// Copyright (c) 2012 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 NET_BASE_BACKOFF_ENTRY_H_
#define NET_BASE_BACKOFF_ENTRY_H_
#include "base/threading/non_thread_safe.h"
#include "base/time/time.h"
#include "net/base/net_export.h"
namespace net {
// Provides the core logic needed for randomized exponential back-off
// on requests to a given resource, given a back-off policy.
//
// This utility class knows nothing about network specifics; it is
// intended for reuse in various networking scenarios.
class NET_EXPORT BackoffEntry : NON_EXPORTED_BASE(public base::NonThreadSafe) {
public:
// The set of parameters that define a back-off policy.
struct Policy {
// Number of initial errors (in sequence) to ignore before applying
// exponential back-off rules.
int num_errors_to_ignore;
// Initial delay. The interpretation of this value depends on
// always_use_initial_delay. It's either how long we wait between
// requests before backoff starts, or how much we delay the first request
// after backoff starts.
int initial_delay_ms;
// Factor by which the waiting time will be multiplied.
double multiply_factor;
// Fuzzing percentage. ex: 10% will spread requests randomly
// between 90%-100% of the calculated time.
double jitter_factor;
// Maximum amount of time we are willing to delay our request, -1
// for no maximum.
int64 maximum_backoff_ms;
// Time to keep an entry from being discarded even when it
// has no significant state, -1 to never discard.
int64 entry_lifetime_ms;
// If true, we always use a delay of initial_delay_ms, even before
// we've seen num_errors_to_ignore errors. Otherwise, initial_delay_ms
// is the first delay once we start exponential backoff.
//
// So if we're ignoring 1 error, we'll see (N, N, Nm, Nm^2, ...) if true,
// and (0, 0, N, Nm, ...) when false, where N is initial_backoff_ms and
// m is multiply_factor, assuming we've already seen one success.
bool always_use_initial_delay;
};
// Lifetime of policy must enclose lifetime of BackoffEntry. The
// pointer must be valid but is not dereferenced during construction.
explicit BackoffEntry(const Policy* const policy);
virtual ~BackoffEntry();
// Inform this item that a request for the network resource it is
// tracking was made, and whether it failed or succeeded.
void InformOfRequest(bool succeeded);
// Returns true if a request for the resource this item tracks should
// be rejected at the present time due to exponential back-off policy.
bool ShouldRejectRequest() const;
// Returns the absolute time after which this entry (given its present
// state) will no longer reject requests.
base::TimeTicks GetReleaseTime() const;
// Returns the time until a request can be sent.
base::TimeDelta GetTimeUntilRelease() const;
// Causes this object reject requests until the specified absolute time.
// This can be used to e.g. implement support for a Retry-After header.
void SetCustomReleaseTime(const base::TimeTicks& release_time);
// Returns true if this object has no significant state (i.e. you could
// just as well start with a fresh BackoffEntry object), and hasn't
// had for Policy::entry_lifetime_ms.
bool CanDiscard() const;
// Resets this entry to a fresh (as if just constructed) state.
void Reset();
// Returns the failure count for this entry.
int failure_count() const { return failure_count_; }
protected:
// Equivalent to TimeTicks::Now(), virtual so unit tests can override.
virtual base::TimeTicks ImplGetTimeNow() const;
private:
// Calculates when requests should again be allowed through.
base::TimeTicks CalculateReleaseTime() const;
// Timestamp calculated by the exponential back-off algorithm at which we are
// allowed to start sending requests again.
base::TimeTicks exponential_backoff_release_time_;
// Counts request errors; decremented on success.
int failure_count_;
const Policy* const policy_;
DISALLOW_COPY_AND_ASSIGN(BackoffEntry);
};
} // namespace net
#endif // NET_BASE_BACKOFF_ENTRY_H_