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
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
|
#pragma once
#include "public.h"
#include "spin_lock_base.h"
#include "spin_lock_count.h"
#include <library/cpp/yt/memory/public.h>
#include <util/system/rwlock.h>
#include <atomic>
namespace NYT::NThreading {
////////////////////////////////////////////////////////////////////////////////
//! Single-writer multiple-readers spin lock.
/*!
* Reader-side acquires are pretty cheap, and readers don't spin unless writers
* are present.
*
* The lock is unfair, but writers are prioritized over readers, that is,
* if AcquireWriter() is called at some time, then some writer
* (not necessarily the same one that called AcquireWriter) will succeed
* in the next time. This is implemented by an additional flag "WriterReady",
* that writers set on arrival. No readers can proceed until this flag is reset.
*
* WARNING: You probably should not use this lock if forks are possible: see
* fork_aware_rw_spin_lock.h for a proper fork-safe lock which does the housekeeping for you.
*
* WARNING: This lock is not recursive: you can't call AcquireReader() twice in the same
* thread, as that may lead to a deadlock. For the same reason you shouldn't do WaitFor or any
* other context switch under lock.
*
* See tla+/spinlock.tla for the formally verified lock's properties.
*/
class TReaderWriterSpinLock
: public TSpinLockBase
{
public:
using TSpinLockBase::TSpinLockBase;
//! Acquires the reader lock.
/*!
* Optimized for the case of read-intensive workloads.
* Cheap (just one atomic increment and no spinning if no writers are present).
*
* WARNING: Don't use this call if forks are possible: forking at some
* intermediate point inside #AcquireReader may corrupt the lock state and
* leave the lock stuck forever for the child process.
*
* WARNING: The lock is not recursive/reentrant, i.e. it assumes that no thread calls
* AcquireReader() if the reader is already acquired for it.
*/
void AcquireReader() noexcept;
//! Acquires the reader lock.
/*!
* A more expensive version of #AcquireReader (includes at least
* one atomic load and CAS; also may spin even if just readers are present).
*
* In contrast to #AcquireReader, this method can be used in the presence of forks.
*
* WARNING: fork-friendliness alone does not provide fork-safety: additional
* actions must be performed to release the lock after a fork. This means you
* probably should NOT use this lock in the presence of forks, consider
* fork_aware_rw_spin_lock.h instead as a proper fork-safe lock.
*/
void AcquireReaderForkFriendly() noexcept;
//! Tries acquiring the reader lock; see #AcquireReader.
//! Returns |true| on success.
bool TryAcquireReader() noexcept;
//! Tries acquiring the reader lock (and does this in a fork-friendly manner); see #AcquireReaderForkFriendly.
//! returns |true| on success.
bool TryAcquireReaderForkFriendly() noexcept;
//! Releases the reader lock.
/*!
* Cheap (just one atomic decrement).
*/
void ReleaseReader() noexcept;
//! Acquires the writer lock.
/*!
* Rather cheap (just one CAS).
*/
void AcquireWriter() noexcept;
//! Tries acquiring the writer lock; see #AcquireWriter.
//! Returns |true| on success.
bool TryAcquireWriter() noexcept;
//! Releases the writer lock.
/*!
* Cheap (just one atomic store).
*/
void ReleaseWriter() noexcept;
//! Returns true if the lock is taken (either by a reader or writer).
/*!
* This is inherently racy.
* Only use for debugging and diagnostic purposes.
*/
bool IsLocked() const noexcept;
//! Returns true if the lock is taken by reader.
/*!
* This is inherently racy.
* Only use for debugging and diagnostic purposes.
*/
bool IsLockedByReader() const noexcept;
//! Returns true if the lock is taken by writer.
/*!
* This is inherently racy.
* Only use for debugging and diagnostic purposes.
*/
bool IsLockedByWriter() const noexcept;
private:
using TValue = ui32;
static constexpr TValue UnlockedValue = 0;
static constexpr TValue WriterMask = 1;
static constexpr TValue WriterReadyMask = 2;
static constexpr TValue ReaderDelta = 4;
std::atomic<TValue> Value_ = UnlockedValue;
bool TryAcquireWriterWithExpectedValue(TValue expected) noexcept;
bool TryAndTryAcquireReader() noexcept;
bool TryAndTryAcquireWriter() noexcept;
void AcquireReaderSlow() noexcept;
void AcquireReaderForkFriendlySlow() noexcept;
void AcquireWriterSlow() noexcept;
};
REGISTER_TRACKED_SPIN_LOCK_CLASS(TReaderWriterSpinLock)
////////////////////////////////////////////////////////////////////////////////
//! A variant of TReaderWriterSpinLock occupying the whole cache line.
class alignas(CacheLineSize) TPaddedReaderWriterSpinLock
: public TReaderWriterSpinLock
{ };
REGISTER_TRACKED_SPIN_LOCK_CLASS(TPaddedReaderWriterSpinLock)
////////////////////////////////////////////////////////////////////////////////
template <class T>
struct TReaderSpinlockTraits
{
static void Acquire(T* spinlock);
static void Release(T* spinlock);
};
template <class T>
struct TForkFriendlyReaderSpinlockTraits
{
static void Acquire(T* spinlock);
static void Release(T* spinlock);
};
template <class T>
struct TWriterSpinlockTraits
{
static void Acquire(T* spinlock);
static void Release(T* spinlock);
};
template <class T>
using TReaderGuard = TGuard<T, TReaderSpinlockTraits<T>>;
template <class T>
using TWriterGuard = TGuard<T, TWriterSpinlockTraits<T>>;
template <class T>
auto ReaderGuard(const T& lock);
template <class T>
auto ReaderGuard(const T* lock);
template <class T>
auto ForkFriendlyReaderGuard(const T& lock);
template <class T>
auto ForkFriendlyReaderGuard(const T* lock);
template <class T>
auto WriterGuard(const T& lock);
template <class T>
auto WriterGuard(const T* lock);
////////////////////////////////////////////////////////////////////////////////
} // namespace NYT::NThreading
#define RW_SPIN_LOCK_INL_H_
#include "rw_spin_lock-inl.h"
#undef RW_SPIN_LOCK_INL_H_
|
