用令牌桶限制速率并保留可控突发

313  // See if the request is forbidden by the default token bucket.314  if (matched_results.empty() || always_consume_default_token_bucket_) {315    if (const bool result = default_token_bucket_->consume(share_factor); !result) {316      // If the request is forbidden by the default token bucket, return the result and the317      // default token bucket.318      return {false, makeOptRefFromPtr<TokenBucketContext>(default_token_bucket_.get())};319    }320321    // If the request is allowed then return the result the token bucket. The descriptor322    // token bucket will be selected as priority if it exists.323    return {true, makeOptRef<TokenBucketContext>(matched_results.empty()324                                                     ? *default_token_bucket_325                                                     : matched_results[0].token_bucket.get())};326  };

159AtomicTokenBucket::AtomicTokenBucket(uint64_t max_tokens, uint64_t tokens_per_fill,160                                     std::chrono::milliseconds fill_interval,161                                     TimeSource& time_source)162    : token_bucket_(max_tokens, time_source,163                    // Calculate the fill rate in tokens per second.164                    tokens_per_fill / std::chrono::duration<double>(fill_interval).count()) {}165166bool AtomicTokenBucket::consume(double factor, uint64_t to_consume) {167  ASSERT(!(factor <= 0.0 || factor > 1.0));168  auto cb = [tokens = to_consume / factor](double total) { return total < tokens ? 0.0 : tokens; };169  return token_bucket_.consume(cb) != 0.0;170}

56  template <class GetConsumedTokens> double consume(const GetConsumedTokens& cb) {57    const double time_now = timeNowInSeconds();5859    double time_old = time_in_seconds_.load(std::memory_order_relaxed);60    double time_new{};61    double consumed{};62    do {63      const double total_tokens = std::min(max_tokens_, (time_now - time_old) * fill_rate_);64      if (consumed = cb(total_tokens); consumed == 0) {65        return 0;66      }

74      // Move the time_in_seconds_ forward by the number of tokens consumed.75      const double total_tokens_new = total_tokens - consumed;76      time_new = time_now - (total_tokens_new / fill_rate_);77    } while (78        !time_in_seconds_.compare_exchange_weak(time_old, time_new, std::memory_order_relaxed));7980    return consumed;81  }