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1 // Copyright (c) 2010 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2010 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 #ifndef BASE_THREAD_RESTRICTIONS_H_ | 5 #ifndef BASE_THREAD_RESTRICTIONS_H_ |
6 #define BASE_THREAD_RESTRICTIONS_H_ | 6 #define BASE_THREAD_RESTRICTIONS_H_ |
7 | 7 |
8 #include "base/basictypes.h" | |
9 | |
10 namespace base { | 8 namespace base { |
11 | 9 |
12 // ThreadRestrictions helps protect threads that should not block from | 10 // ThreadRestrictions helps protect threads that should not block from |
13 // making blocking calls. It works like this: | 11 // making blocking calls. It works like this: |
14 // | 12 // |
15 // 1) If a thread should not be allowed to make IO calls, mark it: | 13 // 1) If a thread should not be allowed to make IO calls, mark it: |
16 // base::ThreadRestrictions::SetIOAllowed(false); | 14 // base::ThreadRestrictions::SetIOAllowed(false); |
17 // By default, threads *are* allowed to make IO calls. | 15 // By default, threads *are* allowed to make IO calls. |
18 // In Chrome browser code, IO calls should be proxied to the File thread. | 16 // In Chrome browser code, IO calls should be proxied to the File thread. |
19 // | 17 // |
20 // 2) If a function makes a call that will go out to disk, check whether the | 18 // 2) If a function makes a call that will go out to disk, check whether the |
21 // current thread is allowed: | 19 // current thread is allowed: |
22 // base::ThreadRestrictions::AssertIOAllowed(); | 20 // base::ThreadRestrictions::AssertIOAllowed(); |
23 // | 21 // |
24 // ThreadRestrictions does nothing in release builds; it is debug-only. | 22 // ThreadRestrictions does nothing in release builds; it is debug-only. |
25 // | 23 // |
26 // Style tip: where should you put AssertIOAllowed checks? It's best | |
27 // if you put them as close to the disk access as possible, at the | |
28 // lowest level. This rule is simple to follow and helps catch all | |
29 // callers. For example, if your function GoDoSomeBlockingDiskCall() | |
30 // only calls other functions in Chrome and not fopen(), you should go | |
31 // add the AssertIOAllowed checks in the helper functions. | |
32 | |
33 class ThreadRestrictions { | 24 class ThreadRestrictions { |
34 public: | 25 public: |
35 // Constructing a ScopedAllowIO temporarily allows IO for the current | |
36 // thread. Doing this is almost certainly always incorrect. This object | |
37 // is available to temporarily work around bugs. | |
38 class ScopedAllowIO { | |
39 public: | |
40 ScopedAllowIO() { previous_value_ = SetIOAllowed(true); } | |
41 ~ScopedAllowIO() { SetIOAllowed(previous_value_); } | |
42 private: | |
43 // Whether IO is allowed when the ScopedAllowIO was constructed. | |
44 bool previous_value_; | |
45 | |
46 DISALLOW_COPY_AND_ASSIGN(ScopedAllowIO); | |
47 }; | |
48 | 26 |
49 #ifndef NDEBUG | 27 #ifndef NDEBUG |
50 // Set whether the current thread to make IO calls. | 28 // Set whether the current thread to make IO calls. |
51 // Threads start out in the *allowed* state. | 29 // Threads start out in the *allowed* state. |
52 // Returns the previous value. | 30 static void SetIOAllowed(bool allowed); |
53 static bool SetIOAllowed(bool allowed); | |
54 | 31 |
55 // Check whether the current thread is allowed to make IO calls, | 32 // Check whether the current thread is allowed to make IO calls, |
56 // and DCHECK if not. See the block comment above the class for | 33 // and DCHECK if not. |
57 // a discussion of where to add these checks. | |
58 static void AssertIOAllowed(); | 34 static void AssertIOAllowed(); |
59 #else | 35 #else |
60 // In Release builds, inline the empty definitions of these functions so | 36 // In Release builds, inline the empty definitions of these functions so |
61 // that they can be compiled out. | 37 // that they can be compiled out. |
62 static bool SetIOAllowed(bool allowed) { return true; } | 38 static void SetIOAllowed(bool allowed) {} |
63 static void AssertIOAllowed() {} | 39 static void AssertIOAllowed() {} |
64 #endif | 40 #endif |
65 | 41 |
66 private: | 42 private: |
67 ThreadRestrictions(); // class for namespacing only | 43 ThreadRestrictions(); // class for namespacing only |
68 }; | 44 }; |
69 | 45 |
70 } // namespace base | 46 } // namespace base |
71 | 47 |
72 #endif // BASE_THREAD_RESTRICTIONS_H_ | 48 #endif // BASE_THREAD_RESTRICTIONS_H_ |
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