/Users/deen/code/yugabyte-db/src/yb/util/thread_restrictions.h
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1 | | // Licensed to the Apache Software Foundation (ASF) under one |
2 | | // or more contributor license agreements. See the NOTICE file |
3 | | // distributed with this work for additional information |
4 | | // regarding copyright ownership. The ASF licenses this file |
5 | | // to you under the Apache License, Version 2.0 (the |
6 | | // "License"); you may not use this file except in compliance |
7 | | // with the License. You may obtain a copy of the License at |
8 | | // |
9 | | // http://www.apache.org/licenses/LICENSE-2.0 |
10 | | // |
11 | | // Unless required by applicable law or agreed to in writing, |
12 | | // software distributed under the License is distributed on an |
13 | | // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
14 | | // KIND, either express or implied. See the License for the |
15 | | // specific language governing permissions and limitations |
16 | | // under the License. |
17 | | // |
18 | | // The following only applies to changes made to this file as part of YugaByte development. |
19 | | // |
20 | | // Portions Copyright (c) YugaByte, Inc. |
21 | | // |
22 | | // Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except |
23 | | // in compliance with the License. You may obtain a copy of the License at |
24 | | // |
25 | | // http://www.apache.org/licenses/LICENSE-2.0 |
26 | | // |
27 | | // Unless required by applicable law or agreed to in writing, software distributed under the License |
28 | | // is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express |
29 | | // or implied. See the License for the specific language governing permissions and limitations |
30 | | // under the License. |
31 | | // |
32 | | // Some portions: Copyright (c) 2012, The Chromium Authors. |
33 | | #ifndef YB_UTIL_THREAD_RESTRICTIONS_H |
34 | | #define YB_UTIL_THREAD_RESTRICTIONS_H |
35 | | |
36 | | #include "yb/gutil/macros.h" |
37 | | |
38 | | #ifndef NDEBUG |
39 | | #define ENABLE_THREAD_RESTRICTIONS 1 |
40 | | #endif |
41 | | |
42 | | namespace yb { |
43 | | |
44 | | // Certain behavior is disallowed on certain threads. ThreadRestrictions helps |
45 | | // enforce these rules. Examples of such rules: |
46 | | // |
47 | | // * Do not do blocking IO |
48 | | // * Do not wait on synchronization variables or sleep |
49 | | // |
50 | | // Here's more about how the protection works: |
51 | | // |
52 | | // 1) If a thread should not be allowed to make IO calls, mark it: |
53 | | // ThreadRestrictions::SetIOAllowed(false); |
54 | | // By default, threads *are* allowed to make IO calls. |
55 | | // In particular, threads like RPC reactors should never do blocking IO |
56 | | // because it may stall other unrelated requests. |
57 | | // |
58 | | // 2) If a function makes a call that will go out to disk, check whether the |
59 | | // current thread is allowed: |
60 | | // ThreadRestrictions::AssertIOAllowed(); |
61 | | // |
62 | | // |
63 | | // Style tip: where should you put AssertIOAllowed checks? It's best |
64 | | // if you put them as close to the disk access as possible, at the |
65 | | // lowest level. This rule is simple to follow and helps catch all |
66 | | // callers. For example, if your function GoDoSomeBlockingDiskCall() |
67 | | // only calls other functions in YB and doesn't access the underlying |
68 | | // disk, you should go add the AssertIOAllowed checks in the helper functions. |
69 | | class ThreadRestrictions { |
70 | | public: |
71 | | // Constructing a ScopedAllowIO temporarily allows IO for the current |
72 | | // thread. Doing this is almost certainly always incorrect, but sometimes |
73 | | // it makes more sense to allow an exception and file a bug in the backlog |
74 | | // to improve it later. |
75 | | class ScopedAllowIO { |
76 | | public: |
77 | 1 | ScopedAllowIO() { previous_value_ = SetIOAllowed(true); } |
78 | 1 | ~ScopedAllowIO() { SetIOAllowed(previous_value_); } |
79 | | private: |
80 | | // Whether IO is allowed when the ScopedAllowIO was constructed. |
81 | | bool previous_value_; |
82 | | |
83 | | DISALLOW_COPY_AND_ASSIGN(ScopedAllowIO); |
84 | | }; |
85 | | |
86 | | // Constructing a ScopedAllowWait temporarily allows waiting on the current |
87 | | // thread. Doing this is almost always incorrect: consider carefully whether |
88 | | // you should instead be deferring work to a different thread. |
89 | | class ScopedAllowWait { |
90 | | public: |
91 | 4.16k | ScopedAllowWait() { previous_value_ = SetWaitAllowed(true); } |
92 | 4.18k | ~ScopedAllowWait() { SetWaitAllowed(previous_value_); } |
93 | | private: |
94 | | // Whether singleton use is allowed when the ScopedAllowWait was |
95 | | // constructed. |
96 | | bool previous_value_; |
97 | | |
98 | | DISALLOW_COPY_AND_ASSIGN(ScopedAllowWait); |
99 | | }; |
100 | | |
101 | | |
102 | | #if ENABLE_THREAD_RESTRICTIONS |
103 | | // Set whether the current thread to make IO calls. |
104 | | // Threads start out in the *allowed* state. |
105 | | // Returns the previous value. |
106 | | static bool SetIOAllowed(bool allowed); |
107 | | |
108 | | // Check whether the current thread is allowed to make IO calls, |
109 | | // and FATALs if not. See the block comment above the class for |
110 | | // a discussion of where to add these checks. |
111 | | static void AssertIOAllowed(); |
112 | | |
113 | | // Set whether the current thread may wait/block. Returns the previous |
114 | | // value. |
115 | | static bool SetWaitAllowed(bool allowed); |
116 | | |
117 | | static bool IsWaitAllowed(); |
118 | | |
119 | | // Check whether the current thread is allowed to wait/block. |
120 | | // FATALs if not. |
121 | | static void AssertWaitAllowed(); |
122 | | #else |
123 | | // Inline the empty definitions of these functions so that they can be |
124 | | // compiled out. |
125 | | static bool SetIOAllowed(bool allowed) { return true; } |
126 | | static void AssertIOAllowed() {} |
127 | | static bool SetWaitAllowed(bool allowed) { return true; } |
128 | | static void AssertWaitAllowed() {} |
129 | | static bool IsWaitAllowed() { return true; } |
130 | | #endif |
131 | | |
132 | | private: |
133 | | DISALLOW_IMPLICIT_CONSTRUCTORS(ThreadRestrictions); |
134 | | }; |
135 | | |
136 | | } // namespace yb |
137 | | |
138 | | #endif /* YB_UTIL_THREAD_RESTRICTIONS_H */ |