1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
|
// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_THREADING_SCOPED_BLOCKING_CALL_H_
#define BASE_THREADING_SCOPED_BLOCKING_CALL_H_
#include "base/base_export.h"
#include "base/functional/callback_forward.h"
#include "base/location.h"
#include "base/strings/string_piece.h"
#include "base/threading/scoped_blocking_call_internal.h"
#include "base/types/strong_alias.h"
namespace base {
// A "blocking call" refers to any call that causes the calling thread to wait
// off-CPU. It includes but is not limited to calls that wait on synchronous
// file I/O operations: read or write a file from disk, interact with a pipe or
// a socket, rename or delete a file, enumerate files in a directory, etc.
// Acquiring a low contention lock is not considered a blocking call.
// BlockingType indicates the likelihood that a blocking call will actually
// block.
enum class BlockingType {
// The call might block (e.g. file I/O that might hit in memory cache).
MAY_BLOCK,
// The call will definitely block (e.g. cache already checked and now pinging
// server synchronously).
WILL_BLOCK
};
// This class must be instantiated in every scope where a blocking call is made
// and serves as a precise annotation of the scope that may/will block for the
// scheduler. When a ScopedBlockingCall is instantiated, it asserts that
// blocking calls are allowed in its scope with a call to
// base::AssertBlockingAllowed(). CPU usage should be minimal within that scope.
// //base APIs that block instantiate their own ScopedBlockingCall; it is not
// necessary to instantiate another ScopedBlockingCall in the scope where these
// APIs are used. Nested ScopedBlockingCalls are supported (mostly a no-op
// except for WILL_BLOCK nested within MAY_BLOCK which will result in immediate
// WILL_BLOCK semantics).
//
// Good:
// Data data;
// {
// ScopedBlockingCall scoped_blocking_call(
// FROM_HERE, BlockingType::WILL_BLOCK);
// data = GetDataFromNetwork();
// }
// CPUIntensiveProcessing(data);
//
// Bad:
// ScopedBlockingCall scoped_blocking_call(FROM_HERE,
// BlockingType::WILL_BLOCK);
// Data data = GetDataFromNetwork();
// CPUIntensiveProcessing(data); // CPU usage within a ScopedBlockingCall.
//
// Good:
// Data a;
// Data b;
// {
// ScopedBlockingCall scoped_blocking_call(
// FROM_HERE, BlockingType::MAY_BLOCK);
// a = GetDataFromMemoryCacheOrNetwork();
// b = GetDataFromMemoryCacheOrNetwork();
// }
// CPUIntensiveProcessing(a);
// CPUIntensiveProcessing(b);
//
// Bad:
// ScopedBlockingCall scoped_blocking_call(
// FROM_HERE, BlockingType::MAY_BLOCK);
// Data a = GetDataFromMemoryCacheOrNetwork();
// Data b = GetDataFromMemoryCacheOrNetwork();
// CPUIntensiveProcessing(a); // CPU usage within a ScopedBlockingCall.
// CPUIntensiveProcessing(b); // CPU usage within a ScopedBlockingCall.
//
// Good:
// base::WaitableEvent waitable_event(...);
// waitable_event.Wait();
//
// Bad:
// base::WaitableEvent waitable_event(...);
// ScopedBlockingCall scoped_blocking_call(
// FROM_HERE, BlockingType::WILL_BLOCK);
// waitable_event.Wait(); // Wait() instantiates its own ScopedBlockingCall.
//
// When a ScopedBlockingCall is instantiated from a ThreadPool parallel or
// sequenced task, the thread pool size is incremented to compensate for the
// blocked thread (more or less aggressively depending on BlockingType).
class BASE_EXPORT [[nodiscard]] ScopedBlockingCall
: public internal::UncheckedScopedBlockingCall {
public:
ScopedBlockingCall(const Location& from_here, BlockingType blocking_type);
~ScopedBlockingCall();
};
// Usage reserved for //base callers.
namespace internal {
// This class must be instantiated in every scope where a sync primitive is
// used. When a ScopedBlockingCallWithBaseSyncPrimitives is instantiated, it
// asserts that sync primitives are allowed in its scope with a call to
// internal::AssertBaseSyncPrimitivesAllowed(). The same guidelines as for
// ScopedBlockingCall should be followed.
class BASE_EXPORT [[nodiscard]] ScopedBlockingCallWithBaseSyncPrimitives
: public UncheckedScopedBlockingCall {
public:
ScopedBlockingCallWithBaseSyncPrimitives(const Location& from_here,
BlockingType blocking_type);
~ScopedBlockingCallWithBaseSyncPrimitives();
};
} // namespace internal
using IOJankReportingCallback =
RepeatingCallback<void(int janky_intervals_per_minute,
int total_janks_per_minute)>;
using OnlyObservedThreadsForTest =
StrongAlias<class OnlyObservedThreadsTag, bool>;
// Enables IO jank monitoring and reporting for this process. Should be called
// at most once per process and only if
// base::TimeTicks::IsConsistentAcrossProcesses() (the algorithm is unsafe
// otherwise). |reporting_callback| will be invoked each time a monitoring
// window completes, see internal::~IOJankMonitoringWindow() for details
// (must be thread-safe). |only_observed_threads| can be set to true to have
// the IOJank implementation ignore ScopedBlockingCalls on threads without a
// BlockingObserver in tests that need to deterministically observe
// ScopedBlockingCall side-effects.
void BASE_EXPORT EnableIOJankMonitoringForProcess(
IOJankReportingCallback reporting_callback,
OnlyObservedThreadsForTest only_observed_threads =
OnlyObservedThreadsForTest(false));
} // namespace base
#endif // BASE_THREADING_SCOPED_BLOCKING_CALL_H_
|
