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Side by Side Diff: base/thread_restrictions.h

Issue 5242002: Reland 66791 (change was innocent)... (Closed) Base URL: svn://svn.chromium.org/chrome/trunk/src/
Patch Set: Created 10 years, 1 month ago
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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" 8 #include "base/basictypes.h"
9 9
10 namespace base { 10 namespace base {
11 11
12 // ThreadRestrictions helps protect threads that should not block from 12 // Certain behavior is disallowed on certain threads. ThreadRestrictions helps
13 // making blocking calls. It works like this: 13 // enforce these rules. Examples of such rules:
14 //
15 // * Do not do blocking IO (makes the thread janky)
16 // * Do not access Singleton/LazyInstance (may lead to shutdown crashes)
17 //
18 // Here's more about how the protection works:
14 // 19 //
15 // 1) If a thread should not be allowed to make IO calls, mark it: 20 // 1) If a thread should not be allowed to make IO calls, mark it:
16 // base::ThreadRestrictions::SetIOAllowed(false); 21 // base::ThreadRestrictions::SetIOAllowed(false);
17 // By default, threads *are* allowed to make IO calls. 22 // By default, threads *are* allowed to make IO calls.
18 // In Chrome browser code, IO calls should be proxied to the File thread. 23 // In Chrome browser code, IO calls should be proxied to the File thread.
19 // 24 //
20 // 2) If a function makes a call that will go out to disk, check whether the 25 // 2) If a function makes a call that will go out to disk, check whether the
21 // current thread is allowed: 26 // current thread is allowed:
22 // base::ThreadRestrictions::AssertIOAllowed(); 27 // base::ThreadRestrictions::AssertIOAllowed();
23 // 28 //
(...skipping 14 matching lines...) Expand all
38 public: 43 public:
39 ScopedAllowIO() { previous_value_ = SetIOAllowed(true); } 44 ScopedAllowIO() { previous_value_ = SetIOAllowed(true); }
40 ~ScopedAllowIO() { SetIOAllowed(previous_value_); } 45 ~ScopedAllowIO() { SetIOAllowed(previous_value_); }
41 private: 46 private:
42 // Whether IO is allowed when the ScopedAllowIO was constructed. 47 // Whether IO is allowed when the ScopedAllowIO was constructed.
43 bool previous_value_; 48 bool previous_value_;
44 49
45 DISALLOW_COPY_AND_ASSIGN(ScopedAllowIO); 50 DISALLOW_COPY_AND_ASSIGN(ScopedAllowIO);
46 }; 51 };
47 52
53 // Constructing a ScopedAllowSingleton temporarily allows accessing for the
54 // current thread. Doing this is almost always incorrect.
55 class ScopedAllowSingleton {
56 public:
57 ScopedAllowSingleton() { previous_value_ = SetSingletonAllowed(true); }
58 ~ScopedAllowSingleton() { SetSingletonAllowed(previous_value_); }
59 private:
60 // Whether singleton use is allowed when the ScopedAllowSingleton was
61 // constructed.
62 bool previous_value_;
63
64 DISALLOW_COPY_AND_ASSIGN(ScopedAllowSingleton);
65 };
66
48 #ifndef NDEBUG 67 #ifndef NDEBUG
49 // Set whether the current thread to make IO calls. 68 // Set whether the current thread to make IO calls.
50 // Threads start out in the *allowed* state. 69 // Threads start out in the *allowed* state.
51 // Returns the previous value. 70 // Returns the previous value.
52 static bool SetIOAllowed(bool allowed); 71 static bool SetIOAllowed(bool allowed);
53 72
54 // Check whether the current thread is allowed to make IO calls, 73 // Check whether the current thread is allowed to make IO calls,
55 // and DCHECK if not. See the block comment above the class for 74 // and DCHECK if not. See the block comment above the class for
56 // a discussion of where to add these checks. 75 // a discussion of where to add these checks.
57 static void AssertIOAllowed(); 76 static void AssertIOAllowed();
77
78 // Set whether the current thread can use singletons. Returns the previous
79 // value.
80 static bool SetSingletonAllowed(bool allowed);
81
82 // Check whether the current thread is allowed to use singletons (Singleton /
83 // LazyInstance). DCHECKs if not.
84 static void AssertSingletonAllowed();
58 #else 85 #else
59 // In Release builds, inline the empty definitions of these functions so 86 // In Release builds, inline the empty definitions of these functions so
60 // that they can be compiled out. 87 // that they can be compiled out.
61 static bool SetIOAllowed(bool allowed) { return true; } 88 static bool SetIOAllowed(bool allowed) { return true; }
62 static void AssertIOAllowed() {} 89 static void AssertIOAllowed() {}
90 static bool SetSingletonAllowed(bool allowed) { return true; }
91 static void AssertSingletonAllowed() {}
63 #endif 92 #endif
64 93
65 private: 94 private:
66 ThreadRestrictions(); // class for namespacing only 95 DISALLOW_IMPLICIT_CONSTRUCTORS(ThreadRestrictions);
67 }; 96 };
68 97
69 } // namespace base 98 } // namespace base
70 99
71 #endif // BASE_THREAD_RESTRICTIONS_H_ 100 #endif // BASE_THREAD_RESTRICTIONS_H_
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