Updated backoff to spec.

doc/connection-backoff.md

@@ -7,9 +7,10 @@ requests) and instead do some form of exponential backoff.
 
 We have several parameters:
  1. INITIAL_BACKOFF (how long to wait after the first failure before retrying)
- 2. MULTIPLIER (factor with which to multiply backoff after a failed retry)
+ 1. MULTIPLIER (factor with which to multiply backoff after a failed retry)
- 3. MAX_BACKOFF (upper bound on backoff)
+ 1. JITTER (by how much to randomize backoffs).
- 4. MIN_CONNECT_TIMEOUT (minimum time we're willing to give a connection to
+ 1. MAX_BACKOFF (upper bound on backoff)
+ 1. MIN_CONNECT_TIMEOUT (minimum time we're willing to give a connection to
     complete)
 
 ## Proposed Backoff Algorithm

src/core/ext/client_channel/subchannel.c

@@ -334,16 +334,18 @@ grpc_subchannel *grpc_subchannel_create(grpc_exec_ctx *exec_ctx,
   int initial_backoff_ms =
       GRPC_SUBCHANNEL_INITIAL_CONNECT_BACKOFF_SECONDS * 1000;
   int max_backoff_ms = GRPC_SUBCHANNEL_RECONNECT_MAX_BACKOFF_SECONDS * 1000;
+  int min_backoff_ms = GRPC_SUBCHANNEL_MIN_CONNECT_TIMEOUT_SECONDS * 1000;
   bool fixed_reconnect_backoff = false;
   if (c->args) {
     for (size_t i = 0; i < c->args->num_args; i++) {
       if (0 == strcmp(c->args->args[i].key,
-                      "grpc.testing.fixed_reconnect_backoff")) {
+                      "grpc.testing.fixed_reconnect_backoff_ms")) {
         GPR_ASSERT(c->args->args[i].type == GRPC_ARG_INTEGER);
         fixed_reconnect_backoff = true;
-        initial_backoff_ms = max_backoff_ms = grpc_channel_arg_get_integer(
+        initial_backoff_ms = min_backoff_ms = max_backoff_ms =
-            &c->args->args[i],
+            grpc_channel_arg_get_integer(
-            (grpc_integer_options){initial_backoff_ms, 100, INT_MAX});
+                &c->args->args[i],
+                (grpc_integer_options){initial_backoff_ms, 100, INT_MAX});
       } else if (0 == strcmp(c->args->args[i].key,
                              GRPC_ARG_MAX_RECONNECT_BACKOFF_MS)) {
         fixed_reconnect_backoff = false;
@@ -360,11 +362,11 @@ grpc_subchannel *grpc_subchannel_create(grpc_exec_ctx *exec_ctx,
     }
   }
   gpr_backoff_init(
-      &c->backoff_state,
+      &c->backoff_state, initial_backoff_ms,
       fixed_reconnect_backoff ? 1.0
                               : GRPC_SUBCHANNEL_RECONNECT_BACKOFF_MULTIPLIER,
       fixed_reconnect_backoff ? 0.0 : GRPC_SUBCHANNEL_RECONNECT_JITTER,
-      initial_backoff_ms, max_backoff_ms);
+      min_backoff_ms, max_backoff_ms);
   gpr_mu_init(&c->mu);
 
   return grpc_subchannel_index_register(exec_ctx, key, c);

src/core/ext/lb_policy/grpclb/grpclb.c

@@ -123,10 +123,11 @@
 #include "src/core/lib/surface/channel.h"
 #include "src/core/lib/transport/static_metadata.h"
 
-#define BACKOFF_MULTIPLIER 1.6
+#define GRPC_GRPCLB_MIN_CONNECT_TIMEOUT_SECONDS 20
-#define BACKOFF_JITTER 0.2
+#define GRPC_GRPCLB_INITIAL_CONNECT_BACKOFF_SECONDS 1
-#define BACKOFF_MIN_SECONDS 10
+#define GRPC_GRPCLB_RECONNECT_BACKOFF_MULTIPLIER 1.6
-#define BACKOFF_MAX_SECONDS 60
+#define GRPC_GRPCLB_RECONNECT_MAX_BACKOFF_SECONDS 120
+#define GRPC_GRPCLB_RECONNECT_JITTER 0.2
 
 int grpc_lb_glb_trace = 0;
 
@@ -1107,9 +1108,12 @@ static void lb_call_init_locked(glb_lb_policy *glb_policy) {
   grpc_closure_init(&glb_policy->lb_on_response_received,
                     lb_on_response_received, glb_policy);
 
-  gpr_backoff_init(&glb_policy->lb_call_backoff_state, BACKOFF_MULTIPLIER,
+  gpr_backoff_init(&glb_policy->lb_call_backoff_state,
-                   BACKOFF_JITTER, BACKOFF_MIN_SECONDS * 1000,
+                   GRPC_GRPCLB_INITIAL_CONNECT_BACKOFF_SECONDS,
-                   BACKOFF_MAX_SECONDS * 1000);
+                   GRPC_GRPCLB_RECONNECT_BACKOFF_MULTIPLIER,
+                   GRPC_GRPCLB_RECONNECT_JITTER,
+                   GRPC_GRPCLB_MIN_CONNECT_TIMEOUT_SECONDS * 1000,
+                   GRPC_GRPCLB_RECONNECT_MAX_BACKOFF_SECONDS * 1000);
 }
 
 static void lb_call_destroy_locked(glb_lb_policy *glb_policy) {

src/core/ext/resolver/dns/native/dns_resolver.c

@@ -46,10 +46,11 @@
 #include "src/core/lib/support/backoff.h"
 #include "src/core/lib/support/string.h"
 
-#define BACKOFF_MULTIPLIER 1.6
+#define GRPC_DNS_MIN_CONNECT_TIMEOUT_SECONDS 1
-#define BACKOFF_JITTER 0.2
+#define GRPC_DNS_INITIAL_CONNECT_BACKOFF_SECONDS 1
-#define BACKOFF_MIN_SECONDS 1
+#define GRPC_DNS_RECONNECT_BACKOFF_MULTIPLIER 1.6
-#define BACKOFF_MAX_SECONDS 120
+#define GRPC_DNS_RECONNECT_MAX_BACKOFF_SECONDS 120
+#define GRPC_DNS_RECONNECT_JITTER 0.2
 
 typedef struct {
   /** base class: must be first */
@@ -269,8 +270,11 @@ static grpc_resolver *dns_create(grpc_resolver_args *args,
   server_name_arg.value.string = (char *)path;
   r->channel_args =
       grpc_channel_args_copy_and_add(args->args, &server_name_arg, 1);
-  gpr_backoff_init(&r->backoff_state, BACKOFF_MULTIPLIER, BACKOFF_JITTER,
+  gpr_backoff_init(&r->backoff_state, GRPC_DNS_INITIAL_CONNECT_BACKOFF_SECONDS,
-                   BACKOFF_MIN_SECONDS * 1000, BACKOFF_MAX_SECONDS * 1000);
+                   GRPC_DNS_RECONNECT_BACKOFF_MULTIPLIER,
+                   GRPC_DNS_RECONNECT_JITTER,
+                   GRPC_DNS_MIN_CONNECT_TIMEOUT_SECONDS * 1000,
+                   GRPC_DNS_RECONNECT_MAX_BACKOFF_SECONDS * 1000);
   return &r->base;
 }
 

src/core/lib/support/backoff.c

@@ -35,8 +35,10 @@
 
 #include <grpc/support/useful.h>
 
-void gpr_backoff_init(gpr_backoff *backoff, double multiplier, double jitter,
+void gpr_backoff_init(gpr_backoff *backoff, int64_t initial_connect_timeout,
+                      double multiplier, double jitter,
                       int64_t min_timeout_millis, int64_t max_timeout_millis) {
+  backoff->initial_connect_timeout = initial_connect_timeout;
   backoff->multiplier = multiplier;
   backoff->jitter = jitter;
   backoff->min_timeout_millis = min_timeout_millis;
@@ -45,9 +47,10 @@ void gpr_backoff_init(gpr_backoff *backoff, double multiplier, double jitter,
 }
 
 gpr_timespec gpr_backoff_begin(gpr_backoff *backoff, gpr_timespec now) {
-  backoff->current_timeout_millis = backoff->min_timeout_millis;
+  backoff->current_timeout_millis = backoff->initial_connect_timeout;
-  return gpr_time_add(
+  const int64_t first_timeout =
-      now, gpr_time_from_millis(backoff->current_timeout_millis, GPR_TIMESPAN));
+      GPR_MAX(backoff->current_timeout_millis, backoff->min_timeout_millis);
+  return gpr_time_add(now, gpr_time_from_millis(first_timeout, GPR_TIMESPAN));
 }
 
 /* Generate a random number between 0 and 1. */
@@ -57,20 +60,28 @@ static double generate_uniform_random_number(uint32_t *rng_state) {
 }
 
 gpr_timespec gpr_backoff_step(gpr_backoff *backoff, gpr_timespec now) {
-  double new_timeout_millis =
+  const double new_timeout_millis =
       backoff->multiplier * (double)backoff->current_timeout_millis;
-  double jitter_range = backoff->jitter * new_timeout_millis;
+  backoff->current_timeout_millis =
-  double jitter =
+      GPR_MIN((int64_t)new_timeout_millis, backoff->max_timeout_millis);
+
+  const double jitter_range_width = backoff->jitter * new_timeout_millis;
+  const double jitter =
       (2 * generate_uniform_random_number(&backoff->rng_state) - 1) *
-      jitter_range;
+      jitter_range_width;
+
   backoff->current_timeout_millis =
-      GPR_CLAMP((int64_t)(new_timeout_millis + jitter),
+      (int64_t)((double)(backoff->current_timeout_millis) + jitter);
-                backoff->min_timeout_millis, backoff->max_timeout_millis);
+
-  return gpr_time_add(
+  const gpr_timespec current_deadline = gpr_time_add(
       now, gpr_time_from_millis(backoff->current_timeout_millis, GPR_TIMESPAN));
+
+  const gpr_timespec min_deadline = gpr_time_add(
+      now, gpr_time_from_millis(backoff->min_timeout_millis, GPR_TIMESPAN));
+
+  return gpr_time_max(current_deadline, min_deadline);
 }
 
 void gpr_backoff_reset(gpr_backoff *backoff) {
-  // forces step() to return a timeout of min_timeout_millis
+  backoff->current_timeout_millis = backoff->initial_connect_timeout;
-  backoff->current_timeout_millis = 0;
 }

src/core/lib/support/backoff.h

@@ -37,7 +37,9 @@
 #include <grpc/support/time.h>
 
 typedef struct {
-  /// const: multiplier between retry attempts
+  /// const:  how long to wait after the first failure before retrying
+  int64_t initial_connect_timeout;
+  /// const: factor with which to multiply backoff after a failed retry
   double multiplier;
   /// const: amount to randomize backoffs
   double jitter;
@@ -54,7 +56,8 @@ typedef struct {
 } gpr_backoff;
 
 /// Initialize backoff machinery - does not need to be destroyed
-void gpr_backoff_init(gpr_backoff *backoff, double multiplier, double jitter,
+void gpr_backoff_init(gpr_backoff *backoff, int64_t initial_connect_timeout,
+                      double multiplier, double jitter,
                       int64_t min_timeout_millis, int64_t max_timeout_millis);
 
 /// Begin retry loop: returns a timespec for the NEXT retry

test/core/client_channel/lb_policies_test.c

@@ -481,7 +481,7 @@ void run_spec(const test_spec *spec) {
   gpr_asprintf(&client_hostport, "ipv4:%s", servers_hostports_str);
 
   arg_array[0].type = GRPC_ARG_INTEGER;
-  arg_array[0].key = "grpc.testing.fixed_reconnect_backoff";
+  arg_array[0].key = "grpc.testing.fixed_reconnect_backoff_ms";
   arg_array[0].value.integer = RETRY_TIMEOUT;
   arg_array[1].type = GRPC_ARG_STRING;
   arg_array[1].key = GRPC_ARG_LB_POLICY_NAME;
@@ -519,7 +519,7 @@ static grpc_channel *create_client(const servers_fixture *f) {
   gpr_asprintf(&client_hostport, "ipv4:%s", servers_hostports_str);
 
   arg_array[0].type = GRPC_ARG_INTEGER;
-  arg_array[0].key = "grpc.testing.fixed_reconnect_backoff";
+  arg_array[0].key = "grpc.testing.fixed_reconnect_backoff_ms";
   arg_array[0].value.integer = RETRY_TIMEOUT;
   arg_array[1].type = GRPC_ARG_STRING;
   arg_array[1].key = GRPC_ARG_LB_POLICY_NAME;

test/core/end2end/goaway_server_test.c

@@ -126,8 +126,16 @@ int main(int argc, char **argv) {
 
   char *addr;
 
+  grpc_channel_args client_args;
+  grpc_arg arg_array[1];
+  arg_array[0].type = GRPC_ARG_INTEGER;
+  arg_array[0].key = "grpc.testing.fixed_reconnect_backoff_ms";
+  arg_array[0].value.integer = 1000;
+  client_args.args = arg_array;
+  client_args.num_args = 1;
+
   /* create a channel that picks first amongst the servers */
-  grpc_channel *chan = grpc_insecure_channel_create("test", NULL, NULL);
+  grpc_channel *chan = grpc_insecure_channel_create("test", &client_args, NULL);
   /* and an initial call to them */
   grpc_call *call1 = grpc_channel_create_call(
       chan, NULL, GRPC_PROPAGATE_DEFAULTS, cq, "/foo", "127.0.0.1",

test/core/end2end/tests/connectivity.c

@@ -68,7 +68,15 @@ static void test_connectivity(grpc_end2end_test_config config) {
   gpr_thd_options thdopt = gpr_thd_options_default();
   gpr_thd_id thdid;
 
-  config.init_client(&f, NULL);
+  grpc_channel_args client_args;
+  grpc_arg arg_array[1];
+  arg_array[0].type = GRPC_ARG_INTEGER;
+  arg_array[0].key = "grpc.testing.fixed_reconnect_backoff_ms";
+  arg_array[0].value.integer = 1000;
+  client_args.args = arg_array;
+  client_args.num_args = 1;
+
+  config.init_client(&f, &client_args);
 
   ce.channel = f.client;
   ce.cq = f.cq;

test/core/end2end/tests/simple_delayed_request.c

@@ -200,21 +200,36 @@ static void simple_delayed_request_body(grpc_end2end_test_config config,
 
 static void test_simple_delayed_request_short(grpc_end2end_test_config config) {
   grpc_end2end_test_fixture f;
+  grpc_channel_args client_args;
+  grpc_arg arg_array[1];
+  arg_array[0].type = GRPC_ARG_INTEGER;
+  arg_array[0].key = "grpc.testing.fixed_reconnect_backoff_ms";
+  arg_array[0].value.integer = 1000;
+  client_args.args = arg_array;
+  client_args.num_args = 1;
 
   gpr_log(GPR_INFO, "%s/%s", "test_simple_delayed_request_short", config.name);
   f = config.create_fixture(NULL, NULL);
-  simple_delayed_request_body(config, &f, NULL, NULL, 100000);
+
+  simple_delayed_request_body(config, &f, &client_args, NULL, 100000);
   end_test(&f);
   config.tear_down_data(&f);
 }
 
 static void test_simple_delayed_request_long(grpc_end2end_test_config config) {
   grpc_end2end_test_fixture f;
+  grpc_channel_args client_args;
+  grpc_arg arg_array[1];
+  arg_array[0].type = GRPC_ARG_INTEGER;
+  arg_array[0].key = "grpc.testing.fixed_reconnect_backoff_ms";
+  arg_array[0].value.integer = 1000;
+  client_args.args = arg_array;
+  client_args.num_args = 1;
 
   gpr_log(GPR_INFO, "%s/%s", "test_simple_delayed_request_long", config.name);
   f = config.create_fixture(NULL, NULL);
   /* This timeout should be longer than a single retry */
-  simple_delayed_request_body(config, &f, NULL, NULL, 1500000);
+  simple_delayed_request_body(config, &f, &client_args, NULL, 1500000);
   end_test(&f);
   config.tear_down_data(&f);
 }

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);
+  GPR_ASSERT(gpr_time_to_millis(gpr_time_sub(next, now)) == 200);
-  now = next;
+}
-  next = gpr_backoff_step(&backoff, now);
+
-  GPR_ASSERT(gpr_time_cmp(gpr_time_from_millis(3, GPR_TIMESPAN), next) == 0);
+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;
 }