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f1717362 | 1 | /* Copyright (C) 2011-2016 Free Software Foundation, Inc. |
4c0315d0 | 2 | Contributed by Torvald Riegel <triegel@redhat.com>. |
3 | ||
4 | This file is part of the GNU Transactional Memory Library (libitm). | |
5 | ||
6 | Libitm is free software; you can redistribute it and/or modify it | |
7 | under the terms of the GNU General Public License as published by | |
8 | the Free Software Foundation; either version 3 of the License, or | |
9 | (at your option) any later version. | |
10 | ||
11 | Libitm is distributed in the hope that it will be useful, but WITHOUT ANY | |
12 | WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS | |
13 | FOR A PARTICULAR PURPOSE. See the GNU General Public License for | |
14 | more details. | |
15 | ||
16 | Under Section 7 of GPL version 3, you are granted additional | |
17 | permissions described in the GCC Runtime Library Exception, version | |
18 | 3.1, as published by the Free Software Foundation. | |
19 | ||
20 | You should have received a copy of the GNU General Public License and | |
21 | a copy of the GCC Runtime Library Exception along with this program; | |
22 | see the files COPYING3 and COPYING.RUNTIME respectively. If not, see | |
23 | <http://www.gnu.org/licenses/>. */ | |
24 | ||
25 | #ifndef GTM_RWLOCK_H | |
26 | #define GTM_RWLOCK_H | |
27 | ||
813b3075 | 28 | #include "local_atomic" |
4c0315d0 | 29 | #include "common.h" |
30 | ||
31 | namespace GTM HIDDEN { | |
32 | ||
33 | struct gtm_thread; | |
34 | ||
35 | // This datastructure is the blocking, futex-based version of the Dekker-style | |
36 | // reader-writer lock used to provide mutual exclusion between active and | |
37 | // serial transactions. | |
38 | // See libitm's documentation for further details. | |
39 | // | |
40 | // In this implementation, writers are given highest priority access but | |
41 | // read-to-write upgrades do not have a higher priority than writers. | |
f20d0394 | 42 | // |
43 | // Do not change the layout of this class; it must remain a POD type with | |
44 | // standard layout, and the WRITERS field must be first (i.e., so the | |
45 | // assembler code can assume that its address is equal to the address of the | |
46 | // respective instance of the class). | |
4c0315d0 | 47 | |
48 | class gtm_rwlock | |
49 | { | |
50 | // TODO Put futexes on different cachelines? | |
813b3075 | 51 | std::atomic<int> writers; // Writers' futex. |
52 | std::atomic<int> writer_readers;// A confirmed writer waits here for readers. | |
53 | std::atomic<int> readers; // Readers wait here for writers (iff true). | |
4c0315d0 | 54 | |
55 | public: | |
56 | gtm_rwlock() : writers(0), writer_readers(0), readers(0) {}; | |
57 | ||
58 | void read_lock (gtm_thread *tx); | |
59 | void read_unlock (gtm_thread *tx); | |
60 | ||
61 | void write_lock (); | |
62 | void write_unlock (); | |
63 | ||
64 | bool write_upgrade (gtm_thread *tx); | |
c4c0a912 | 65 | void write_upgrade_finish (gtm_thread *tx); |
4c0315d0 | 66 | |
5b35a791 | 67 | // Returns true iff there is a concurrent active or waiting writer. |
68 | // This is primarily useful for simple HyTM approaches, and the value being | |
69 | // checked is loaded with memory_order_relaxed. | |
70 | bool is_write_locked() | |
71 | { | |
72 | return writers.load (memory_order_relaxed) != 0; | |
73 | } | |
74 | ||
4c0315d0 | 75 | protected: |
76 | bool write_lock_generic (gtm_thread *tx); | |
77 | }; | |
78 | ||
79 | } // namespace GTM | |
80 | ||
81 | #endif // GTM_RWLOCK_H |