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// 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.
#include "src/heap/cppgc/gc-info-table.h"
#include <algorithm>
#include <limits>
#include <memory>
#include "include/cppgc/internal/gc-info.h"
#include "include/cppgc/platform.h"
#include "src/base/bits.h"
#include "src/base/lazy-instance.h"
#include "src/base/page-allocator.h"
#include "src/heap/cppgc/platform.h"
namespace cppgc {
namespace internal {
namespace {
// GCInfoTable::table_, the table which holds GCInfos, is maintained as a
// contiguous array reserved upfront. Subparts of the array are (re-)committed
// as read/write or read-only in OS pages, whose size is a power of 2. To avoid
// having GCInfos that cross the boundaries between these subparts we force the
// size of GCInfo to be a power of 2 as well.
constexpr size_t kEntrySize = sizeof(GCInfo);
static_assert(v8::base::bits::IsPowerOfTwo(kEntrySize),
"GCInfoTable entries size must be power of "
"two");
} // namespace
GCInfoTable* GlobalGCInfoTable::global_table_ = nullptr;
constexpr GCInfoIndex GCInfoTable::kMaxIndex;
constexpr GCInfoIndex GCInfoTable::kMinIndex;
constexpr GCInfoIndex GCInfoTable::kInitialWantedLimit;
// static
void GlobalGCInfoTable::Initialize(PageAllocator& page_allocator) {
static v8::base::LeakyObject<GCInfoTable> table(page_allocator,
GetGlobalOOMHandler());
if (!global_table_) {
global_table_ = table.get();
} else {
CHECK_EQ(&page_allocator, &global_table_->allocator());
}
}
GCInfoTable::GCInfoTable(PageAllocator& page_allocator,
FatalOutOfMemoryHandler& oom_handler)
: page_allocator_(page_allocator),
oom_handler_(oom_handler),
table_(static_cast<decltype(table_)>(page_allocator_.AllocatePages(
nullptr, MaxTableSize(), page_allocator_.AllocatePageSize(),
PageAllocator::kNoAccess))),
read_only_table_end_(reinterpret_cast<uint8_t*>(table_)) {
if (!table_) {
oom_handler_("Oilpan: GCInfoTable initial reservation.");
}
Resize();
}
GCInfoTable::~GCInfoTable() {
page_allocator_.ReleasePages(const_cast<GCInfo*>(table_), MaxTableSize(), 0);
}
size_t GCInfoTable::MaxTableSize() const {
return RoundUp(GCInfoTable::kMaxIndex * kEntrySize,
page_allocator_.AllocatePageSize());
}
GCInfoIndex GCInfoTable::InitialTableLimit() const {
// Different OSes have different page sizes, so we have to choose the minimum
// of memory wanted and OS page size.
constexpr size_t memory_wanted = kInitialWantedLimit * kEntrySize;
const size_t initial_limit =
RoundUp(memory_wanted, page_allocator_.AllocatePageSize()) / kEntrySize;
CHECK_GT(std::numeric_limits<GCInfoIndex>::max(), initial_limit);
return static_cast<GCInfoIndex>(
std::min(static_cast<size_t>(kMaxIndex), initial_limit));
}
void GCInfoTable::Resize() {
const GCInfoIndex new_limit = (limit_) ? 2 * limit_ : InitialTableLimit();
CHECK_GT(new_limit, limit_);
const size_t old_committed_size = limit_ * kEntrySize;
const size_t new_committed_size = new_limit * kEntrySize;
CHECK(table_);
CHECK_EQ(0u, new_committed_size % page_allocator_.AllocatePageSize());
CHECK_GE(MaxTableSize(), new_committed_size);
// Recommit new area as read/write.
uint8_t* current_table_end =
reinterpret_cast<uint8_t*>(table_) + old_committed_size;
const size_t table_size_delta = new_committed_size - old_committed_size;
if (!page_allocator_.SetPermissions(current_table_end, table_size_delta,
PageAllocator::kReadWrite)) {
oom_handler_("Oilpan: GCInfoTable resize.");
}
// Recommit old area as read-only.
if (read_only_table_end_ != current_table_end) {
DCHECK_GT(current_table_end, read_only_table_end_);
const size_t read_only_delta = current_table_end - read_only_table_end_;
CHECK(page_allocator_.SetPermissions(read_only_table_end_, read_only_delta,
PageAllocator::kRead));
read_only_table_end_ += read_only_delta;
}
// Check that newly-committed memory is zero-initialized.
CheckMemoryIsZeroed(reinterpret_cast<uintptr_t*>(current_table_end),
table_size_delta / sizeof(uintptr_t));
limit_ = new_limit;
}
void GCInfoTable::CheckMemoryIsZeroed(uintptr_t* base, size_t len) {
#if DEBUG
for (size_t i = 0; i < len; ++i) {
DCHECK(!base[i]);
}
#endif // DEBUG
}
GCInfoIndex GCInfoTable::RegisterNewGCInfo(
std::atomic<GCInfoIndex>& registered_index, const GCInfo& info) {
// Ensuring a new index involves current index adjustment as well as
// potentially resizing the table. For simplicity we use a lock.
v8::base::MutexGuard guard(&table_mutex_);
// Check the registered index again after taking the lock as some other
// thread may have registered the info at the same time.
const GCInfoIndex index = registered_index.load(std::memory_order_relaxed);
if (index) {
return index;
}
if (current_index_ == limit_) {
Resize();
}
const GCInfoIndex new_index = current_index_++;
CHECK_LT(new_index, GCInfoTable::kMaxIndex);
table_[new_index] = info;
registered_index.store(new_index, std::memory_order_release);
return new_index;
}
} // namespace internal
} // namespace cppgc
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