Introduce the EventEngine internal Poller interface (#30413)

* Introduce the EventEngine internal Poller interface

* EventEngine::Duration

* StatusOr

* autodeps

* using Events

* faster

* Automated change: Fix sanity tests

Co-authored-by: drfloob <drfloob@users.noreply.github.com>

BUILD

@@ -2235,6 +2235,21 @@ grpc_cc_library(
     deps = ["gpr_base"],
 )
 
+grpc_cc_library(
+    name = "event_engine_poller",
+    hdrs = [
+        "src/core/lib/event_engine/poller.h",
+    ],
+    external_deps = [
+        "absl/container:inlined_vector",
+        "absl/types:variant",
+    ],
+    deps = [
+        "event_engine_base_hdrs",
+        "gpr_platform",
+    ],
+)
+
 grpc_cc_library(
     name = "iomgr_ee_timer",
     srcs = [

src/core/lib/event_engine/poller.h

@@ -0,0 +1,54 @@
+// Copyright 2022 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+#ifndef GRPC_CORE_LIB_EVENT_ENGINE_POLLER_H
+#define GRPC_CORE_LIB_EVENT_ENGINE_POLLER_H
+
+#include <grpc/support/port_platform.h>
+
+#include "absl/container/inlined_vector.h"
+#include "absl/types/variant.h"
+
+#include <grpc/event_engine/event_engine.h>
+
+namespace grpc_event_engine {
+namespace experimental {
+
+// A generic cross-platform "poller" concept.
+// Concrete implementations will likely manage a set of sockets/file
+// descriptors/etc, allowing threads to drive polling and event processing via
+// Work(...).
+class Poller {
+ public:
+  // This initial vector size may need to be tuned
+  using Events = absl::InlinedVector<EventEngine::Closure*, 5>;
+  struct DeadlineExceeded {};
+  struct Kicked {};
+  using WorkResult = absl::variant<Events, DeadlineExceeded, Kicked>;
+
+  virtual ~Poller() = default;
+  // Poll once for events, returning a collection of Closures to be executed.
+  //
+  // Returns:
+  //  * absl::AbortedError if it was Kicked.
+  //  * absl::DeadlineExceeded if timeout occurred
+  //  * A collection of closures to execute, otherwise
+  virtual WorkResult Work(EventEngine::Duration timeout) = 0;
+  // Trigger the threads executing Work(..) to break out as soon as possible.
+  virtual void Kick() = 0;
+};
+
+}  // namespace experimental
+}  // namespace grpc_event_engine
+
+#endif  // GRPC_CORE_LIB_EVENT_ENGINE_POLLER_H