Linear back-off

FAQ.md

@@ -3447,8 +3447,11 @@ for example if the internet connection is bad or a firewall or a VPN is blocking
 FairEmail will retry one time after waiting 8 seconds while keeping the device awake (=use battery power).
 If this fails, FairEmail will schedule an alarm to retry after 5, 15, 30 and eventually every 60 minutes and let the device sleep (=no battery usage).
 
+By temporarily enabling debug mode in the miscellaneous settings, you can disable this logarithmic back-off scheme (since version 1.1855).
+This will result in using a linear back-off scheme, which means that after each failure the wait time will be increased by 1 minute up to 60 minutes.
+
 Note that [Android doze mode](https://developer.android.com/training/monitoring-device-state/doze-standby)
-does not allow to wake the device earlier than after 15 minutes.
+does not allow to wake the device earlier than after 15 minutes when doze mode is enabled.
 
 *Force sync* in the three-dots menu of the unified inbox can be used to let FairEmail attempt to reconnect without waiting.
 

app/src/main/java/eu/faircode/email/ServiceSynchronize.java

@@ -2315,7 +2315,9 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
 
                 if (state.isRunning()) {
                     long now = new Date().getTime();
+                    boolean logarithmic_backoff = prefs.getBoolean("logarithmic_backoff", true);
 
+                    if (logarithmic_backoff) {
                         // Check for fast successive server, connectivity, etc failures
                         long poll_interval = Math.min(account.poll_interval, CONNECT_BACKOFF_ALARM_START);
                         long fail_threshold = poll_interval * 60 * 1000L * FAST_FAIL_THRESHOLD / 100;
@@ -2362,18 +2364,16 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
                             fast_fails = 0;
                             first_fail = 0;
                         }
+                    }
 
                     int backoff = state.getBackoff();
                     int recently = (lastLost + LOST_RECENTLY < now ? 1 : 2);
-                    boolean logarithmic_backoff = prefs.getBoolean("logarithmic_backoff", true);
                     EntityLog.log(this, EntityLog.Type.Account, account,
                             account.name + " backoff=" + backoff +
                                     " recently=" + recently + "x" +
                                     " logarithmic=" + logarithmic_backoff);
 
-                    if (!logarithmic_backoff)
+                    if (logarithmic_backoff) {
-                        backoff = CONNECT_BACKOFF_START;
-
                         if (backoff < CONNECT_BACKOFF_MAX)
                             state.setBackoff(backoff * 2);
                         else if (backoff == CONNECT_BACKOFF_MAX)
@@ -2389,6 +2389,13 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
                                 b = CONNECT_BACKOFF_ALARM_MAX * 60;
                             state.setBackoff(b);
                         }
+                    } else {
+                        // Linear back-off
+                        int b = backoff + 60;
+                        if (b > CONNECT_BACKOFF_ALARM_MAX * 60)
+                            b = CONNECT_BACKOFF_ALARM_MAX * 60;
+                        state.setBackoff(b);
+                    }
 
                     if (backoff <= CONNECT_BACKOFF_MAX) {
                         // Short back-off period, keep device awake