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
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
|
// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef Y_ABSL_SYNCHRONIZATION_INTERNAL_KERNEL_TIMEOUT_H_
#define Y_ABSL_SYNCHRONIZATION_INTERNAL_KERNEL_TIMEOUT_H_
#ifndef _WIN32
#include <sys/types.h>
#endif
#include <algorithm>
#include <chrono> // NOLINT(build/c++11)
#include <cstdint>
#include <ctime>
#include <limits>
#include "y_absl/base/config.h"
#include "y_absl/base/internal/raw_logging.h"
#include "y_absl/time/clock.h"
#include "y_absl/time/time.h"
namespace y_absl {
Y_ABSL_NAMESPACE_BEGIN
namespace synchronization_internal {
// An optional timeout, with nanosecond granularity.
//
// This is a private low-level API for use by a handful of low-level
// components. Higher-level components should build APIs based on
// y_absl::Time and y_absl::Duration.
class KernelTimeout {
public:
// Construct an absolute timeout that should expire at `t`.
explicit KernelTimeout(y_absl::Time t);
// Construct a relative timeout that should expire after `d`.
explicit KernelTimeout(y_absl::Duration d);
// Infinite timeout.
constexpr KernelTimeout() : rep_(kNoTimeout) {}
// A more explicit factory for those who prefer it.
// Equivalent to `KernelTimeout()`.
static constexpr KernelTimeout Never() { return KernelTimeout(); }
// Returns true if there is a timeout that will eventually expire.
// Returns false if the timeout is infinite.
bool has_timeout() const { return rep_ != kNoTimeout; }
// If `has_timeout()` is true, returns true if the timeout was provided as an
// `y_absl::Time`. The return value is undefined if `has_timeout()` is false
// because all indefinite timeouts are equivalent.
bool is_absolute_timeout() const { return (rep_ & 1) == 0; }
// If `has_timeout()` is true, returns true if the timeout was provided as an
// `y_absl::Duration`. The return value is undefined if `has_timeout()` is false
// because all indefinite timeouts are equivalent.
bool is_relative_timeout() const { return (rep_ & 1) == 1; }
// Convert to `struct timespec` for interfaces that expect an absolute
// timeout. If !has_timeout() or is_relative_timeout(), attempts to convert to
// a reasonable absolute timeout, but callers should to test has_timeout() and
// is_relative_timeout() and prefer to use a more appropriate interface.
struct timespec MakeAbsTimespec() const;
// Convert to `struct timespec` for interfaces that expect a relative
// timeout. If !has_timeout() or is_absolute_timeout(), attempts to convert to
// a reasonable relative timeout, but callers should to test has_timeout() and
// is_absolute_timeout() and prefer to use a more appropriate interface. Since
// the return value is a relative duration, it should be recomputed by calling
// this method in the case of a spurious wakeup.
struct timespec MakeRelativeTimespec() const;
#ifndef _WIN32
// Convert to `struct timespec` for interfaces that expect an absolute timeout
// on a specific clock `c`. This is similar to `MakeAbsTimespec()`, but
// callers usually want to use this method with `CLOCK_MONOTONIC` when
// relative timeouts are requested, and when the appropriate interface expects
// an absolute timeout relative to a specific clock (for example,
// pthread_cond_clockwait() or sem_clockwait()). If !has_timeout(), attempts
// to convert to a reasonable absolute timeout, but callers should to test
// has_timeout() prefer to use a more appropriate interface.
struct timespec MakeClockAbsoluteTimespec(clockid_t c) const;
#endif
// Convert to unix epoch nanos for interfaces that expect an absolute timeout
// in nanoseconds. If !has_timeout() or is_relative_timeout(), attempts to
// convert to a reasonable absolute timeout, but callers should to test
// has_timeout() and is_relative_timeout() and prefer to use a more
// appropriate interface.
int64_t MakeAbsNanos() const;
// Converts to milliseconds from now, or INFINITE when
// !has_timeout(). For use by SleepConditionVariableSRW on
// Windows. Callers should recognize that the return value is a
// relative duration (it should be recomputed by calling this method
// in the case of a spurious wakeup).
// This header file may be included transitively by public header files,
// so we define our own DWORD and INFINITE instead of getting them from
// <intsafe.h> and <WinBase.h>.
typedef unsigned long DWord; // NOLINT
DWord InMillisecondsFromNow() const;
// Convert to std::chrono::time_point for interfaces that expect an absolute
// timeout, like std::condition_variable::wait_until(). If !has_timeout() or
// is_relative_timeout(), attempts to convert to a reasonable absolute
// timeout, but callers should test has_timeout() and is_relative_timeout()
// and prefer to use a more appropriate interface.
std::chrono::time_point<std::chrono::system_clock> ToChronoTimePoint() const;
// Convert to std::chrono::time_point for interfaces that expect a relative
// timeout, like std::condition_variable::wait_for(). If !has_timeout() or
// is_absolute_timeout(), attempts to convert to a reasonable relative
// timeout, but callers should test has_timeout() and is_absolute_timeout()
// and prefer to use a more appropriate interface. Since the return value is a
// relative duration, it should be recomputed by calling this method in the
// case of a spurious wakeup.
std::chrono::nanoseconds ToChronoDuration() const;
// Returns true if steady (aka monotonic) clocks are supported by the system.
// This method exists because go/btm requires synchronized clocks, and
// thus requires we use the system (aka walltime) clock.
static constexpr bool SupportsSteadyClock() { return true; }
private:
// Returns the current time, expressed as a count of nanoseconds since the
// epoch used by an arbitrary clock. The implementation tries to use a steady
// (monotonic) clock if one is available.
static int64_t SteadyClockNow();
// Internal representation.
// - If the value is kNoTimeout, then the timeout is infinite, and
// has_timeout() will return true.
// - If the low bit is 0, then the high 63 bits is the number of nanoseconds
// after the unix epoch.
// - If the low bit is 1, then the high 63 bits is the number of nanoseconds
// after the epoch used by SteadyClockNow().
//
// In all cases the time is stored as an absolute time, the only difference is
// the clock epoch. The use of absolute times is important since in the case
// of a relative timeout with a spurious wakeup, the program would have to
// restart the wait, and thus needs a way of recomputing the remaining time.
uint64_t rep_;
// Returns the number of nanoseconds stored in the internal representation.
// When combined with the clock epoch indicated by the low bit (which is
// accessed through is_absolute_timeout() and is_relative_timeout()), the
// return value is used to compute when the timeout should occur.
int64_t RawAbsNanos() const { return static_cast<int64_t>(rep_ >> 1); }
// Converts to nanoseconds from now. Since the return value is a relative
// duration, it should be recomputed by calling this method in the case of a
// spurious wakeup.
int64_t InNanosecondsFromNow() const;
// A value that represents no timeout (or an infinite timeout).
static constexpr uint64_t kNoTimeout = (std::numeric_limits<uint64_t>::max)();
// The maximum value that can be stored in the high 63 bits.
static constexpr int64_t kMaxNanos = (std::numeric_limits<int64_t>::max)();
};
} // namespace synchronization_internal
Y_ABSL_NAMESPACE_END
} // namespace y_absl
#endif // Y_ABSL_SYNCHRONIZATION_INTERNAL_KERNEL_TIMEOUT_H_
|
