Current File : //usr/local/include/google/protobuf/arena_impl.h
// Protocol Buffers - Google's data interchange format
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// https://developers.google.com/protocol-buffers/
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// This file defines an Arena allocator for better allocation performance.
#ifndef GOOGLE_PROTOBUF_ARENA_IMPL_H__
#define GOOGLE_PROTOBUF_ARENA_IMPL_H__
#include <atomic>
#include <limits>
#include <typeinfo>
#include <google/protobuf/stubs/common.h>
#include <google/protobuf/stubs/logging.h>
#ifdef ADDRESS_SANITIZER
#include <sanitizer/asan_interface.h>
#endif // ADDRESS_SANITIZER
#include <google/protobuf/port_def.inc>
namespace google {
namespace protobuf {
namespace internal {
inline constexpr size_t AlignUpTo8(size_t n) {
// Align n to next multiple of 8 (from Hacker's Delight, Chapter 3.)
return (n + 7) & static_cast<size_t>(-8);
}
using LifecycleIdAtomic = uint64_t;
// MetricsCollector collects stats for a particular arena.
class PROTOBUF_EXPORT ArenaMetricsCollector {
public:
ArenaMetricsCollector(bool record_allocs) : record_allocs_(record_allocs) {}
// Invoked when the arena is about to be destroyed. This method will
// typically finalize any metric collection and delete the collector.
// space_allocated is the space used by the arena.
virtual void OnDestroy(uint64 space_allocated) = 0;
// OnReset() is called when the associated arena is reset.
// space_allocated is the space used by the arena just before the reset.
virtual void OnReset(uint64 space_allocated) = 0;
// OnAlloc is called when an allocation happens.
// type_info is promised to be static - its lifetime extends to
// match program's lifetime (It is given by typeid operator).
// Note: typeid(void) will be passed as allocated_type every time we
// intentionally want to avoid monitoring an allocation. (i.e. internal
// allocations for managing the arena)
virtual void OnAlloc(const std::type_info* allocated_type,
uint64 alloc_size) = 0;
// Does OnAlloc() need to be called? If false, metric collection overhead
// will be reduced since we will not do extra work per allocation.
bool RecordAllocs() { return record_allocs_; }
protected:
// This class is destructed by the call to OnDestroy().
~ArenaMetricsCollector() = default;
const bool record_allocs_;
};
struct AllocationPolicy {
static constexpr size_t kDefaultStartBlockSize = 256;
static constexpr size_t kDefaultMaxBlockSize = 8192;
size_t start_block_size = kDefaultStartBlockSize;
size_t max_block_size = kDefaultMaxBlockSize;
void* (*block_alloc)(size_t) = nullptr;
void (*block_dealloc)(void*, size_t) = nullptr;
ArenaMetricsCollector* metrics_collector = nullptr;
bool IsDefault() const {
return start_block_size == kDefaultMaxBlockSize &&
max_block_size == kDefaultMaxBlockSize && block_alloc == nullptr &&
block_dealloc == nullptr && metrics_collector == nullptr;
}
};
// A simple arena allocator. Calls to allocate functions must be properly
// serialized by the caller, hence this class cannot be used as a general
// purpose allocator in a multi-threaded program. It serves as a building block
// for ThreadSafeArena, which provides a thread-safe arena allocator.
//
// This class manages
// 1) Arena bump allocation + owning memory blocks.
// 2) Maintaining a cleanup list.
// It delagetes the actual memory allocation back to ThreadSafeArena, which
// contains the information on block growth policy and backing memory allocation
// used.
class PROTOBUF_EXPORT SerialArena {
public:
struct Memory {
void* ptr;
size_t size;
};
// Node contains the ptr of the object to be cleaned up and the associated
// cleanup function ptr.
struct CleanupNode {
void* elem; // Pointer to the object to be cleaned up.
void (*cleanup)(void*); // Function pointer to the destructor or deleter.
};
// Creates a new SerialArena inside mem using the remaining memory as for
// future allocations.
static SerialArena* New(SerialArena::Memory mem, void* owner);
// Free SerialArena returning the memory passed in to New
template <typename Deallocator>
Memory Free(Deallocator deallocator);
void CleanupList();
uint64 SpaceAllocated() const {
return space_allocated_.load(std::memory_order_relaxed);
}
uint64 SpaceUsed() const;
bool HasSpace(size_t n) { return n <= static_cast<size_t>(limit_ - ptr_); }
void* AllocateAligned(size_t n, const AllocationPolicy* policy) {
GOOGLE_DCHECK_EQ(internal::AlignUpTo8(n), n); // Must be already aligned.
GOOGLE_DCHECK_GE(limit_, ptr_);
if (PROTOBUF_PREDICT_FALSE(!HasSpace(n))) {
return AllocateAlignedFallback(n, policy);
}
void* ret = ptr_;
ptr_ += n;
#ifdef ADDRESS_SANITIZER
ASAN_UNPOISON_MEMORY_REGION(ret, n);
#endif // ADDRESS_SANITIZER
return ret;
}
// Allocate space if the current region provides enough space.
bool MaybeAllocateAligned(size_t n, void** out) {
GOOGLE_DCHECK_EQ(internal::AlignUpTo8(n), n); // Must be already aligned.
GOOGLE_DCHECK_GE(limit_, ptr_);
if (PROTOBUF_PREDICT_FALSE(!HasSpace(n))) return false;
void* ret = ptr_;
ptr_ += n;
#ifdef ADDRESS_SANITIZER
ASAN_UNPOISON_MEMORY_REGION(ret, n);
#endif // ADDRESS_SANITIZER
*out = ret;
return true;
}
std::pair<void*, CleanupNode*> AllocateAlignedWithCleanup(
size_t n, const AllocationPolicy* policy) {
if (PROTOBUF_PREDICT_FALSE(!HasSpace(n + kCleanupSize))) {
return AllocateAlignedWithCleanupFallback(n, policy);
}
void* ret = ptr_;
ptr_ += n;
limit_ -= kCleanupSize;
#ifdef ADDRESS_SANITIZER
ASAN_UNPOISON_MEMORY_REGION(ret, n);
ASAN_UNPOISON_MEMORY_REGION(limit_, kCleanupSize);
#endif // ADDRESS_SANITIZER
return CreatePair(ret, reinterpret_cast<CleanupNode*>(limit_));
}
void AddCleanup(void* elem, void (*cleanup)(void*),
const AllocationPolicy* policy) {
auto res = AllocateAlignedWithCleanup(0, policy);
res.second->elem = elem;
res.second->cleanup = cleanup;
}
void* owner() const { return owner_; }
SerialArena* next() const { return next_; }
void set_next(SerialArena* next) { next_ = next; }
private:
// Blocks are variable length malloc-ed objects. The following structure
// describes the common header for all blocks.
struct Block {
char* Pointer(size_t n) {
GOOGLE_DCHECK(n <= size);
return reinterpret_cast<char*>(this) + n;
}
Block* next;
size_t size;
CleanupNode* start;
// data follows
};
void* owner_; // &ThreadCache of this thread;
Block* head_; // Head of linked list of blocks.
SerialArena* next_; // Next SerialArena in this linked list.
size_t space_used_ = 0; // Necessary for metrics.
std::atomic<size_t> space_allocated_;
// Next pointer to allocate from. Always 8-byte aligned. Points inside
// head_ (and head_->pos will always be non-canonical). We keep these
// here to reduce indirection.
char* ptr_;
char* limit_;
// Constructor is private as only New() should be used.
inline SerialArena(Block* b, void* owner);
void* AllocateAlignedFallback(size_t n, const AllocationPolicy* policy);
std::pair<void*, CleanupNode*> AllocateAlignedWithCleanupFallback(
size_t n, const AllocationPolicy* policy);
void AllocateNewBlock(size_t n, const AllocationPolicy* policy);
std::pair<void*, CleanupNode*> CreatePair(void* ptr, CleanupNode* node) {
return {ptr, node};
}
public:
static constexpr size_t kBlockHeaderSize = AlignUpTo8(sizeof(Block));
static constexpr size_t kCleanupSize = AlignUpTo8(sizeof(CleanupNode));
};
// This class provides the core Arena memory allocation library. Different
// implementations only need to implement the public interface below.
// Arena is not a template type as that would only be useful if all protos
// in turn would be templates, which will/cannot happen. However separating
// the memory allocation part from the cruft of the API users expect we can
// use #ifdef the select the best implementation based on hardware / OS.
class PROTOBUF_EXPORT ThreadSafeArena {
public:
ThreadSafeArena() { Init(false); }
ThreadSafeArena(char* mem, size_t size) { InitializeFrom(mem, size); }
explicit ThreadSafeArena(void* mem, size_t size,
const AllocationPolicy& policy) {
if (policy.IsDefault()) {
// Legacy code doesn't use the API above, but provides the initial block
// through ArenaOptions. I suspect most do not touch the allocation
// policy parameters.
InitializeFrom(mem, size);
} else {
auto collector = policy.metrics_collector;
bool record_allocs = collector && collector->RecordAllocs();
InitializeWithPolicy(mem, size, record_allocs, policy);
}
}
// Destructor deletes all owned heap allocated objects, and destructs objects
// that have non-trivial destructors, except for proto2 message objects whose
// destructors can be skipped. Also, frees all blocks except the initial block
// if it was passed in.
~ThreadSafeArena();
uint64 Reset();
uint64 SpaceAllocated() const;
uint64 SpaceUsed() const;
void* AllocateAligned(size_t n, const std::type_info* type) {
SerialArena* arena;
if (PROTOBUF_PREDICT_TRUE(GetSerialArenaFast(tag_and_id_, &arena))) {
return arena->AllocateAligned(n, AllocPolicy());
} else {
return AllocateAlignedFallback(n, type);
}
}
// This function allocates n bytes if the common happy case is true and
// returns true. Otherwise does nothing and returns false. This strange
// semantics is necessary to allow callers to program functions that only
// have fallback function calls in tail position. This substantially improves
// code for the happy path.
PROTOBUF_NDEBUG_INLINE bool MaybeAllocateAligned(size_t n, void** out) {
SerialArena* a;
if (PROTOBUF_PREDICT_TRUE(GetSerialArenaFromThreadCache(tag_and_id_, &a))) {
return a->MaybeAllocateAligned(n, out);
}
return false;
}
std::pair<void*, SerialArena::CleanupNode*> AllocateAlignedWithCleanup(
size_t n, const std::type_info* type);
// Add object pointer and cleanup function pointer to the list.
void AddCleanup(void* elem, void (*cleanup)(void*));
private:
// Unique for each arena. Changes on Reset().
uint64 tag_and_id_;
// The LSB of tag_and_id_ indicates if allocs in this arena are recorded.
enum { kRecordAllocs = 1 };
intptr_t alloc_policy_ = 0; // Tagged pointer to AllocPolicy.
// The LSB of alloc_policy_ indicates if the user owns the initial block.
enum { kUserOwnedInitialBlock = 1 };
// Pointer to a linked list of SerialArena.
std::atomic<SerialArena*> threads_;
std::atomic<SerialArena*> hint_; // Fast thread-local block access
const AllocationPolicy* AllocPolicy() const {
return reinterpret_cast<const AllocationPolicy*>(alloc_policy_ & -8);
}
void InitializeFrom(void* mem, size_t size);
void InitializeWithPolicy(void* mem, size_t size, bool record_allocs,
AllocationPolicy policy);
void* AllocateAlignedFallback(size_t n, const std::type_info* type);
std::pair<void*, SerialArena::CleanupNode*>
AllocateAlignedWithCleanupFallback(size_t n, const std::type_info* type);
void AddCleanupFallback(void* elem, void (*cleanup)(void*));
void Init(bool record_allocs);
void SetInitialBlock(void* mem, size_t size);
// Delete or Destruct all objects owned by the arena.
void CleanupList();
inline bool ShouldRecordAlloc() const { return tag_and_id_ & kRecordAllocs; }
inline uint64 LifeCycleId() const {
return tag_and_id_ & (-kRecordAllocs - 1);
}
inline void RecordAlloc(const std::type_info* allocated_type,
size_t n) const {
AllocPolicy()->metrics_collector->OnAlloc(allocated_type, n);
}
inline void CacheSerialArena(SerialArena* serial) {
thread_cache().last_serial_arena = serial;
thread_cache().last_lifecycle_id_seen = LifeCycleId();
// TODO(haberman): evaluate whether we would gain efficiency by getting rid
// of hint_. It's the only write we do to ThreadSafeArena in the allocation
// path, which will dirty the cache line.
hint_.store(serial, std::memory_order_release);
}
PROTOBUF_NDEBUG_INLINE bool GetSerialArenaFast(uint64 lifecycle_id,
SerialArena** arena) {
if (GetSerialArenaFromThreadCache(lifecycle_id, arena)) return true;
if (lifecycle_id & kRecordAllocs) return false;
// Check whether we own the last accessed SerialArena on this arena. This
// fast path optimizes the case where a single thread uses multiple arenas.
ThreadCache* tc = &thread_cache();
SerialArena* serial = hint_.load(std::memory_order_acquire);
if (PROTOBUF_PREDICT_TRUE(serial != NULL && serial->owner() == tc)) {
*arena = serial;
return true;
}
return false;
}
PROTOBUF_NDEBUG_INLINE bool GetSerialArenaFromThreadCache(
uint64 lifecycle_id, SerialArena** arena) {
// If this thread already owns a block in this arena then try to use that.
// This fast path optimizes the case where multiple threads allocate from
// the same arena.
ThreadCache* tc = &thread_cache();
if (PROTOBUF_PREDICT_TRUE(tc->last_lifecycle_id_seen == lifecycle_id)) {
*arena = tc->last_serial_arena;
return true;
}
return false;
}
SerialArena* GetSerialArenaFallback(void* me);
template <typename Functor>
void PerSerialArena(Functor fn) {
// By omitting an Acquire barrier we ensure that any user code that doesn't
// properly synchronize Reset() or the destructor will throw a TSAN warning.
SerialArena* serial = threads_.load(std::memory_order_relaxed);
for (; serial; serial = serial->next()) fn(serial);
}
// Releases all memory except the first block which it returns. The first
// block might be owned by the user and thus need some extra checks before
// deleting.
SerialArena::Memory Free(size_t* space_allocated);
#ifdef _MSC_VER
#pragma warning(disable : 4324)
#endif
struct alignas(64) ThreadCache {
#if defined(GOOGLE_PROTOBUF_NO_THREADLOCAL)
// If we are using the ThreadLocalStorage class to store the ThreadCache,
// then the ThreadCache's default constructor has to be responsible for
// initializing it.
ThreadCache()
: next_lifecycle_id(0),
last_lifecycle_id_seen(-1),
last_serial_arena(NULL) {}
#endif
// Number of per-thread lifecycle IDs to reserve. Must be power of two.
// To reduce contention on a global atomic, each thread reserves a batch of
// IDs. The following number is calculated based on a stress test with
// ~6500 threads all frequently allocating a new arena.
static constexpr size_t kPerThreadIds = 256;
// Next lifecycle ID available to this thread. We need to reserve a new
// batch, if `next_lifecycle_id & (kPerThreadIds - 1) == 0`.
uint64 next_lifecycle_id;
// The ThreadCache is considered valid as long as this matches the
// lifecycle_id of the arena being used.
uint64 last_lifecycle_id_seen;
SerialArena* last_serial_arena;
};
// Lifecycle_id can be highly contended variable in a situation of lots of
// arena creation. Make sure that other global variables are not sharing the
// cacheline.
#ifdef _MSC_VER
#pragma warning(disable : 4324)
#endif
struct alignas(64) CacheAlignedLifecycleIdGenerator {
std::atomic<LifecycleIdAtomic> id;
};
static CacheAlignedLifecycleIdGenerator lifecycle_id_generator_;
#if defined(GOOGLE_PROTOBUF_NO_THREADLOCAL)
// Android ndk does not support __thread keyword so we use a custom thread
// local storage class we implemented.
// iOS also does not support the __thread keyword.
static ThreadCache& thread_cache();
#elif defined(PROTOBUF_USE_DLLS)
// Thread local variables cannot be exposed through DLL interface but we can
// wrap them in static functions.
static ThreadCache& thread_cache();
#else
static PROTOBUF_THREAD_LOCAL ThreadCache thread_cache_;
static ThreadCache& thread_cache() { return thread_cache_; }
#endif
GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ThreadSafeArena);
// All protos have pointers back to the arena hence Arena must have
// pointer stability.
ThreadSafeArena(ThreadSafeArena&&) = delete;
ThreadSafeArena& operator=(ThreadSafeArena&&) = delete;
public:
// kBlockHeaderSize is sizeof(Block), aligned up to the nearest multiple of 8
// to protect the invariant that pos is always at a multiple of 8.
static constexpr size_t kBlockHeaderSize = SerialArena::kBlockHeaderSize;
static constexpr size_t kSerialArenaSize =
(sizeof(SerialArena) + 7) & static_cast<size_t>(-8);
static_assert(kBlockHeaderSize % 8 == 0,
"kBlockHeaderSize must be a multiple of 8.");
static_assert(kSerialArenaSize % 8 == 0,
"kSerialArenaSize must be a multiple of 8.");
};
} // namespace internal
} // namespace protobuf
} // namespace google
#include <google/protobuf/port_undef.inc>
#endif // GOOGLE_PROTOBUF_ARENA_IMPL_H__
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