lb_policy.h | Explore in Territory

//
// Copyright 2015 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

#ifndef GRPC_SRC_CORE_LIB_LOAD_BALANCING_LB_POLICY_H
#define GRPC_SRC_CORE_LIB_LOAD_BALANCING_LB_POLICY_H

#include <grpc/support/port_platform.h>

#include <stddef.h>
#include <stdint.h>

#include <memory>
#include <string>
#include <utility>
#include <vector>

#include "absl/base/thread_annotations.h"
#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/strings/string_view.h"
#include "absl/types/optional.h"
#include "absl/types/variant.h"

#include <grpc/event_engine/event_engine.h>
#include <grpc/impl/connectivity_state.h>

#include "src/core/ext/filters/client_channel/lb_policy/backend_metric_data.h"
#include "src/core/lib/channel/channel_args.h"
#include "src/core/lib/debug/trace.h"
#include "src/core/lib/gprpp/debug_location.h"
#include "src/core/lib/gprpp/dual_ref_counted.h"
#include "src/core/lib/gprpp/orphanable.h"
#include "src/core/lib/gprpp/ref_counted.h"
#include "src/core/lib/gprpp/ref_counted_ptr.h"
#include "src/core/lib/gprpp/sync.h"
#include "src/core/lib/gprpp/work_serializer.h"
#include "src/core/lib/iomgr/iomgr_fwd.h"
#include "src/core/lib/load_balancing/subchannel_interface.h"
#include "src/core/lib/resolver/server_address.h"

namespace grpc_core {

extern DebugOnlyTraceFlag grpc_trace_lb_policy_refcount;

/// Interface for load balancing policies.
///
/// The following concepts are used here:
///
/// Channel: An abstraction that manages connections to backend servers
///   on behalf of a client application.  The application creates a channel
///   for a given server name and then sends calls (RPCs) on it, and the
///   channel figures out which backend server to send each call to.  A channel
///   contains a resolver, a load balancing policy (or a tree of LB policies),
///   and a set of one or more subchannels.
///
/// Subchannel: A subchannel represents a connection to one backend server.
///   The LB policy decides which subchannels to create, manages the
///   connectivity state of those subchannels, and decides which subchannel
///   to send any given call to.
///
/// Resolver: A plugin that takes a gRPC server URI and resolves it to a
///   list of one or more addresses and a service config, as described
///   in https://github.com/grpc/grpc/blob/master/doc/naming.md.  See
///   resolver.h for the resolver API.
///
/// Load Balancing (LB) Policy: A plugin that takes a list of addresses
///   from the resolver, maintains and manages a subchannel for each
///   backend address, and decides which subchannel to send each call on.
///   An LB policy has two parts:
///   - A LoadBalancingPolicy, which deals with the control plane work of
///     managing subchannels.
///   - A SubchannelPicker, which handles the data plane work of
///     determining which subchannel a given call should be sent on.

/// LoadBalacingPolicy API.
///
/// Note: All methods with a "Locked" suffix must be called from the
/// work_serializer passed to the constructor.
///
/// Any I/O done by the LB policy should be done under the pollset_set
/// returned by \a interested_parties().
// TODO(roth): Once we move to EventManager-based polling, remove the
// interested_parties() hooks from the API.
class LoadBalancingPolicy : public InternallyRefCounted<LoadBalancingPolicy> { … };

}  // namespace grpc_core

#endif  // GRPC_SRC_CORE_LIB_LOAD_BALANCING_LB_POLICY_H
chromium/third_party/grpc/src/src/core/lib/load_balancing/lb_policy.h
