BackoffEntry: Add the option to always use a delay.

net/base/backoff_entry.h

 // Copyright (c) 2011 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_ITEM_H_
-#define NET_BASE_BACKOFF_ITEM_H_
+#ifndef NET_BASE_BACKOFF_ENTRY_H_
+#define NET_BASE_BACKOFF_ENTRY_H_
 #pragma once
 
 #include "base/threading/non_thread_safe.h"
 #include "base/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_PRIVATE BackoffEntry
-    : NON_EXPORTED_BASE(public base::NonThreadSafe) {
+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 for exponential back-off.
-    int initial_backoff_ms;
+    // 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_.
+  // 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; reset on success.
+  // Counts request errors; decremented on success.
   int failure_count_;
 
   const Policy* const policy_;
 
   DISALLOW_COPY_AND_ASSIGN(BackoffEntry);
 };
 
 }  // namespace net
 
-#endif  // NET_BASE_BACKOFF_ITEM_H_
+#endif  // NET_BASE_BACKOFF_ENTRY_H_