Fix back-off retries

Author: trask

core/src/main/java/com/microsoft/applicationinsights/internal/channel/common/ExponentialBackOffTimesPolicy.java

@@ -51,8 +51,7 @@ final class ExponentialBackOffTimesPolicy implements BackOffTimesPolicy {
             FIVE_SECONDS_IN_MILLIS,
             FOUR_MINUTES_IN_MILLIS,
             FIVE_SECONDS_IN_MILLIS,
-            SIX_MINUTES_IN_MILLIS,
-            FIVE_SECONDS_IN_MILLIS
+            SIX_MINUTES_IN_MILLIS
     };
 
     @Override

core/src/main/java/com/microsoft/applicationinsights/internal/channel/common/SenderThreadLocalBackOffData.java

@@ -87,13 +87,8 @@ public void onDoneSending() {
     public long backOffTimerValue() {
         try {
             lock.lock();
-            ++currentBackOffIndex;
-            if (currentBackOffIndex == backOffTimeoutsInMillis.length) {
-                currentBackOffIndex = -1;
-
-                // Exhausted the back-offs
-                return -1;
-            }
+            // when the last backoff index is hit, stay there until backoff is reset
+            currentBackOffIndex = Math.min(currentBackOffIndex + 1, backOffTimeoutsInMillis.length - 1);
 
             if (!instanceIsActive) {
                return 0;

core/src/test/java/com/microsoft/applicationinsights/internal/channel/common/ExponentialBackOffTimesPolicyTest.java

@@ -35,7 +35,7 @@ public final class ExponentialBackOffTimesPolicyTest {
     public void testBackOffs() {
         long[] backOffs = new ExponentialBackOffTimesPolicy().getBackOffTimeoutsInMillis();
         assertNotNull(backOffs);
-        assertTrue(backOffs.length % 2 == 1);
+        assertTrue(backOffs.length % 2 == 0);
         int couples = backOffs.length / 2;
         long lastEventValue = BackOffTimesPolicy.MIN_TIME_TO_BACK_OFF_IN_MILLS;
         for (int i = 0; i < couples; ++i) {