low_level_scheduling.h
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1 // Copyright 2017 The Abseil Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 //
15 // Core interfaces and definitions used by by low-level interfaces such as
16 // SpinLock.
17 
18 #ifndef ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
19 #define ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
20 
22 #include "absl/base/macros.h"
23 
24 // The following two declarations exist so SchedulingGuard may friend them with
25 // the appropriate language linkage. These callbacks allow libc internals, such
26 // as function level statics, to schedule cooperatively when locking.
27 extern "C" bool __google_disable_rescheduling(void);
28 extern "C" void __google_enable_rescheduling(bool disable_result);
29 
30 namespace absl {
31 namespace base_internal {
32 
33 class SchedulingHelper; // To allow use of SchedulingGuard.
34 class SpinLock; // To allow use of SchedulingGuard.
35 
36 // SchedulingGuard
37 // Provides guard semantics that may be used to disable cooperative rescheduling
38 // of the calling thread within specific program blocks. This is used to
39 // protect resources (e.g. low-level SpinLocks or Domain code) that cooperative
40 // scheduling depends on.
41 //
42 // Domain implementations capable of rescheduling in reaction to involuntary
43 // kernel thread actions (e.g blocking due to a pagefault or syscall) must
44 // guarantee that an annotated thread is not allowed to (cooperatively)
45 // reschedule until the annotated region is complete.
46 //
47 // It is an error to attempt to use a cooperatively scheduled resource (e.g.
48 // Mutex) within a rescheduling-disabled region.
49 //
50 // All methods are async-signal safe.
52  public:
53  // Returns true iff the calling thread may be cooperatively rescheduled.
54  static bool ReschedulingIsAllowed();
55 
56  private:
57  // Disable cooperative rescheduling of the calling thread. It may still
58  // initiate scheduling operations (e.g. wake-ups), however, it may not itself
59  // reschedule. Nestable. The returned result is opaque, clients should not
60  // attempt to interpret it.
61  // REQUIRES: Result must be passed to a pairing EnableScheduling().
62  static bool DisableRescheduling();
63 
64  // Marks the end of a rescheduling disabled region, previously started by
65  // DisableRescheduling().
66  // REQUIRES: Pairs with innermost call (and result) of DisableRescheduling().
67  static void EnableRescheduling(bool disable_result);
68 
69  // A scoped helper for {Disable, Enable}Rescheduling().
70  // REQUIRES: destructor must run in same thread as constructor.
71  struct ScopedDisable {
74 
75  bool disabled;
76  };
77 
78  // Access to SchedulingGuard is explicitly white-listed.
79  friend class SchedulingHelper;
80  friend class SpinLock;
81 
82  SchedulingGuard(const SchedulingGuard&) = delete;
83  SchedulingGuard& operator=(const SchedulingGuard&) = delete;
84 };
85 
86 //------------------------------------------------------------------------------
87 // End of public interfaces.
88 //------------------------------------------------------------------------------
89 
91  return false;
92 }
93 
95  return false;
96 }
97 
98 inline void SchedulingGuard::EnableRescheduling(bool /* disable_result */) {
99  return;
100 }
101 
102 } // namespace base_internal
103 } // namespace absl
104 
105 #endif // ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
void __google_enable_rescheduling(bool disable_result)
bool __google_disable_rescheduling(void)
Definition: algorithm.h:29
SchedulingGuard & operator=(const SchedulingGuard &)=delete
SchedulingGuard(const SchedulingGuard &)=delete
static void EnableRescheduling(bool disable_result)


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autogenerated on Wed Jun 19 2019 19:19:57