1/*****************************************************************************
2
3Copyright (c) 2013, 2021, Oracle and/or its affiliates.
4
5Portions of this file contain modifications contributed and copyrighted by
6Google, Inc. Those modifications are gratefully acknowledged and are described
7briefly in the InnoDB documentation. The contributions by Google are
8incorporated with their permission, and subject to the conditions contained in
9the file COPYING.Google.
10
11This program is free software; you can redistribute it and/or modify
12it under the terms of the GNU General Public License, version 2.0,
13as published by the Free Software Foundation.
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15This program is also distributed with certain software (including
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17as designated in a particular file or component or in included license
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20separately licensed software that they have included with MySQL.
21
22This program is distributed in the hope that it will be useful,
23but WITHOUT ANY WARRANTY; without even the implied warranty of
24MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
25GNU General Public License, version 2.0, for more details.
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27You should have received a copy of the GNU General Public License along with
28this program; if not, write to the Free Software Foundation, Inc.,
2951 Franklin Street, Suite 500, Boston, MA 02110-1335 USA
30
31*****************************************************************************/
32
33/**************************************************//**
34@file include/ut0mutex.ic
35Mutex implementation include file
36
37Created 2012/08/21 Sunny Bains
38*******************************************************/
39
40#include "sync0arr.h"
41#include "sync0debug.h"
42
43/**
44Wait in the sync array.
45@return true if the mutex acquisition was successful. */
46
47template <template <typename> class Policy>
48bool
49TTASEventMutex<Policy>::wait(
50	const char*	filename,
51	uint32_t	line,
52	uint32_t	spin)
53	UNIV_NOTHROW
54{
55	sync_cell_t*	cell;
56	sync_array_t*	sync_arr;
57
58	sync_arr = sync_array_get_and_reserve_cell(
59		this,
60		(m_policy.get_id() == LATCH_ID_BUF_BLOCK_MUTEX
61		 || m_policy.get_id() == LATCH_ID_BUF_POOL_ZIP)
62		? SYNC_BUF_BLOCK
63		: SYNC_MUTEX,
64		filename, line, &cell);
65
66	/* The memory order of the array reservation and
67	the change in the waiters field is important: when
68	we suspend a thread, we first reserve the cell and
69	then set waiters field to 1. When threads are released
70	in mutex_exit, the waiters field is first set to zero
71	and then the event is set to the signaled state. */
72
73	set_waiters();
74
75	/* Try to reserve still a few times. */
76
77	for (uint32_t i = 0; i < spin; ++i) {
78
79		if (try_lock()) {
80
81			sync_array_free_cell(sync_arr, cell);
82
83			/* Note that in this case we leave
84			the waiters field set to 1. We cannot
85			reset it to zero, as we do not know if
86			there are other waiters. */
87
88			return(true);
89		}
90	}
91
92	/* Now we know that there has been some thread
93	holding the mutex after the change in the wait
94	array and the waiters field was made.  Now there
95	is no risk of infinite wait on the event. */
96
97	sync_array_wait_event(sync_arr, cell);
98
99	return(false);
100}
101
102
103/** Wakeup any waiting thread(s). */
104
105template <template <typename> class Policy>
106void
107TTASEventMutex<Policy>::signal() UNIV_NOTHROW
108{
109	clear_waiters();
110
111	/* The memory order of resetting the waiters field and
112	signaling the object is important. See LEMMA 1 above. */
113	os_event_set(m_event);
114
115	sync_array_object_signalled();
116}
117