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
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
|
/* Copyright (C) 2008 MySQL AB
This program 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; version 2 of the License.
This program 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.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
#ifndef _waiting_threads_h
#define _waiting_threads_h
#include <my_global.h>
#include <my_sys.h>
#include <lf.h>
C_MODE_START
typedef struct st_wt_resource_id WT_RESOURCE_ID;
typedef struct st_wt_resource_type {
int (*compare)(void *a, void *b);
const void *(*make_key)(WT_RESOURCE_ID *id, uint *len);
} WT_RESOURCE_TYPE;
/* we want to compare this struct with memcmp, make it packed */
#pragma pack(push,1)
struct st_wt_resource_id {
ulonglong value;
WT_RESOURCE_TYPE *type;
};
#pragma pack(pop)
#define WT_WAIT_STATS 24
#define WT_CYCLE_STATS 32
extern ulonglong wt_wait_table[WT_WAIT_STATS];
extern uint32 wt_wait_stats[WT_WAIT_STATS+1];
extern uint32 wt_cycle_stats[2][WT_CYCLE_STATS+1];
extern uint32 wt_success_stats;
/*
'lock' protects 'owners', 'state', and 'waiter_count'
'id' is read-only
a resource is picked up from a hash in a lock-free manner
it's returned pinned, so it cannot be freed at once
but it may be freed right after the pin is removed
to free a resource it should be
1. have no owners
2. have no waiters
two ways to access a resource:
1. find it in a hash
- it's returned pinned.
a) take a lock in exclusive mode
b) check the state, it should be ACTIVE
c) unpin
2. by a direct reference
- could only used if a resource cannot be freed
e.g. accessing a resource by thd->waiting_for is safe,
a resource cannot be freed as there's a thread waiting for it
*/
typedef struct st_wt_resource {
WT_RESOURCE_ID id;
uint waiter_count;
enum { ACTIVE, FREE } state;
#ifndef DBUG_OFF
pthread_mutex_t *mutex;
#endif
/*
before the 'lock' all elements are mutable, after (and including) -
immutable in the sense that lf_hash_insert() won't memcpy() over them.
See wt_init().
*/
#ifdef WT_RWLOCKS_USE_MUTEXES
/*
we need a special rwlock-like 'lock' to allow readers bypass
waiting writers, otherwise readers can deadlock.
writer starvation is technically possible, but unlikely, because
the contention is expected to be low.
*/
struct {
pthread_cond_t cond;
pthread_mutex_t mutex;
uint readers: 16;
uint pending_writers: 15;
uint write_locked: 1;
} lock;
#else
rw_lock_t lock;
#endif
pthread_cond_t cond;
DYNAMIC_ARRAY owners;
} WT_RESOURCE;
typedef struct st_wt_thd {
/*
XXX
there's no protection (mutex) against concurrent access of
the dynarray below. it is assumed that a caller will have it
automatically (not to protect this array but to protect its
own - caller's - data structures, and we'll get it for free.
If not, we'll need to add a mutex
*/
DYNAMIC_ARRAY my_resources;
/*
'waiting_for' is modified under waiting_for->lock, and only by thd itself
'waiting_for' is read lock-free (using pinning protocol), but a thd object
can read its own 'waiting_for' without any locks or tricks.
*/
WT_RESOURCE *waiting_for;
LF_PINS *pins;
/* pointers to values */
ulong *timeout_short, *deadlock_search_depth_short;
ulong *timeout_long, *deadlock_search_depth_long;
/*
weight relates to the desirability of a transaction being killed if it's
part of a deadlock. In a deadlock situation transactions with lower weights
are killed first.
Examples of using the weight to implement different selection strategies:
1. Latest
Keep all weights equal.
2. Random
Assight weights at random.
(variant: modify a weight randomly before every lock request)
3. Youngest
Set weight to -NOW()
4. Minimum locks
count locks granted in your lock manager, store the value as a weight
5. Minimum work
depends on the definition of "work". For example, store the number
of rows modifies in this transaction (or a length of REDO log for a
transaction) as a weight.
It is only statistically relevant and is not protected by any locks.
*/
ulong volatile weight;
/*
'killed' is indirectly protected by waiting_for->lock -
a killed thread needs to clear its 'waiting_for', and thus needs a lock.
That is a thread needs an exclusive lock to read 'killed' reliably.
But other threads may change 'killed' from 0 to 1, a shared
lock is enough for that.
*/
my_bool volatile killed;
#ifndef DBUG_OFF
const char *name;
#endif
} WT_THD;
#define WT_TIMEOUT ETIMEDOUT
#define WT_OK 0
#define WT_DEADLOCK -1
#define WT_DEPTH_EXCEEDED -2
void wt_init(void);
void wt_end(void);
void wt_thd_lazy_init(WT_THD *, ulong *, ulong *, ulong *, ulong *);
void wt_thd_destroy(WT_THD *);
int wt_thd_will_wait_for(WT_THD *, WT_THD *, WT_RESOURCE_ID *);
int wt_thd_cond_timedwait(WT_THD *, pthread_mutex_t *);
void wt_thd_release(WT_THD *, WT_RESOURCE_ID *);
#define wt_thd_release_all(THD) wt_thd_release((THD), 0)
int wt_resource_id_memcmp(void *, void *);
C_MODE_END
#endif
|
