| // Copyright (c) 2015 The Chromium 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 "base/metrics/persistent_memory_allocator.h" |
| |
| #include <assert.h> |
| #include <algorithm> |
| |
| #if defined(OS_WIN) |
| #include "winbase.h" |
| #elif defined(OS_POSIX) |
| #include <sys/mman.h> |
| #endif |
| |
| #include "base/files/memory_mapped_file.h" |
| #include "base/logging.h" |
| #include "base/memory/shared_memory.h" |
| #include "base/metrics/histogram_macros.h" |
| |
| namespace { |
| |
| // Limit of memory segment size. It has to fit in an unsigned 32-bit number |
| // and should be a power of 2 in order to accomodate almost any page size. |
| const uint32_t kSegmentMaxSize = 1 << 30; // 1 GiB |
| |
| // A constant (random) value placed in the shared metadata to identify |
| // an already initialized memory segment. |
| const uint32_t kGlobalCookie = 0x408305DC; |
| |
| // The current version of the metadata. If updates are made that change |
| // the metadata, the version number can be queried to operate in a backward- |
| // compatible manner until the memory segment is completely re-initalized. |
| const uint32_t kGlobalVersion = 1; |
| |
| // Constant values placed in the block headers to indicate its state. |
| const uint32_t kBlockCookieFree = 0; |
| const uint32_t kBlockCookieQueue = 1; |
| const uint32_t kBlockCookieWasted = (uint32_t)-1; |
| const uint32_t kBlockCookieAllocated = 0xC8799269; |
| |
| // TODO(bcwhite): When acceptable, consider moving flags to std::atomic<char> |
| // types rather than combined bitfield. |
| |
| // Flags stored in the flags_ field of the SharedMetaData structure below. |
| enum : int { |
| kFlagCorrupt = 1 << 0, |
| kFlagFull = 1 << 1 |
| }; |
| |
| bool CheckFlag(const volatile std::atomic<uint32_t>* flags, int flag) { |
| uint32_t loaded_flags = flags->load(std::memory_order_relaxed); |
| return (loaded_flags & flag) != 0; |
| } |
| |
| void SetFlag(volatile std::atomic<uint32_t>* flags, int flag) { |
| uint32_t loaded_flags = flags->load(std::memory_order_relaxed); |
| for (;;) { |
| uint32_t new_flags = (loaded_flags & ~flag) | flag; |
| // In the failue case, actual "flags" value stored in loaded_flags. |
| if (flags->compare_exchange_weak(loaded_flags, new_flags)) |
| break; |
| } |
| } |
| |
| } // namespace |
| |
| namespace base { |
| |
| // All allocations and data-structures must be aligned to this byte boundary. |
| // Alignment as large as the physical bus between CPU and RAM is _required_ |
| // for some architectures, is simply more efficient on other CPUs, and |
| // generally a Good Idea(tm) for all platforms as it reduces/eliminates the |
| // chance that a type will span cache lines. Alignment mustn't be less |
| // than 8 to ensure proper alignment for all types. The rest is a balance |
| // between reducing spans across multiple cache lines and wasted space spent |
| // padding out allocations. An alignment of 16 would ensure that the block |
| // header structure always sits in a single cache line. An average of about |
| // 1/2 this value will be wasted with every allocation. |
| const uint32_t PersistentMemoryAllocator::kAllocAlignment = 8; |
| |
| // The block-header is placed at the top of every allocation within the |
| // segment to describe the data that follows it. |
| struct PersistentMemoryAllocator::BlockHeader { |
| uint32_t size; // Number of bytes in this block, including header. |
| uint32_t cookie; // Constant value indicating completed allocation. |
| std::atomic<uint32_t> type_id; // Arbitrary number indicating data type. |
| std::atomic<uint32_t> next; // Pointer to the next block when iterating. |
| }; |
| |
| // The shared metadata exists once at the top of the memory segment to |
| // describe the state of the allocator to all processes. |
| struct PersistentMemoryAllocator::SharedMetadata { |
| uint32_t cookie; // Some value that indicates complete initialization. |
| uint32_t size; // Total size of memory segment. |
| uint32_t page_size; // Paging size within memory segment. |
| uint32_t version; // Version code so upgrades don't break. |
| uint64_t id; // Arbitrary ID number given by creator. |
| uint32_t name; // Reference to stored name string. |
| |
| // Above is read-only after first construction. Below may be changed and |
| // so must be marked "volatile" to provide correct inter-process behavior. |
| |
| // Bitfield of information flags. Access to this should be done through |
| // the CheckFlag() and SetFlag() methods defined above. |
| volatile std::atomic<uint32_t> flags; |
| |
| // Offset/reference to first free space in segment. |
| volatile std::atomic<uint32_t> freeptr; |
| |
| // The "iterable" queue is an M&S Queue as described here, append-only: |
| // https://www.research.ibm.com/people/m/michael/podc-1996.pdf |
| volatile std::atomic<uint32_t> tailptr; // Last block of iteration queue. |
| volatile BlockHeader queue; // Empty block for linked-list head/tail. |
| }; |
| |
| // The "queue" block header is used to detect "last node" so that zero/null |
| // can be used to indicate that it hasn't been added at all. It is part of |
| // the SharedMetadata structure which itself is always located at offset zero. |
| const PersistentMemoryAllocator::Reference |
| PersistentMemoryAllocator::kReferenceQueue = |
| offsetof(SharedMetadata, queue); |
| |
| const base::FilePath::CharType PersistentMemoryAllocator::kFileExtension[] = |
| FILE_PATH_LITERAL(".pma"); |
| |
| |
| PersistentMemoryAllocator::Iterator::Iterator( |
| const PersistentMemoryAllocator* allocator) |
| : allocator_(allocator), last_record_(kReferenceQueue), record_count_(0) {} |
| |
| PersistentMemoryAllocator::Iterator::Iterator( |
| const PersistentMemoryAllocator* allocator, |
| Reference starting_after) |
| : allocator_(allocator), last_record_(starting_after), record_count_(0) { |
| // Ensure that the starting point is a valid, iterable block (meaning it can |
| // be read and has a non-zero "next" pointer). |
| const volatile BlockHeader* block = |
| allocator_->GetBlock(starting_after, 0, 0, false, false); |
| if (!block || block->next.load(std::memory_order_relaxed) == 0) { |
| NOTREACHED(); |
| last_record_.store(kReferenceQueue, std::memory_order_release); |
| } |
| } |
| |
| PersistentMemoryAllocator::Reference |
| PersistentMemoryAllocator::Iterator::GetNext(uint32_t* type_return) { |
| // Make a copy of the existing count of found-records, acquiring all changes |
| // made to the allocator, notably "freeptr" (see comment in loop for why |
| // the load of that value cannot be moved above here) that occurred during |
| // any previous runs of this method, including those by parallel threads |
| // that interrupted it. It pairs with the Release at the end of this method. |
| // |
| // Otherwise, if the compiler were to arrange the two loads such that |
| // "count" was fetched _after_ "freeptr" then it would be possible for |
| // this thread to be interrupted between them and other threads perform |
| // multiple allocations, make-iterables, and iterations (with the included |
| // increment of |record_count_|) culminating in the check at the bottom |
| // mistakenly determining that a loop exists. Isn't this stuff fun? |
| uint32_t count = record_count_.load(std::memory_order_acquire); |
| |
| Reference last = last_record_.load(std::memory_order_acquire); |
| Reference next; |
| while (true) { |
| const volatile BlockHeader* block = |
| allocator_->GetBlock(last, 0, 0, true, false); |
| if (!block) // Invalid iterator state. |
| return kReferenceNull; |
| |
| // The compiler and CPU can freely reorder all memory accesses on which |
| // there are no dependencies. It could, for example, move the load of |
| // "freeptr" to above this point because there are no explicit dependencies |
| // between it and "next". If it did, however, then another block could |
| // be queued after that but before the following load meaning there is |
| // one more queued block than the future "detect loop by having more |
| // blocks that could fit before freeptr" will allow. |
| // |
| // By "acquiring" the "next" value here, it's synchronized to the enqueue |
| // of the node which in turn is synchronized to the allocation (which sets |
| // freeptr). Thus, the scenario above cannot happen. |
| next = block->next.load(std::memory_order_acquire); |
| if (next == kReferenceQueue) // No next allocation in queue. |
| return kReferenceNull; |
| block = allocator_->GetBlock(next, 0, 0, false, false); |
| if (!block) { // Memory is corrupt. |
| allocator_->SetCorrupt(); |
| return kReferenceNull; |
| } |
| |
| // Update the "last_record" pointer to be the reference being returned. |
| // If it fails then another thread has already iterated past it so loop |
| // again. Failing will also load the existing value into "last" so there |
| // is no need to do another such load when the while-loop restarts. A |
| // "strong" compare-exchange is used because failing unnecessarily would |
| // mean repeating some fairly costly validations above. |
| if (last_record_.compare_exchange_strong(last, next)) { |
| *type_return = block->type_id.load(std::memory_order_relaxed); |
| break; |
| } |
| } |
| |
| // Memory corruption could cause a loop in the list. Such must be detected |
| // so as to not cause an infinite loop in the caller. This is done by simply |
| // making sure it doesn't iterate more times than the absolute maximum |
| // number of allocations that could have been made. Callers are likely |
| // to loop multiple times before it is detected but at least it stops. |
| const uint32_t freeptr = std::min( |
| allocator_->shared_meta()->freeptr.load(std::memory_order_relaxed), |
| allocator_->mem_size_); |
| const uint32_t max_records = |
| freeptr / (sizeof(BlockHeader) + kAllocAlignment); |
| if (count > max_records) { |
| allocator_->SetCorrupt(); |
| return kReferenceNull; |
| } |
| |
| // Increment the count and release the changes made above. It pairs with |
| // the Acquire at the top of this method. Note that this operation is not |
| // strictly synchonized with fetching of the object to return, which would |
| // have to be done inside the loop and is somewhat complicated to achieve. |
| // It does not matter if it falls behind temporarily so long as it never |
| // gets ahead. |
| record_count_.fetch_add(1, std::memory_order_release); |
| return next; |
| } |
| |
| PersistentMemoryAllocator::Reference |
| PersistentMemoryAllocator::Iterator::GetNextOfType(uint32_t type_match) { |
| Reference ref; |
| uint32_t type_found; |
| while ((ref = GetNext(&type_found)) != 0) { |
| if (type_found == type_match) |
| return ref; |
| } |
| return kReferenceNull; |
| } |
| |
| |
| // static |
| bool PersistentMemoryAllocator::IsMemoryAcceptable(const void* base, |
| size_t size, |
| size_t page_size, |
| bool readonly) { |
| return ((base && reinterpret_cast<uintptr_t>(base) % kAllocAlignment == 0) && |
| (size >= sizeof(SharedMetadata) && size <= kSegmentMaxSize) && |
| (size % kAllocAlignment == 0 || readonly) && |
| (page_size == 0 || size % page_size == 0 || readonly)); |
| } |
| |
| PersistentMemoryAllocator::PersistentMemoryAllocator( |
| void* base, |
| size_t size, |
| size_t page_size, |
| uint64_t id, |
| base::StringPiece name, |
| bool readonly) |
| : mem_base_(static_cast<char*>(base)), |
| mem_size_(static_cast<uint32_t>(size)), |
| mem_page_(static_cast<uint32_t>((page_size ? page_size : size))), |
| readonly_(readonly), |
| corrupt_(0), |
| allocs_histogram_(nullptr), |
| used_histogram_(nullptr) { |
| static_assert(sizeof(BlockHeader) % kAllocAlignment == 0, |
| "BlockHeader is not a multiple of kAllocAlignment"); |
| static_assert(sizeof(SharedMetadata) % kAllocAlignment == 0, |
| "SharedMetadata is not a multiple of kAllocAlignment"); |
| static_assert(kReferenceQueue % kAllocAlignment == 0, |
| "\"queue\" is not aligned properly; must be at end of struct"); |
| |
| // Ensure that memory segment is of acceptable size. |
| CHECK(IsMemoryAcceptable(base, size, page_size, readonly)); |
| |
| // These atomics operate inter-process and so must be lock-free. The local |
| // casts are to make sure it can be evaluated at compile time to a constant. |
| CHECK(((SharedMetadata*)0)->freeptr.is_lock_free()); |
| CHECK(((SharedMetadata*)0)->flags.is_lock_free()); |
| CHECK(((BlockHeader*)0)->next.is_lock_free()); |
| CHECK(corrupt_.is_lock_free()); |
| |
| if (shared_meta()->cookie != kGlobalCookie) { |
| if (readonly) { |
| SetCorrupt(); |
| return; |
| } |
| |
| // This block is only executed when a completely new memory segment is |
| // being initialized. It's unshared and single-threaded... |
| volatile BlockHeader* const first_block = |
| reinterpret_cast<volatile BlockHeader*>(mem_base_ + |
| sizeof(SharedMetadata)); |
| if (shared_meta()->cookie != 0 || |
| shared_meta()->size != 0 || |
| shared_meta()->version != 0 || |
| shared_meta()->freeptr.load(std::memory_order_relaxed) != 0 || |
| shared_meta()->flags.load(std::memory_order_relaxed) != 0 || |
| shared_meta()->id != 0 || |
| shared_meta()->name != 0 || |
| shared_meta()->tailptr != 0 || |
| shared_meta()->queue.cookie != 0 || |
| shared_meta()->queue.next.load(std::memory_order_relaxed) != 0 || |
| first_block->size != 0 || |
| first_block->cookie != 0 || |
| first_block->type_id.load(std::memory_order_relaxed) != 0 || |
| first_block->next != 0) { |
| // ...or something malicious has been playing with the metadata. |
| SetCorrupt(); |
| } |
| |
| // This is still safe to do even if corruption has been detected. |
| shared_meta()->cookie = kGlobalCookie; |
| shared_meta()->size = mem_size_; |
| shared_meta()->page_size = mem_page_; |
| shared_meta()->version = kGlobalVersion; |
| shared_meta()->id = id; |
| shared_meta()->freeptr.store(sizeof(SharedMetadata), |
| std::memory_order_release); |
| |
| // Set up the queue of iterable allocations. |
| shared_meta()->queue.size = sizeof(BlockHeader); |
| shared_meta()->queue.cookie = kBlockCookieQueue; |
| shared_meta()->queue.next.store(kReferenceQueue, std::memory_order_release); |
| shared_meta()->tailptr.store(kReferenceQueue, std::memory_order_release); |
| |
| // Allocate space for the name so other processes can learn it. |
| if (!name.empty()) { |
| const size_t name_length = name.length() + 1; |
| shared_meta()->name = Allocate(name_length, 0); |
| char* name_cstr = GetAsObject<char>(shared_meta()->name, 0); |
| if (name_cstr) |
| memcpy(name_cstr, name.data(), name.length()); |
| } |
| } else { |
| if (shared_meta()->size == 0 || |
| shared_meta()->version == 0 || |
| shared_meta()->freeptr.load(std::memory_order_relaxed) == 0 || |
| shared_meta()->tailptr == 0 || |
| shared_meta()->queue.cookie == 0 || |
| shared_meta()->queue.next.load(std::memory_order_relaxed) == 0) { |
| SetCorrupt(); |
| } |
| if (!readonly) { |
| // The allocator is attaching to a previously initialized segment of |
| // memory. If the initialization parameters differ, make the best of it |
| // by reducing the local construction parameters to match those of |
| // the actual memory area. This ensures that the local object never |
| // tries to write outside of the original bounds. |
| // Because the fields are const to ensure that no code other than the |
| // constructor makes changes to them as well as to give optimization |
| // hints to the compiler, it's necessary to const-cast them for changes |
| // here. |
| if (shared_meta()->size < mem_size_) |
| *const_cast<uint32_t*>(&mem_size_) = shared_meta()->size; |
| if (shared_meta()->page_size < mem_page_) |
| *const_cast<uint32_t*>(&mem_page_) = shared_meta()->page_size; |
| |
| // Ensure that settings are still valid after the above adjustments. |
| if (!IsMemoryAcceptable(base, mem_size_, mem_page_, readonly)) |
| SetCorrupt(); |
| } |
| } |
| } |
| |
| PersistentMemoryAllocator::~PersistentMemoryAllocator() { |
| // It's strictly forbidden to do any memory access here in case there is |
| // some issue with the underlying memory segment. The "Local" allocator |
| // makes use of this to allow deletion of the segment on the heap from |
| // within its destructor. |
| } |
| |
| uint64_t PersistentMemoryAllocator::Id() const { |
| return shared_meta()->id; |
| } |
| |
| const char* PersistentMemoryAllocator::Name() const { |
| Reference name_ref = shared_meta()->name; |
| const char* name_cstr = GetAsObject<char>(name_ref, 0); |
| if (!name_cstr) |
| return ""; |
| |
| size_t name_length = GetAllocSize(name_ref); |
| if (name_cstr[name_length - 1] != '\0') { |
| NOTREACHED(); |
| SetCorrupt(); |
| return ""; |
| } |
| |
| return name_cstr; |
| } |
| |
| void PersistentMemoryAllocator::CreateTrackingHistograms( |
| base::StringPiece name) { |
| if (name.empty() || readonly_) |
| return; |
| |
| std::string name_string = name.as_string(); |
| DCHECK(!used_histogram_); |
| used_histogram_ = LinearHistogram::FactoryGet( |
| "UMA.PersistentAllocator." + name_string + ".UsedPct", 1, 101, 21, |
| HistogramBase::kUmaTargetedHistogramFlag); |
| |
| DCHECK(!allocs_histogram_); |
| allocs_histogram_ = Histogram::FactoryGet( |
| "UMA.PersistentAllocator." + name_string + ".Allocs", 1, 10000, 50, |
| HistogramBase::kUmaTargetedHistogramFlag); |
| } |
| |
| size_t PersistentMemoryAllocator::used() const { |
| return std::min(shared_meta()->freeptr.load(std::memory_order_relaxed), |
| mem_size_); |
| } |
| |
| size_t PersistentMemoryAllocator::GetAllocSize(Reference ref) const { |
| const volatile BlockHeader* const block = GetBlock(ref, 0, 0, false, false); |
| if (!block) |
| return 0; |
| uint32_t size = block->size; |
| // Header was verified by GetBlock() but a malicious actor could change |
| // the value between there and here. Check it again. |
| if (size <= sizeof(BlockHeader) || ref + size > mem_size_) { |
| SetCorrupt(); |
| return 0; |
| } |
| return size - sizeof(BlockHeader); |
| } |
| |
| uint32_t PersistentMemoryAllocator::GetType(Reference ref) const { |
| const volatile BlockHeader* const block = GetBlock(ref, 0, 0, false, false); |
| if (!block) |
| return 0; |
| return block->type_id.load(std::memory_order_relaxed); |
| } |
| |
| bool PersistentMemoryAllocator::ChangeType(Reference ref, |
| uint32_t to_type_id, |
| uint32_t from_type_id) { |
| DCHECK(!readonly_); |
| volatile BlockHeader* const block = GetBlock(ref, 0, 0, false, false); |
| if (!block) |
| return false; |
| |
| // This is a "strong" exchange because there is no loop that can retry in |
| // the wake of spurious failures possible with "weak" exchanges. |
| return block->type_id.compare_exchange_strong(from_type_id, to_type_id); |
| } |
| |
| PersistentMemoryAllocator::Reference PersistentMemoryAllocator::Allocate( |
| size_t req_size, |
| uint32_t type_id) { |
| Reference ref = AllocateImpl(req_size, type_id); |
| if (ref) { |
| // Success: Record this allocation in usage stats (if active). |
| if (allocs_histogram_) |
| allocs_histogram_->Add(static_cast<HistogramBase::Sample>(req_size)); |
| } else { |
| // Failure: Record an allocation of zero for tracking. |
| if (allocs_histogram_) |
| allocs_histogram_->Add(0); |
| } |
| return ref; |
| } |
| |
| PersistentMemoryAllocator::Reference PersistentMemoryAllocator::AllocateImpl( |
| size_t req_size, |
| uint32_t type_id) { |
| DCHECK(!readonly_); |
| |
| // Validate req_size to ensure it won't overflow when used as 32-bit value. |
| if (req_size > kSegmentMaxSize - sizeof(BlockHeader)) { |
| NOTREACHED(); |
| return kReferenceNull; |
| } |
| |
| // Round up the requested size, plus header, to the next allocation alignment. |
| uint32_t size = static_cast<uint32_t>(req_size + sizeof(BlockHeader)); |
| size = (size + (kAllocAlignment - 1)) & ~(kAllocAlignment - 1); |
| if (size <= sizeof(BlockHeader) || size > mem_page_) { |
| NOTREACHED(); |
| return kReferenceNull; |
| } |
| |
| // Get the current start of unallocated memory. Other threads may |
| // update this at any time and cause us to retry these operations. |
| // This value should be treated as "const" to avoid confusion through |
| // the code below but recognize that any failed compare-exchange operation |
| // involving it will cause it to be loaded with a more recent value. The |
| // code should either exit or restart the loop in that case. |
| /* const */ uint32_t freeptr = |
| shared_meta()->freeptr.load(std::memory_order_acquire); |
| |
| // Allocation is lockless so we do all our caculation and then, if saving |
| // indicates a change has occurred since we started, scrap everything and |
| // start over. |
| for (;;) { |
| if (IsCorrupt()) |
| return kReferenceNull; |
| |
| if (freeptr + size > mem_size_) { |
| SetFlag(&shared_meta()->flags, kFlagFull); |
| return kReferenceNull; |
| } |
| |
| // Get pointer to the "free" block. If something has been allocated since |
| // the load of freeptr above, it is still safe as nothing will be written |
| // to that location until after the compare-exchange below. |
| volatile BlockHeader* const block = GetBlock(freeptr, 0, 0, false, true); |
| if (!block) { |
| SetCorrupt(); |
| return kReferenceNull; |
| } |
| |
| // An allocation cannot cross page boundaries. If it would, create a |
| // "wasted" block and begin again at the top of the next page. This |
| // area could just be left empty but we fill in the block header just |
| // for completeness sake. |
| const uint32_t page_free = mem_page_ - freeptr % mem_page_; |
| if (size > page_free) { |
| if (page_free <= sizeof(BlockHeader)) { |
| SetCorrupt(); |
| return kReferenceNull; |
| } |
| const uint32_t new_freeptr = freeptr + page_free; |
| if (shared_meta()->freeptr.compare_exchange_strong(freeptr, |
| new_freeptr)) { |
| block->size = page_free; |
| block->cookie = kBlockCookieWasted; |
| } |
| continue; |
| } |
| |
| // Don't leave a slice at the end of a page too small for anything. This |
| // can result in an allocation up to two alignment-sizes greater than the |
| // minimum required by requested-size + header + alignment. |
| if (page_free - size < sizeof(BlockHeader) + kAllocAlignment) |
| size = page_free; |
| |
| const uint32_t new_freeptr = freeptr + size; |
| if (new_freeptr > mem_size_) { |
| SetCorrupt(); |
| return kReferenceNull; |
| } |
| |
| // Save our work. Try again if another thread has completed an allocation |
| // while we were processing. A "weak" exchange would be permissable here |
| // because the code will just loop and try again but the above processing |
| // is significant so make the extra effort of a "strong" exchange. |
| if (!shared_meta()->freeptr.compare_exchange_strong(freeptr, new_freeptr)) |
| continue; |
| |
| // Given that all memory was zeroed before ever being given to an instance |
| // of this class and given that we only allocate in a monotomic fashion |
| // going forward, it must be that the newly allocated block is completely |
| // full of zeros. If we find anything in the block header that is NOT a |
| // zero then something must have previously run amuck through memory, |
| // writing beyond the allocated space and into unallocated space. |
| if (block->size != 0 || |
| block->cookie != kBlockCookieFree || |
| block->type_id.load(std::memory_order_relaxed) != 0 || |
| block->next.load(std::memory_order_relaxed) != 0) { |
| SetCorrupt(); |
| return kReferenceNull; |
| } |
| |
| block->size = size; |
| block->cookie = kBlockCookieAllocated; |
| block->type_id.store(type_id, std::memory_order_relaxed); |
| return freeptr; |
| } |
| } |
| |
| void PersistentMemoryAllocator::GetMemoryInfo(MemoryInfo* meminfo) const { |
| uint32_t remaining = std::max( |
| mem_size_ - shared_meta()->freeptr.load(std::memory_order_relaxed), |
| (uint32_t)sizeof(BlockHeader)); |
| meminfo->total = mem_size_; |
| meminfo->free = IsCorrupt() ? 0 : remaining - sizeof(BlockHeader); |
| } |
| |
| void PersistentMemoryAllocator::MakeIterable(Reference ref) { |
| DCHECK(!readonly_); |
| if (IsCorrupt()) |
| return; |
| volatile BlockHeader* block = GetBlock(ref, 0, 0, false, false); |
| if (!block) // invalid reference |
| return; |
| if (block->next.load(std::memory_order_acquire) != 0) // Already iterable. |
| return; |
| block->next.store(kReferenceQueue, std::memory_order_release); // New tail. |
| |
| // Try to add this block to the tail of the queue. May take multiple tries. |
| // If so, tail will be automatically updated with a more recent value during |
| // compare-exchange operations. |
| uint32_t tail = shared_meta()->tailptr.load(std::memory_order_acquire); |
| for (;;) { |
| // Acquire the current tail-pointer released by previous call to this |
| // method and validate it. |
| block = GetBlock(tail, 0, 0, true, false); |
| if (!block) { |
| SetCorrupt(); |
| return; |
| } |
| |
| // Try to insert the block at the tail of the queue. The tail node always |
| // has an existing value of kReferenceQueue; if that is somehow not the |
| // existing value then another thread has acted in the meantime. A "strong" |
| // exchange is necessary so the "else" block does not get executed when |
| // that is not actually the case (which can happen with a "weak" exchange). |
| uint32_t next = kReferenceQueue; // Will get replaced with existing value. |
| if (block->next.compare_exchange_strong(next, ref, |
| std::memory_order_acq_rel, |
| std::memory_order_acquire)) { |
| // Update the tail pointer to the new offset. If the "else" clause did |
| // not exist, then this could be a simple Release_Store to set the new |
| // value but because it does, it's possible that other threads could add |
| // one or more nodes at the tail before reaching this point. We don't |
| // have to check the return value because it either operates correctly |
| // or the exact same operation has already been done (by the "else" |
| // clause) on some other thread. |
| shared_meta()->tailptr.compare_exchange_strong(tail, ref, |
| std::memory_order_release, |
| std::memory_order_relaxed); |
| return; |
| } else { |
| // In the unlikely case that a thread crashed or was killed between the |
| // update of "next" and the update of "tailptr", it is necessary to |
| // perform the operation that would have been done. There's no explicit |
| // check for crash/kill which means that this operation may also happen |
| // even when the other thread is in perfect working order which is what |
| // necessitates the CompareAndSwap above. |
| shared_meta()->tailptr.compare_exchange_strong(tail, next, |
| std::memory_order_acq_rel, |
| std::memory_order_acquire); |
| } |
| } |
| } |
| |
| // The "corrupted" state is held both locally and globally (shared). The |
| // shared flag can't be trusted since a malicious actor could overwrite it. |
| // Because corruption can be detected during read-only operations such as |
| // iteration, this method may be called by other "const" methods. In this |
| // case, it's safe to discard the constness and modify the local flag and |
| // maybe even the shared flag if the underlying data isn't actually read-only. |
| void PersistentMemoryAllocator::SetCorrupt() const { |
| LOG(ERROR) << "Corruption detected in shared-memory segment."; |
| const_cast<std::atomic<bool>*>(&corrupt_)->store(true, |
| std::memory_order_relaxed); |
| if (!readonly_) { |
| SetFlag(const_cast<volatile std::atomic<uint32_t>*>(&shared_meta()->flags), |
| kFlagCorrupt); |
| } |
| } |
| |
| bool PersistentMemoryAllocator::IsCorrupt() const { |
| if (corrupt_.load(std::memory_order_relaxed) || |
| CheckFlag(&shared_meta()->flags, kFlagCorrupt)) { |
| SetCorrupt(); // Make sure all indicators are set. |
| return true; |
| } |
| return false; |
| } |
| |
| bool PersistentMemoryAllocator::IsFull() const { |
| return CheckFlag(&shared_meta()->flags, kFlagFull); |
| } |
| |
| // Dereference a block |ref| and ensure that it's valid for the desired |
| // |type_id| and |size|. |special| indicates that we may try to access block |
| // headers not available to callers but still accessed by this module. By |
| // having internal dereferences go through this same function, the allocator |
| // is hardened against corruption. |
| const volatile PersistentMemoryAllocator::BlockHeader* |
| PersistentMemoryAllocator::GetBlock(Reference ref, uint32_t type_id, |
| uint32_t size, bool queue_ok, |
| bool free_ok) const { |
| // Validation of parameters. |
| if (ref % kAllocAlignment != 0) |
| return nullptr; |
| if (ref < (queue_ok ? kReferenceQueue : sizeof(SharedMetadata))) |
| return nullptr; |
| size += sizeof(BlockHeader); |
| if (ref + size > mem_size_) |
| return nullptr; |
| |
| // Validation of referenced block-header. |
| if (!free_ok) { |
| uint32_t freeptr = std::min( |
| shared_meta()->freeptr.load(std::memory_order_relaxed), mem_size_); |
| if (ref + size > freeptr) |
| return nullptr; |
| const volatile BlockHeader* const block = |
| reinterpret_cast<volatile BlockHeader*>(mem_base_ + ref); |
| if (block->size < size) |
| return nullptr; |
| if (ref + block->size > freeptr) |
| return nullptr; |
| if (ref != kReferenceQueue && block->cookie != kBlockCookieAllocated) |
| return nullptr; |
| if (type_id != 0 && |
| block->type_id.load(std::memory_order_relaxed) != type_id) { |
| return nullptr; |
| } |
| } |
| |
| // Return pointer to block data. |
| return reinterpret_cast<const volatile BlockHeader*>(mem_base_ + ref); |
| } |
| |
| const volatile void* PersistentMemoryAllocator::GetBlockData( |
| Reference ref, |
| uint32_t type_id, |
| uint32_t size) const { |
| DCHECK(size > 0); |
| const volatile BlockHeader* block = |
| GetBlock(ref, type_id, size, false, false); |
| if (!block) |
| return nullptr; |
| return reinterpret_cast<const volatile char*>(block) + sizeof(BlockHeader); |
| } |
| |
| void PersistentMemoryAllocator::UpdateTrackingHistograms() { |
| DCHECK(!readonly_); |
| if (used_histogram_) { |
| MemoryInfo meminfo; |
| GetMemoryInfo(&meminfo); |
| HistogramBase::Sample used_percent = static_cast<HistogramBase::Sample>( |
| ((meminfo.total - meminfo.free) * 100ULL / meminfo.total)); |
| used_histogram_->Add(used_percent); |
| } |
| } |
| |
| |
| //----- LocalPersistentMemoryAllocator ----------------------------------------- |
| |
| LocalPersistentMemoryAllocator::LocalPersistentMemoryAllocator( |
| size_t size, |
| uint64_t id, |
| base::StringPiece name) |
| : PersistentMemoryAllocator(AllocateLocalMemory(size), |
| size, 0, id, name, false) {} |
| |
| LocalPersistentMemoryAllocator::~LocalPersistentMemoryAllocator() { |
| DeallocateLocalMemory(const_cast<char*>(mem_base_), mem_size_); |
| } |
| |
| // static |
| void* LocalPersistentMemoryAllocator::AllocateLocalMemory(size_t size) { |
| #if defined(OS_WIN) |
| void* address = |
| ::VirtualAlloc(nullptr, size, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE); |
| DPCHECK(address); |
| return address; |
| #elif defined(OS_POSIX) |
| // MAP_ANON is deprecated on Linux but MAP_ANONYMOUS is not universal on Mac. |
| // MAP_SHARED is not available on Linux <2.4 but required on Mac. |
| void* address = ::mmap(nullptr, size, PROT_READ | PROT_WRITE, |
| MAP_ANON | MAP_SHARED, -1, 0); |
| DPCHECK(MAP_FAILED != address); |
| return address; |
| #else |
| #error This architecture is not (yet) supported. |
| #endif |
| } |
| |
| // static |
| void LocalPersistentMemoryAllocator::DeallocateLocalMemory(void* memory, |
| size_t size) { |
| #if defined(OS_WIN) |
| BOOL success = ::VirtualFree(memory, 0, MEM_DECOMMIT); |
| DPCHECK(success); |
| #elif defined(OS_POSIX) |
| int result = ::munmap(memory, size); |
| DPCHECK(0 == result); |
| #else |
| #error This architecture is not (yet) supported. |
| #endif |
| } |
| |
| |
| //----- SharedPersistentMemoryAllocator ---------------------------------------- |
| |
| SharedPersistentMemoryAllocator::SharedPersistentMemoryAllocator( |
| std::unique_ptr<SharedMemory> memory, |
| uint64_t id, |
| base::StringPiece name, |
| bool read_only) |
| : PersistentMemoryAllocator(static_cast<uint8_t*>(memory->memory()), |
| memory->mapped_size(), |
| 0, |
| id, |
| name, |
| read_only), |
| shared_memory_(std::move(memory)) {} |
| |
| SharedPersistentMemoryAllocator::~SharedPersistentMemoryAllocator() {} |
| |
| // static |
| bool SharedPersistentMemoryAllocator::IsSharedMemoryAcceptable( |
| const SharedMemory& memory) { |
| return IsMemoryAcceptable(memory.memory(), memory.mapped_size(), 0, false); |
| } |
| |
| |
| #if !defined(OS_NACL) |
| //----- FilePersistentMemoryAllocator ------------------------------------------ |
| |
| FilePersistentMemoryAllocator::FilePersistentMemoryAllocator( |
| std::unique_ptr<MemoryMappedFile> file, |
| size_t max_size, |
| uint64_t id, |
| base::StringPiece name, |
| bool read_only) |
| : PersistentMemoryAllocator(const_cast<uint8_t*>(file->data()), |
| max_size != 0 ? max_size : file->length(), |
| 0, |
| id, |
| name, |
| read_only), |
| mapped_file_(std::move(file)) {} |
| |
| FilePersistentMemoryAllocator::~FilePersistentMemoryAllocator() {} |
| |
| // static |
| bool FilePersistentMemoryAllocator::IsFileAcceptable( |
| const MemoryMappedFile& file, |
| bool read_only) { |
| return IsMemoryAcceptable(file.data(), file.length(), 0, read_only); |
| } |
| #endif // !defined(OS_NACL) |
| |
| } // namespace base |