1 // Copyright 2022 gRPC authors.
2 //
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
6 //
7 //     http://www.apache.org/licenses/LICENSE-2.0
8 //
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 
15 #ifndef GRPC_SRC_CORE_LIB_CHANNEL_CALL_FINALIZATION_H
16 #define GRPC_SRC_CORE_LIB_CHANNEL_CALL_FINALIZATION_H
17 
18 #include <grpc/support/port_platform.h>
19 
20 #include <utility>
21 
22 #include "src/core/lib/channel/channel_stack.h"
23 #include "src/core/lib/promise/context.h"
24 #include "src/core/lib/resource_quota/arena.h"
25 
26 namespace grpc_core {
27 
28 // Call finalization context.
29 // Sometimes a filter needs to perform some operation after the last byte of
30 // data is flushed to the wire. This context is used to perform that
31 // finalization.
32 // Filters can register a finalizer by calling Add().
33 // The finalizer will be called before the call is destroyed but after
34 // the top level promise is completed.
35 class CallFinalization {
36  public:
37   // Add a step to the finalization context.
38   // Takes a callable with a signature compatible with:
39   // (const grpc_call_final_info*) -> void.
40   // Finalizers are run in the reverse order they are added.
41   template <typename F>
Add(F && t)42   void Add(F&& t) {
43     first_ =
44         GetContext<Arena>()->New<FuncFinalizer<F>>(std::forward<F>(t), first_);
45   }
46 
Run(const grpc_call_final_info * final_info)47   void Run(const grpc_call_final_info* final_info) {
48     if (Finalizer* f = std::exchange(first_, nullptr)) f->Run(final_info);
49   }
50 
51  private:
52   // Base class for finalizer implementations.
53   class Finalizer {
54    public:
55     // Run the finalizer and call the destructor of this Finalizer.
56     virtual void Run(const grpc_call_final_info* final_info) = 0;
57 
58    protected:
~Finalizer()59     ~Finalizer() {}
60   };
61   // Specialization for callable objects.
62   template <typename F>
63   class FuncFinalizer final : public Finalizer {
64    public:
FuncFinalizer(F && f,Finalizer * next)65     FuncFinalizer(F&& f, Finalizer* next)
66         : next_(next), f_(std::forward<F>(f)) {}
67 
Run(const grpc_call_final_info * final_info)68     void Run(const grpc_call_final_info* final_info) override {
69       f_(final_info);
70       Finalizer* next = next_;
71       this->~FuncFinalizer();
72       if (next != nullptr) next->Run(final_info);
73     }
74 
75    private:
76     Finalizer* next_;
77     F f_;
78   };
79   // The first finalizer in the chain.
80   Finalizer* first_ = nullptr;
81 };
82 
83 template <>
84 struct ContextType<CallFinalization> {};
85 
86 }  // namespace grpc_core
87 
88 #endif  // GRPC_SRC_CORE_LIB_CHANNEL_CALL_FINALIZATION_H
89