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- // 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.
- #ifndef SERVICES_DEVICE_GEOLOCATION_WIFI_POLLING_POLICY_H_
- #define SERVICES_DEVICE_GEOLOCATION_WIFI_POLLING_POLICY_H_
- #include <memory>
- #include "base/check.h"
- #include "base/time/time.h"
- namespace device {
- // Allows sharing and mocking of the update polling policy function.
- class WifiPollingPolicy {
- public:
- WifiPollingPolicy(const WifiPollingPolicy&) = delete;
- WifiPollingPolicy& operator=(const WifiPollingPolicy&) = delete;
- 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;
- protected:
- WifiPollingPolicy() = default;
- };
- // Generic polling policy, constants are compile-time parameterized to allow
- // tuning on a per-platform basis.
- template <int DEFAULT_INTERVAL,
- int NO_CHANGE_INTERVAL,
- int TWO_NO_CHANGE_INTERVAL,
- int NO_WIFI_INTERVAL>
- class GenericWifiPollingPolicy : public WifiPollingPolicy {
- public:
- 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;
- }
- private:
- 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::Milliseconds(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
- #endif // SERVICES_DEVICE_GEOLOCATION_WIFI_POLLING_POLICY_H_
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