legacy-libs/grpc-cloned/deps/grpc/src/core/ext/filters/client_channel/resolving_lb_policy.h

   1 /*
   2  *
   3  * Copyright 2018 gRPC authors.
   4  *
   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
   8  *
   9  *     http://www.apache.org/licenses/LICENSE-2.0
  10  *
  11  * Unless required by applicable law or agreed to in writing, software
  12  * distributed under the License is distributed on an "AS IS" BASIS,
  13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14  * See the License for the specific language governing permissions and
  15  * limitations under the License.
  16  *
  17  */
  18
  19 #ifndef GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_RESOLVING_LB_POLICY_H
  20 #define GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_RESOLVING_LB_POLICY_H
  21
  22 #include <grpc/support/port_platform.h>
  23
  24 #include "src/core/ext/filters/client_channel/lb_policy.h"
  25 #include "src/core/ext/filters/client_channel/lb_policy_factory.h"
  26 #include "src/core/ext/filters/client_channel/resolver.h"
  27 #include "src/core/lib/channel/channel_args.h"
  28 #include "src/core/lib/channel/channel_stack.h"
  29 #include "src/core/lib/debug/trace.h"
  30 #include "src/core/lib/gprpp/inlined_vector.h"
  31 #include "src/core/lib/gprpp/orphanable.h"
  32 #include "src/core/lib/iomgr/call_combiner.h"
  33 #include "src/core/lib/iomgr/closure.h"
  34 #include "src/core/lib/iomgr/polling_entity.h"
  35 #include "src/core/lib/iomgr/pollset_set.h"
  36 #include "src/core/lib/transport/connectivity_state.h"
  37 #include "src/core/lib/transport/metadata_batch.h"
  38
  39 namespace grpc_core {
  40
  41 // An LB policy that wraps a resolver and a child LB policy to make use
  42 // of the addresses returned by the resolver.
  43 //
  44 // When used in the client_channel code, the resolver will attempt to
  45 // fetch the service config, and the child LB policy name and config
  46 // will be determined based on the service config.
  47 //
  48 // When used in an LB policy implementation that needs to do another
  49 // round of resolution before creating a child policy, the resolver does
  50 // not fetch the service config, and the caller must pre-determine the
  51 // child LB policy and config to use.
  52 class ResolvingLoadBalancingPolicy : public LoadBalancingPolicy {
  53  public:
  54   // Synchronous callback that takes the resolver result and sets
  55   // lb_policy_name and lb_policy_config to point to the right data.
  56   // Returns true if the service config has changed since the last result.
  57   // If the returned service_config_error is not none and lb_policy_name is
  58   // empty, it means that we don't have a valid service config to use, and we
  59   // should set the channel to be in TRANSIENT_FAILURE.
  60   typedef bool (*ProcessResolverResultCallback)(
  61       void* user_data, const Resolver::Result& result,
  62       const char** lb_policy_name,
  63       RefCountedPtr<LoadBalancingPolicy::Config>* lb_policy_config,
  64       grpc_error** service_config_error);
  65   // If error is set when this returns, then construction failed, and
  66   // the caller may not use the new object.
  67   ResolvingLoadBalancingPolicy(
  68       Args args, TraceFlag* tracer, UniquePtr<char> target_uri,
  69       ProcessResolverResultCallback process_resolver_result,
  70       void* process_resolver_result_user_data);
  71
  72   virtual const char* name() const override { return "resolving_lb"; }
  73
  74   // No-op -- should never get updates from the channel.
  75   // TODO(roth): Need to support updating child LB policy's config for xds
  76   // use case.
  77   void UpdateLocked(UpdateArgs args) override {}
  78
  79   void ExitIdleLocked() override;
  80
  81   void ResetBackoffLocked() override;
  82
  83  private:
  84   using TraceStringVector = InlinedVector<char*, 3>;
  85
  86   class ResolverResultHandler;
  87   class ResolvingControlHelper;
  88
  89   ~ResolvingLoadBalancingPolicy();
  90
  91   void ShutdownLocked() override;
  92
  93   void OnResolverError(grpc_error* error);
  94   void CreateOrUpdateLbPolicyLocked(
  95       const char* lb_policy_name,
  96       RefCountedPtr<LoadBalancingPolicy::Config> lb_policy_config,
  97       Resolver::Result result, TraceStringVector* trace_strings);
  98   OrphanablePtr<LoadBalancingPolicy> CreateLbPolicyLocked(
  99       const char* lb_policy_name, const grpc_channel_args& args,
 100       TraceStringVector* trace_strings);
 101   void MaybeAddTraceMessagesForAddressChangesLocked(
 102       bool resolution_contains_addresses, TraceStringVector* trace_strings);
 103   void ConcatenateAndAddChannelTraceLocked(
 104       TraceStringVector* trace_strings) const;
 105   void OnResolverResultChangedLocked(Resolver::Result result);
 106
 107   // Passed in from caller at construction time.
 108   TraceFlag* tracer_;
 109   UniquePtr<char> target_uri_;
 110   ProcessResolverResultCallback process_resolver_result_ = nullptr;
 111   void* process_resolver_result_user_data_ = nullptr;
 112   UniquePtr<char> child_policy_name_;
 113   RefCountedPtr<LoadBalancingPolicy::Config> child_lb_config_;
 114
 115   // Resolver and associated state.
 116   OrphanablePtr<Resolver> resolver_;
 117   bool previous_resolution_contained_addresses_ = false;
 118
 119   // Child LB policy.
 120   OrphanablePtr<LoadBalancingPolicy> lb_policy_;
 121   OrphanablePtr<LoadBalancingPolicy> pending_lb_policy_;
 122 };
 123
 124 }  // namespace grpc_core
 125
 126 #endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_RESOLVING_LB_POLICY_H */