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// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "mojo/public/cpp/base/shared_memory_version.h"
#include <atomic>
#include <limits>
#include "base/check_op.h"
#include "base/logging.h"
#include "base/memory/read_only_shared_memory_region.h"
#include "base/memory/structured_shared_memory.h"
#include "base/metrics/histogram_functions.h"
namespace mojo {
SharedMemoryVersionController::SharedMemoryVersionController()
: mapped_region_(
// Clients may use `kInvalidVersion` as a special value to indicate
// the version in the absence of shared memory communication. Make
// sure the version starts at `kInitialVersion` to avoid any
// confusion.
base::AtomicSharedMemory<VersionType>::Create(
shared_memory_version::kInitialVersion)) {
base::UmaHistogramBoolean(
"Mojo.SharedMemoryVersion.SharedMemoryAllocationSucceeded",
mapped_region_.has_value());
}
SharedMemoryVersionController::~SharedMemoryVersionController() = default;
base::ReadOnlySharedMemoryRegion
SharedMemoryVersionController::GetSharedMemoryRegion() const {
if (!mapped_region_.has_value()) {
return base::ReadOnlySharedMemoryRegion();
}
return mapped_region_->DuplicateReadOnlyRegion();
}
VersionType SharedMemoryVersionController::GetSharedVersion() const {
if (!mapped_region_.has_value()) {
return shared_memory_version::kInvalidVersion;
}
// Relaxed memory order because no other memory operation depends on the
// version.
return mapped_region_->ReadOnlyRef().load(std::memory_order_relaxed);
}
void SharedMemoryVersionController::Increment() {
if (!mapped_region_.has_value()) {
return;
}
// Relaxed memory order because no other memory operation depends on the
// version.
const VersionType version =
mapped_region_->WritableRef().fetch_add(1, std::memory_order_relaxed);
// The version wrapping around is not supported and should not happen.
CHECK_LE(version, std::numeric_limits<VersionType>::max());
}
void SharedMemoryVersionController::SetVersion(VersionType version) {
if (!mapped_region_.has_value()) {
return;
}
// The version wrapping around is not supported and should not happen.
CHECK_LT(version, std::numeric_limits<VersionType>::max());
// Version cannot decrease.
CHECK_GE(version, GetSharedVersion());
// Relaxed memory order because no other memory operation depends on the
// version.
mapped_region_->WritableRef().store(version, std::memory_order_relaxed);
}
SharedMemoryVersionClient::SharedMemoryVersionClient(
base::ReadOnlySharedMemoryRegion shared_region)
: read_only_mapping_(
base::AtomicSharedMemory<VersionType>::MapReadOnlyRegion(
std::move(shared_region))) {}
SharedMemoryVersionClient::~SharedMemoryVersionClient() = default;
bool SharedMemoryVersionClient::SharedVersionIsLessThan(
VersionType version) const {
// Invalid version numbers cannot be compared. Default to IPC.
if (version == shared_memory_version::kInvalidVersion) {
return true;
}
return GetSharedVersion() < version;
}
bool SharedMemoryVersionClient::SharedVersionIsGreaterThan(
VersionType version) const {
// Invalid version numbers cannot be compared. Default to IPC.
if (version == shared_memory_version::kInvalidVersion) {
return true;
}
return GetSharedVersion() > version;
}
VersionType SharedMemoryVersionClient::GetSharedVersion() const {
if (!read_only_mapping_.has_value()) {
return shared_memory_version::kInvalidVersion;
}
// Relaxed memory order because no other memory operation depends on the
// version.
return read_only_mapping_->ReadOnlyRef().load(std::memory_order_relaxed);
}
} // namespace mojo
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