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1 // Copyright (c) 2015 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2015 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 #include "base/metrics/persistent_memory_allocator.h" | 5 #include "base/metrics/persistent_memory_allocator.h" |
6 | 6 |
7 #include <assert.h> | 7 #include <assert.h> |
8 #include <algorithm> | 8 #include <algorithm> |
9 | 9 |
10 #if defined(OS_WIN) | 10 #if defined(OS_WIN) |
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1126 DCHECK_NE(0U, type_); | 1126 DCHECK_NE(0U, type_); |
1127 DCHECK_LT(0U, size_); | 1127 DCHECK_LT(0U, size_); |
1128 DCHECK(reference_); | 1128 DCHECK(reference_); |
1129 } | 1129 } |
1130 | 1130 |
1131 DelayedPersistentAllocation::~DelayedPersistentAllocation() {} | 1131 DelayedPersistentAllocation::~DelayedPersistentAllocation() {} |
1132 | 1132 |
1133 void* DelayedPersistentAllocation::Get() const { | 1133 void* DelayedPersistentAllocation::Get() const { |
1134 // Relaxed operations are acceptable here because it's not protecting the | 1134 // Relaxed operations are acceptable here because it's not protecting the |
1135 // contents of the allocation in any way. | 1135 // contents of the allocation in any way. |
1136 Reference ref = reference_->load(std::memory_order_relaxed); | 1136 Reference ref = reference_->load(std::memory_order_acquire); |
1137 if (!ref) { | 1137 if (!ref) { |
1138 ref = allocator_->Allocate(size_, type_); | 1138 ref = allocator_->Allocate(size_, type_); |
1139 if (!ref) | 1139 if (!ref) |
1140 return nullptr; | 1140 return nullptr; |
1141 | 1141 |
1142 // Store the new reference in its proper location using compare-and-swap. | 1142 // Store the new reference in its proper location using compare-and-swap. |
1143 // Use a "strong" exchange to ensure no false-negatives since the operation | 1143 // Use a "strong" exchange to ensure no false-negatives since the operation |
1144 // cannot be retried. | 1144 // cannot be retried. |
1145 Reference existing = 0; // Must be mutable; receives actual value. | 1145 Reference existing = 0; // Must be mutable; receives actual value. |
1146 if (reference_->compare_exchange_strong(existing, ref, | 1146 if (reference_->compare_exchange_strong(existing, ref, |
1147 std::memory_order_relaxed, | 1147 std::memory_order_release, |
1148 std::memory_order_relaxed)) { | 1148 std::memory_order_relaxed)) { |
1149 if (make_iterable_) | 1149 if (make_iterable_) |
1150 allocator_->MakeIterable(ref); | 1150 allocator_->MakeIterable(ref); |
1151 } else { | 1151 } else { |
1152 // Failure indicates that something else has raced ahead, performed the | 1152 // Failure indicates that something else has raced ahead, performed the |
1153 // allocation, and stored its reference. Purge the allocation that was | 1153 // allocation, and stored its reference. Purge the allocation that was |
1154 // just done and use the other one instead. | 1154 // just done and use the other one instead. |
1155 DCHECK_EQ(type_, allocator_->GetType(existing)); | 1155 DCHECK_EQ(type_, allocator_->GetType(existing)); |
1156 DCHECK_LE(size_, allocator_->GetAllocSize(existing)); | 1156 DCHECK_LE(size_, allocator_->GetAllocSize(existing)); |
1157 allocator_->ChangeType(ref, 0, type_, /*clear=*/false); | 1157 allocator_->ChangeType(ref, 0, type_, /*clear=*/false); |
1158 ref = existing; | 1158 ref = existing; |
1159 } | 1159 } |
1160 } | 1160 } |
1161 | 1161 |
1162 char* mem = allocator_->GetAsArray<char>(ref, type_, size_); | 1162 char* mem = allocator_->GetAsArray<char>(ref, type_, size_); |
1163 if (!mem) { | 1163 if (!mem) { |
1164 // This should never happen but be tolerant if it does as corruption from | 1164 // This should never happen but be tolerant if it does as corruption from |
1165 // the outside is something to guard against. | 1165 // the outside is something to guard against. |
1166 NOTREACHED(); | 1166 NOTREACHED(); |
1167 return nullptr; | 1167 return nullptr; |
1168 } | 1168 } |
1169 return mem + offset_; | 1169 return mem + offset_; |
1170 } | 1170 } |
1171 | 1171 |
1172 } // namespace base | 1172 } // namespace base |
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