1 // Copyright 2021 The gRPC Authors
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
7 // http://www.apache.org/licenses/LICENSE-2.0
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 #ifndef GRPC_EVENT_ENGINE_EVENT_ENGINE_H
15 #define GRPC_EVENT_ENGINE_EVENT_ENGINE_H
17 #include <grpc/support/port_platform.h>
22 #include "absl/status/status.h"
23 #include "absl/status/statusor.h"
24 #include "absl/time/time.h"
26 #include "grpc/event_engine/endpoint_config.h"
27 #include "grpc/event_engine/port.h"
28 #include "grpc/event_engine/slice_allocator.h"
30 // TODO(hork): Define the Endpoint::Write metrics collection system
31 namespace grpc_event_engine {
32 namespace experimental {
34 ////////////////////////////////////////////////////////////////////////////////
35 /// The EventEngine encapsulates all platform-specific behaviors related to low
36 /// level network I/O, timers, asynchronous execution, and DNS resolution.
38 /// This interface allows developers to provide their own event management and
39 /// network stacks. Motivating uses cases for supporting custom EventEngines
40 /// include the ability to hook into external event loops, and using different
41 /// EventEngine instances for each channel to better insulate network I/O and
42 /// callback processing from other channels.
44 /// A default cross-platform EventEngine instance is provided by gRPC.
46 /// LIFESPAN AND OWNERSHIP
48 /// gRPC takes shared ownership of EventEngines via std::shared_ptrs to ensure
49 /// that the engines remain available until they are no longer needed. Depending
50 /// on the use case, engines may live until gRPC is shut down.
52 /// EXAMPLE USAGE (Not yet implemented)
54 /// Custom EventEngines can be specified per channel, and allow configuration
55 /// for both clients and servers. To set a custom EventEngine for a client
56 /// channel, you can do something like the following:
58 /// ChannelArguments args;
59 /// std::shared_ptr<EventEngine> engine = std::make_shared<MyEngine>(...);
60 /// args.SetEventEngine(engine);
61 /// MyAppClient client(grpc::CreateCustomChannel(
62 /// "localhost:50051", grpc::InsecureChannelCredentials(), args));
64 /// A gRPC server can use a custom EventEngine by calling the
65 /// ServerBuilder::SetEventEngine method:
67 /// ServerBuilder builder;
68 /// std::shared_ptr<EventEngine> engine = std::make_shared<MyEngine>(...);
69 /// builder.SetEventEngine(engine);
70 /// std::unique_ptr<Server> server(builder.BuildAndStart());
73 ////////////////////////////////////////////////////////////////////////////////
76 /// A basic callable function. The first argument to all callbacks is an
77 /// absl::Status indicating the status of the operation associated with this
78 /// callback. Each EventEngine method that takes a callback parameter, defines
79 /// the expected sets and meanings of statuses for that use case.
80 using Callback = std::function<void(absl::Status)>;
81 /// A callback handle, used to cancel a callback.
85 /// A thin wrapper around a platform-specific sockaddr type. A sockaddr struct
86 /// exists on all platforms that gRPC supports.
88 /// Platforms are expected to provide definitions for:
92 class ResolvedAddress {
94 static constexpr socklen_t MAX_SIZE_BYTES = 128;
96 ResolvedAddress(const sockaddr* address, socklen_t size);
97 ResolvedAddress() = default;
98 ResolvedAddress(const ResolvedAddress&) = default;
99 const struct sockaddr* address() const;
100 socklen_t size() const;
103 char address_[MAX_SIZE_BYTES];
107 /// An Endpoint represents one end of a connection between a gRPC client and
108 /// server. Endpoints are created when connections are established, and
109 /// Endpoint operations are gRPC's primary means of communication.
111 /// Endpoints must use the provided SliceAllocator for all data buffer memory
112 /// allocations. gRPC allows applications to set memory constraints per
113 /// Channel or Server, and the implementation depends on all dynamic memory
114 /// allocation being handled by the quota system.
117 /// The Endpoint destructor is responsible for shutting down all connections
118 /// and invoking all pending read or write callbacks with an error status.
119 virtual ~Endpoint() = default;
120 /// Read data from the Endpoint.
122 /// When data is available on the connection, that data is moved into the
123 /// \a buffer, and the \a on_read callback is called. The caller must ensure
124 /// that the callback has access to the buffer when executed later.
125 /// Ownership of the buffer is not transferred. Valid slices *may* be placed
126 /// into the buffer even if the callback is invoked with a non-OK Status.
128 /// For failed read operations, implementations should pass the appropriate
129 /// statuses to \a on_read. For example, callbacks might expect to receive
130 /// CANCELLED on endpoint shutdown.
131 virtual void Read(Callback on_read, SliceBuffer* buffer) = 0;
132 /// Write data out on the connection.
134 /// \a on_writable is called when the connection is ready for more data. The
135 /// Slices within the \a data buffer may be mutated at will by the Endpoint
136 /// until \a on_writable is called. The \a data SliceBuffer will remain
137 /// valid after calling \a Write, but its state is otherwise undefined.
139 /// For failed write operations, implementations should pass the appropriate
140 /// statuses to \a on_writable. For example, callbacks might expect to
141 /// receive CANCELLED on endpoint shutdown.
142 virtual void Write(Callback on_writable, SliceBuffer* data) = 0;
143 /// These methods return an address in the format described in DNSResolver.
144 /// The returned values are owned by the Endpoint and are expected to remain
145 /// valid for the life of the Endpoint.
146 virtual const ResolvedAddress& GetPeerAddress() const = 0;
147 virtual const ResolvedAddress& GetLocalAddress() const = 0;
150 /// Called when a new connection is established.
152 /// If the connection attempt was not successful, implementations should pass
153 /// the appropriate statuses to this callback. For example, callbacks might
154 /// expect to receive DEADLINE_EXCEEDED statuses when appropriate, or
155 /// CANCELLED statuses on EventEngine shutdown.
156 using OnConnectCallback =
157 std::function<void(absl::StatusOr<std::unique_ptr<Endpoint>>)>;
159 /// An EventEngine Listener listens for incoming connection requests from gRPC
160 /// clients and initiates request processing once connections are established.
163 /// Called when the listener has accepted a new client connection.
164 using AcceptCallback = std::function<void(std::unique_ptr<Endpoint>)>;
165 virtual ~Listener() = default;
166 /// Bind an address/port to this Listener.
168 /// It is expected that multiple addresses/ports can be bound to this
169 /// Listener before Listener::Start has been called. Returns either the
170 /// bound port or an appropriate error status.
171 virtual absl::StatusOr<int> Bind(const ResolvedAddress& addr) = 0;
172 virtual absl::Status Start() = 0;
175 /// Factory method to create a network listener / server.
177 /// Once a \a Listener is created and started, the \a on_accept callback will
178 /// be called once asynchronously for each established connection. Note that
179 /// unlike other callbacks, there is no status code parameter since the
180 /// callback will only be called in healthy scenarios where connections can be
183 /// This method may return a non-OK status immediately if an error was
184 /// encountered in any synchronous steps required to create the Listener. In
185 /// this case, \a on_shutdown will never be called.
187 /// If this method returns a Listener, then \a on_shutdown will be invoked
188 /// exactly once, when the Listener is shut down. The status passed to it will
189 /// indicate if there was a problem during shutdown.
191 /// The provided \a SliceAllocatorFactory is used to create \a SliceAllocators
192 /// for Endpoint construction.
193 virtual absl::StatusOr<std::unique_ptr<Listener>> CreateListener(
194 Listener::AcceptCallback on_accept, Callback on_shutdown,
195 const EndpointConfig& args,
196 std::unique_ptr<SliceAllocatorFactory> slice_allocator_factory) = 0;
197 /// Creates a client network connection to a remote network listener.
199 /// \a Connect may return an error status immediately if there was a failure
200 /// in the synchronous part of establishing a connection. In that event, the
201 /// \a on_connect callback *will not* have been executed. Otherwise, it is
202 /// expected that the \a on_connect callback will be asynchronously executed
203 /// exactly once by the EventEngine.
205 /// Implementation Note: it is important that the \a slice_allocator be used
206 /// for all read/write buffer allocations in the EventEngine implementation.
207 /// This allows gRPC's \a ResourceQuota system to monitor and control memory
208 /// usage with graceful degradation mechanisms. Please see the \a
209 /// SliceAllocator API for more information.
210 virtual absl::Status Connect(OnConnectCallback on_connect,
211 const ResolvedAddress& addr,
212 const EndpointConfig& args,
213 std::unique_ptr<SliceAllocator> slice_allocator,
214 absl::Time deadline) = 0;
216 /// The DNSResolver that provides asynchronous resolution.
219 /// A task handle for DNS Resolution requests.
220 struct LookupTaskHandle {
223 /// A DNS SRV record type.
230 /// Called with the collection of sockaddrs that were resolved from a given
232 using LookupHostnameCallback =
233 std::function<void(absl::StatusOr<std::vector<ResolvedAddress>>)>;
234 /// Called with a collection of SRV records.
235 using LookupSRVCallback =
236 std::function<void(absl::StatusOr<std::vector<SRVRecord>>)>;
237 /// Called with the result of a TXT record lookup
238 using LookupTXTCallback = std::function<void(absl::StatusOr<std::string>)>;
240 virtual ~DNSResolver() = default;
242 /// Asynchronously resolve an address.
244 /// \a default_port may be a non-numeric named service port, and will only
245 /// be used if \a address does not already contain a port component.
247 /// When the lookup is complete, the \a on_resolve callback will be invoked
248 /// with a status indicating the success or failure of the lookup.
249 /// Implementations should pass the appropriate statuses to the callback.
250 /// For example, callbacks might expect to receive DEADLINE_EXCEEDED when
251 /// the deadline is exceeded or CANCELLED if the lookup was cancelled.
252 virtual LookupTaskHandle LookupHostname(LookupHostnameCallback on_resolve,
253 absl::string_view address,
254 absl::string_view default_port,
255 absl::Time deadline) = 0;
256 /// Asynchronously perform an SRV record lookup.
258 /// \a on_resolve has the same meaning and expectations as \a
259 /// LookupHostname's \a on_resolve callback.
260 virtual LookupTaskHandle LookupSRV(LookupSRVCallback on_resolve,
261 absl::string_view name,
262 absl::Time deadline) = 0;
263 /// Asynchronously perform a TXT record lookup.
265 /// \a on_resolve has the same meaning and expectations as \a
266 /// LookupHostname's \a on_resolve callback.
267 virtual LookupTaskHandle LookupTXT(LookupTXTCallback on_resolve,
268 absl::string_view name,
269 absl::Time deadline) = 0;
270 /// Cancel an asynchronous lookup operation.
271 virtual void TryCancelLookup(LookupTaskHandle handle) = 0;
274 virtual ~EventEngine() = default;
276 // TODO(nnoble): consider whether we can remove this method before we
277 // de-experimentalize this API.
278 virtual bool IsWorkerThread() = 0;
280 // TODO(hork): define return status codes
281 /// Retrieves an instance of a DNSResolver.
282 virtual absl::StatusOr<std::unique_ptr<DNSResolver>> GetDNSResolver() = 0;
284 /// Intended for future expansion of Task run functionality.
285 struct RunOptions {};
286 /// Run a callback as soon as possible.
288 /// The \a fn callback's \a status argument is used to indicate whether it was
289 /// executed normally. For example, the status may be CANCELLED if
290 /// \a TryCancel was called, or if the EventEngine is being shut down.
291 virtual TaskHandle Run(Callback fn, RunOptions opts) = 0;
292 /// Synonymous with scheduling an alarm to run at time \a when.
294 /// The callback \a fn will execute when either when time \a when arrives
295 /// (receiving status OK), or when the \a fn is cancelled (reveiving status
296 /// CANCELLED). The callback is guaranteed to be called exactly once.
297 virtual TaskHandle RunAt(absl::Time when, Callback fn, RunOptions opts) = 0;
298 /// Immediately tries to cancel a callback.
299 /// Note that this is a "best effort" cancellation. No guarantee is made that
300 /// the callback will be cancelled, the call could be in any stage.
302 /// There are three scenarios in which we may cancel a scheduled function:
303 /// 1. We cancel the execution before it has run.
304 /// 2. The callback has already run.
305 /// 3. We can't cancel it because it is "in flight".
307 /// In all cases, the cancellation is still considered successful, the
308 /// callback will be run exactly once from either cancellation or from its
310 virtual void TryCancel(TaskHandle handle) = 0;
311 /// Immediately run all callbacks with status indicating the shutdown. Every
312 /// EventEngine is expected to shut down exactly once. No new callbacks/tasks
313 /// should be scheduled after shutdown has begun, no new connections should be
316 /// If the \a on_shutdown_complete callback is given a non-OK status, errors
317 /// are expected to be unrecoverable. For example, an implementation could
318 /// warn callers about leaks if memory cannot be freed within a certain
320 virtual void Shutdown(Callback on_shutdown_complete) = 0;
323 // TODO(hork): finalize the API and document it. We need to firm up the story
324 // around user-provided EventEngines.
325 std::shared_ptr<EventEngine> DefaultEventEngineFactory();
327 } // namespace experimental
328 } // namespace grpc_event_engine
330 #endif // GRPC_EVENT_ENGINE_EVENT_ENGINE_H