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1 // Copyright 2016 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 #ifndef BASE_TASK_SCHEDULER_TASK_TRAITS_H_ | |
6 #define BASE_TASK_SCHEDULER_TASK_TRAITS_H_ | |
7 | |
8 #include "base/base_export.h" | |
9 #include "build/build_config.h" | |
10 | |
11 namespace base { | |
12 | |
13 using TaskPriorityUnderlyingType = char; | |
14 | |
15 enum class TaskPriority : TaskPriorityUnderlyingType { | |
16 // This task affects UI immediately after a user interaction. | |
17 // Example: Generating data shown in the UI immediately after a click. | |
18 USER_BLOCKING = 2, | |
19 // This task affects UI or responsiveness of future user interactions. It is | |
20 // not an immediate response to a user interaction. | |
21 // Examples: | |
22 // - Updating the UI to reflect that a long task was completed. | |
23 // - Loading data that might be shown in the UI after a future user | |
24 // interaction. | |
25 USER_VISIBLE = 1, | |
26 // Everything else (user won't notice if this takes an arbitrarily long time | |
27 // to complete). | |
28 BACKGROUND = 0, | |
29 }; | |
30 | |
31 const TaskPriorityUnderlyingType kNumTaskPriorities = 3; | |
32 | |
33 enum class TaskShutdownBehavior { | |
34 // Tasks posted with this mode which have not started executing before | |
35 // shutdown is initiated will never run. Tasks with this mode running at | |
36 // shutdown will be ignored (the worker thread will not be joined). | |
37 // | |
38 // This option provides a nice way to post stuff you don't want blocking | |
39 // shutdown. For example, you might be doing a slow DNS lookup and if it's | |
40 // blocked on the OS, you may not want to stop shutdown, since the result | |
41 // doesn't really matter at that point. | |
42 // | |
43 // However, you need to be very careful what you do in your callback when you | |
44 // use this option. Since the thread will continue to run until the OS | |
45 // terminates the process, the app can be in the process of tearing down when | |
46 // you're running. This means any singletons or global objects you use may | |
47 // suddenly become invalid out from under you. For this reason, it's best to | |
48 // use this only for slow but simple operations like the DNS example. | |
49 CONTINUE_ON_SHUTDOWN, | |
50 | |
51 // Tasks posted with this mode that have not started executing at | |
52 // shutdown will never run. However, any task that has already begun | |
53 // executing when shutdown is invoked will be allowed to continue and | |
54 // will block shutdown until completion. | |
55 // | |
56 // Note: Because TaskScheduler::Shutdown() may block while these tasks are | |
57 // executing, care must be taken to ensure that they do not block on the | |
58 // thread that called TaskScheduler::Shutdown(), as this may lead to deadlock. | |
59 SKIP_ON_SHUTDOWN, | |
60 | |
61 // Tasks posted with this mode before shutdown is complete will block shutdown | |
62 // until they're executed. Generally, this should be used only to save | |
63 // critical user data. | |
64 // | |
65 // Note: Tasks with BACKGROUND priority that block shutdown will be promoted | |
66 // to USER_VISIBLE priority during shutdown. | |
67 BLOCK_SHUTDOWN, | |
68 }; | |
69 | |
70 // TaskTraits holds metadata about a task and prevents the combinatorial | |
71 // explosion of PostTaskWith*() call sites. | |
72 // Usage example: | |
73 // PostTaskWithTraits( | |
74 // FROM_HERE, TaskTraits().WithFileIO().WithPriority(USER_VISIBLE), | |
75 // Bind(...)); | |
76 struct BASE_EXPORT TaskTraits { | |
77 // Constructs a default TaskTraits for tasks with | |
78 // (1) no I/O, | |
79 // (2) low priority, and | |
80 // (3) may block shutdown or be skipped on shutdown. | |
81 // Tasks that require stricter guarantees should highlight those by requesting | |
82 // explicit traits below. | |
83 TaskTraits(); | |
84 ~TaskTraits(); | |
85 | |
86 // Allows tasks with these traits to do file I/O. | |
87 TaskTraits& WithFileIO(); | |
88 | |
89 // Applies a priority to tasks with these traits. | |
90 TaskTraits& WithPriority(TaskPriority priority); | |
91 | |
92 // Applies a shutdown behavior to tasks with these traits. | |
93 TaskTraits& WithShutdownBehavior(TaskShutdownBehavior behavior); | |
94 | |
95 // Returns true if file I/O is allowed by these traits. | |
96 bool with_file_io() const { return with_file_io_; } | |
97 | |
98 // Returns the priority of tasks with these traits. | |
99 TaskPriority priority() const { return priority_; } | |
100 | |
101 // Returns the shutdown behavior of tasks with these traits. | |
102 TaskShutdownBehavior shutdown_behavior() const { return shutdown_behavior_; } | |
103 | |
104 private: | |
105 bool with_file_io_; | |
106 TaskPriority priority_; | |
107 TaskShutdownBehavior shutdown_behavior_; | |
108 }; | |
109 | |
110 enum class ExecutionMode { | |
fdoray
2016/02/11 17:30:33
Add a comment explaining that this is used to crea
fdoray
2016/02/12 04:16:20
Done.
| |
111 // Can execute multiple tasks at a time. High priority tasks will execute | |
112 // first under contention. | |
113 PARALLEL, | |
114 | |
115 // Executes one task at a time. Tasks are guaranteed to run in posting order. | |
116 // The sequence’s priority will be that of its pending task with the highest | |
117 // priority. | |
118 SEQUENCED, | |
119 | |
120 // Executes one task at a time on a single thread. Tasks are guaranteed to run | |
121 // in posting order. | |
122 SINGLE_THREADED, | |
123 | |
124 #if defined(OS_WIN) | |
125 // Executes one task at a time on a single thread that has initialized the COM | |
126 // library with the single-threaded apartment (STA) concurrency model. Tasks | |
127 // are guaranteed to run in posting order and the assigned thread will also | |
128 // process COM messages so long as the associated TaskRunner is kept alive. | |
129 SINGLE_THREADED_COM_STA, | |
130 #endif // defined(OS_WIN) | |
131 }; | |
132 | |
133 } // namespace base | |
134 | |
135 #endif // BASE_TASK_SCHEDULER_TASK_TRAITS_H_ | |
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