1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
|
/* Copyright (C) 2011-2014 Free Software Foundation, Inc.
Contributed by Torvald Riegel <triegel@redhat.com>.
This file is part of the GNU Transactional Memory Library (libitm).
Libitm is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
Libitm is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for
more details.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<http://www.gnu.org/licenses/>. */
#ifndef GTM_RWLOCK_H
#define GTM_RWLOCK_H
#include "local_atomic"
#include "common.h"
namespace GTM HIDDEN {
struct gtm_thread;
// This datastructure is the blocking, futex-based version of the Dekker-style
// reader-writer lock used to provide mutual exclusion between active and
// serial transactions.
// See libitm's documentation for further details.
//
// In this implementation, writers are given highest priority access but
// read-to-write upgrades do not have a higher priority than writers.
//
// Do not change the layout of this class; it must remain a POD type with
// standard layout, and the WRITERS field must be first (i.e., so the
// assembler code can assume that its address is equal to the address of the
// respective instance of the class).
class gtm_rwlock
{
// TODO Put futexes on different cachelines?
std::atomic<int> writers; // Writers' futex.
std::atomic<int> writer_readers;// A confirmed writer waits here for readers.
std::atomic<int> readers; // Readers wait here for writers (iff true).
public:
gtm_rwlock() : writers(0), writer_readers(0), readers(0) {};
void read_lock (gtm_thread *tx);
void read_unlock (gtm_thread *tx);
void write_lock ();
void write_unlock ();
bool write_upgrade (gtm_thread *tx);
void write_upgrade_finish (gtm_thread *tx);
// Returns true iff there is a concurrent active or waiting writer.
// This is primarily useful for simple HyTM approaches, and the value being
// checked is loaded with memory_order_relaxed.
bool is_write_locked()
{
return writers.load (memory_order_relaxed) != 0;
}
protected:
bool write_lock_generic (gtm_thread *tx);
};
} // namespace GTM
#endif // GTM_RWLOCK_H
|
