| /* |
| * |
| * Copyright 2016 gRPC 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 |
| * |
| * http://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 <grpc/support/port_platform.h> |
| |
| #include "src/core/lib/backoff/backoff.h" |
| |
| #include <algorithm> |
| |
| #include "src/core/lib/gpr/useful.h" |
| |
| namespace grpc_core { |
| |
| namespace { |
| |
| /* Generate a random number between 0 and 1. We roll our own RNG because seeding |
| * rand() modifies a global variable we have no control over. */ |
| double generate_uniform_random_number(uint32_t* rng_state) { |
| constexpr uint32_t two_raise_31 = uint32_t(1) << 31; |
| *rng_state = (1103515245 * *rng_state + 12345) % two_raise_31; |
| return *rng_state / static_cast<double>(two_raise_31); |
| } |
| |
| double generate_uniform_random_number_between(uint32_t* rng_state, double a, |
| double b) { |
| if (a == b) return a; |
| if (a > b) GPR_SWAP(double, a, b); // make sure a < b |
| const double range = b - a; |
| return a + generate_uniform_random_number(rng_state) * range; |
| } |
| |
| } // namespace |
| |
| BackOff::BackOff(const Options& options) |
| : options_(options), |
| rng_state_(static_cast<uint32_t>(gpr_now(GPR_CLOCK_REALTIME).tv_nsec)) { |
| Reset(); |
| } |
| |
| grpc_millis BackOff::NextAttemptTime() { |
| if (initial_) { |
| initial_ = false; |
| return current_backoff_ + grpc_core::ExecCtx::Get()->Now(); |
| } |
| current_backoff_ = static_cast<grpc_millis>( |
| std::min(current_backoff_ * options_.multiplier(), |
| static_cast<double>(options_.max_backoff()))); |
| const double jitter = generate_uniform_random_number_between( |
| &rng_state_, -options_.jitter() * current_backoff_, |
| options_.jitter() * current_backoff_); |
| const grpc_millis next_timeout = |
| static_cast<grpc_millis>(current_backoff_ + jitter); |
| return next_timeout + grpc_core::ExecCtx::Get()->Now(); |
| } |
| |
| void BackOff::Reset() { |
| current_backoff_ = options_.initial_backoff(); |
| initial_ = true; |
| } |
| |
| void BackOff::SetRandomSeed(uint32_t seed) { rng_state_ = seed; } |
| |
| } // namespace grpc_core |