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1 | // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- |
2 | // vim: ts=8 sw=2 smarttab | |
3 | /* | |
4 | * Ceph - scalable distributed file system | |
5 | * | |
6 | * Copyright (C) 2018 Red Hat, Inc. | |
7 | * | |
8 | * This is free software; you can redistribute it and/or | |
9 | * modify it under the terms of the GNU Lesser General Public | |
10 | * License version 2.1, as published by the Free Software | |
11 | * Foundation. See file COPYING. | |
12 | * | |
13 | */ | |
14 | ||
15 | #ifndef COMMON_STACKSTRINGSTREAM_H | |
16 | #define COMMON_STACKSTRINGSTREAM_H | |
17 | ||
18 | #include <boost/container/small_vector.hpp> | |
19 | ||
20 | #include <algorithm> | |
21 | #include <iostream> | |
22 | #include <memory> | |
23 | #include <ostream> | |
24 | #include <sstream> | |
25 | #include <string_view> | |
26 | #include <vector> | |
27 | ||
28 | #include "include/inline_memory.h" | |
29 | ||
30 | template<std::size_t SIZE> | |
31 | class StackStringBuf : public std::basic_streambuf<char> | |
32 | { | |
33 | public: | |
34 | StackStringBuf() | |
35 | : vec{SIZE, boost::container::default_init_t{}} | |
36 | { | |
37 | setp(vec.data(), vec.data() + vec.size()); | |
38 | } | |
39 | StackStringBuf(const StackStringBuf&) = delete; | |
40 | StackStringBuf& operator=(const StackStringBuf&) = delete; | |
41 | StackStringBuf(StackStringBuf&& o) = delete; | |
42 | StackStringBuf& operator=(StackStringBuf&& o) = delete; | |
43 | ~StackStringBuf() override = default; | |
44 | ||
45 | void clear() | |
46 | { | |
47 | vec.resize(SIZE); | |
48 | setp(vec.data(), vec.data() + SIZE); | |
49 | } | |
50 | ||
51 | std::string_view strv() const | |
52 | { | |
53 | return std::string_view(pbase(), pptr() - pbase()); | |
54 | } | |
55 | ||
56 | protected: | |
20effc67 | 57 | std::streamsize xsputn(const char *s, std::streamsize n) final |
11fdf7f2 TL |
58 | { |
59 | std::streamsize capacity = epptr() - pptr(); | |
60 | std::streamsize left = n; | |
61 | if (capacity >= left) { | |
62 | maybe_inline_memcpy(pptr(), s, left, 32); | |
63 | pbump(left); | |
64 | } else { | |
65 | maybe_inline_memcpy(pptr(), s, capacity, 64); | |
66 | s += capacity; | |
67 | left -= capacity; | |
68 | vec.insert(vec.end(), s, s + left); | |
69 | setp(vec.data(), vec.data() + vec.size()); | |
70 | pbump(vec.size()); | |
71 | } | |
72 | return n; | |
73 | } | |
74 | ||
20effc67 | 75 | int overflow(int c) final |
11fdf7f2 TL |
76 | { |
77 | if (traits_type::not_eof(c)) { | |
78 | char str = traits_type::to_char_type(c); | |
79 | vec.push_back(str); | |
80 | return c; | |
81 | } else { | |
82 | return traits_type::eof(); | |
83 | } | |
84 | } | |
85 | ||
86 | private: | |
87 | ||
88 | boost::container::small_vector<char, SIZE> vec; | |
89 | }; | |
90 | ||
91 | template<std::size_t SIZE> | |
92 | class StackStringStream : public std::basic_ostream<char> | |
93 | { | |
94 | public: | |
95 | StackStringStream() : basic_ostream<char>(&ssb), default_fmtflags(flags()) {} | |
96 | StackStringStream(const StackStringStream& o) = delete; | |
97 | StackStringStream& operator=(const StackStringStream& o) = delete; | |
98 | StackStringStream(StackStringStream&& o) = delete; | |
99 | StackStringStream& operator=(StackStringStream&& o) = delete; | |
100 | ~StackStringStream() override = default; | |
101 | ||
102 | void reset() { | |
103 | clear(); /* reset state flags */ | |
104 | flags(default_fmtflags); /* reset fmtflags to constructor defaults */ | |
105 | ssb.clear(); | |
106 | } | |
107 | ||
108 | std::string_view strv() const { | |
109 | return ssb.strv(); | |
110 | } | |
f67539c2 TL |
111 | std::string str() const { |
112 | return std::string(ssb.strv()); | |
113 | } | |
11fdf7f2 TL |
114 | |
115 | private: | |
116 | StackStringBuf<SIZE> ssb; | |
117 | fmtflags const default_fmtflags; | |
118 | }; | |
119 | ||
120 | /* In an ideal world, we could use StackStringStream indiscriminately, but alas | |
121 | * it's very expensive to construct/destruct. So, we cache them in a | |
122 | * thread_local vector. DO NOT share these with other threads. The copy/move | |
123 | * constructors are deliberately restrictive to make this more difficult to | |
124 | * accidentally do. | |
125 | */ | |
126 | class CachedStackStringStream { | |
127 | public: | |
128 | using sss = StackStringStream<4096>; | |
129 | using osptr = std::unique_ptr<sss>; | |
130 | ||
131 | CachedStackStringStream() { | |
132 | if (cache.destructed || cache.c.empty()) { | |
133 | osp = std::make_unique<sss>(); | |
134 | } else { | |
135 | osp = std::move(cache.c.back()); | |
136 | cache.c.pop_back(); | |
137 | osp->reset(); | |
138 | } | |
139 | } | |
140 | CachedStackStringStream(const CachedStackStringStream&) = delete; | |
141 | CachedStackStringStream& operator=(const CachedStackStringStream&) = delete; | |
142 | CachedStackStringStream(CachedStackStringStream&&) = delete; | |
143 | CachedStackStringStream& operator=(CachedStackStringStream&&) = delete; | |
144 | ~CachedStackStringStream() { | |
145 | if (!cache.destructed && cache.c.size() < max_elems) { | |
146 | cache.c.emplace_back(std::move(osp)); | |
147 | } | |
148 | } | |
149 | ||
150 | sss& operator*() { | |
151 | return *osp; | |
152 | } | |
153 | sss const& operator*() const { | |
154 | return *osp; | |
155 | } | |
156 | sss* operator->() { | |
157 | return osp.get(); | |
158 | } | |
159 | sss const* operator->() const { | |
160 | return osp.get(); | |
161 | } | |
162 | ||
163 | sss const* get() const { | |
164 | return osp.get(); | |
165 | } | |
166 | sss* get() { | |
167 | return osp.get(); | |
168 | } | |
169 | ||
170 | private: | |
171 | static constexpr std::size_t max_elems = 8; | |
172 | ||
173 | /* The thread_local cache may be destructed before other static structures. | |
174 | * If those destructors try to create a CachedStackStringStream (e.g. for | |
175 | * logging) and access this cache, that access will be undefined. So note if | |
176 | * the cache has been destructed and check before use. | |
177 | */ | |
178 | struct Cache { | |
179 | using container = std::vector<osptr>; | |
180 | ||
181 | Cache() {} | |
182 | ~Cache() { destructed = true; } | |
183 | ||
184 | container c; | |
185 | bool destructed = false; | |
186 | }; | |
187 | ||
188 | inline static thread_local Cache cache; | |
189 | osptr osp; | |
190 | }; | |
191 | ||
192 | #endif |