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
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
|
/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
* QemuLockCnt implementation
*
* Copyright Red Hat, Inc. 2017
*
* Author:
* Paolo Bonzini <pbonzini@redhat.com>
*
*/
#ifndef QEMU_LOCKCNT_H
#define QEMU_LOCKCNT_H
#include "qemu/thread.h"
typedef struct QemuLockCnt QemuLockCnt;
struct QemuLockCnt {
#ifndef CONFIG_LINUX
QemuMutex mutex;
#endif
unsigned count;
};
/**
* qemu_lockcnt_init: initialize a QemuLockcnt
* @lockcnt: the lockcnt to initialize
*
* Initialize lockcnt's counter to zero and prepare its mutex
* for usage.
*/
void qemu_lockcnt_init(QemuLockCnt *lockcnt);
/**
* qemu_lockcnt_destroy: destroy a QemuLockcnt
* @lockcnt: the lockcnt to destruct
*
* Destroy lockcnt's mutex.
*/
void qemu_lockcnt_destroy(QemuLockCnt *lockcnt);
/**
* qemu_lockcnt_inc: increment a QemuLockCnt's counter
* @lockcnt: the lockcnt to operate on
*
* If the lockcnt's count is zero, wait for critical sections
* to finish and increment lockcnt's count to 1. If the count
* is not zero, just increment it.
*
* Because this function can wait on the mutex, it must not be
* called while the lockcnt's mutex is held by the current thread.
* For the same reason, qemu_lockcnt_inc can also contribute to
* AB-BA deadlocks. This is a sample deadlock scenario::
*
* thread 1 thread 2
* -------------------------------------------------------
* qemu_lockcnt_lock(&lc1);
* qemu_lockcnt_lock(&lc2);
* qemu_lockcnt_inc(&lc2);
* qemu_lockcnt_inc(&lc1);
*/
void qemu_lockcnt_inc(QemuLockCnt *lockcnt);
/**
* qemu_lockcnt_dec: decrement a QemuLockCnt's counter
* @lockcnt: the lockcnt to operate on
*/
void qemu_lockcnt_dec(QemuLockCnt *lockcnt);
/**
* qemu_lockcnt_dec_and_lock: decrement a QemuLockCnt's counter and
* possibly lock it.
* @lockcnt: the lockcnt to operate on
*
* Decrement lockcnt's count. If the new count is zero, lock
* the mutex and return true. Otherwise, return false.
*/
bool qemu_lockcnt_dec_and_lock(QemuLockCnt *lockcnt);
/**
* qemu_lockcnt_dec_if_lock: possibly decrement a QemuLockCnt's counter and
* lock it.
* @lockcnt: the lockcnt to operate on
*
* If the count is 1, decrement the count to zero, lock
* the mutex and return true. Otherwise, return false.
*/
bool qemu_lockcnt_dec_if_lock(QemuLockCnt *lockcnt);
/**
* qemu_lockcnt_lock: lock a QemuLockCnt's mutex.
* @lockcnt: the lockcnt to operate on
*
* Remember that concurrent visits are not blocked unless the count is
* also zero. You can use qemu_lockcnt_count to check for this inside a
* critical section.
*/
void qemu_lockcnt_lock(QemuLockCnt *lockcnt);
/**
* qemu_lockcnt_unlock: release a QemuLockCnt's mutex.
* @lockcnt: the lockcnt to operate on.
*/
void qemu_lockcnt_unlock(QemuLockCnt *lockcnt);
/**
* qemu_lockcnt_inc_and_unlock: combined unlock/increment on a QemuLockCnt.
* @lockcnt: the lockcnt to operate on.
*
* This is the same as
*
* qemu_lockcnt_unlock(lockcnt);
* qemu_lockcnt_inc(lockcnt);
*
* but more efficient.
*/
void qemu_lockcnt_inc_and_unlock(QemuLockCnt *lockcnt);
/**
* qemu_lockcnt_count: query a LockCnt's count.
* @lockcnt: the lockcnt to query.
*
* Note that the count can change at any time. Still, while the
* lockcnt is locked, one can usefully check whether the count
* is non-zero.
*/
unsigned qemu_lockcnt_count(QemuLockCnt *lockcnt);
#endif
|
