Move base to DEPS

base/memory/discardable_shared_memory.cc

-// Copyright 2014 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/memory/discardable_shared_memory.h"
-
-#if defined(OS_POSIX)
-#include <unistd.h>
-#endif
-
-#include <algorithm>
-
-#include "base/atomicops.h"
-#include "base/logging.h"
-#include "base/numerics/safe_math.h"
-#include "base/process/process_metrics.h"
-
-#if defined(OS_ANDROID)
-#include "third_party/ashmem/ashmem.h"
-#endif
-
-namespace base {
-namespace {
-
-// Use a machine-sized pointer as atomic type. It will use the Atomic32 or
-// Atomic64 routines, depending on the architecture.
-typedef intptr_t AtomicType;
-typedef uintptr_t UAtomicType;
-
-// Template specialization for timestamp serialization/deserialization. This
-// is used to serialize timestamps using Unix time on systems where AtomicType
-// does not have enough precision to contain a timestamp in the standard
-// serialized format.
-template <int>
-Time TimeFromWireFormat(int64 value);
-template <int>
-int64 TimeToWireFormat(Time time);
-
-// Serialize to Unix time when using 4-byte wire format.
-// Note: 19 January 2038, this will cease to work.
-template <>
-Time ALLOW_UNUSED_TYPE TimeFromWireFormat<4>(int64 value) {
-  return value ? Time::UnixEpoch() + TimeDelta::FromSeconds(value) : Time();
-}
-template <>
-int64 ALLOW_UNUSED_TYPE TimeToWireFormat<4>(Time time) {
-  return time > Time::UnixEpoch() ? (time - Time::UnixEpoch()).InSeconds() : 0;
-}
-
-// Standard serialization format when using 8-byte wire format.
-template <>
-Time ALLOW_UNUSED_TYPE TimeFromWireFormat<8>(int64 value) {
-  return Time::FromInternalValue(value);
-}
-template <>
-int64 ALLOW_UNUSED_TYPE TimeToWireFormat<8>(Time time) {
-  return time.ToInternalValue();
-}
-
-struct SharedState {
-  enum LockState { UNLOCKED = 0, LOCKED = 1 };
-
-  explicit SharedState(AtomicType ivalue) { value.i = ivalue; }
-  SharedState(LockState lock_state, Time timestamp) {
-    int64 wire_timestamp = TimeToWireFormat<sizeof(AtomicType)>(timestamp);
-    DCHECK_GE(wire_timestamp, 0);
-    DCHECK_EQ(lock_state & ~1, 0);
-    value.u = (static_cast<UAtomicType>(wire_timestamp) << 1) | lock_state;
-  }
-
-  LockState GetLockState() const { return static_cast<LockState>(value.u & 1); }
-
-  Time GetTimestamp() const {
-    return TimeFromWireFormat<sizeof(AtomicType)>(value.u >> 1);
-  }
-
-  // Bit 1: Lock state. Bit is set when locked.
-  // Bit 2..sizeof(AtomicType)*8: Usage timestamp. NULL time when locked or
-  // purged.
-  union {
-    AtomicType i;
-    UAtomicType u;
-  } value;
-};
-
-// Shared state is stored at offset 0 in shared memory segments.
-SharedState* SharedStateFromSharedMemory(const SharedMemory& shared_memory) {
-  DCHECK(shared_memory.memory());
-  return static_cast<SharedState*>(shared_memory.memory());
-}
-
-// Round up |size| to a multiple of alignment, which must be a power of two.
-size_t Align(size_t alignment, size_t size) {
-  DCHECK_EQ(alignment & (alignment - 1), 0u);
-  return (size + alignment - 1) & ~(alignment - 1);
-}
-
-// Round up |size| to a multiple of page size.
-size_t AlignToPageSize(size_t size) {
-  return Align(base::GetPageSize(), size);
-}
-
-}  // namespace
-
-DiscardableSharedMemory::DiscardableSharedMemory()
-    : mapped_size_(0), locked_page_count_(0) {
-}
-
-DiscardableSharedMemory::DiscardableSharedMemory(
-    SharedMemoryHandle shared_memory_handle)
-    : shared_memory_(shared_memory_handle, false),
-      mapped_size_(0),
-      locked_page_count_(0) {
-}
-
-DiscardableSharedMemory::~DiscardableSharedMemory() {
-}
-
-bool DiscardableSharedMemory::CreateAndMap(size_t size) {
-  CheckedNumeric<size_t> checked_size = size;
-  checked_size += AlignToPageSize(sizeof(SharedState));
-  if (!checked_size.IsValid())
-    return false;
-
-  if (!shared_memory_.CreateAndMapAnonymous(checked_size.ValueOrDie()))
-    return false;
-
-  mapped_size_ =
-      shared_memory_.mapped_size() - AlignToPageSize(sizeof(SharedState));
-
-  locked_page_count_ = AlignToPageSize(mapped_size_) / base::GetPageSize();
-#if DCHECK_IS_ON()
-  for (size_t page = 0; page < locked_page_count_; ++page)
-    locked_pages_.insert(page);
-#endif
-
-  DCHECK(last_known_usage_.is_null());
-  SharedState new_state(SharedState::LOCKED, Time());
-  subtle::Release_Store(&SharedStateFromSharedMemory(shared_memory_)->value.i,
-                        new_state.value.i);
-  return true;
-}
-
-bool DiscardableSharedMemory::Map(size_t size) {
-  if (!shared_memory_.Map(AlignToPageSize(sizeof(SharedState)) + size))
-    return false;
-
-  mapped_size_ =
-      shared_memory_.mapped_size() - AlignToPageSize(sizeof(SharedState));
-
-  locked_page_count_ = AlignToPageSize(mapped_size_) / base::GetPageSize();
-#if DCHECK_IS_ON()
-  for (size_t page = 0; page < locked_page_count_; ++page)
-    locked_pages_.insert(page);
-#endif
-
-  return true;
-}
-
-bool DiscardableSharedMemory::Unmap() {
-  if (!shared_memory_.Unmap())
-    return false;
-
-  mapped_size_ = 0;
-  return true;
-}
-
-DiscardableSharedMemory::LockResult DiscardableSharedMemory::Lock(
-    size_t offset, size_t length) {
-  DCHECK_EQ(AlignToPageSize(offset), offset);
-  DCHECK_EQ(AlignToPageSize(length), length);
-
-  // Calls to this function must be synchronized properly.
-  DFAKE_SCOPED_LOCK(thread_collision_warner_);
-
-  DCHECK(shared_memory_.memory());
-
-  // We need to successfully acquire the platform independent lock before
-  // individual pages can be locked.
-  if (!locked_page_count_) {
-    // Return false when instance has been purged or not initialized properly
-    // by checking if |last_known_usage_| is NULL.
-    if (last_known_usage_.is_null())
-      return FAILED;
-
-    SharedState old_state(SharedState::UNLOCKED, last_known_usage_);
-    SharedState new_state(SharedState::LOCKED, Time());
-    SharedState result(subtle::Acquire_CompareAndSwap(
-        &SharedStateFromSharedMemory(shared_memory_)->value.i,
-        old_state.value.i,
-        new_state.value.i));
-    if (result.value.u != old_state.value.u) {
-      // Update |last_known_usage_| in case the above CAS failed because of
-      // an incorrect timestamp.
-      last_known_usage_ = result.GetTimestamp();
-      return FAILED;
-    }
-  }
-
-  // Zero for length means "everything onward".
-  if (!length)
-    length = AlignToPageSize(mapped_size_) - offset;
-
-  size_t start = offset / base::GetPageSize();
-  size_t end = start + length / base::GetPageSize();
-  DCHECK_LT(start, end);
-  DCHECK_LE(end, AlignToPageSize(mapped_size_) / base::GetPageSize());
-
-  // Add pages to |locked_page_count_|.
-  // Note: Locking a page that is already locked is an error.
-  locked_page_count_ += end - start;
-#if DCHECK_IS_ON()
-  // Detect incorrect usage by keeping track of exactly what pages are locked.
-  for (auto page = start; page < end; ++page) {
-    auto result = locked_pages_.insert(page);
-    DCHECK(result.second);
-  }
-  DCHECK_EQ(locked_pages_.size(), locked_page_count_);
-#endif
-
-#if defined(OS_ANDROID)
-  SharedMemoryHandle handle = shared_memory_.handle();
-  if (SharedMemory::IsHandleValid(handle)) {
-    if (ashmem_pin_region(
-            handle.fd, AlignToPageSize(sizeof(SharedState)) + offset, length)) {
-      return PURGED;
-    }
-  }
-#endif
-
-  return SUCCESS;
-}
-
-void DiscardableSharedMemory::Unlock(size_t offset, size_t length) {
-  DCHECK_EQ(AlignToPageSize(offset), offset);
-  DCHECK_EQ(AlignToPageSize(length), length);
-
-  // Calls to this function must be synchronized properly.
-  DFAKE_SCOPED_LOCK(thread_collision_warner_);
-
-  // Zero for length means "everything onward".
-  if (!length)
-    length = AlignToPageSize(mapped_size_) - offset;
-
-  DCHECK(shared_memory_.memory());
-
-#if defined(OS_ANDROID)
-  SharedMemoryHandle handle = shared_memory_.handle();
-  if (SharedMemory::IsHandleValid(handle)) {
-    if (ashmem_unpin_region(
-            handle.fd, AlignToPageSize(sizeof(SharedState)) + offset, length)) {
-      DPLOG(ERROR) << "ashmem_unpin_region() failed";
-    }
-  }
-#endif
-
-  size_t start = offset / base::GetPageSize();
-  size_t end = start + length / base::GetPageSize();
-  DCHECK_LT(start, end);
-  DCHECK_LE(end, AlignToPageSize(mapped_size_) / base::GetPageSize());
-
-  // Remove pages from |locked_page_count_|.
-  // Note: Unlocking a page that is not locked is an error.
-  DCHECK_GE(locked_page_count_, end - start);
-  locked_page_count_ -= end - start;
-#if DCHECK_IS_ON()
-  // Detect incorrect usage by keeping track of exactly what pages are locked.
-  for (auto page = start; page < end; ++page) {
-    auto erased_count = locked_pages_.erase(page);
-    DCHECK_EQ(1u, erased_count);
-  }
-  DCHECK_EQ(locked_pages_.size(), locked_page_count_);
-#endif
-
-  // Early out and avoid releasing the platform independent lock if some pages
-  // are still locked.
-  if (locked_page_count_)
-    return;
-
-  Time current_time = Now();
-  DCHECK(!current_time.is_null());
-
-  SharedState old_state(SharedState::LOCKED, Time());
-  SharedState new_state(SharedState::UNLOCKED, current_time);
-  // Note: timestamp cannot be NULL as that is a unique value used when
-  // locked or purged.
-  DCHECK(!new_state.GetTimestamp().is_null());
-  // Timestamp precision should at least be accurate to the second.
-  DCHECK_EQ((new_state.GetTimestamp() - Time::UnixEpoch()).InSeconds(),
-            (current_time - Time::UnixEpoch()).InSeconds());
-  SharedState result(subtle::Release_CompareAndSwap(
-      &SharedStateFromSharedMemory(shared_memory_)->value.i,
-      old_state.value.i,
-      new_state.value.i));
-
-  DCHECK_EQ(old_state.value.u, result.value.u);
-
-  last_known_usage_ = current_time;
-}
-
-void* DiscardableSharedMemory::memory() const {
-  return reinterpret_cast<uint8*>(shared_memory_.memory()) +
-         AlignToPageSize(sizeof(SharedState));
-}
-
-bool DiscardableSharedMemory::Purge(Time current_time) {
-  // Calls to this function must be synchronized properly.
-  DFAKE_SCOPED_LOCK(thread_collision_warner_);
-
-  // Early out if not mapped. This can happen if the segment was previously
-  // unmapped using a call to Close().
-  if (!shared_memory_.memory())
-    return true;
-
-  SharedState old_state(SharedState::UNLOCKED, last_known_usage_);
-  SharedState new_state(SharedState::UNLOCKED, Time());
-  SharedState result(subtle::Acquire_CompareAndSwap(
-      &SharedStateFromSharedMemory(shared_memory_)->value.i,
-      old_state.value.i,
-      new_state.value.i));
-
-  // Update |last_known_usage_| to |current_time| if the memory is locked. This
-  // allows the caller to determine if purging failed because last known usage
-  // was incorrect or memory was locked. In the second case, the caller should
-  // most likely wait for some amount of time before attempting to purge the
-  // the memory again.
-  if (result.value.u != old_state.value.u) {
-    last_known_usage_ = result.GetLockState() == SharedState::LOCKED
-                            ? current_time
-                            : result.GetTimestamp();
-    return false;
-  }
-
-  last_known_usage_ = Time();
-  return true;
-}
-
-bool DiscardableSharedMemory::IsMemoryResident() const {
-  DCHECK(shared_memory_.memory());
-
-  SharedState result(subtle::NoBarrier_Load(
-      &SharedStateFromSharedMemory(shared_memory_)->value.i));
-
-  return result.GetLockState() == SharedState::LOCKED ||
-         !result.GetTimestamp().is_null();
-}
-
-void DiscardableSharedMemory::Close() {
-  shared_memory_.Close();
-}
-
-#if defined(DISCARDABLE_SHARED_MEMORY_SHRINKING)
-void DiscardableSharedMemory::Shrink() {
-#if defined(OS_POSIX)
-  SharedMemoryHandle handle = shared_memory_.handle();
-  if (!SharedMemory::IsHandleValid(handle))
-    return;
-
-  // Truncate shared memory to size of SharedState.
-  if (HANDLE_EINTR(ftruncate(SharedMemory::GetFdFromSharedMemoryHandle(handle),
-                             AlignToPageSize(sizeof(SharedState)))) != 0) {
-    DPLOG(ERROR) << "ftruncate() failed";
-    return;
-  }
-  mapped_size_ = 0;
-#else
-  NOTIMPLEMENTED();
-#endif
-}
-#endif
-
-Time DiscardableSharedMemory::Now() const {
-  return Time::Now();
-}
-
-}  // namespace base