| // 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. |
| |
| #ifndef BASE_METRICS_PERSISTENT_MEMORY_ALLOCATOR_H_ |
| #define BASE_METRICS_PERSISTENT_MEMORY_ALLOCATOR_H_ |
| |
| #include <stdint.h> |
| #include <atomic> |
| |
| #include "base/atomicops.h" |
| #include "base/base_export.h" |
| #include "base/gtest_prod_util.h" |
| #include "base/macros.h" |
| #include "base/memory/scoped_ptr.h" |
| #include "base/strings/string_piece.h" |
| |
| namespace base { |
| |
| class HistogramBase; |
| class MemoryMappedFile; |
| class SharedMemory; |
| |
| // Simple allocator for pieces of a memory block that may be persistent |
| // to some storage or shared across multiple processes. This class resides |
| // under base/metrics because it was written for that purpose. It is, |
| // however, fully general-purpose and can be freely moved to base/memory |
| // if other uses are found. |
| // |
| // This class provides for thread-secure (i.e. safe against other threads |
| // or processes that may be compromised and thus have malicious intent) |
| // allocation of memory within a designated block and also a mechanism by |
| // which other threads can learn of these allocations. |
| // |
| // There is (currently) no way to release an allocated block of data because |
| // doing so would risk invalidating pointers held by other processes and |
| // greatly complicate the allocation algorithm. |
| // |
| // Construction of this object can accept new, clean (i.e. zeroed) memory |
| // or previously initialized memory. In the first case, construction must |
| // be allowed to complete before letting other allocators attach to the same |
| // segment. In other words, don't share the segment until at least one |
| // allocator has been attached to it. |
| // |
| // Note that memory not in active use is not accessed so it is possible to |
| // use virtual memory, including memory-mapped files, as backing storage with |
| // the OS "pinning" new (zeroed) physical RAM pages only as they are needed. |
| class BASE_EXPORT PersistentMemoryAllocator { |
| public: |
| typedef uint32_t Reference; |
| |
| // Internal state information when iterating over memory allocations. |
| class Iterator { |
| public: |
| Iterator() : last(0) {} |
| |
| bool operator==(const Iterator& rhs) const { return last == rhs.last; } |
| bool operator!=(const Iterator& rhs) const { return last != rhs.last; } |
| |
| void clear() { last = 0; } |
| bool is_clear() const { return last == 0; } |
| |
| private: |
| friend class PersistentMemoryAllocator; |
| |
| Reference last; |
| uint32_t niter; |
| }; |
| |
| // Returned information about the internal state of the heap. |
| struct MemoryInfo { |
| size_t total; |
| size_t free; |
| }; |
| |
| enum : uint32_t { |
| kTypeIdAny = 0 // Match any type-id inside GetAsObject(). |
| }; |
| |
| // The allocator operates on any arbitrary block of memory. Creation and |
| // persisting or sharing of that block with another process is the |
| // responsibility of the caller. The allocator needs to know only the |
| // block's |base| address, the total |size| of the block, and any internal |
| // |page| size (zero if not paged) across which allocations should not span. |
| // The |id| is an arbitrary value the caller can use to identify a |
| // particular memory segment. It will only be loaded during the initial |
| // creation of the segment and can be checked by the caller for consistency. |
| // The |name|, if provided, is used to distinguish histograms for this |
| // allocator. Only the primary owner of the segment should define this value; |
| // other processes can learn it from the shared state. If the underlying |
| // memory is |readonly| then no changes will be made to it. The resulting |
| // object should be stored as a "const" pointer. |
| // |
| // PersistentMemoryAllocator does NOT take ownership of the memory block. |
| // The caller must manage it and ensure it stays available throughout the |
| // lifetime of this object. |
| // |
| // Memory segments for sharing must have had an allocator attached to them |
| // before actually being shared. If the memory segment was just created, it |
| // should be zeroed before being passed here. If it was an existing segment, |
| // the values here will be compared to copies stored in the shared segment |
| // as a guard against corruption. |
| // |
| // Make sure that the memory segment is acceptable (see IsMemoryAcceptable() |
| // method below) before construction if the definition of the segment can |
| // vary in any way at run-time. Invalid memory segments will cause a crash. |
| PersistentMemoryAllocator(void* base, size_t size, size_t page_size, |
| uint64_t id, base::StringPiece name, |
| bool readonly); |
| virtual ~PersistentMemoryAllocator(); |
| |
| // Check if memory segment is acceptable for creation of an Allocator. This |
| // doesn't do any analysis of the data and so doesn't guarantee that the |
| // contents are valid, just that the paramaters won't cause the program to |
| // abort. The IsCorrupt() method will report detection of data problems |
| // found during construction and general operation. |
| static bool IsMemoryAcceptable(const void* data, size_t size, |
| size_t page_size, bool readonly); |
| |
| // Get the internal identifier for this persistent memory segment. |
| uint64_t Id() const; |
| |
| // Get the internal name of this allocator (possibly an empty string). |
| const char* Name() const; |
| |
| // Is this segment open only for read? |
| bool IsReadonly() { return readonly_; } |
| |
| // Create internal histograms for tracking memory use and allocation sizes |
| // for allocator of |name| (which can simply be the result of Name()). This |
| // is done seperately from construction for situations such as when the |
| // histograms will be backed by memory provided by this very allocator. |
| // |
| // IMPORTANT: Callers must update tools/metrics/histograms/histograms.xml |
| // with the following histograms: |
| // UMA.PersistentAllocator.name.Allocs |
| // UMA.PersistentAllocator.name.UsedPct |
| void CreateTrackingHistograms(base::StringPiece name); |
| |
| // Direct access to underlying memory segment. If the segment is shared |
| // across threads or processes, reading data through these values does |
| // not guarantee consistency. Use with care. Do not write. |
| const void* data() const { return const_cast<const char*>(mem_base_); } |
| size_t length() const { return mem_size_; } |
| size_t used() const; |
| |
| // Get an object referenced by a |ref|. For safety reasons, the |type_id| |
| // code and size-of(|T|) are compared to ensure the reference is valid |
| // and cannot return an object outside of the memory segment. A |type_id| of |
| // kTypeIdAny (zero) will match any though the size is still checked. NULL is |
| // returned if any problem is detected, such as corrupted storage or incorrect |
| // parameters. Callers MUST check that the returned value is not-null EVERY |
| // TIME before accessing it or risk crashing! Once dereferenced, the pointer |
| // is safe to reuse forever. |
| // |
| // NOTE: Though this method will guarantee that an object of the specified |
| // type can be accessed without going outside the bounds of the memory |
| // segment, it makes no guarantees of the validity of the data within the |
| // object itself. If it is expected that the contents of the segment could |
| // be compromised with malicious intent, the object must be hardened as well. |
| // |
| // Though the persistent data may be "volatile" if it is shared with |
| // other processes, such is not necessarily the case. The internal |
| // "volatile" designation is discarded so as to not propagate the viral |
| // nature of that keyword to the caller. It can add it back, if necessary, |
| // based on knowledge of how the allocator is being used. |
| template <typename T> |
| T* GetAsObject(Reference ref, uint32_t type_id) { |
| static_assert(!std::is_polymorphic<T>::value, "no polymorphic objects"); |
| return const_cast<T*>( |
| reinterpret_cast<volatile T*>(GetBlockData(ref, type_id, sizeof(T)))); |
| } |
| template <typename T> |
| const T* GetAsObject(Reference ref, uint32_t type_id) const { |
| static_assert(!std::is_polymorphic<T>::value, "no polymorphic objects"); |
| return const_cast<const T*>( |
| reinterpret_cast<const volatile T*>(GetBlockData( |
| ref, type_id, sizeof(T)))); |
| } |
| |
| // Get the number of bytes allocated to a block. This is useful when storing |
| // arrays in order to validate the ending boundary. The returned value will |
| // include any padding added to achieve the required alignment and so could |
| // be larger than given in the original Allocate() request. |
| size_t GetAllocSize(Reference ref) const; |
| |
| // Access the internal "type" of an object. This generally isn't necessary |
| // but can be used to "clear" the type and so effectively mark it as deleted |
| // even though the memory stays valid and allocated. |
| uint32_t GetType(Reference ref) const; |
| void SetType(Reference ref, uint32_t type_id); |
| |
| // Reserve space in the memory segment of the desired |size| and |type_id|. |
| // A return value of zero indicates the allocation failed, otherwise the |
| // returned reference can be used by any process to get a real pointer via |
| // the GetAsObject() call. |
| Reference Allocate(size_t size, uint32_t type_id); |
| |
| // Allocated objects can be added to an internal list that can then be |
| // iterated over by other processes. If an allocated object can be found |
| // another way, such as by having its reference within a different object |
| // that will be made iterable, then this call is not necessary. This always |
| // succeeds unless corruption is detected; check IsCorrupted() to find out. |
| // Once an object is made iterable, its position in iteration can never |
| // change; new iterable objects will always be added after it in the series. |
| void MakeIterable(Reference ref); |
| |
| // Get the information about the amount of free space in the allocator. The |
| // amount of free space should be treated as approximate due to extras from |
| // alignment and metadata. Concurrent allocations from other threads will |
| // also make the true amount less than what is reported. |
| void GetMemoryInfo(MemoryInfo* meminfo) const; |
| |
| // Iterating uses a |state| structure (initialized by CreateIterator) and |
| // returns both the reference to the object as well as the |type_id| of |
| // that object. A zero return value indicates there are currently no more |
| // objects to be found but future attempts can be made without having to |
| // reset the iterator to "first". Creating an iterator |starting_after| |
| // a known iterable object allows "resume" from that point with the next |
| // call to GetNextIterable returning the object after it. |
| void CreateIterator(Iterator* state) const { CreateIterator(state, 0); }; |
| void CreateIterator(Iterator* state, Reference starting_after) const; |
| Reference GetNextIterable(Iterator* state, uint32_t* type_id) const; |
| |
| // If there is some indication that the memory has become corrupted, |
| // calling this will attempt to prevent further damage by indicating to |
| // all processes that something is not as expected. |
| void SetCorrupt() const; |
| |
| // This can be called to determine if corruption has been detected in the |
| // segment, possibly my a malicious actor. Once detected, future allocations |
| // will fail and iteration may not locate all objects. |
| bool IsCorrupt() const; |
| |
| // Flag set if an allocation has failed because the memory segment was full. |
| bool IsFull() const; |
| |
| // Update those "tracking" histograms which do not get updates during regular |
| // operation, such as how much memory is currently used. This should be |
| // called before such information is to be displayed or uploaded. |
| void UpdateTrackingHistograms(); |
| |
| protected: |
| volatile char* const mem_base_; // Memory base. (char so sizeof guaranteed 1) |
| const uint32_t mem_size_; // Size of entire memory segment. |
| const uint32_t mem_page_; // Page size allocations shouldn't cross. |
| |
| private: |
| struct SharedMetadata; |
| struct BlockHeader; |
| static const uint32_t kAllocAlignment; |
| static const Reference kReferenceQueue; |
| static const Reference kReferenceNull; |
| |
| // The shared metadata is always located at the top of the memory segment. |
| // These convenience functions eliminate constant casting of the base |
| // pointer within the code. |
| const SharedMetadata* shared_meta() const { |
| return reinterpret_cast<const SharedMetadata*>( |
| const_cast<const char*>(mem_base_)); |
| } |
| SharedMetadata* shared_meta() { |
| return reinterpret_cast<SharedMetadata*>(const_cast<char*>(mem_base_)); |
| } |
| |
| // Actual method for doing the allocation. |
| Reference AllocateImpl(size_t size, uint32_t type_id); |
| |
| // Get the block header associated with a specific reference. |
| const volatile BlockHeader* GetBlock(Reference ref, uint32_t type_id, |
| uint32_t size, bool queue_ok, |
| bool free_ok) const; |
| volatile BlockHeader* GetBlock(Reference ref, uint32_t type_id, uint32_t size, |
| bool queue_ok, bool free_ok) { |
| return const_cast<volatile BlockHeader*>( |
| const_cast<const PersistentMemoryAllocator*>(this)->GetBlock( |
| ref, type_id, size, queue_ok, free_ok)); |
| } |
| |
| // Get the actual data within a block associated with a specific reference. |
| const volatile void* GetBlockData(Reference ref, uint32_t type_id, |
| uint32_t size) const; |
| volatile void* GetBlockData(Reference ref, uint32_t type_id, |
| uint32_t size) { |
| return const_cast<volatile void*>( |
| const_cast<const PersistentMemoryAllocator*>(this)->GetBlockData( |
| ref, type_id, size)); |
| } |
| |
| const bool readonly_; // Indicates access to read-only memory. |
| std::atomic<bool> corrupt_; // Local version of "corrupted" flag. |
| |
| HistogramBase* allocs_histogram_; // Histogram recording allocs. |
| HistogramBase* used_histogram_; // Histogram recording used space. |
| |
| friend class PersistentMemoryAllocatorTest; |
| FRIEND_TEST_ALL_PREFIXES(PersistentMemoryAllocatorTest, AllocateAndIterate); |
| DISALLOW_COPY_AND_ASSIGN(PersistentMemoryAllocator); |
| }; |
| |
| |
| // This allocator uses a local memory block it allocates from the general |
| // heap. It is generally used when some kind of "death rattle" handler will |
| // save the contents to persistent storage during process shutdown. It is |
| // also useful for testing. |
| class BASE_EXPORT LocalPersistentMemoryAllocator |
| : public PersistentMemoryAllocator { |
| public: |
| LocalPersistentMemoryAllocator(size_t size, uint64_t id, |
| base::StringPiece name); |
| ~LocalPersistentMemoryAllocator() override; |
| |
| private: |
| DISALLOW_COPY_AND_ASSIGN(LocalPersistentMemoryAllocator); |
| }; |
| |
| |
| // This allocator takes a shared-memory object and performs allocation from |
| // it. The memory must be previously mapped via Map() or MapAt(). The allocator |
| // takes ownership of the memory object. |
| class BASE_EXPORT SharedPersistentMemoryAllocator |
| : public PersistentMemoryAllocator { |
| public: |
| SharedPersistentMemoryAllocator(scoped_ptr<SharedMemory> memory, uint64_t id, |
| base::StringPiece name, bool read_only); |
| ~SharedPersistentMemoryAllocator() override; |
| |
| SharedMemory* shared_memory() { return shared_memory_.get(); } |
| |
| // Ensure that the memory isn't so invalid that it won't crash when passing it |
| // to the allocator. This doesn't guarantee the data is valid, just that it |
| // won't cause the program to abort. The existing IsCorrupt() call will handle |
| // the rest. |
| static bool IsSharedMemoryAcceptable(const SharedMemory& memory); |
| |
| private: |
| scoped_ptr<SharedMemory> shared_memory_; |
| |
| DISALLOW_COPY_AND_ASSIGN(SharedPersistentMemoryAllocator); |
| }; |
| |
| |
| // This allocator takes a memory-mapped file object and performs allocation |
| // from it. The allocator takes ownership of the file object. Only read access |
| // is provided due to limitions of the MemoryMappedFile class. |
| class BASE_EXPORT FilePersistentMemoryAllocator |
| : public PersistentMemoryAllocator { |
| public: |
| FilePersistentMemoryAllocator(scoped_ptr<MemoryMappedFile> file, uint64_t id, |
| base::StringPiece name); |
| ~FilePersistentMemoryAllocator() override; |
| |
| // Ensure that the file isn't so invalid that it won't crash when passing it |
| // to the allocator. This doesn't guarantee the file is valid, just that it |
| // won't cause the program to abort. The existing IsCorrupt() call will handle |
| // the rest. |
| static bool IsFileAcceptable(const MemoryMappedFile& file); |
| |
| private: |
| scoped_ptr<MemoryMappedFile> mapped_file_; |
| |
| DISALLOW_COPY_AND_ASSIGN(FilePersistentMemoryAllocator); |
| }; |
| |
| } // namespace base |
| |
| #endif // BASE_METRICS_PERSISTENT_MEMORY_ALLOCATOR_H_ |