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rust-rocksdb/env/unique_id_gen.h

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// Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
// This file is for functions that generate unique identifiers by
// (at least in part) by extracting novel entropy or sources of uniqueness
// from the execution environment. (By contrast, random.h is for algorithmic
// pseudorandomness.)
//
// These functions could eventually migrate to public APIs, such as in Env.
#pragma once
#include <array>
#include <atomic>
#include <cstdint>
#include <type_traits>
#include "port/port.h"
#include "rocksdb/rocksdb_namespace.h"
namespace ROCKSDB_NAMESPACE {
// Generates a new 128-bit identifier that is universally unique
// (with high probability) for each call. The result is split into
// two 64-bit pieces. This function has NOT been validated for use in
// cryptography.
//
// This is used in generating DB session IDs and by Env::GenerateUniqueId
// (used for DB IDENTITY) if the platform does not provide a generator of
// RFC 4122 UUIDs or fails somehow. (Set exclude_port_uuid=true if this
// function is used as a fallback for GenerateRfcUuid, because no need
// trying it again.)
void GenerateRawUniqueId(uint64_t* a, uint64_t* b,
bool exclude_port_uuid = false);
#ifndef NDEBUG
// A version of above with options for challenge testing
void TEST_GenerateRawUniqueId(uint64_t* a, uint64_t* b, bool exclude_port_uuid,
bool exclude_env_details,
bool exclude_random_device);
#endif
// Generates globally unique ids with lower probability of any collisions
// vs. each unique id being independently random (GenerateRawUniqueId).
// We call this "semi-structured" because between different
// SemiStructuredUniqueIdGen objects, the IDs are separated by random
// intervals (unstructured), but within a single SemiStructuredUniqueIdGen
// object, the generated IDs are trivially related (structured). See
// https://github.com/pdillinger/unique_id for how this improves probability
// of no collision. In short, if we have n SemiStructuredUniqueIdGen
// objects each generating m IDs, the first collision is expected at
// around n = sqrt(2^128 / m), equivalently n * sqrt(m) = 2^64,
// rather than n * m = 2^64 for fully random IDs.
class SemiStructuredUniqueIdGen {
public:
// Initializes with random starting state (from GenerateRawUniqueId)
SemiStructuredUniqueIdGen() { Reset(); }
// Re-initializes, but not thread safe
void Reset();
// Assuming no fork(), `lower` is guaranteed unique from one call
// to the next (thread safe).
void GenerateNext(uint64_t* upper, uint64_t* lower);
// For generating smaller values. Will cycle through all the possibilities
// before repeating.
template <typename T>
T GenerateNext() {
static_assert(sizeof(T) <= sizeof(uint64_t));
static_assert(std::is_integral_v<T>);
uint64_t ignore, val;
GenerateNext(&ignore, &val);
return static_cast<T>(val);
}
uint64_t GetBaseUpper() const { return base_upper_; }
private:
uint64_t base_upper_;
uint64_t base_lower_;
std::atomic<uint64_t> counter_;
int64_t saved_process_id_;
};
// A unique id generator that should provide reasonable security against
// predicting the output from previous outputs, but is NOT known to be
// cryptographically secure. Unlike std::random_device, this is guaranteed
// not to block once initialized.
class ALIGN_AS(CACHE_LINE_SIZE) UnpredictableUniqueIdGen {
public:
// Initializes with random starting state (from several GenerateRawUniqueId)
UnpredictableUniqueIdGen() { Reset(); }
// Re-initializes, but not thread safe
void Reset();
// Generate next probabilistically unique value. Thread safe. Uses timing
// information to add to the entropy pool.
void GenerateNext(uint64_t* upper, uint64_t* lower);
// Explicitly include given value for entropy pool instead of timing
// information.
void GenerateNextWithEntropy(uint64_t* upper, uint64_t* lower,
uint64_t extra_entropy);
#ifndef NDEBUG
struct TEST_ZeroInitialized {};
explicit UnpredictableUniqueIdGen(TEST_ZeroInitialized);
std::atomic<uint64_t>& TEST_counter() { return counter_; }
#endif
private:
// 256 bit entropy pool
std::array<std::atomic<uint64_t>, 4> pool_;
// Counter to ensure unique hash inputs
std::atomic<uint64_t> counter_;
};
} // namespace ROCKSDB_NAMESPACE