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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.
#include <memory>
#include "base/callback.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/memory/weak_ptr.h"
#include "base/time/time.h"
#include "components/policy/core/common/schema_map.h"
#include "components/policy/policy_export.h"
namespace base {
class SequencedTaskRunner;
namespace policy {
class PolicyBundle;
// Base implementation for platform-specific policy loaders. Together with the
// AsyncPolicyProvider, this base implementation takes care of the initial load,
// periodic reloads, watching file changes, refreshing policies and object
// lifetime.
// All methods are invoked on the background |task_runner_|, including the
// destructor. The only exceptions are the constructor (which may be called on
// any thread), InitialLoad() which is called on the thread that owns the
// provider and the calls of Load() and LastModificationTime() during the
// initial load.
// Also, during tests the destructor may be called on the main thread.
class POLICY_EXPORT AsyncPolicyLoader {
explicit AsyncPolicyLoader(
const scoped_refptr<base::SequencedTaskRunner>& task_runner);
virtual ~AsyncPolicyLoader();
// Gets a SequencedTaskRunner backed by the background thread.
base::SequencedTaskRunner* task_runner() const { return task_runner_.get(); }
// Returns the currently configured policies. Load() is always invoked on
// the background thread, except for the initial Load() at startup which is
// invoked from the thread that owns the provider.
virtual std::unique_ptr<PolicyBundle> Load() = 0;
// Allows implementations to finalize their initialization on the background
// thread (e.g. setup file watchers).
virtual void InitOnBackgroundThread() = 0;
// Implementations should return the time of the last modification detected,
// or base::Time() if it doesn't apply, which is the default.
virtual base::Time LastModificationTime();
// Used by the AsyncPolicyProvider to do the initial Load(). The first load
// is also used to initialize |last_modification_time_| and
// |schema_map_|.
std::unique_ptr<PolicyBundle> InitialLoad(
const scoped_refptr<SchemaMap>& schemas);
// Implementations should invoke Reload() when a change is detected. This
// must be invoked from the background thread and will trigger a Load(),
// and pass the returned bundle to the provider.
// The load is immediate when |force| is true. Otherwise, the loader
// reschedules the reload until the LastModificationTime() is a couple of
// seconds in the past. This mitigates the problem of reading files that are
// currently being written to, and whose contents are incomplete.
// A reload is posted periodically, if it hasn't been triggered recently. This
// makes sure the policies are reloaded if the update events aren't triggered.
void Reload(bool force);
const scoped_refptr<SchemaMap>& schema_map() const { return schema_map_; }
// Allow AsyncPolicyProvider to call Init().
friend class AsyncPolicyProvider;
typedef base::Callback<void(std::unique_ptr<PolicyBundle>)> UpdateCallback;
// Used by the AsyncPolicyProvider to install the |update_callback_|.
// Invoked on the background thread.
void Init(const UpdateCallback& update_callback);
// Used by the AsyncPolicyProvider to reload with an updated SchemaMap.
void RefreshPolicies(scoped_refptr<SchemaMap> schema_map);
// Cancels any pending periodic reload and posts one |delay| time units from
// now.
void ScheduleNextReload(base::TimeDelta delay);
// Checks if the underlying files haven't changed recently, by checking the
// LastModificationTime(). |delay| is updated with a suggested time to wait
// before retrying when this returns false.
bool IsSafeToReload(const base::Time& now, base::TimeDelta* delay);
// Task runner for running background jobs.
const scoped_refptr<base::SequencedTaskRunner> task_runner_;
// Callback for updates, passed in Init().
UpdateCallback update_callback_;
// Records last known modification timestamp.
base::Time last_modification_time_;
// The wall clock time at which the last modification timestamp was
// recorded. It's better to not assume the file notification time and the
// wall clock times come from the same source, just in case there is some
// non-local filesystem involved.
base::Time last_modification_clock_;
// The current policy schemas that this provider should load.
scoped_refptr<SchemaMap> schema_map_;
// Used to get WeakPtrs for the periodic reload task.
base::WeakPtrFactory<AsyncPolicyLoader> weak_factory_{this};
} // namespace policy