3 * Copyright 2015-2016 gRPC authors.
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
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14 * See the License for the specific language governing permissions and
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19 /// A completion queue implements a concurrent producer-consumer queue, with
20 /// two main API-exposed methods: \a Next and \a AsyncNext. These
21 /// methods are the essential component of the gRPC C++ asynchronous API.
22 /// There is also a \a Shutdown method to indicate that a given completion queue
23 /// will no longer have regular events. This must be called before the
24 /// completion queue is destroyed.
25 /// All completion queue APIs are thread-safe and may be used concurrently with
26 /// any other completion queue API invocation; it is acceptable to have
27 /// multiple threads calling \a Next or \a AsyncNext on the same or different
28 /// completion queues, or to call these methods concurrently with a \a Shutdown
30 /// \remark{All other API calls on completion queue should be completed before
31 /// a completion queue destructor is called.}
32 #ifndef GRPCPP_IMPL_CODEGEN_COMPLETION_QUEUE_IMPL_H
33 #define GRPCPP_IMPL_CODEGEN_COMPLETION_QUEUE_IMPL_H
35 #include <grpc/impl/codegen/atm.h>
36 #include <grpcpp/impl/codegen/completion_queue_tag.h>
37 #include <grpcpp/impl/codegen/core_codegen_interface.h>
38 #include <grpcpp/impl/codegen/grpc_library.h>
39 #include <grpcpp/impl/codegen/status.h>
40 #include <grpcpp/impl/codegen/time.h>
42 struct grpc_completion_queue;
50 } // namespace grpc_impl
57 template <class W, class R>
58 class ClientReaderWriter;
64 template <class W, class R>
65 class ServerReaderWriterBody;
66 } // namespace internal
68 class ChannelInterface;
69 class ServerInterface;
72 class CompletionQueueTag;
74 template <class ServiceType, class RequestType, class ResponseType>
75 class RpcMethodHandler;
76 template <class ServiceType, class RequestType, class ResponseType>
77 class ClientStreamingHandler;
78 template <class ServiceType, class RequestType, class ResponseType>
79 class ServerStreamingHandler;
80 template <class ServiceType, class RequestType, class ResponseType>
81 class BidiStreamingHandler;
82 template <class Streamer, bool WriteNeeded>
83 class TemplatedBidiStreamingHandler;
84 template <StatusCode code>
85 class ErrorMethodHandler;
86 template <class InputMessage, class OutputMessage>
87 class BlockingUnaryCallImpl;
88 template <class Op1, class Op2, class Op3, class Op4, class Op5, class Op6>
90 } // namespace internal
92 extern CoreCodegenInterface* g_core_codegen_interface;
98 /// A thin wrapper around \ref grpc_completion_queue (see \ref
99 /// src/core/lib/surface/completion_queue.h).
100 /// See \ref doc/cpp/perf_notes.md for notes on best practices for high
101 /// performance servers.
102 class CompletionQueue : private ::grpc::GrpcLibraryCodegen {
104 /// Default constructor. Implicitly creates a \a grpc_completion_queue
107 : CompletionQueue(grpc_completion_queue_attributes{
108 GRPC_CQ_CURRENT_VERSION, GRPC_CQ_NEXT, GRPC_CQ_DEFAULT_POLLING,
111 /// Wrap \a take, taking ownership of the instance.
113 /// \param take The completion queue instance to wrap. Ownership is taken.
114 explicit CompletionQueue(grpc_completion_queue* take);
116 /// Destructor. Destroys the owned wrapped completion queue / instance.
118 ::grpc::g_core_codegen_interface->grpc_completion_queue_destroy(cq_);
121 /// Tri-state return for AsyncNext: SHUTDOWN, GOT_EVENT, TIMEOUT.
123 SHUTDOWN, ///< The completion queue has been shutdown and fully-drained
124 GOT_EVENT, ///< Got a new event; \a tag will be filled in with its
125 ///< associated value; \a ok indicating its success.
126 TIMEOUT ///< deadline was reached.
129 /// Read from the queue, blocking until an event is available or the queue is
132 /// \param tag [out] Updated to point to the read event's tag.
133 /// \param ok [out] true if read a successful event, false otherwise.
135 /// Note that each tag sent to the completion queue (through RPC operations
136 /// or alarms) will be delivered out of the completion queue by a call to
137 /// Next (or a related method), regardless of whether the operation succeeded
138 /// or not. Success here means that this operation completed in the normal
141 /// Server-side RPC request: \a ok indicates that the RPC has indeed
142 /// been started. If it is false, the server has been Shutdown
143 /// before this particular call got matched to an incoming RPC.
145 /// Client-side StartCall/RPC invocation: \a ok indicates that the RPC is
146 /// going to go to the wire. If it is false, it not going to the wire. This
147 /// would happen if the channel is either permanently broken or
148 /// transiently broken but with the fail-fast option. (Note that async unary
149 /// RPCs don't post a CQ tag at this point, nor do client-streaming
150 /// or bidi-streaming RPCs that have the initial metadata corked option set.)
152 /// Client-side Write, Client-side WritesDone, Server-side Write,
153 /// Server-side Finish, Server-side SendInitialMetadata (which is
154 /// typically included in Write or Finish when not done explicitly):
155 /// \a ok means that the data/metadata/status/etc is going to go to the
156 /// wire. If it is false, it not going to the wire because the call
157 /// is already dead (i.e., canceled, deadline expired, other side
158 /// dropped the channel, etc).
160 /// Client-side Read, Server-side Read, Client-side
161 /// RecvInitialMetadata (which is typically included in Read if not
162 /// done explicitly): \a ok indicates whether there is a valid message
163 /// that got read. If not, you know that there are certainly no more
164 /// messages that can ever be read from this stream. For the client-side
165 /// operations, this only happens because the call is dead. For the
166 /// server-sider operation, though, this could happen because the client
167 /// has done a WritesDone already.
169 /// Client-side Finish: \a ok should always be true
171 /// Server-side AsyncNotifyWhenDone: \a ok should always be true
173 /// Alarm: \a ok is true if it expired, false if it was canceled
175 /// \return true if got an event, false if the queue is fully drained and
177 bool Next(void** tag, bool* ok) {
178 return (AsyncNextInternal(tag, ok,
179 ::grpc::g_core_codegen_interface->gpr_inf_future(
180 GPR_CLOCK_REALTIME)) != SHUTDOWN);
183 /// Read from the queue, blocking up to \a deadline (or the queue's shutdown).
184 /// Both \a tag and \a ok are updated upon success (if an event is available
185 /// within the \a deadline). A \a tag points to an arbitrary location usually
186 /// employed to uniquely identify an event.
188 /// \param tag [out] Upon success, updated to point to the event's tag.
189 /// \param ok [out] Upon success, true if a successful event, false otherwise
190 /// See documentation for CompletionQueue::Next for explanation of ok
191 /// \param deadline [in] How long to block in wait for an event.
193 /// \return The type of event read.
194 template <typename T>
195 NextStatus AsyncNext(void** tag, bool* ok, const T& deadline) {
196 ::grpc::TimePoint<T> deadline_tp(deadline);
197 return AsyncNextInternal(tag, ok, deadline_tp.raw_time());
201 /// First executes \a F, then reads from the queue, blocking up to
202 /// \a deadline (or the queue's shutdown).
203 /// Both \a tag and \a ok are updated upon success (if an event is available
204 /// within the \a deadline). A \a tag points to an arbitrary location usually
205 /// employed to uniquely identify an event.
207 /// \param f [in] Function to execute before calling AsyncNext on this queue.
208 /// \param tag [out] Upon success, updated to point to the event's tag.
209 /// \param ok [out] Upon success, true if read a regular event, false
211 /// \param deadline [in] How long to block in wait for an event.
213 /// \return The type of event read.
214 template <typename T, typename F>
215 NextStatus DoThenAsyncNext(F&& f, void** tag, bool* ok, const T& deadline) {
216 CompletionQueueTLSCache cache = CompletionQueueTLSCache(this);
218 if (cache.Flush(tag, ok)) {
221 return AsyncNext(tag, ok, deadline);
225 /// Request the shutdown of the queue.
227 /// \warning This method must be called at some point if this completion queue
228 /// is accessed with Next or AsyncNext. \a Next will not return false
229 /// until this method has been called and all pending tags have been drained.
230 /// (Likewise for \a AsyncNext returning \a NextStatus::SHUTDOWN .)
231 /// Only once either one of these methods does that (that is, once the queue
232 /// has been \em drained) can an instance of this class be destroyed.
233 /// Also note that applications must ensure that no work is enqueued on this
234 /// completion queue after this method is called.
237 /// Returns a \em raw pointer to the underlying \a grpc_completion_queue
240 /// \warning Remember that the returned instance is owned. No transfer of
241 /// owership is performed.
242 grpc_completion_queue* cq() { return cq_; }
245 /// Private constructor of CompletionQueue only visible to friend classes
246 CompletionQueue(const grpc_completion_queue_attributes& attributes) {
247 cq_ = ::grpc::g_core_codegen_interface->grpc_completion_queue_create(
248 ::grpc::g_core_codegen_interface->grpc_completion_queue_factory_lookup(
251 InitialAvalanching(); // reserve this for the future shutdown
255 // Friend synchronous wrappers so that they can access Pluck(), which is
256 // a semi-private API geared towards the synchronous implementation.
258 friend class ::grpc::ClientReader;
260 friend class ::grpc::ClientWriter;
261 template <class W, class R>
262 friend class ::grpc::ClientReaderWriter;
264 friend class ::grpc::ServerReader;
266 friend class ::grpc::ServerWriter;
267 template <class W, class R>
268 friend class ::grpc::internal::ServerReaderWriterBody;
269 template <class ServiceType, class RequestType, class ResponseType>
270 friend class ::grpc::internal::RpcMethodHandler;
271 template <class ServiceType, class RequestType, class ResponseType>
272 friend class ::grpc::internal::ClientStreamingHandler;
273 template <class ServiceType, class RequestType, class ResponseType>
274 friend class ::grpc::internal::ServerStreamingHandler;
275 template <class Streamer, bool WriteNeeded>
276 friend class ::grpc::internal::TemplatedBidiStreamingHandler;
277 template <::grpc::StatusCode code>
278 friend class ::grpc::internal::ErrorMethodHandler;
279 friend class ::grpc_impl::Server;
280 friend class ::grpc_impl::ServerContext;
281 friend class ::grpc::ServerInterface;
282 template <class InputMessage, class OutputMessage>
283 friend class ::grpc::internal::BlockingUnaryCallImpl;
285 // Friends that need access to constructor for callback CQ
286 friend class ::grpc_impl::Channel;
288 // For access to Register/CompleteAvalanching
289 template <class Op1, class Op2, class Op3, class Op4, class Op5, class Op6>
290 friend class ::grpc::internal::CallOpSet;
293 /// Creates a Thread Local cache to store the first event
294 /// On this completion queue queued from this thread. Once
295 /// initialized, it must be flushed on the same thread.
296 class CompletionQueueTLSCache {
298 CompletionQueueTLSCache(CompletionQueue* cq);
299 ~CompletionQueueTLSCache();
300 bool Flush(void** tag, bool* ok);
303 CompletionQueue* cq_;
307 NextStatus AsyncNextInternal(void** tag, bool* ok, gpr_timespec deadline);
309 /// Wraps \a grpc_completion_queue_pluck.
310 /// \warning Must not be mixed with calls to \a Next.
311 bool Pluck(::grpc::internal::CompletionQueueTag* tag) {
313 ::grpc::g_core_codegen_interface->gpr_inf_future(GPR_CLOCK_REALTIME);
315 auto ev = ::grpc::g_core_codegen_interface->grpc_completion_queue_pluck(
316 cq_, tag, deadline, nullptr);
317 bool ok = ev.success != 0;
319 if (tag->FinalizeResult(&ignored, &ok)) {
320 GPR_CODEGEN_ASSERT(ignored == tag);
326 /// Performs a single polling pluck on \a tag.
327 /// \warning Must not be mixed with calls to \a Next.
329 /// TODO: sreek - This calls tag->FinalizeResult() even if the cq_ is already
330 /// shutdown. This is most likely a bug and if it is a bug, then change this
331 /// implementation to simple call the other TryPluck function with a zero
333 /// TryPluck(tag, gpr_time_0(GPR_CLOCK_REALTIME))
334 void TryPluck(::grpc::internal::CompletionQueueTag* tag) {
336 ::grpc::g_core_codegen_interface->gpr_time_0(GPR_CLOCK_REALTIME);
337 auto ev = ::grpc::g_core_codegen_interface->grpc_completion_queue_pluck(
338 cq_, tag, deadline, nullptr);
339 if (ev.type == GRPC_QUEUE_TIMEOUT) return;
340 bool ok = ev.success != 0;
342 // the tag must be swallowed if using TryPluck
343 GPR_CODEGEN_ASSERT(!tag->FinalizeResult(&ignored, &ok));
346 /// Performs a single polling pluck on \a tag. Calls tag->FinalizeResult if
347 /// the pluck() was successful and returned the tag.
349 /// This exects tag->FinalizeResult (if called) to return 'false' i.e expects
350 /// that the tag is internal not something that is returned to the user.
351 void TryPluck(::grpc::internal::CompletionQueueTag* tag,
352 gpr_timespec deadline) {
353 auto ev = ::grpc::g_core_codegen_interface->grpc_completion_queue_pluck(
354 cq_, tag, deadline, nullptr);
355 if (ev.type == GRPC_QUEUE_TIMEOUT || ev.type == GRPC_QUEUE_SHUTDOWN) {
359 bool ok = ev.success != 0;
361 GPR_CODEGEN_ASSERT(!tag->FinalizeResult(&ignored, &ok));
364 /// Manage state of avalanching operations : completion queue tags that
365 /// trigger other completion queue operations. The underlying core completion
366 /// queue should not really shutdown until all avalanching operations have
367 /// been finalized. Note that we maintain the requirement that an avalanche
368 /// registration must take place before CQ shutdown (which must be maintained
370 void InitialAvalanching() {
371 gpr_atm_rel_store(&avalanches_in_flight_, static_cast<gpr_atm>(1));
373 void RegisterAvalanching() {
374 gpr_atm_no_barrier_fetch_add(&avalanches_in_flight_,
375 static_cast<gpr_atm>(1));
377 void CompleteAvalanching() {
378 if (gpr_atm_no_barrier_fetch_add(&avalanches_in_flight_,
379 static_cast<gpr_atm>(-1)) == 1) {
380 ::grpc::g_core_codegen_interface->grpc_completion_queue_shutdown(cq_);
384 grpc_completion_queue* cq_; // owned
386 gpr_atm avalanches_in_flight_;
389 /// A specific type of completion queue used by the processing of notifications
390 /// by servers. Instantiated by \a ServerBuilder.
391 class ServerCompletionQueue : public CompletionQueue {
393 bool IsFrequentlyPolled() { return polling_type_ != GRPC_CQ_NON_LISTENING; }
396 /// Default constructor
397 ServerCompletionQueue() : polling_type_(GRPC_CQ_DEFAULT_POLLING) {}
400 /// \param completion_type indicates whether this is a NEXT or CALLBACK
401 /// completion queue.
402 /// \param polling_type Informs the GRPC library about the type of polling
403 /// allowed on this completion queue. See grpc_cq_polling_type's description
404 /// in grpc_types.h for more details.
405 /// \param shutdown_cb is the shutdown callback used for CALLBACK api queues
406 ServerCompletionQueue(grpc_cq_completion_type completion_type,
407 grpc_cq_polling_type polling_type,
408 grpc_experimental_completion_queue_functor* shutdown_cb)
409 : CompletionQueue(grpc_completion_queue_attributes{
410 GRPC_CQ_CURRENT_VERSION, completion_type, polling_type,
412 polling_type_(polling_type) {}
414 grpc_cq_polling_type polling_type_;
415 friend class ::grpc_impl::ServerBuilder;
416 friend class ::grpc_impl::Server;
419 } // namespace grpc_impl
421 #endif // GRPCPP_IMPL_CODEGEN_COMPLETION_QUEUE_IMPL_H