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1 | /* | |
2 | * Copyright (C) 1996-2020 The Squid Software Foundation and contributors | |
3 | * | |
4 | * Squid software is distributed under GPLv2+ license and includes | |
5 | * contributions from numerous individuals and organizations. | |
6 | * Please see the COPYING and CONTRIBUTORS files for details. | |
7 | */ | |
8 | ||
9 | /* DEBUG: section 54 Interprocess Communication */ | |
10 | ||
11 | #include "squid.h" | |
12 | #include "ipc/ReadWriteLock.h" | |
13 | #include "Store.h" | |
14 | ||
15 | void Ipc::AssertFlagIsSet(std::atomic_flag &flag) | |
16 | { | |
17 | // If the flag was false, then we set it to true and assert. A true flag | |
18 | // may help keep other processes away from this broken entry. | |
19 | // Otherwise, we just set an already set flag, which is probably a no-op. | |
20 | assert(flag.test_and_set(std::memory_order_relaxed)); | |
21 | } | |
22 | ||
23 | bool | |
24 | Ipc::ReadWriteLock::lockShared() | |
25 | { | |
26 | ++readLevel; // this locks "new" writers out | |
27 | if (!writeLevel || appending) { // nobody is writing, or sharing is OK | |
28 | ++readers; | |
29 | return true; | |
30 | } | |
31 | --readLevel; | |
32 | return false; | |
33 | } | |
34 | ||
35 | bool | |
36 | Ipc::ReadWriteLock::lockExclusive() | |
37 | { | |
38 | if (!writeLevel++) { // we are the first writer + lock "new" readers out | |
39 | if (!readLevel) { // no old readers and nobody is becoming one | |
40 | writing = true; | |
41 | return true; | |
42 | } | |
43 | } | |
44 | --writeLevel; | |
45 | return false; | |
46 | } | |
47 | ||
48 | bool | |
49 | Ipc::ReadWriteLock::lockHeaders() | |
50 | { | |
51 | if (lockShared()) { | |
52 | if (!updating.test_and_set(std::memory_order_acquire)) | |
53 | return true; // we got here first | |
54 | // the updating lock was already set by somebody else | |
55 | unlockShared(); | |
56 | } | |
57 | return false; | |
58 | } | |
59 | ||
60 | void | |
61 | Ipc::ReadWriteLock::unlockShared() | |
62 | { | |
63 | assert(readers > 0); | |
64 | --readers; | |
65 | --readLevel; | |
66 | } | |
67 | ||
68 | void | |
69 | Ipc::ReadWriteLock::unlockExclusive() | |
70 | { | |
71 | assert(writing); | |
72 | appending = false; | |
73 | writing = false; | |
74 | --writeLevel; | |
75 | } | |
76 | ||
77 | void | |
78 | Ipc::ReadWriteLock::unlockHeaders() | |
79 | { | |
80 | AssertFlagIsSet(updating); | |
81 | updating.clear(std::memory_order_release); | |
82 | unlockShared(); | |
83 | } | |
84 | ||
85 | void | |
86 | Ipc::ReadWriteLock::switchExclusiveToShared() | |
87 | { | |
88 | assert(writing); | |
89 | ++readLevel; // must be done before we release exclusive control | |
90 | ++readers; | |
91 | unlockExclusive(); | |
92 | } | |
93 | ||
94 | void | |
95 | Ipc::ReadWriteLock::startAppending() | |
96 | { | |
97 | assert(writing); | |
98 | appending = true; | |
99 | } | |
100 | ||
101 | void | |
102 | Ipc::ReadWriteLock::updateStats(ReadWriteLockStats &stats) const | |
103 | { | |
104 | if (readers) { | |
105 | ++stats.readable; | |
106 | stats.readers += readers; | |
107 | } else if (writing) { | |
108 | ++stats.writeable; | |
109 | ++stats.writers; | |
110 | stats.appenders += appending; | |
111 | } else { | |
112 | ++stats.idle; | |
113 | } | |
114 | ++stats.count; | |
115 | } | |
116 | ||
117 | /* Ipc::ReadWriteLockStats */ | |
118 | ||
119 | Ipc::ReadWriteLockStats::ReadWriteLockStats() | |
120 | { | |
121 | memset(this, 0, sizeof(*this)); | |
122 | } | |
123 | ||
124 | void | |
125 | Ipc::ReadWriteLockStats::dump(StoreEntry &e) const | |
126 | { | |
127 | storeAppendPrintf(&e, "Available locks: %9d\n", count); | |
128 | ||
129 | if (!count) | |
130 | return; | |
131 | ||
132 | storeAppendPrintf(&e, "Reading: %9d %6.2f%%\n", | |
133 | readable, (100.0 * readable / count)); | |
134 | storeAppendPrintf(&e, "Writing: %9d %6.2f%%\n", | |
135 | writeable, (100.0 * writeable / count)); | |
136 | storeAppendPrintf(&e, "Idle: %9d %6.2f%%\n", | |
137 | idle, (100.0 * idle / count)); | |
138 | ||
139 | if (readers || writers) { | |
140 | const int locked = readers + writers; | |
141 | storeAppendPrintf(&e, "Readers: %9d %6.2f%%\n", | |
142 | readers, (100.0 * readers / locked)); | |
143 | const double appPerc = writers ? (100.0 * appenders / writers) : 0.0; | |
144 | storeAppendPrintf(&e, "Writers: %9d %6.2f%% including Appenders: %9d %6.2f%%\n", | |
145 | writers, (100.0 * writers / locked), | |
146 | appenders, appPerc); | |
147 | } | |
148 | } | |
149 |