[EventEngine] Add invalid handle types to the public API

include/grpc/event_engine/event_engine.h

@@ -85,6 +85,7 @@ class EventEngine : public std::enable_shared_from_this<EventEngine> {
   /// caller - the EventEngine will never delete a Closure, and upon
   /// cancellation, the EventEngine will simply forget the Closure exists. The
   /// caller is responsible for all necessary cleanup.
+
   class Closure {
    public:
     Closure() = default;
@@ -103,12 +104,14 @@ class EventEngine : public std::enable_shared_from_this<EventEngine> {
   struct TaskHandle {
     intptr_t keys[2];
   };
+  static constexpr TaskHandle kInvalidTaskHandle{-1, -1};
   /// A handle to a cancellable connection attempt.
   ///
   /// Returned by \a Connect, and can be passed to \a CancelConnect.
   struct ConnectionHandle {
     intptr_t keys[2];
   };
+  static constexpr ConnectionHandle kInvalidConnectionHandle{-1, -1};
   /// Thin wrapper around a platform-specific sockaddr type. A sockaddr struct
   /// exists on all platforms that gRPC supports.
   ///

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

@@ -232,7 +232,7 @@ EventEngine::ConnectionHandle PosixEventEngine::ConnectInternal(
          ep = absl::FailedPreconditionError(absl::StrCat(
              "connect failed: ", "invalid addr: ",
              addr_uri.value()))]() mutable { on_connect(std::move(ep)); });
-    return {0, 0};
+    return EventEngine::kInvalidConnectionHandle;
   }
 
   std::string name = absl::StrCat("tcp-client:", addr_uri.value());
@@ -253,7 +253,7 @@ EventEngine::ConnectionHandle PosixEventEngine::ConnectInternal(
                                   std::move(allocator), options)]() mutable {
       on_connect(std::move(ep));
     });
-    return {0, 0};
+    return EventEngine::kInvalidConnectionHandle;
   }
   if (saved_errno != EWOULDBLOCK && saved_errno != EINPROGRESS) {
     // Connection already failed. Return 0 to discourage any cancellation
@@ -265,7 +265,7 @@ EventEngine::ConnectionHandle PosixEventEngine::ConnectInternal(
                           " error: ", std::strerror(saved_errno)))]() mutable {
       on_connect(std::move(ep));
     });
-    return {0, 0};
+    return EventEngine::kInvalidConnectionHandle;
   }
   AsyncConnect* ac = new AsyncConnect(
       std::move(on_connect), shared_from_this(), executor_.get(), handle,
@@ -554,7 +554,7 @@ EventEngine::ConnectionHandle PosixEventEngine::Connect(
   if (!socket.ok()) {
     Run([on_connect = std::move(on_connect),
          status = socket.status()]() mutable { on_connect(status); });
-    return {0, 0};
+    return EventEngine::kInvalidConnectionHandle;
   }
   return ConnectInternal((*socket).sock, std::move(on_connect),
                          (*socket).mapped_target_addr,

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

@@ -216,7 +216,7 @@ EventEngine::ConnectionHandle WindowsEventEngine::Connect(
     Run([on_connect = std::move(on_connect), status = uri.status()]() mutable {
       on_connect(status);
     });
-    return invalid_connection_handle;
+    return EventEngine::kInvalidConnectionHandle;
   }
   GRPC_EVENT_ENGINE_TRACE("EventEngine::%p connecting to %s", this,
                           uri->c_str());
@@ -233,14 +233,14 @@ EventEngine::ConnectionHandle WindowsEventEngine::Connect(
          status = GRPC_WSA_ERROR(WSAGetLastError(), "WSASocket")]() mutable {
       on_connect(status);
     });
-    return invalid_connection_handle;
+    return EventEngine::kInvalidConnectionHandle;
   }
   status = PrepareSocket(sock);
   if (!status.ok()) {
     Run([on_connect = std::move(on_connect), status]() mutable {
       on_connect(status);
     });
-    return invalid_connection_handle;
+    return EventEngine::kInvalidConnectionHandle;
   }
   // Grab the function pointer for ConnectEx for that specific socket It may
   // change depending on the interface.
@@ -257,7 +257,7 @@ EventEngine::ConnectionHandle WindowsEventEngine::Connect(
              "WSAIoctl(SIO_GET_EXTENSION_FUNCTION_POINTER)")]() mutable {
       on_connect(status);
     });
-    return invalid_connection_handle;
+    return EventEngine::kInvalidConnectionHandle;
   }
   // bind the local address
   auto local_address = ResolvedAddressMakeWild6(0);
@@ -267,7 +267,7 @@ EventEngine::ConnectionHandle WindowsEventEngine::Connect(
          status = GRPC_WSA_ERROR(WSAGetLastError(), "bind")]() mutable {
       on_connect(status);
     });
-    return invalid_connection_handle;
+    return EventEngine::kInvalidConnectionHandle;
   }
   // Connect
   auto watched_socket = iocp_.Watch(sock);
@@ -285,7 +285,7 @@ EventEngine::ConnectionHandle WindowsEventEngine::Connect(
         on_connect(status);
       });
       watched_socket->MaybeShutdown(status);
-      return invalid_connection_handle;
+      return EventEngine::kInvalidConnectionHandle;
     }
   }
   GPR_ASSERT(watched_socket != nullptr);
@@ -321,8 +321,8 @@ EventEngine::ConnectionHandle WindowsEventEngine::Connect(
 }
 
 bool WindowsEventEngine::CancelConnect(EventEngine::ConnectionHandle handle) {
-  if (TaskHandleComparator<ConnectionHandle>::Eq()(handle,
-                                                   invalid_connection_handle)) {
+  if (TaskHandleComparator<ConnectionHandle>::Eq()(
+          handle, EventEngine::kInvalidConnectionHandle)) {
     GRPC_EVENT_ENGINE_TRACE("%s",
                             "Attempted to cancel an invalid connection handle");
     return false;

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

@@ -45,10 +45,6 @@ namespace experimental {
 class WindowsEventEngine : public EventEngine,
                            public grpc_core::KeepsGrpcInitialized {
  public:
-  constexpr static TaskHandle invalid_handle{-1, -1};
-  constexpr static EventEngine::ConnectionHandle invalid_connection_handle{-1,
-                                                                           -1};
-
   class WindowsListener : public EventEngine::Listener {
    public:
     ~WindowsListener() override;