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
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
|
// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef INCLUDE_CPPGC_CROSS_THREAD_PERSISTENT_H_
#define INCLUDE_CPPGC_CROSS_THREAD_PERSISTENT_H_
#include <atomic>
#include "cppgc/internal/persistent-node.h"
#include "cppgc/internal/pointer-policies.h"
#include "cppgc/persistent.h"
#include "cppgc/visitor.h"
namespace cppgc {
namespace internal {
template <typename T, typename WeaknessPolicy, typename LocationPolicy,
typename CheckingPolicy>
class BasicCrossThreadPersistent final : public PersistentBase,
public LocationPolicy,
private WeaknessPolicy,
private CheckingPolicy {
public:
using typename WeaknessPolicy::IsStrongPersistent;
using PointeeType = T;
~BasicCrossThreadPersistent() { Clear(); }
BasicCrossThreadPersistent( // NOLINT
const SourceLocation& loc = SourceLocation::Current())
: LocationPolicy(loc) {}
BasicCrossThreadPersistent( // NOLINT
std::nullptr_t, const SourceLocation& loc = SourceLocation::Current())
: LocationPolicy(loc) {}
BasicCrossThreadPersistent( // NOLINT
SentinelPointer s, const SourceLocation& loc = SourceLocation::Current())
: PersistentBase(s), LocationPolicy(loc) {}
BasicCrossThreadPersistent( // NOLINT
T* raw, const SourceLocation& loc = SourceLocation::Current())
: PersistentBase(raw), LocationPolicy(loc) {
if (!IsValid(raw)) return;
PersistentRegionLock guard;
CrossThreadPersistentRegion& region = this->GetPersistentRegion(raw);
SetNode(region.AllocateNode(this, &Trace));
this->CheckPointer(raw);
}
class UnsafeCtorTag {
private:
UnsafeCtorTag() = default;
template <typename U, typename OtherWeaknessPolicy,
typename OtherLocationPolicy, typename OtherCheckingPolicy>
friend class BasicCrossThreadPersistent;
};
BasicCrossThreadPersistent( // NOLINT
UnsafeCtorTag, T* raw,
const SourceLocation& loc = SourceLocation::Current())
: PersistentBase(raw), LocationPolicy(loc) {
if (!IsValid(raw)) return;
CrossThreadPersistentRegion& region = this->GetPersistentRegion(raw);
SetNode(region.AllocateNode(this, &Trace));
this->CheckPointer(raw);
}
BasicCrossThreadPersistent( // NOLINT
T& raw, const SourceLocation& loc = SourceLocation::Current())
: BasicCrossThreadPersistent(&raw, loc) {}
template <typename U, typename MemberBarrierPolicy,
typename MemberWeaknessTag, typename MemberCheckingPolicy,
typename = std::enable_if_t<std::is_base_of<T, U>::value>>
BasicCrossThreadPersistent( // NOLINT
internal::BasicMember<U, MemberBarrierPolicy, MemberWeaknessTag,
MemberCheckingPolicy>
member,
const SourceLocation& loc = SourceLocation::Current())
: BasicCrossThreadPersistent(member.Get(), loc) {}
BasicCrossThreadPersistent(
const BasicCrossThreadPersistent& other,
const SourceLocation& loc = SourceLocation::Current())
: BasicCrossThreadPersistent(loc) {
// Invoke operator=.
*this = other;
}
// Heterogeneous ctor.
template <typename U, typename OtherWeaknessPolicy,
typename OtherLocationPolicy, typename OtherCheckingPolicy,
typename = std::enable_if_t<std::is_base_of<T, U>::value>>
BasicCrossThreadPersistent( // NOLINT
const BasicCrossThreadPersistent<U, OtherWeaknessPolicy,
OtherLocationPolicy,
OtherCheckingPolicy>& other,
const SourceLocation& loc = SourceLocation::Current())
: BasicCrossThreadPersistent(loc) {
*this = other;
}
BasicCrossThreadPersistent(
BasicCrossThreadPersistent&& other,
const SourceLocation& loc = SourceLocation::Current()) noexcept {
// Invoke operator=.
*this = std::move(other);
}
BasicCrossThreadPersistent& operator=(
const BasicCrossThreadPersistent& other) {
PersistentRegionLock guard;
AssignUnsafe(other.Get());
return *this;
}
template <typename U, typename OtherWeaknessPolicy,
typename OtherLocationPolicy, typename OtherCheckingPolicy,
typename = std::enable_if_t<std::is_base_of<T, U>::value>>
BasicCrossThreadPersistent& operator=(
const BasicCrossThreadPersistent<U, OtherWeaknessPolicy,
OtherLocationPolicy,
OtherCheckingPolicy>& other) {
PersistentRegionLock guard;
AssignUnsafe(other.Get());
return *this;
}
BasicCrossThreadPersistent& operator=(BasicCrossThreadPersistent&& other) {
if (this == &other) return *this;
Clear();
PersistentRegionLock guard;
PersistentBase::operator=(std::move(other));
LocationPolicy::operator=(std::move(other));
if (!IsValid(GetValue())) return *this;
GetNode()->UpdateOwner(this);
other.SetValue(nullptr);
other.SetNode(nullptr);
this->CheckPointer(GetValue());
return *this;
}
BasicCrossThreadPersistent& operator=(T* other) {
Assign(other);
return *this;
}
// Assignment from member.
template <typename U, typename MemberBarrierPolicy,
typename MemberWeaknessTag, typename MemberCheckingPolicy,
typename = std::enable_if_t<std::is_base_of<T, U>::value>>
BasicCrossThreadPersistent& operator=(
internal::BasicMember<U, MemberBarrierPolicy, MemberWeaknessTag,
MemberCheckingPolicy>
member) {
return operator=(member.Get());
}
BasicCrossThreadPersistent& operator=(std::nullptr_t) {
Clear();
return *this;
}
BasicCrossThreadPersistent& operator=(SentinelPointer s) {
Assign(s);
return *this;
}
/**
* Returns a pointer to the stored object.
*
* Note: **Not thread-safe.**
*
* \returns a pointer to the stored object.
*/
// CFI cast exemption to allow passing SentinelPointer through T* and support
// heterogeneous assignments between different Member and Persistent handles
// based on their actual types.
V8_CLANG_NO_SANITIZE("cfi-unrelated-cast") T* Get() const {
return static_cast<T*>(const_cast<void*>(GetValue()));
}
/**
* Clears the stored object.
*/
void Clear() {
// Simplified version of `Assign()` to allow calling without a complete type
// `T`.
const void* old_value = GetValue();
if (IsValid(old_value)) {
PersistentRegionLock guard;
old_value = GetValue();
// The fast path check (IsValid()) does not acquire the lock. Reload
// the value to ensure the reference has not been cleared.
if (IsValid(old_value)) {
CrossThreadPersistentRegion& region =
this->GetPersistentRegion(old_value);
region.FreeNode(GetNode());
SetNode(nullptr);
} else {
CPPGC_DCHECK(!GetNode());
}
}
SetValue(nullptr);
}
/**
* Returns a pointer to the stored object and releases it.
*
* Note: **Not thread-safe.**
*
* \returns a pointer to the stored object.
*/
T* Release() {
T* result = Get();
Clear();
return result;
}
/**
* Conversio to boolean.
*
* Note: **Not thread-safe.**
*
* \returns true if an actual object has been stored and false otherwise.
*/
explicit operator bool() const { return Get(); }
/**
* Conversion to object of type T.
*
* Note: **Not thread-safe.**
*
* \returns the object.
*/
operator T*() const { return Get(); } // NOLINT
/**
* Dereferences the stored object.
*
* Note: **Not thread-safe.**
*/
T* operator->() const { return Get(); }
T& operator*() const { return *Get(); }
template <typename U, typename OtherWeaknessPolicy = WeaknessPolicy,
typename OtherLocationPolicy = LocationPolicy,
typename OtherCheckingPolicy = CheckingPolicy>
BasicCrossThreadPersistent<U, OtherWeaknessPolicy, OtherLocationPolicy,
OtherCheckingPolicy>
To() const {
using OtherBasicCrossThreadPersistent =
BasicCrossThreadPersistent<U, OtherWeaknessPolicy, OtherLocationPolicy,
OtherCheckingPolicy>;
PersistentRegionLock guard;
return OtherBasicCrossThreadPersistent(
typename OtherBasicCrossThreadPersistent::UnsafeCtorTag(),
static_cast<U*>(Get()));
}
template <typename U = T,
typename = typename std::enable_if<!BasicCrossThreadPersistent<
U, WeaknessPolicy>::IsStrongPersistent::value>::type>
BasicCrossThreadPersistent<U, internal::StrongCrossThreadPersistentPolicy>
Lock() const {
return BasicCrossThreadPersistent<
U, internal::StrongCrossThreadPersistentPolicy>(*this);
}
private:
static bool IsValid(const void* ptr) {
return ptr && ptr != kSentinelPointer;
}
static void Trace(Visitor* v, const void* ptr) {
const auto* handle = static_cast<const BasicCrossThreadPersistent*>(ptr);
v->TraceRoot(*handle, handle->Location());
}
void Assign(T* ptr) {
const void* old_value = GetValue();
if (IsValid(old_value)) {
PersistentRegionLock guard;
old_value = GetValue();
// The fast path check (IsValid()) does not acquire the lock. Reload
// the value to ensure the reference has not been cleared.
if (IsValid(old_value)) {
CrossThreadPersistentRegion& region =
this->GetPersistentRegion(old_value);
if (IsValid(ptr) && (®ion == &this->GetPersistentRegion(ptr))) {
SetValue(ptr);
this->CheckPointer(ptr);
return;
}
region.FreeNode(GetNode());
SetNode(nullptr);
} else {
CPPGC_DCHECK(!GetNode());
}
}
SetValue(ptr);
if (!IsValid(ptr)) return;
PersistentRegionLock guard;
SetNode(this->GetPersistentRegion(ptr).AllocateNode(this, &Trace));
this->CheckPointer(ptr);
}
void AssignUnsafe(T* ptr) {
PersistentRegionLock::AssertLocked();
const void* old_value = GetValue();
if (IsValid(old_value)) {
CrossThreadPersistentRegion& region =
this->GetPersistentRegion(old_value);
if (IsValid(ptr) && (®ion == &this->GetPersistentRegion(ptr))) {
SetValue(ptr);
this->CheckPointer(ptr);
return;
}
region.FreeNode(GetNode());
SetNode(nullptr);
}
SetValue(ptr);
if (!IsValid(ptr)) return;
SetNode(this->GetPersistentRegion(ptr).AllocateNode(this, &Trace));
this->CheckPointer(ptr);
}
void ClearFromGC() const {
if (IsValid(GetValue())) {
WeaknessPolicy::GetPersistentRegion(GetValue()).FreeNode(GetNode());
PersistentBase::ClearFromGC();
}
}
friend class cppgc::Visitor;
};
template <typename T, typename LocationPolicy, typename CheckingPolicy>
struct IsWeak<
BasicCrossThreadPersistent<T, internal::WeakCrossThreadPersistentPolicy,
LocationPolicy, CheckingPolicy>>
: std::true_type {};
} // namespace internal
namespace subtle {
/**
* **DO NOT USE: Has known caveats, see below.**
*
* CrossThreadPersistent allows retaining objects from threads other than the
* thread the owning heap is operating on.
*
* Known caveats:
* - Does not protect the heap owning an object from terminating.
* - Reaching transitively through the graph is unsupported as objects may be
* moved concurrently on the thread owning the object.
*/
template <typename T>
using CrossThreadPersistent = internal::BasicCrossThreadPersistent<
T, internal::StrongCrossThreadPersistentPolicy>;
/**
* **DO NOT USE: Has known caveats, see below.**
*
* CrossThreadPersistent allows weakly retaining objects from threads other than
* the thread the owning heap is operating on.
*
* Known caveats:
* - Does not protect the heap owning an object from terminating.
* - Reaching transitively through the graph is unsupported as objects may be
* moved concurrently on the thread owning the object.
*/
template <typename T>
using WeakCrossThreadPersistent = internal::BasicCrossThreadPersistent<
T, internal::WeakCrossThreadPersistentPolicy>;
} // namespace subtle
} // namespace cppgc
#endif // INCLUDE_CPPGC_CROSS_THREAD_PERSISTENT_H_
|