c-ares resolver changes

1 files changed, 74 insertions, 18 deletions

diff --git a/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc b/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc
index 6ba5f932f0..375cd743fb 100644
--- a/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc
+++ b/src/core/ext/filters/client_channel/resolver/dns/c_ares/dns_resolver_ares.cc
@@ -66,7 +66,7 @@ typedef struct {
   grpc_pollset_set* interested_parties;
 
   /** Closures used by the combiner */
-  grpc_closure dns_ares_on_retry_timer_locked;
+  grpc_closure dns_ares_on_next_resolution_timer_locked;
   grpc_closure dns_ares_on_resolved_locked;
 
   /** Combiner guarding the rest of the state */
@@ -86,11 +86,17 @@ typedef struct {
   /** current (fully resolved) result */
   grpc_channel_args* resolved_result;
   /** retry timer */
-  bool have_retry_timer;
-  grpc_timer retry_timer;
+  bool have_next_resolution_timer;
+  grpc_timer next_resolution_timer;
   /** retry backoff state */
   grpc_core::ManualConstructor<grpc_core::BackOff> backoff;
-
+  /** min resolution period. Max one resolution will happen per period */
+  grpc_millis min_time_between_resolutions;
+  /** when was the last resolution? If no resolution has happened yet, equals
+   * gpr_inf_past() */
+  grpc_millis last_resolution_timestamp;
+  /** To be invoked once the cooldown period is over */
+  grpc_closure deferred_resolution_closure;
   /** currently resolving addresses */
   grpc_lb_addresses* lb_addresses;
   /** currently resolving service config */
@@ -100,6 +106,7 @@ typedef struct {
 static void dns_ares_destroy(grpc_resolver* r);
 
 static void dns_ares_start_resolving_locked(ares_dns_resolver* r);
+static void dns_ares_maybe_start_resolving_locked(ares_dns_resolver* r);
 static void dns_ares_maybe_finish_next_locked(ares_dns_resolver* r);
 
 static void dns_ares_shutdown_locked(grpc_resolver* r);
@@ -114,8 +121,8 @@ static const grpc_resolver_vtable dns_ares_resolver_vtable = {
 
 static void dns_ares_shutdown_locked(grpc_resolver* resolver) {
   ares_dns_resolver* r = (ares_dns_resolver*)resolver;
-  if (r->have_retry_timer) {
-    grpc_timer_cancel(&r->retry_timer);
+  if (r->have_next_resolution_timer) {
+    grpc_timer_cancel(&r->next_resolution_timer);
   }
   if (r->pending_request != nullptr) {
     grpc_cancel_ares_request(r->pending_request);
@@ -132,19 +139,20 @@ static void dns_ares_channel_saw_error_locked(grpc_resolver* resolver) {
   ares_dns_resolver* r = (ares_dns_resolver*)resolver;
   if (!r->resolving) {
     r->backoff->Reset();
-    dns_ares_start_resolving_locked(r);
+    dns_ares_maybe_start_resolving_locked(r);
   }
 }
 
-static void dns_ares_on_retry_timer_locked(void* arg, grpc_error* error) {
+static void dns_ares_on_next_resolution_timer_locked(void* arg,
+                                                     grpc_error* error) {
   ares_dns_resolver* r = (ares_dns_resolver*)arg;
-  r->have_retry_timer = false;
+  r->have_next_resolution_timer = false;
   if (error == GRPC_ERROR_NONE) {
     if (!r->resolving) {
-      dns_ares_start_resolving_locked(r);
+      dns_ares_maybe_start_resolving_locked(r);
     }
   }
-  GRPC_RESOLVER_UNREF(&r->base, "retry-timer");
+  GRPC_RESOLVER_UNREF(&r->base, "next_resolution_timer");
 }
 
 static bool value_in_json_array(grpc_json* array, const char* value) {
@@ -268,21 +276,22 @@ static void dns_ares_on_resolved_locked(void* arg, grpc_error* error) {
     grpc_millis timeout = next_try - grpc_core::ExecCtx::Get()->Now();
     gpr_log(GPR_INFO, "dns resolution failed (will retry): %s",
             grpc_error_string(error));
-    GPR_ASSERT(!r->have_retry_timer);
-    r->have_retry_timer = true;
-    GRPC_RESOLVER_REF(&r->base, "retry-timer");
+    GPR_ASSERT(!r->have_next_resolution_timer);
+    r->have_next_resolution_timer = true;
+    GRPC_RESOLVER_REF(&r->base, "next_resolution_timer");
     if (timeout > 0) {
       gpr_log(GPR_DEBUG, "retrying in %" PRIdPTR " milliseconds", timeout);
     } else {
       gpr_log(GPR_DEBUG, "retrying immediately");
     }
-    grpc_timer_init(&r->retry_timer, next_try,
-                    &r->dns_ares_on_retry_timer_locked);
+    grpc_timer_init(&r->next_resolution_timer, next_try,
+                    &r->dns_ares_on_next_resolution_timer_locked);
   }
   if (r->resolved_result != nullptr) {
     grpc_channel_args_destroy(r->resolved_result);
   }
   r->resolved_result = result;
+  r->last_resolution_timestamp = grpc_core::ExecCtx::Get()->Now();
   r->resolved_version++;
   dns_ares_maybe_finish_next_locked(r);
   GRPC_RESOLVER_UNREF(&r->base, "dns-resolving");
@@ -330,6 +339,36 @@ static void dns_ares_maybe_finish_next_locked(ares_dns_resolver* r) {
   }
 }
 
+static void dns_ares_maybe_start_resolving_locked(ares_dns_resolver* r) {
+  gpr_log(GPR_INFO, "IN %s, LAST RESOLUTION TS: %lu", __func__,
+          r->last_resolution_timestamp);
+  if (r->last_resolution_timestamp >= 0) {
+    const grpc_millis earliest_next_resolution =
+        r->last_resolution_timestamp + r->min_time_between_resolutions;
+    const grpc_millis ms_until_next_resolution =
+        earliest_next_resolution - grpc_core::ExecCtx::Get()->Now();
+    if (ms_until_next_resolution > 0) {
+      const grpc_millis last_resolution_ago =
+          grpc_core::ExecCtx::Get()->Now() - r->last_resolution_timestamp;
+      gpr_log(
+          GPR_DEBUG,
+          "In cooldown from last resolution (from %ld ms ago). Will resolve "
+          "again in %ld ms",
+          last_resolution_ago, ms_until_next_resolution);
+      if (!r->have_next_resolution_timer) {
+        r->have_next_resolution_timer = true;
+        GRPC_RESOLVER_REF(&r->base, "next_resolution_timer_cooldown");
+        grpc_timer_init(&r->next_resolution_timer, ms_until_next_resolution,
+                        &r->deferred_resolution_closure);
+      }
+      ++r->resolved_version;
+      dns_ares_maybe_finish_next_locked(r);
+      return;
+    }
+  }
+  dns_ares_start_resolving_locked(r);
+}
+
 static void dns_ares_destroy(grpc_resolver* gr) {
   gpr_log(GPR_DEBUG, "dns_ares_destroy");
   ares_dns_resolver* r = (ares_dns_resolver*)gr;
@@ -344,6 +383,15 @@ static void dns_ares_destroy(grpc_resolver* gr) {
   gpr_free(r);
 }
 
+static void ares_cooldown_cb(void* arg, grpc_error* error) {
+  ares_dns_resolver* r = (ares_dns_resolver*)arg;
+  r->have_next_resolution_timer = false;
+  if (error == GRPC_ERROR_NONE && !r->resolving) {
+    dns_ares_start_resolving_locked(r);
+  }
+  GRPC_RESOLVER_UNREF(&r->base, "next_resolution_timer_cooldown");
+}
+
 static grpc_resolver* dns_ares_create(grpc_resolver_args* args,
                                       const char* default_port) {
   /* Get name from args. */
@@ -374,12 +422,20 @@ static grpc_resolver* dns_ares_create(grpc_resolver_args* args,
       .set_jitter(GRPC_DNS_RECONNECT_JITTER)
       .set_max_backoff(GRPC_DNS_RECONNECT_MAX_BACKOFF_SECONDS * 1000);
   r->backoff.Init(grpc_core::BackOff(backoff_options));
-  GRPC_CLOSURE_INIT(&r->dns_ares_on_retry_timer_locked,
-                    dns_ares_on_retry_timer_locked, r,
+  GRPC_CLOSURE_INIT(&r->dns_ares_on_next_resolution_timer_locked,
+                    dns_ares_on_next_resolution_timer_locked, r,
                     grpc_combiner_scheduler(r->base.combiner));
   GRPC_CLOSURE_INIT(&r->dns_ares_on_resolved_locked,
                     dns_ares_on_resolved_locked, r,
                     grpc_combiner_scheduler(r->base.combiner));
+  const grpc_arg* period_arg = grpc_channel_args_find(
+      args->args, GRPC_ARG_DNS_MIN_TIME_BETWEEN_RESOLUTIONS_MS);
+  const grpc_millis min_time_between_resolutions =
+      grpc_channel_arg_get_integer(period_arg, {1000, 0, INT_MAX});
+  r->min_time_between_resolutions = min_time_between_resolutions;
+  r->last_resolution_timestamp = -1;
+  GRPC_CLOSURE_INIT(&r->deferred_resolution_closure, ares_cooldown_cb, r,
+                    grpc_combiner_scheduler(r->base.combiner));
   return &r->base;
 }