator=(const StackStringBuf&) = delete;
StackStringBuf(StackStringBuf&& o) = delete;
StackStringBuf& operator=(StackStringBuf&& o) = delete;
~StackStringBuf() override = default;
void clear()
{
vec.resize(SIZE);
setp(vec.data(), vec.data() + SIZE);
}
std::string_view strv() const
{
return std::string_view(pbase(), pptr() - pbase());
}
protected:
std::streamsize xsputn(const char *s, std::streamsize n)
{
std::streamsize capacity = epptr() - pptr();
std::streamsize left = n;
if (capacity >= left) {
maybe_inline_memcpy(pptr(), s, left, 32);
pbump(left);
} else {
maybe_inline_memcpy(pptr(), s, capacity, 64);
s += capacity;
left -= capacity;
vec.insert(vec.end(), s, s + left);
setp(vec.data(), vec.data() + vec.size());
pbump(vec.size());
}
return n;
}
int overflow(int c)
{
if (traits_type::not_eof(c)) {
char str = traits_type::to_char_type(c);
vec.push_back(str);
return c;
} else {
return traits_type::eof();
}
}
private:
boost::container::small_vector<char, SIZE> vec;
};
template<std::size_t SIZE>
class StackStringStream : public std::basic_ostream<char>
{
public:
StackStringStream() : basic_ostream<char>(&ssb), default_fmtflags(flags()) {}
StackStringStream(const StackStringStream& o) = delete;
StackStringStream& operator=(const StackStringStream& o) = delete;
StackStringStream(StackStringStream&& o) = delete;
StackStringStream& operator=(StackStringStream&& o) = delete;
~StackStringStream() override = default;
void reset() {
clear(); /* reset state flags */
flags(default_fmtflags); /* reset fmtflags to constructor defaults */
ssb.clear();
}
std::string_view strv() const {
return ssb.strv();
}
private:
StackStringBuf<SIZE> ssb;
fmtflags const default_fmtflags;
};
/* In an ideal world, we could use StackStringStream indiscriminately, but alas
* it's very expensive to construct/destruct. So, we cache them in a
* thread_local vector. DO NOT share these with other threads. The copy/move
* constructors are deliberately restrictive to make this more difficult to
* accidentally do.
*/
class CachedStackStringStream {
public:
using sss = StackStringStream<4096>;
using osptr = std::unique_ptr<sss>;
CachedStackStringStream() {
if (cache.destructed || cache.c.empty()) {
osp = std::make_unique<sss>();
} else {
osp = std::move(cache.c.back());
cache.c.pop_back();
osp->reset();
}
}
CachedStackStringStream(const CachedStackStringStream&) = delete;
CachedStackStringStream& operator=(const CachedStackStringStream&) = delete;
CachedStackStringStream(CachedStackStringStream&&) = delete;
CachedStackStringStream& operator=(CachedStackStringStream&&) = delete;
~CachedStackStringStream() {
if (!cache.destructed && cache.c.size() < max_elems) {
cache.c.emplace_back(std::move(osp));
}
}
sss& operator*() {
return *osp;
}
sss const& operator*() const {
return *osp;
}
sss* operator->() {
return osp.get();
}
sss const* operator->() const {
return osp.get();
}
sss const* get() const {
return osp.get();
}
sss* get() {
return osp.get();
}
private:
static constexpr std::size_t max_elems = 8;
/* The thread_local cache may be destructed before other static structures.
* If those destructors try to create a CachedStackStringStream (e.g. for
* logging) and access this cache, that access will be undefined. So note if
* the cache has been destructed and check before use.
*/
struct Cache {
using container = std::vector<osptr>;
Cache() {}
~Cache() { destructed = true; }
container c;
bool destructed = false;
};
inline static thread_local Cache cache;
osptr osp;
};
#endif
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