blob: 9b084b3302314bdb36b86719d057f4c57a2ad30e (
plain) (
blame)
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
|
// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef _LIBCPP___THREAD_POLL_WITH_BACKOFF_H
#define _LIBCPP___THREAD_POLL_WITH_BACKOFF_H
#include <__availability>
#include <__config>
#include <chrono>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#endif
_LIBCPP_BEGIN_NAMESPACE_STD
static _LIBCPP_CONSTEXPR const int __libcpp_polling_count = 64;
// Polls a thread for a condition given by a predicate, and backs off based on a backoff policy
// before polling again.
//
// - __f is the "test function" that should return true if polling succeeded, and false if it failed.
//
// - __bf is the "backoff policy", which is called with the duration since we started polling. It should
// return false in order to resume polling, and true if polling should stop entirely for some reason.
// In general, backoff policies sleep for some time before returning control to the polling loop.
//
// - __max_elapsed is the maximum duration to try polling for. If the maximum duration is exceeded,
// the polling loop will return false to report a timeout.
template<class _Fn, class _BFn>
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI
bool __libcpp_thread_poll_with_backoff(_Fn&& __f, _BFn&& __bf, chrono::nanoseconds __max_elapsed = chrono::nanoseconds::zero()) {
auto const __start = chrono::high_resolution_clock::now();
for (int __count = 0;;) {
if (__f())
return true; // _Fn completion means success
if (__count < __libcpp_polling_count) {
__count += 1;
continue;
}
chrono::nanoseconds const __elapsed = chrono::high_resolution_clock::now() - __start;
if (__max_elapsed != chrono::nanoseconds::zero() && __max_elapsed < __elapsed)
return false; // timeout failure
if (__bf(__elapsed))
return false; // _BFn completion means failure
}
}
// A trivial backoff policy that always immediately returns the control to
// the polling loop.
//
// This is not very well-behaved since it will cause the polling loop to spin,
// so this should most likely only be used on single-threaded systems where there
// are no other threads to compete with.
struct __spinning_backoff_policy {
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
bool operator()(chrono::nanoseconds const&) const {
return false;
}
};
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP___THREAD_POLL_WITH_BACKOFF_H
|
