pool_urbg.cc | Explore in Territory

// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "absl/random/internal/pool_urbg.h"

#include <algorithm>
#include <atomic>
#include <cstdint>
#include <cstring>
#include <iterator>

#include "absl/base/attributes.h"
#include "absl/base/call_once.h"
#include "absl/base/config.h"
#include "absl/base/internal/endian.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/base/internal/spinlock.h"
#include "absl/base/internal/sysinfo.h"
#include "absl/base/internal/unaligned_access.h"
#include "absl/base/optimization.h"
#include "absl/random/internal/randen.h"
#include "absl/random/internal/seed_material.h"
#include "absl/random/seed_gen_exception.h"

SpinLock;
SpinLockHolder;

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace random_internal {
namespace {

// RandenPoolEntry is a thread-safe pseudorandom bit generator, implementing a
// single generator within a RandenPool<T>. It is an internal implementation
// detail, and does not aim to conform to [rand.req.urng].
//
// NOTE: There are alignment issues when used on ARM, for instance.
// See the allocation code in PoolAlignedAlloc().
class RandenPoolEntry { … };

template <>
inline uint8_t RandenPoolEntry::Generate<uint8_t>() { … }

template <>
inline uint16_t RandenPoolEntry::Generate<uint16_t>() { … }

template <>
inline uint32_t RandenPoolEntry::Generate<uint32_t>() { … }

template <>
inline uint64_t RandenPoolEntry::Generate<uint64_t>() { … }

void RandenPoolEntry::Fill(uint8_t* out, size_t bytes) { … }

// Number of pooled urbg entries.
static constexpr size_t kPoolSize = …;

// Shared pool entries.
static absl::once_flag pool_once;
ABSL_CACHELINE_ALIGNED static RandenPoolEntry* shared_pools[kPoolSize];

// Returns an id in the range [0 ... kPoolSize), which indexes into the
// pool of random engines.
//
// Each thread to access the pool is assigned a sequential ID (without reuse)
// from the pool-id space; the id is cached in a thread_local variable.
// This id is assigned based on the arrival-order of the thread to the
// GetPoolID call; this has no binary, CL, or runtime stability because
// on subsequent runs the order within the same program may be significantly
// different. However, as other thread IDs are not assigned sequentially,
// this is not expected to matter.
size_t GetPoolID() { … }

// Allocate a RandenPoolEntry with at least 32-byte alignment, which is required
// by ARM platform code.
RandenPoolEntry* PoolAlignedAlloc() { … }

// Allocate and initialize kPoolSize objects of type RandenPoolEntry.
//
// The initialization strategy is to initialize one object directly from
// OS entropy, then to use that object to seed all of the individual
// pool instances.
void InitPoolURBG() { … }

// Returns the pool entry for the current thread.
RandenPoolEntry* GetPoolForCurrentThread() { … }

}  // namespace

template <typename T>
typename RandenPool<T>::result_type RandenPool<T>::Generate() { … }

template <typename T>
void RandenPool<T>::Fill(absl::Span<result_type> data) { … }

template class RandenPool<uint8_t>;
template class RandenPool<uint16_t>;
template class RandenPool<uint32_t>;
template class RandenPool<uint64_t>;

}  // namespace random_internal
ABSL_NAMESPACE_END
}  // namespace absl
chromium/third_party/abseil-cpp/absl/random/internal/pool_urbg.cc
