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f67539c2 TL |
1 | // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:nil -*- |
2 | // vim: ts=8 sw=2 smarttab | |
3 | ||
4 | #include "tri_mutex.h" | |
5 | ||
6 | seastar::future<> read_lock::lock() | |
7 | { | |
8 | return static_cast<tri_mutex*>(this)->lock_for_read(); | |
9 | } | |
10 | ||
11 | void read_lock::unlock() | |
12 | { | |
13 | static_cast<tri_mutex*>(this)->unlock_for_read(); | |
14 | } | |
15 | ||
16 | seastar::future<> write_lock::lock() | |
17 | { | |
18 | return static_cast<tri_mutex*>(this)->lock_for_write(false); | |
19 | } | |
20 | ||
21 | void write_lock::unlock() | |
22 | { | |
23 | static_cast<tri_mutex*>(this)->unlock_for_write(); | |
24 | } | |
25 | ||
26 | seastar::future<> excl_lock::lock() | |
27 | { | |
28 | return static_cast<tri_mutex*>(this)->lock_for_excl(); | |
29 | } | |
30 | ||
31 | void excl_lock::unlock() | |
32 | { | |
33 | static_cast<tri_mutex*>(this)->unlock_for_excl(); | |
34 | } | |
35 | ||
36 | seastar::future<> excl_lock_from_read::lock() | |
37 | { | |
38 | static_cast<tri_mutex*>(this)->promote_from_read(); | |
39 | return seastar::make_ready_future<>(); | |
40 | } | |
41 | ||
42 | void excl_lock_from_read::unlock() | |
43 | { | |
44 | static_cast<tri_mutex*>(this)->demote_to_read(); | |
45 | } | |
46 | ||
47 | seastar::future<> excl_lock_from_write::lock() | |
48 | { | |
49 | static_cast<tri_mutex*>(this)->promote_from_write(); | |
50 | return seastar::make_ready_future<>(); | |
51 | } | |
52 | ||
53 | void excl_lock_from_write::unlock() | |
54 | { | |
55 | static_cast<tri_mutex*>(this)->demote_to_write(); | |
56 | } | |
57 | ||
58 | seastar::future<> excl_lock_from_excl::lock() | |
59 | { | |
60 | return seastar::make_ready_future<>(); | |
61 | } | |
62 | ||
63 | void excl_lock_from_excl::unlock() | |
64 | { | |
65 | } | |
66 | ||
67 | tri_mutex::~tri_mutex() | |
68 | { | |
69 | assert(!is_acquired()); | |
70 | } | |
71 | ||
72 | seastar::future<> tri_mutex::lock_for_read() | |
73 | { | |
74 | if (try_lock_for_read()) { | |
75 | return seastar::make_ready_future<>(); | |
76 | } | |
77 | waiters.emplace_back(seastar::promise<>(), type_t::read); | |
78 | return waiters.back().pr.get_future(); | |
79 | } | |
80 | ||
81 | bool tri_mutex::try_lock_for_read() noexcept | |
82 | { | |
83 | if (!writers && !exclusively_used && waiters.empty()) { | |
84 | ++readers; | |
85 | return true; | |
86 | } else { | |
87 | return false; | |
88 | } | |
89 | } | |
90 | ||
91 | void tri_mutex::unlock_for_read() | |
92 | { | |
93 | assert(readers > 0); | |
94 | if (--readers == 0) { | |
95 | wake(); | |
96 | } | |
97 | } | |
98 | ||
99 | void tri_mutex::promote_from_read() | |
100 | { | |
101 | assert(readers == 1); | |
102 | --readers; | |
103 | exclusively_used = true; | |
104 | } | |
105 | ||
106 | void tri_mutex::demote_to_read() | |
107 | { | |
108 | assert(exclusively_used); | |
109 | exclusively_used = false; | |
110 | ++readers; | |
111 | } | |
112 | ||
113 | seastar::future<> tri_mutex::lock_for_write(bool greedy) | |
114 | { | |
115 | if (try_lock_for_write(greedy)) { | |
116 | return seastar::make_ready_future<>(); | |
117 | } | |
118 | waiters.emplace_back(seastar::promise<>(), type_t::write); | |
119 | return waiters.back().pr.get_future(); | |
120 | } | |
121 | ||
122 | bool tri_mutex::try_lock_for_write(bool greedy) noexcept | |
123 | { | |
124 | if (!readers && !exclusively_used) { | |
125 | if (greedy || waiters.empty()) { | |
126 | ++writers; | |
127 | return true; | |
128 | } | |
129 | } | |
130 | return false; | |
131 | } | |
132 | ||
133 | void tri_mutex::unlock_for_write() | |
134 | { | |
135 | assert(writers > 0); | |
136 | if (--writers == 0) { | |
137 | wake(); | |
138 | } | |
139 | } | |
140 | ||
141 | void tri_mutex::promote_from_write() | |
142 | { | |
143 | assert(writers == 1); | |
144 | --writers; | |
145 | exclusively_used = true; | |
146 | } | |
147 | ||
148 | void tri_mutex::demote_to_write() | |
149 | { | |
150 | assert(exclusively_used); | |
151 | exclusively_used = false; | |
152 | ++writers; | |
153 | } | |
154 | ||
155 | // for exclusive users | |
156 | seastar::future<> tri_mutex::lock_for_excl() | |
157 | { | |
158 | if (try_lock_for_excl()) { | |
159 | return seastar::make_ready_future<>(); | |
160 | } | |
161 | waiters.emplace_back(seastar::promise<>(), type_t::exclusive); | |
162 | return waiters.back().pr.get_future(); | |
163 | } | |
164 | ||
165 | bool tri_mutex::try_lock_for_excl() noexcept | |
166 | { | |
167 | if (!readers && !writers && !exclusively_used) { | |
168 | exclusively_used = true; | |
169 | return true; | |
170 | } else { | |
171 | return false; | |
172 | } | |
173 | } | |
174 | ||
175 | void tri_mutex::unlock_for_excl() | |
176 | { | |
177 | assert(exclusively_used); | |
178 | exclusively_used = false; | |
179 | wake(); | |
180 | } | |
181 | ||
182 | bool tri_mutex::is_acquired() const | |
183 | { | |
184 | if (readers) { | |
185 | return true; | |
186 | } else if (writers) { | |
187 | return true; | |
188 | } else if (exclusively_used) { | |
189 | return true; | |
190 | } else { | |
191 | return false; | |
192 | } | |
193 | } | |
194 | ||
195 | void tri_mutex::wake() | |
196 | { | |
197 | assert(!readers && !writers && !exclusively_used); | |
198 | type_t type = type_t::none; | |
199 | while (!waiters.empty()) { | |
200 | auto& waiter = waiters.front(); | |
201 | if (type == type_t::exclusive) { | |
202 | break; | |
203 | } if (type == type_t::none) { | |
204 | type = waiter.type; | |
205 | } else if (type != waiter.type) { | |
206 | // to be woken in the next batch | |
207 | break; | |
208 | } | |
209 | switch (type) { | |
210 | case type_t::read: | |
211 | ++readers; | |
212 | break; | |
213 | case type_t::write: | |
214 | ++writers; | |
215 | break; | |
216 | case type_t::exclusive: | |
217 | exclusively_used = true; | |
218 | break; | |
219 | default: | |
220 | assert(0); | |
221 | } | |
222 | waiter.pr.set_value(); | |
223 | waiters.pop_front(); | |
224 | } | |
225 | } |