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/*
*
* 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 "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
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