uint64_id_allocator.cpp

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// Copyright 2023 owent
 
#include <libcopp/utils/config/libcopp_build_features.h>
 
#include <libcopp/utils/atomic_int_type.h>
#include <libcopp/utils/uint64_id_allocator.h>
 
// clang-format off
#include <libcopp/utils/config/stl_include_prefix.h>  // NOLINT(build/include_order)
// clang-format on
#if defined(THREAD_TLS_USE_PTHREAD) && THREAD_TLS_USE_PTHREAD
#  include <pthread.h>
#endif
#include <ctime>
// clang-format off
#include <libcopp/utils/config/stl_include_suffix.h>  // NOLINT(build/include_order)
// clang-format on
 
LIBCOPP_COPP_NAMESPACE_BEGIN
namespace util {
namespace details {
 
// TIMESTAMP:32|SEQUENCE:24 -> about 16M id per second
static uint64_t allocate_id_by_atomic() {
  static LIBCOPP_COPP_NAMESPACE_ID::util::lock::atomic_int_type<uint64_t> seq_alloc(0);
 
  //
  static constexpr const size_t seq_bits = 24;
  static constexpr const uint64_t time_mask = (static_cast<uint64_t>(1) << 32) - 1;
 
  // always do not allocate 0 as a valid ID
  uint64_t ret = 0;
  while (0 == ret) {
    uint64_t res = seq_alloc.load();
    uint64_t time_part = res >> seq_bits;
 
    uint64_t next_ret = res + 1;
    uint64_t next_time_part = next_ret >> seq_bits;
    if (0 == time_part || time_part != next_time_part) {
      uint64_t now_time = time_part;
      while (time_part == now_time) {
        now_time = (static_cast<uint64_t>(time(nullptr)) & time_mask) - 1577836800;  // 2020-01-01 00:00:00+00:00 UTC
      }
 
      // if failed, maybe another thread do it
      if (seq_alloc.compare_exchange_strong(res, now_time << seq_bits,
                                            LIBCOPP_COPP_NAMESPACE_ID::util::lock::memory_order_acq_rel,
                                            LIBCOPP_COPP_NAMESPACE_ID::util::lock::memory_order_acquire)) {
        ret = now_time << seq_bits;
      }
    } else {
      if (seq_alloc.compare_exchange_weak(res, next_ret, LIBCOPP_COPP_NAMESPACE_ID::util::lock::memory_order_acq_rel,
                                          LIBCOPP_COPP_NAMESPACE_ID::util::lock::memory_order_acquire)) {
        ret = next_ret;
      }
    }
  }
 
  return ret;
}
 
struct uint64_id_allocator_tls_cache_t {
  uint64_t base;
  uint64_t inner_seq;
};
 
#if defined(THREAD_TLS_USE_PTHREAD) && THREAD_TLS_USE_PTHREAD
static pthread_once_t gt_uint64_id_allocator_tls_once = PTHREAD_ONCE_INIT;
static pthread_key_t gt_uint64_id_allocator_tls_key;
 
static void dtor_pthread_uint64_id_allocator_tls(void *p) {
  uint64_id_allocator_tls_cache_t *cache = reinterpret_cast<uint64_id_allocator_tls_cache_t *>(p);
  if (nullptr != cache) {
    delete cache;
  }
}
 
static void init_pthread_uint64_id_allocator_tls() {
  (void)pthread_key_create(&gt_uint64_id_allocator_tls_key, dtor_pthread_uint64_id_allocator_tls);
}
 
struct gt_uint64_id_allocator_tls_cache_main_thread_dtor_t {
  gt_uint64_id_allocator_tls_cache_main_thread_dtor_t() {}
 
  ~gt_uint64_id_allocator_tls_cache_main_thread_dtor_t() {
    void *cache_ptr = pthread_getspecific(gt_uint64_id_allocator_tls_key);
    pthread_setspecific(gt_uint64_id_allocator_tls_key, nullptr);
    dtor_pthread_uint64_id_allocator_tls(cache_ptr);
  }
};
static void init_pthread_get_log_tls_main_thread_dtor() {
  static gt_uint64_id_allocator_tls_cache_main_thread_dtor_t gt_uint64_id_allocator_tls_cache_main_thread_dtor;
  (void)gt_uint64_id_allocator_tls_cache_main_thread_dtor;
}
 
static uint64_id_allocator_tls_cache_t *get_uint64_id_allocator_tls_cache() {
  init_pthread_get_log_tls_main_thread_dtor();
  (void)pthread_once(&gt_uint64_id_allocator_tls_once, init_pthread_uint64_id_allocator_tls);
  uint64_id_allocator_tls_cache_t *ret =
      reinterpret_cast<uint64_id_allocator_tls_cache_t *>(pthread_getspecific(gt_uint64_id_allocator_tls_key));
  if (nullptr == ret) {
    ret = new uint64_id_allocator_tls_cache_t();
    ret->base = 0;
    ret->inner_seq = 0;
    pthread_setspecific(gt_uint64_id_allocator_tls_key, ret);
  }
  return ret;
}
 
#else
uint64_id_allocator_tls_cache_t *get_uint64_id_allocator_tls_cache() {
  static thread_local uint64_id_allocator_tls_cache_t ret = {0, 0};
  return &ret;
}
#endif
}  // namespace details
 
LIBCOPP_COPP_API uint64_id_allocator::value_type uint64_id_allocator::allocate() LIBCOPP_MACRO_NOEXCEPT {
  // details::allocate_id_by_atomic() takes 56 bits, we use 5 bits here
  details::uint64_id_allocator_tls_cache_t *tls_cache = details::get_uint64_id_allocator_tls_cache();
  if (nullptr == tls_cache) {
    return 0;
  }
 
  static constexpr const uint64_t tls_cache_count = (static_cast<uint64_t>(1) << 5);
 
  while (0 == tls_cache->base || tls_cache->inner_seq >= tls_cache_count) {
    tls_cache->base = details::allocate_id_by_atomic();
    tls_cache->inner_seq = 0;
  }
 
  return (tls_cache->base << 5) + (tls_cache->inner_seq++);
}
 
LIBCOPP_COPP_API void uint64_id_allocator::deallocate(value_type) LIBCOPP_MACRO_NOEXCEPT {}
}  // namespace util
LIBCOPP_COPP_NAMESPACE_END