[EventEngine] Respect the `dns_resolver` config var in windows engine (#36901)

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Closes #36901

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36901 from yijiem:ares-windows-fix 7c16a8a741
PiperOrigin-RevId: 645182157

src/core/BUILD

@@ -2438,7 +2438,6 @@ grpc_cc_library(
         "posix_event_engine_timer_manager",
         "ref_counted_dns_resolver_interface",
         "useful",
-        "//:config_vars",
         "//:event_engine_base_hdrs",
         "//:gpr",
         "//:grpc_trace",
@@ -2857,6 +2856,7 @@ grpc_cc_library(
         "resolved_address",
         "slice",
         "windows_iocp",
+        "//:config_vars",
         "//:debug_location",
         "//:event_engine_base_hdrs",
         "//:gpr",

src/core/lib/event_engine/ares_resolver.cc

@@ -65,6 +65,7 @@
 
 #include "src/core/lib/address_utils/parse_address.h"
 #include "src/core/lib/address_utils/sockaddr_utils.h"
+#include "src/core/lib/config/config_vars.h"
 #include "src/core/lib/debug/trace.h"
 #include "src/core/lib/event_engine/grpc_polled_fd.h"
 #include "src/core/lib/event_engine/time_util.h"
@@ -788,4 +789,50 @@ void (*event_engine_grpc_ares_test_only_inject_config)(ares_channel* channel) =
 
 bool g_event_engine_grpc_ares_test_only_force_tcp = false;
 
+bool ShouldUseAresDnsResolver() {
+#if defined(GRPC_POSIX_SOCKET_ARES_EV_DRIVER) || \
+    defined(GRPC_WINDOWS_SOCKET_ARES_EV_DRIVER)
+  auto resolver_env = grpc_core::ConfigVars::Get().DnsResolver();
+  return resolver_env.empty() || absl::EqualsIgnoreCase(resolver_env, "ares");
+#else   // defined(GRPC_POSIX_SOCKET_ARES_EV_DRIVER) ||
+        // defined(GRPC_WINDOWS_SOCKET_ARES_EV_DRIVER)
+  return false;
+#endif  // defined(GRPC_POSIX_SOCKET_ARES_EV_DRIVER) ||
+        // defined(GRPC_WINDOWS_SOCKET_ARES_EV_DRIVER)
+}
+
+absl::Status AresInit() {
+  if (ShouldUseAresDnsResolver()) {
+    address_sorting_init();
+    // ares_library_init and ares_library_cleanup are currently no-op except
+    // under Windows. Calling them may cause race conditions when other parts of
+    // the binary calls these functions concurrently.
+#ifdef GPR_WINDOWS
+    int status = ares_library_init(ARES_LIB_INIT_ALL);
+    if (status != ARES_SUCCESS) {
+      return GRPC_ERROR_CREATE(
+          absl::StrCat("ares_library_init failed: ", ares_strerror(status)));
+    }
+#endif  // GPR_WINDOWS
+  }
+  return absl::OkStatus();
+}
+void AresShutdown() {
+  if (ShouldUseAresDnsResolver()) {
+    address_sorting_shutdown();
+    // ares_library_init and ares_library_cleanup are currently no-op except
+    // under Windows. Calling them may cause race conditions when other parts of
+    // the binary calls these functions concurrently.
+#ifdef GPR_WINDOWS
+    ares_library_cleanup();
+#endif  // GPR_WINDOWS
+  }
+}
+
+#else  // GRPC_ARES == 1
+
+bool ShouldUseAresDnsResolver() { return false; }
+absl::Status AresInit() { return absl::OkStatus(); }
+void AresShutdown() {}
+
 #endif  // GRPC_ARES == 1

src/core/lib/event_engine/ares_resolver.h

@@ -16,6 +16,8 @@
 
 #include <utility>
 
+#include "absl/status/status.h"
+
 #include <grpc/support/port_platform.h>
 
 #include "src/core/lib/debug/trace.h"
@@ -29,7 +31,6 @@
 
 #include "absl/base/thread_annotations.h"
 #include "absl/container/flat_hash_map.h"
-#include "absl/status/status.h"
 #include "absl/status/statusor.h"
 #include "absl/strings/string_view.h"
 #include "absl/types/optional.h"
@@ -146,4 +147,9 @@ extern void (*event_engine_grpc_ares_test_only_inject_config)(
 extern bool g_event_engine_grpc_ares_test_only_force_tcp;
 
 #endif  // GRPC_ARES == 1
+
+bool ShouldUseAresDnsResolver();
+absl::Status AresInit();
+void AresShutdown();
+
 #endif  // GRPC_SRC_CORE_LIB_EVENT_ENGINE_ARES_RESOLVER_H

src/core/lib/event_engine/posix_engine/posix_engine.cc

@@ -38,7 +38,6 @@
 #include <grpc/support/log.h>
 #include <grpc/support/port_platform.h>
 
-#include "src/core/lib/config/config_vars.h"
 #include "src/core/lib/debug/trace.h"
 #include "src/core/lib/event_engine/ares_resolver.h"
 #include "src/core/lib/event_engine/forkable.h"
@@ -94,15 +93,6 @@ class TimerForkCallbackMethods {
   static void PostforkChild() { g_timer_fork_manager->PostforkChild(); }
 };
 
-bool ShouldUseAresDnsResolver() {
-#if GRPC_ARES == 1 && defined(GRPC_POSIX_SOCKET_ARES_EV_DRIVER)
-  auto resolver_env = grpc_core::ConfigVars::Get().DnsResolver();
-  return resolver_env.empty() || absl::EqualsIgnoreCase(resolver_env, "ares");
-#else   // GRPC_ARES == 1 && defined(GRPC_POSIX_SOCKET_ARES_EV_DRIVER)
-  return false;
-#endif  // GRPC_ARES == 1 && defined(GRPC_POSIX_SOCKET_ARES_EV_DRIVER)
-}
-
 }  // namespace
 
 #ifdef GRPC_POSIX_SOCKET_TCP

src/core/lib/event_engine/windows/windows_engine.cc

@@ -322,21 +322,24 @@ void WindowsEventEngine::WindowsDNSResolver::LookupTXT(
 absl::StatusOr<std::unique_ptr<EventEngine::DNSResolver>>
 WindowsEventEngine::GetDNSResolver(
     EventEngine::DNSResolver::ResolverOptions const& options) {
+  if (ShouldUseAresDnsResolver()) {
 #if GRPC_ARES == 1 && defined(GRPC_WINDOWS_SOCKET_ARES_EV_DRIVER)
-  auto ares_resolver = AresResolver::CreateAresResolver(
-      options.dns_server,
-      std::make_unique<GrpcPolledFdFactoryWindows>(poller()),
-      shared_from_this());
-  if (!ares_resolver.ok()) {
-    return ares_resolver.status();
+    GRPC_TRACE_LOG(event_engine_dns, INFO)
+        << "WindowsEventEngine::" << this << " creating AresResolver";
+    auto ares_resolver = AresResolver::CreateAresResolver(
+        options.dns_server,
+        std::make_unique<GrpcPolledFdFactoryWindows>(poller()),
+        shared_from_this());
+    if (!ares_resolver.ok()) {
+      return ares_resolver.status();
+    }
+    return std::make_unique<WindowsEventEngine::WindowsDNSResolver>(
+        std::move(*ares_resolver));
+#endif  // GRPC_ARES == 1 && defined(GRPC_WINDOWS_SOCKET_ARES_EV_DRIVER)
   }
-  return std::make_unique<WindowsEventEngine::WindowsDNSResolver>(
-      std::move(*ares_resolver));
-#else   // GRPC_ARES == 1 && defined(GRPC_WINDOWS_SOCKET_ARES_EV_DRIVER)
   GRPC_TRACE_LOG(event_engine_dns, INFO)
       << "WindowsEventEngine::" << this << " creating NativeWindowsDNSResolver";
   return std::make_unique<NativeWindowsDNSResolver>(shared_from_this());
-#endif  // GRPC_ARES == 1 && defined(GRPC_WINDOWS_SOCKET_ARES_EV_DRIVER)
 }
 
 bool WindowsEventEngine::IsWorkerThread() { grpc_core::Crash("unimplemented"); }

src/core/lib/surface/init.cc

@@ -34,6 +34,7 @@
 #include "src/core/lib/debug/trace.h"
 #include "src/core/lib/event_engine/posix_engine/timer_manager.h"
 #include "src/core/lib/experiments/config.h"
+#include "src/core/lib/experiments/experiments.h"
 #include "src/core/lib/gprpp/fork.h"
 #include "src/core/lib/gprpp/sync.h"
 #include "src/core/lib/gprpp/thd.h"
@@ -51,6 +52,10 @@
 // Remnants of the old plugin system
 void grpc_resolver_dns_ares_init(void);
 void grpc_resolver_dns_ares_shutdown(void);
+void grpc_resolver_dns_ares_reset_dns_resolver(void);
+
+extern absl::Status AresInit();
+extern void AresShutdown();
 
 #define MAX_PLUGINS 128
 
@@ -109,7 +114,17 @@ void grpc_init(void) {
       g_shutting_down_cv->SignalAll();
     }
     grpc_iomgr_init();
-    grpc_resolver_dns_ares_init();
+    if (grpc_core::IsEventEngineDnsEnabled()) {
+      auto status = AresInit();
+      if (!status.ok()) {
+        VLOG(2) << "AresInit failed: " << status.message();
+      } else {
+        // TODO(yijiem): remove this once we remove the iomgr dns system.
+        grpc_resolver_dns_ares_reset_dns_resolver();
+      }
+    } else {
+      grpc_resolver_dns_ares_init();
+    }
     grpc_iomgr_start();
   }
 
@@ -122,7 +137,11 @@ void grpc_shutdown_internal_locked(void)
     grpc_core::ExecCtx exec_ctx(0);
     grpc_iomgr_shutdown_background_closure();
     grpc_timer_manager_set_threading(false);  // shutdown timer_manager thread
-    grpc_resolver_dns_ares_shutdown();
+    if (grpc_core::IsEventEngineDnsEnabled()) {
+      AresShutdown();
+    } else {
+      grpc_resolver_dns_ares_shutdown();
+    }
     grpc_iomgr_shutdown();
   }
   g_shutting_down = false;

src/core/resolver/dns/c_ares/dns_resolver_ares.cc

@@ -743,6 +743,13 @@ void grpc_resolver_dns_ares_shutdown() {
   }
 }
 
+void grpc_resolver_dns_ares_reset_dns_resolver() {
+  if (grpc_core::ShouldUseAresDnsResolver(
+          grpc_core::ConfigVars::Get().DnsResolver())) {
+    grpc_core::ResetDNSResolver(std::make_unique<grpc_core::AresDNSResolver>());
+  }
+}
+
 #else  // GRPC_ARES == 1
 
 namespace grpc_core {
@@ -756,4 +763,6 @@ void grpc_resolver_dns_ares_init() {}
 
 void grpc_resolver_dns_ares_shutdown() {}
 
+void grpc_resolver_dns_ares_reset_dns_resolver() {}
+
 #endif  // GRPC_ARES == 1