blob: 4d201b66f28a24d5232bc1e4982b3725101e2e5b [file] [log] [blame]
// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <memory>
#include "base/macros.h"
#include "base/time/time.h"
namespace device {
// Allows sharing and mocking of the update polling policy function.
class WifiPollingPolicy {
virtual ~WifiPollingPolicy() = default;
// Methods for managing the single instance of WifiPollingPolicy. The WiFi
// policy is global so it can outlive the WifiDataProvider instance, which is
// shut down and destroyed when no WiFi scanning is active.
static void Initialize(std::unique_ptr<WifiPollingPolicy>);
static void Shutdown();
static WifiPollingPolicy* Get();
static bool IsInitialized();
// Calculates the new polling interval for wifi scans, given the previous
// interval and whether the last scan produced new results.
virtual void UpdatePollingInterval(bool scan_results_differ) = 0;
// Use InitialInterval to schedule the initial scan when the wifi data
// provider is first started. Returns the number of milliseconds before the
// initial scan should be performed. May return zero if the policy allows a
// scan to be performed immediately.
virtual int InitialInterval() = 0;
// Use PollingInterval to schedule a new scan after the previous scan results
// are available. Only use PollingInterval if WLAN hardware is available and
// can perform scans for nearby access points. If the current interval is
// complete, PollingInterval returns the duration for a new interval starting
// at the current time.
virtual int PollingInterval() = 0;
// Use NoWifiInterval to schedule a new scan after the previous scan results
// are available. NoWifiInterval is typically shorter than PollingInterval
// and should not be used if wifi scanning is available in order to conserve
// power. If the current interval is complete, NoWifiInterval returns the
// duration for a new interval starting at the current time.
virtual int NoWifiInterval() = 0;
WifiPollingPolicy() = default;
// Generic polling policy, constants are compile-time parameterized to allow
// tuning on a per-platform basis.
template <int DEFAULT_INTERVAL,
class GenericWifiPollingPolicy : public WifiPollingPolicy {
GenericWifiPollingPolicy() = default;
// WifiPollingPolicy
void UpdatePollingInterval(bool scan_results_differ) override {
if (scan_results_differ) {
polling_interval_ = DEFAULT_INTERVAL;
} else if (polling_interval_ == DEFAULT_INTERVAL) {
polling_interval_ = NO_CHANGE_INTERVAL;
} else {
DCHECK(polling_interval_ == NO_CHANGE_INTERVAL ||
polling_interval_ == TWO_NO_CHANGE_INTERVAL);
polling_interval_ = TWO_NO_CHANGE_INTERVAL;
int InitialInterval() override { return ComputeInterval(polling_interval_); }
int PollingInterval() override {
int interval = ComputeInterval(polling_interval_);
return interval <= 0 ? polling_interval_ : interval;
int NoWifiInterval() override {
int interval = ComputeInterval(NO_WIFI_INTERVAL);
return interval <= 0 ? NO_WIFI_INTERVAL : interval;
int ComputeInterval(int polling_interval) {
base::Time now = base::Time::Now();
int64_t remaining_millis = 0;
if (!interval_start_.is_null()) {
// If the new interval duration differs from the initial duration, use the
// shorter duration.
if (polling_interval < interval_duration_)
interval_duration_ = polling_interval;
// Compute the remaining duration of the current interval. If the interval
// is not yet complete, we will schedule a scan to occur once it is.
base::TimeDelta remaining =
interval_start_ +
base::TimeDelta::FromMilliseconds(interval_duration_) - now;
remaining_millis = remaining.InMilliseconds();
// If the current interval is complete (or if this is our first scan),
// start a new interval beginning now.
if (remaining_millis <= 0) {
interval_start_ = now;
interval_duration_ = polling_interval;
remaining_millis = 0;
return remaining_millis;
// The current duration of the polling interval. When wifi data is
// substantially the same from one scan to the next, this may be increased to
// reduce the frequency of wifi scanning.
int polling_interval_ = DEFAULT_INTERVAL;
// The start time for the most recent interval. Initialized to the "null" time
// value.
base::Time interval_start_;
// Duration for the interval starting at |interval_start_|.
int interval_duration_ = DEFAULT_INTERVAL;
} // namespace device