1 files changed, 71 insertions, 20 deletions
diff --git a/test/core/support/backoff_test.c b/test/core/support/backoff_test.c
index 13cba7d750..ad6e5a98f2 100644
--- a/test/core/support/backoff_test.c
+++ b/test/core/support/backoff_test.c
@@ -39,61 +39,110 @@
 
 static void test_constant_backoff(void) {
   gpr_backoff backoff;
-  gpr_backoff_init(&backoff, 1.0, 0.0, 1000, 1000);
+  gpr_backoff_init(&backoff, 200 /* initial timeout */, 1.0 /* multiplier */,
+                   0.0 /* jitter */, 100 /* min timeout */,
+                   1000 /* max timeout */);
 
   gpr_timespec now = gpr_time_0(GPR_TIMESPAN);
   gpr_timespec next = gpr_backoff_begin(&backoff, now);
-  GPR_ASSERT(gpr_time_to_millis(gpr_time_sub(next, now)) == 1000);
+  GPR_ASSERT(gpr_time_to_millis(gpr_time_sub(next, now)) == 200);
   for (int i = 0; i < 10000; i++) {
     next = gpr_backoff_step(&backoff, now);
-    GPR_ASSERT(gpr_time_to_millis(gpr_time_sub(next, now)) == 1000);
+    GPR_ASSERT(gpr_time_to_millis(gpr_time_sub(next, now)) == 200);
     now = next;
   }
 }
 
-static void test_no_jitter_backoff(void) {
+static void test_min_connect(void) {
   gpr_backoff backoff;
-  gpr_backoff_init(&backoff, 2.0, 0.0, 1, 513);
+  gpr_backoff_init(&backoff, 100 /* initial timeout */, 1.0 /* multiplier */,
+                   0.0 /* jitter */, 200 /* min timeout */,
+                   1000 /* max timeout */);
 
   gpr_timespec now = gpr_time_0(GPR_TIMESPAN);
   gpr_timespec next = gpr_backoff_begin(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(1, GPR_TIMESPAN), next) == 0);
-  now = next;
-  next = gpr_backoff_step(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(3, GPR_TIMESPAN), next) == 0);
+  GPR_ASSERT(gpr_time_to_millis(gpr_time_sub(next, now)) == 200);
+}
+
+static void test_no_jitter_backoff(void) {
+  gpr_backoff backoff;
+  gpr_backoff_init(&backoff, 2 /* initial timeout */, 2.0 /* multiplier */,
+                   0.0 /* jitter */, 1 /* min timeout */,
+                   513 /* max timeout */);
+  // x_1 = 2
+  // x_n = 2**i + x_{i-1} ( = 2**(n+1) - 2 )
+  gpr_timespec now = gpr_time_0(GPR_TIMESPAN);
+  gpr_timespec next = gpr_backoff_begin(&backoff, now);
+  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(2, GPR_TIMESPAN), next) == 0);
   now = next;
   next = gpr_backoff_step(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(7, GPR_TIMESPAN), next) == 0);
+  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(6, GPR_TIMESPAN), next) == 0);
   now = next;
   next = gpr_backoff_step(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(15, GPR_TIMESPAN), next) == 0);
+  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(14, GPR_TIMESPAN), next) == 0);
   now = next;
   next = gpr_backoff_step(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(31, GPR_TIMESPAN), next) == 0);
+  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(30, GPR_TIMESPAN), next) == 0);
   now = next;
   next = gpr_backoff_step(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(63, GPR_TIMESPAN), next) == 0);
+  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(62, GPR_TIMESPAN), next) == 0);
   now = next;
   next = gpr_backoff_step(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(127, GPR_TIMESPAN), next) == 0);
+  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(126, GPR_TIMESPAN), next) == 0);
   now = next;
   next = gpr_backoff_step(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(255, GPR_TIMESPAN), next) == 0);
+  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(254, GPR_TIMESPAN), next) == 0);
   now = next;
   next = gpr_backoff_step(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(511, GPR_TIMESPAN), next) == 0);
+  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(510, GPR_TIMESPAN), next) == 0);
   now = next;
   next = gpr_backoff_step(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(1023, GPR_TIMESPAN), next) == 0);
+  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(1022, GPR_TIMESPAN), next) == 0);
   now = next;
   next = gpr_backoff_step(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(1536, GPR_TIMESPAN), next) == 0);
+  // Hit the maximum timeout. From this point onwards, retries will increase
+  // only by max timeout.
+  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(1535, GPR_TIMESPAN), next) == 0);
   now = next;
   next = gpr_backoff_step(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(2049, GPR_TIMESPAN), next) == 0);
+  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(2048, GPR_TIMESPAN), next) == 0);
   now = next;
   next = gpr_backoff_step(&backoff, now);
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(2562, GPR_TIMESPAN), next) == 0);
+  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(2561, GPR_TIMESPAN), next) == 0);
+}
+
+static void test_jitter_backoff(void) {
+  const int64_t initial_timeout = 500;
+  const double jitter = 0.1;
+  gpr_backoff backoff;
+  gpr_backoff_init(&backoff, initial_timeout, 1.0 /* multiplier */, jitter,
+                   100 /* min timeout */, 1000 /* max timeout */);
+
+  backoff.rng_state = 0;  // force consistent PRNG
+
+  gpr_timespec now = gpr_time_0(GPR_TIMESPAN);
+  gpr_timespec next = gpr_backoff_begin(&backoff, now);
+  GPR_ASSERT(gpr_time_to_millis(gpr_time_sub(next, now)) == 500);
+
+  int64_t expected_next_lower_bound =
+      (int64_t)((double)initial_timeout * (1 - jitter));
+  int64_t expected_next_upper_bound =
+      (int64_t)((double)initial_timeout * (1 + jitter));
+
+  for (int i = 0; i < 10000; i++) {
+    next = gpr_backoff_step(&backoff, now);
+
+    // next-now must be within (jitter*100)% of the previous timeout.
+    const int64_t timeout_millis = gpr_time_to_millis(gpr_time_sub(next, now));
+    GPR_ASSERT(timeout_millis >= expected_next_lower_bound);
+    GPR_ASSERT(timeout_millis <= expected_next_upper_bound);
+
+    expected_next_lower_bound =
+        (int64_t)((double)timeout_millis * (1 - jitter));
+    expected_next_upper_bound =
+        (int64_t)((double)timeout_millis * (1 + jitter));
+    now = next;
+  }
 }
 
 int main(int argc, char **argv) {
@@ -101,7 +150,9 @@ int main(int argc, char **argv) {
   gpr_time_init();
 
   test_constant_backoff();
+  test_min_connect();
   test_no_jitter_backoff();
+  test_jitter_backoff();
 
   return 0;
 }