AU: Implement exponential back off for 500 and 503 HTTP response codes.

update_check_scheduler.cc

Index: update_check_scheduler.cc
diff --git a/update_check_scheduler.cc b/update_check_scheduler.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c0a52ab8540257ec79916b0448a85c616930398e
--- /dev/null
+++ b/update_check_scheduler.cc
@@ -0,0 +1,128 @@
+// Copyright (c) 2010 The Chromium OS 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 "update_engine/update_check_scheduler.h"
+
+#include "update_engine/utils.h"
+
+namespace chromeos_update_engine {
+
+const int UpdateCheckScheduler::kTimeoutOnce = 7 * 60;  // at 7 minutes
+const int UpdateCheckScheduler::kTimeoutPeriodic = 45 * 60;  // every 45 minutes
+const int UpdateCheckScheduler::kTimeoutRegularFuzz = 10 * 60;  // +/- 5 minutes
+const int UpdateCheckScheduler::kTimeoutMaxBackoff = 4 * 60 * 60;  // 4 hours
+
+UpdateCheckScheduler::UpdateCheckScheduler(UpdateAttempter* update_attempter)
+    : update_attempter_(update_attempter),
+      enabled_(false),
+      scheduled_(false),
+      last_interval_(0) {}
+
+UpdateCheckScheduler::~UpdateCheckScheduler() {}
+
+void UpdateCheckScheduler::Run() {
+  enabled_ = false;
+  update_attempter_->set_update_check_scheduler(NULL);
+
+  if (!IsOfficialBuild()) {
+    LOG(WARNING) << "Non-official build: periodic update checks disabled.";
+    return;
+  }
+  if (IsBootDeviceRemovable()) {
+    LOG(WARNING) << "Removable device boot: periodic update checks disabled.";
+    return;
+  }
+  enabled_ = true;
+
+  // Registers this scheduler with the update attempter so that scheduler can be
+  // notified of update status changes.
+  update_attempter_->set_update_check_scheduler(this);
+
+  // Kicks off periodic update checks. The first check is scheduled
+  // |kTimeoutOnce| seconds from now. Subsequent checks are scheduled by
+  // ScheduleNextCheck, normally at |kTimeoutPeriodic|-second intervals.
+  ScheduleCheck(kTimeoutOnce, kTimeoutRegularFuzz);
+}
+
+bool UpdateCheckScheduler::IsBootDeviceRemovable() {
+  return utils::IsRemovableDevice(utils::RootDevice(utils::BootDevice()));
+}
+
+bool UpdateCheckScheduler::IsOfficialBuild() {
+  return utils::IsOfficialBuild();
+}
+
+guint UpdateCheckScheduler::GTimeoutAddSeconds(guint interval,
+                                               GSourceFunc function) {
+  return g_timeout_add_seconds(interval, function, this);
+}
+
+void UpdateCheckScheduler::ScheduleCheck(int interval, int fuzz) {
+  if (!CanSchedule()) {
+    return;
+  }
+  last_interval_ = interval;
+  interval = utils::FuzzInt(interval, fuzz);
+  if (interval < 0) {
+    interval = 0;
+  }
+  GTimeoutAddSeconds(interval, StaticCheck);
+  scheduled_ = true;
+  LOG(INFO) << "Next update check in " << interval << " seconds.";
+}
+
+gboolean UpdateCheckScheduler::StaticCheck(void* scheduler) {
+  UpdateCheckScheduler* me = reinterpret_cast<UpdateCheckScheduler*>(scheduler);
+  CHECK(me->scheduled_);
+  me->scheduled_ = false;
+  me->update_attempter_->Update("", "");
+  // This check ensures that future update checks will be or are already
+  // scheduled. The check should never fail. A check failure means that there's
+  // a bug that will most likely prevent further automatic update checks. It
+  // seems better to crash in such cases and restart the update_engine daemon
+  // into, hopefully, a known good state.
+  CHECK(me->update_attempter_->status() != UPDATE_STATUS_IDLE ||
+        !me->CanSchedule());
+  return FALSE;  // Don't run again.
+}
+
+void UpdateCheckScheduler::ComputeNextIntervalAndFuzz(int* next_interval,
+                                                      int* next_fuzz) {
+  int interval = 0;
+  int fuzz = 0;
+  // Implements exponential back off on 500 (Internal Server Error) and 503
+  // (Service Unavailable) HTTP response codes.
+  if (update_attempter_->http_response_code() == 500 ||
+      update_attempter_->http_response_code() == 503) {
+    interval = 2 * last_interval_;
+    if (interval > kTimeoutMaxBackoff) {
+      interval = kTimeoutMaxBackoff;
+    }
+    // Exponential back off is fuzzed by +/- |interval|/2.
+    fuzz = interval;
+  }
+  // Ensures that under normal conditions the regular update check interval and
+  // fuzz are used. Also covers the case where back off is required based on the
+  // initial update check.
+  if (interval < kTimeoutPeriodic) {
+    interval = kTimeoutPeriodic;
+    fuzz = kTimeoutRegularFuzz;
+  }
+  *next_interval = interval;
+  *next_fuzz = fuzz;
+}
+
+void UpdateCheckScheduler::ScheduleNextCheck() {
+  int interval, fuzz;
+  ComputeNextIntervalAndFuzz(&interval, &fuzz);
+  ScheduleCheck(interval, fuzz);
+}
+
+void UpdateCheckScheduler::SetUpdateStatus(UpdateStatus status) {
+  if (status == UPDATE_STATUS_IDLE) {
+    ScheduleNextCheck();
+  }
+}
+
+}  // namespace chromeos_update_engine