Simulate transient error and verify exponential backoff.

chrome/browser/sync/retry_verifier.cc

+// 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.
+
+#include "chrome/browser/sync/retry_verifier.h"
+
+#include <algorithm>
+
+#include "base/logging.h"
+#include "chrome/browser/sync/engine/polling_constants.h"
+#include "chrome/browser/sync/sessions/session_state.h"
+
+// Given the current delay calculate the minimum and maximum wait times for
+// the next retry.
+DelayInfo CalculateDelay(int64 current_delay) {
+  int64 backoff_s = std::max(static_cast<int64>(1), current_delay *
+                             browser_sync::kBackoffRandomizationFactor);
+
+  DelayInfo delay_info;
+  delay_info.min_delay = backoff_s + (-1 * current_delay/
+                             browser_sync::kBackoffRandomizationFactor);
+  delay_info.max_delay = backoff_s + current_delay/2;
+
+  delay_info.min_delay = std::max(static_cast<int64>(1),
+      std::min(delay_info.min_delay, browser_sync::kMaxBackoffSeconds));
+
+  delay_info.max_delay = std::max(static_cast<int64>(1),
+      std::min(delay_info.max_delay, browser_sync::kMaxBackoffSeconds));
+
+  return delay_info;
+}
+
+// Fills the table with the maximum and minimum values for each retry, upto
+// |count| number of retries.
+void FillDelayTable(DelayInfo* delay_table, int count) {
+  DCHECK(count > 1);
+
+  // We start off with the minimum value of 2 seconds.
+  delay_table[0].min_delay = static_cast<int64>(2);
+  delay_table[0].max_delay = static_cast<int64>(2);
+
+  for (int i = 1 ; i < count ; ++i) {
+    delay_table[i].min_delay = CalculateDelay(delay_table[i-1].min_delay).
+                               min_delay;
+    delay_table[i].max_delay = CalculateDelay(delay_table[i-1].max_delay).
+                               max_delay;
+  }
+}
+
+// Verifies if the current retry is on time. Note that we dont use the
+// maximum value of the retry range in verifying, only the minimum. Reason
+// being there is no guarantee that the retry will be on the dot. However in
+// practice it is on the dot. But making that assumption for all the platforms
+// would make the test flaky. However we have the global timeout for the
+// verification which would make sure all retries take place in a reasonable
+// amount of time. The global timeout is defined in PSH as
+// |kExponentialBackoffVerificationTimeoutMs|.
+bool IsRetryOnTime(DelayInfo* delay_table, int retry_count,
+                   const base::TimeDelta& time_elapsed) {
+  VLOG(1) << "Retry Count : " << retry_count
+          << " Time elapsed : " << time_elapsed.InSeconds()
+          << " Retry table min: " << delay_table[retry_count].min_delay
+          << " Retry table max: " << delay_table[retry_count].max_delay;
+  return ((time_elapsed.InSeconds() >= delay_table[retry_count].min_delay));
+}
+
+RetryVerifier::RetryVerifier() : retry_count_(0) {
+}
+
+RetryVerifier::~RetryVerifier() {
+}
+
+// Initializes the state for verification.
+void RetryVerifier::Initialize(
+    const browser_sync::sessions::SyncSessionSnapshot& snap) {
+  retry_count_ = 0;
+  last_sync_time_ = snap.sync_start_time;
+  FillDelayTable(delay_table_, kMaxRetry);
+}
+
+bool RetryVerifier::VerifyRetryInterval(
+    const browser_sync::sessions::SyncSessionSnapshot& snap) {
+  DCHECK(retry_count_ < kMaxRetry);
+  if (retry_count_ == 0) {
+    if (snap.sync_start_time != last_sync_time_) {
+      retry_count_++;
+      last_sync_time_ = snap.sync_start_time;
+    }
+    return true;
+  }
+
+  // Check if the sync start time has changed. If so indicates a new sync
+  // has taken place.
+  if (snap.sync_start_time != last_sync_time_) {
+    base::TimeDelta delta = snap.sync_start_time - last_sync_time_;
+    bool result = IsRetryOnTime(delay_table_,retry_count_ -1, delta);
+    last_sync_time_ = snap.sync_start_time;
+    ++retry_count_;
+    return result;
+  }
+
+  return true;
+}
+