sync/engine/backoff_delay_provider.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "sync/engine/backoff_delay_provider.h"
   6
   7 #include "base/rand_util.h"
   8 #include "sync/internal_api/public/engine/polling_constants.h"
   9 #include "sync/internal_api/public/sessions/model_neutral_state.h"
  10 #include "sync/internal_api/public/util/syncer_error.h"
  11
  12 using base::TimeDelta;
  13
  14 namespace syncer {
  15
  16 // static
  17 BackoffDelayProvider* BackoffDelayProvider::FromDefaults() {
  18   return new BackoffDelayProvider(
  19       TimeDelta::FromSeconds(kInitialBackoffRetrySeconds),
  20       TimeDelta::FromSeconds(kInitialBackoffImmediateRetrySeconds));
  21 }
  22
  23 // static
  24 BackoffDelayProvider* BackoffDelayProvider::WithShortInitialRetryOverride() {
  25   return new BackoffDelayProvider(
  26       TimeDelta::FromSeconds(kInitialBackoffShortRetrySeconds),
  27       TimeDelta::FromSeconds(kInitialBackoffImmediateRetrySeconds));
  28 }
  29
  30 BackoffDelayProvider::BackoffDelayProvider(
  31     const base::TimeDelta& default_initial_backoff,
  32     const base::TimeDelta& short_initial_backoff)
  33     : default_initial_backoff_(default_initial_backoff),
  34       short_initial_backoff_(short_initial_backoff) {
  35 }
  36
  37 BackoffDelayProvider::~BackoffDelayProvider() {}
  38
  39 TimeDelta BackoffDelayProvider::GetDelay(const base::TimeDelta& last_delay) {
  40   if (last_delay.InSeconds() >= kMaxBackoffSeconds)
  41     return TimeDelta::FromSeconds(kMaxBackoffSeconds);
  42
  43   // This calculates approx. base_delay_seconds * 2 +/- base_delay_seconds / 2
  44   int64 backoff_s =
  45       std::max(static_cast<int64>(1),
  46                last_delay.InSeconds() * kBackoffRandomizationFactor);
  47
  48   // Flip a coin to randomize backoff interval by +/- 50%.
  49   int rand_sign = base::RandInt(0, 1) * 2 - 1;
  50
  51   // Truncation is adequate for rounding here.
  52   backoff_s = backoff_s +
  53       (rand_sign * (last_delay.InSeconds() / kBackoffRandomizationFactor));
  54
  55   // Cap the backoff interval.
  56   backoff_s = std::max(static_cast<int64>(1),
  57                        std::min(backoff_s, kMaxBackoffSeconds));
  58
  59   return TimeDelta::FromSeconds(backoff_s);
  60 }
  61
  62 TimeDelta BackoffDelayProvider::GetInitialDelay(
  63     const sessions::ModelNeutralState& state) const {
  64   // NETWORK_CONNECTION_UNAVAILABLE implies we did not even manage to hit the
  65   // wire; the failure occurred locally. Note that if commit_result is *not*
  66   // UNSET, this implies download_updates_result succeeded.  Also note that
  67   // last_get_key_result is coupled to last_download_updates_result in that
  68   // they are part of the same GetUpdates request, so we only check if
  69   // the download request is CONNECTION_UNAVAILABLE.
  70   //
  71   // TODO(tim): Should we treat NETWORK_IO_ERROR similarly? It's different
  72   // from CONNECTION_UNAVAILABLE in that a request may well have succeeded
  73   // in contacting the server (e.g we got a 200 back), but we failed
  74   // trying to parse the response (actual content length != HTTP response
  75   // header content length value).  For now since we're considering
  76   // merging this code to branches and I haven't audited all the
  77   // NETWORK_IO_ERROR cases carefully, I'm going to target the fix
  78   // very tightly (see bug chromium-os:35073). DIRECTORY_LOOKUP_FAILED is
  79   // another example of something that shouldn't backoff, though the
  80   // scheduler should probably be handling these cases differently. See
  81   // the TODO(rlarocque) in ScheduleNextSync.
  82   if (state.commit_result == NETWORK_CONNECTION_UNAVAILABLE ||
  83       state.last_download_updates_result == NETWORK_CONNECTION_UNAVAILABLE) {
  84     return short_initial_backoff_;
  85   }
  86
  87   if (SyncerErrorIsError(state.last_get_key_result))
  88     return default_initial_backoff_;
  89
  90   // Note: If we received a MIGRATION_DONE on download updates, then commit
  91   // should not have taken place.  Moreover, if we receive a MIGRATION_DONE
  92   // on commit, it means that download updates succeeded.  Therefore, we only
  93   // need to check if either code is equal to SERVER_RETURN_MIGRATION_DONE,
  94   // and not if there were any more serious errors requiring the long retry.
  95   if (state.last_download_updates_result == SERVER_RETURN_MIGRATION_DONE ||
  96       state.commit_result == SERVER_RETURN_MIGRATION_DONE) {
  97     return short_initial_backoff_;
  98   }
  99
 100   // If a datatype decides the GetUpdates must be retried (e.g. because the
 101   // context has been updated since the request), use the short delay.
 102   if (state.last_download_updates_result == DATATYPE_TRIGGERED_RETRY)
 103     return short_initial_backoff_;
 104
 105   // When the server tells us we have a conflict, then we should download the
 106   // latest updates so we can see the conflict ourselves, resolve it locally,
 107   // then try again to commit.  Running another sync cycle will do all these
 108   // things.  There's no need to back off, we can do this immediately.
 109   //
 110   // TODO(sync): We shouldn't need to handle this in BackoffDelayProvider.
 111   // There should be a way to deal with protocol errors before we get to this
 112   // point.
 113   if (state.commit_result == SERVER_RETURN_CONFLICT)
 114     return short_initial_backoff_;
 115
 116   return default_initial_backoff_;
 117 }
 118
 119 }  // namespace syncer