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
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
|
<?xml version="1.0" encoding="GB2312" standalone="no"?>
<!--
The FreeBSD Documentation Project
The FreeBSD SMP Next Generation Project
The FreeBSD Simplified Chinese Project
Original Revision: 1.11
$FreeBSD$
-->
<chapter id="locking">
<chapterinfo>
<authorgroup>
<author>
&author.cn.intron;
<contrib>&cnproj.translated.by;</contrib>
</author>
</authorgroup>
</chapterinfo>
<title>内核中的锁</title>
<indexterm><primary>SMP Next Generation Project(下一代对称多处理工程)</primary></indexterm>
<para><emphasis>这一章由 FreeBSD SMP Next Generation Project 维护。
请将评论和建议发送给&a.smp;.</emphasis></para>
<indexterm><primary>locking(锁)</primary></indexterm>
<indexterm><primary>multi-processing(多处理)</primary></indexterm>
<indexterm><primary>mutexes(同时/独占, mutual exclusion)</primary></indexterm>
<indexterm><primary>lockmgr(锁管理器)</primary></indexterm>
<indexterm><primary>atomic operations(原子操作)</primary></indexterm>
<para>这篇文档提纲挈领的讲述了在FreeBSD内核中的锁，这些锁使得有效的多处理成为可能。
锁可以用几种方式获得。数据结构可以用mutex或&man.lockmgr.9;保护。
对于为数不多的若干个变量，假如总是使用原子操作访问它们，这些变量就可以得到保护。
<tip><title>译者注</title><para>仅读本章内容，还不足以找出<quote>mutex</quote>
和<quote>共享互斥锁</quote>的区别。似乎它们的功能有重叠之处，
前者比后者的功能选项更多。它们似乎都是&man.lockmgr.9;的子集。</para></tip></para>
<sect1 id="locking-mutexes">
<title>Mutex</title>
<para>Mutex就是一种用来解决共享/排它矛盾的锁。
一个mutex在一个时刻只可以被一个实体拥有。如果另一个实体要获得已经被拥有的mutex，
就会进入等待，直到这个mutex被释放。在FreeBSD内核中，mutex被进程所拥有。</para>
<para>Mutex可以被递归的索要，但是mutex一般只被一个实体拥有较短的一段时间，
因此一个实体不能在持有mutex时睡眠。如果你需要在持有mutex时睡眠，
可使用一个 &man.lockmgr.9; 的锁。</para>
<para>每个mutex有几个令人感兴趣的属性:</para>
<variablelist>
<varlistentry>
<term>变量名</term>
<listitem>
<para>在内核源代码中<type>struct mtx</type>变量的名字</para>
</listitem>
</varlistentry>
<varlistentry>
<term>逻辑名</term>
<listitem>
<para>由函数<function>mtx_init</function>指派的mutex的名字。
这个名字显示在KTR跟踪消息和witness出错与警告信息里。
这个名字还用于区分标识在witness代码中的各个mutex</para>
</listitem>
</varlistentry>
<varlistentry>
<term>类型</term>
<listitem>
<para>Mutex的类型，用标志<constant>MTX_*</constant>表示。
每个标志的意义在&man.mutex.9;有所描述。</para>
<variablelist>
<varlistentry>
<term><constant>MTX_DEF</constant></term>
<listitem>
<para>一个睡眠mutex</para>
</listitem>
</varlistentry>
<varlistentry>
<term><constant>MTX_SPIN</constant></term>
<listitem>
<para>一个循环mutex</para>
</listitem>
</varlistentry>
<varlistentry>
<term><constant>MTX_RECURSE</constant></term>
<listitem>
<para>这个mutex允许递归</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term>保护对象</term>
<listitem>
<para>这个入口所要保护的数据结构列表或数据结构成员列表。
对于数据结构成员，将按照
<structname>结构名</structname>.<structfield>成员名</structfield>的形式命名。</para>
</listitem>
</varlistentry>
<varlistentry>
<term>依赖函数</term>
<listitem>
<para>仅当mutex被持有时才可以被调用的函数</para>
</listitem>
</varlistentry>
</variablelist>
<table frame="all" colsep="1" rowsep="1" pgwide="1">
<title>Mutex列表</title>
<indexterm><primary>locks(锁)</primary>
<secondary>sched_lock(调度器锁)</secondary></indexterm>
<indexterm><primary>locks(锁)</primary>
<secondary>vm86pcb_lock(虚拟8086模式进程控制块锁)</secondary></indexterm>
<indexterm><primary>locks(锁)</primary>
<secondary>Giant(巨锁)</secondary></indexterm>
<indexterm><primary>locks(锁)</primary>
<secondary>callout_lock(延时调用锁)</secondary></indexterm>
<tgroup cols="5">
<thead>
<row>
<entry>变量名</entry>
<entry>逻辑名</entry>
<entry>类型</entry>
<entry>保护对象</entry>
<entry>依赖函数</entry>
</row>
</thead>
<!-- The scheduler lock -->
<tbody>
<row>
<entry>sched_lock</entry>
<entry><quote>sched lock</quote>(调度器锁)</entry>
<entry>
<constant>MTX_SPIN</constant> |
<constant>MTX_RECURSE</constant>
</entry>
<entry>
<varname>_gmonparam</varname>,
<varname>cnt.v_swtch</varname>,
<varname>cp_time</varname>,
<varname>curpriority</varname>,
<structname>mtx</structname>.<structfield>mtx_blocked</structfield>,
<structname>mtx</structname>.<structfield>mtx_contested</structfield>,
<structname>proc</structname>.<structfield>p_procq</structfield>,
<structname>proc</structname>.<structfield>p_slpq</structfield>,
<structname>proc</structname>.<structfield>p_sflag</structfield>,
<structname>proc</structname>.<structfield>p_stat</structfield>,
<structname>proc</structname>.<structfield>p_estcpu</structfield>,
<structname>proc</structname>.<structfield>p_cpticks</structfield>
<structname>proc</structname>.<structfield>p_pctcpu</structfield>,
<structname>proc</structname>.<structfield>p_wchan</structfield>,
<structname>proc</structname>.<structfield>p_wmesg</structfield>,
<structname>proc</structname>.<structfield>p_swtime</structfield>,
<structname>proc</structname>.<structfield>p_slptime</structfield>,
<structname>proc</structname>.<structfield>p_runtime</structfield>,
<structname>proc</structname>.<structfield>p_uu</structfield>,
<structname>proc</structname>.<structfield>p_su</structfield>,
<structname>proc</structname>.<structfield>p_iu</structfield>,
<structname>proc</structname>.<structfield>p_uticks</structfield>,
<structname>proc</structname>.<structfield>p_sticks</structfield>,
<structname>proc</structname>.<structfield>p_iticks</structfield>,
<structname>proc</structname>.<structfield>p_oncpu</structfield>,
<structname>proc</structname>.<structfield>p_lastcpu</structfield>,
<structname>proc</structname>.<structfield>p_rqindex</structfield>,
<structname>proc</structname>.<structfield>p_heldmtx</structfield>,
<structname>proc</structname>.<structfield>p_blocked</structfield>,
<structname>proc</structname>.<structfield>p_mtxname</structfield>,
<structname>proc</structname>.<structfield>p_contested</structfield>,
<structname>proc</structname>.<structfield>p_priority</structfield>,
<structname>proc</structname>.<structfield>p_usrpri</structfield>,
<structname>proc</structname>.<structfield>p_nativepri</structfield>,
<structname>proc</structname>.<structfield>p_nice</structfield>,
<structname>proc</structname>.<structfield>p_rtprio</structfield>,
<varname>pscnt</varname>,
<varname>slpque</varname>,
<varname>itqueuebits</varname>,
<varname>itqueues</varname>,
<varname>rtqueuebits</varname>,
<varname>rtqueues</varname>,
<varname>queuebits</varname>,
<varname>queues</varname>,
<varname>idqueuebits</varname>,
<varname>idqueues</varname>,
<varname>switchtime</varname>,
<varname>switchticks</varname>
</entry>
<entry>
<function>setrunqueue</function>,
<function>remrunqueue</function>,
<function>mi_switch</function>,
<function>chooseproc</function>,
<function>schedclock</function>,
<function>resetpriority</function>,
<function>updatepri</function>,
<function>maybe_resched</function>,
<function>cpu_switch</function>,
<function>cpu_throw</function>,
<function>need_resched</function>,
<function>resched_wanted</function>,
<function>clear_resched</function>,
<function>aston</function>,
<function>astoff</function>,
<function>astpending</function>,
<function>calcru</function>,
<function>proc_compare</function>
</entry>
</row>
<!-- The vm86 pcb lock -->
<row>
<entry>vm86pcb_lock</entry>
<entry><quote>vm86pcb lock</quote>(虚拟8086模式进程控制块锁)</entry>
<entry>
<constant>MTX_DEF</constant>
</entry>
<entry>
<varname>vm86pcb</varname>
</entry>
<entry>
<function>vm86_bioscall</function>
</entry>
</row>
<!-- Giant -->
<row>
<entry>Giant</entry>
<entry><quote>Giant</quote>(巨锁)</entry>
<entry>
<constant>MTX_DEF</constant> |
<constant>MTX_RECURSE</constant>
</entry>
<entry>几乎可以是任何东西</entry>
<entry>许多</entry>
</row>
<!-- The callout lock -->
<row>
<entry>callout_lock</entry>
<entry><quote>callout lock</quote>(延时调用锁)</entry>
<entry>
<constant>MTX_SPIN</constant> |
<constant>MTX_RECURSE</constant>
</entry>
<entry>
<varname>callfree</varname>,
<varname>callwheel</varname>,
<varname>nextsoftcheck</varname>,
<structname>proc</structname>.<structfield>p_itcallout</structfield>,
<structname>proc</structname>.<structfield>p_slpcallout</structfield>,
<varname>softticks</varname>,
<varname>ticks</varname>
</entry>
<entry>
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="locking-sx">
<title>共享互斥锁</title>
<para>这些锁提供基本的读/写类型的功能，可以被一个正在睡眠的进程持有。
现在它们被统一到&man.lockmgr.9;之中。</para>
<indexterm><primary>locks(锁)</primary>
<secondary>shared exclusive(共享互斥)</secondary></indexterm>
<table>
<title>共享互斥锁列表</title>
<indexterm><primary>locks(锁)</primary>
<secondary>allproc_lock(全进程锁)</secondary></indexterm>
<indexterm><primary>locks(锁)</primary>
<secondary>proctree_lock(进程树锁)</secondary></indexterm>
<tgroup cols="2">
<thead>
<row>
<entry>变量名</entry>
<entry>保护对象</entry>
</row>
</thead>
<tbody>
<row>
<entry><varname>allproc_lock</varname></entry>
<entry>
<varname>allproc</varname>
<varname>zombproc</varname>
<varname>pidhashtbl</varname>
<structname>proc</structname>.<structfield>p_list</structfield>
<structname>proc</structname>.<structfield>p_hash</structfield>
<varname>nextpid</varname>
</entry>
</row>
<row>
<entry><varname>proctree_lock</varname></entry>
<entry>
<structname>proc</structname>.<structfield>p_children</structfield>
<structname>proc</structname>.<structfield>p_sibling</structfield>
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="locking-atomic">
<title>原子保护变量</title>
<indexterm><primary>atomically protected variables(原子保护变量)</primary></indexterm>
<para>原子保护变量并非由一个显在的锁保护的特殊变量，而是：
对这些变量的所有数据访问都要使用特殊的原子操作(&man.atomic.9;)。
尽管其它的基本同步机制(例如mutex)就是用原子保护变量实现的，
但是很少有变量直接使用这种处理方式。</para>
<itemizedlist>
<listitem>
<para><structname>mtx</structname>.<structfield>mtx_lock</structfield></para>
</listitem>
</itemizedlist>
</sect1>
</chapter>
|
