New gRPC channel manager

[rcameronm]

This pull request refactors the gRPC connection management system by replacing the old connection pooling approach with a new ChannelManager abstraction. The main goal is to provide a more flexible and configurable way to manage gRPC channels, making it easier to customize channel behavior and support different channel management strategies. The most significant changes are outlined below.

Core Refactor: Channel Management Abstraction

• Introduced a new abstract base class ChannelManager in emissary.grpc.channel, which centralizes configuration and management of gRPC ManagedChannel connections. This class supports various channel options (keep-alive, load balancing, message sizes) and provides a factory method for instantiating subclasses via reflection. (src/main/java/emissary/grpc/channel/ChannelManager.java)

• Updated GrpcRoutingPlace to use ChannelManager instead of the previous ConnectionFactory and pooling approach. Each target now has a dedicated GrpcInvoker backed by a ChannelManager, improving configurability and resource management. (src/main/java/emissary/grpc/GrpcRoutingPlace.java) [1] [2] [3] [4] [5]

Configuration and API Updates

• Added support for specifying the channel manager class via the GRPC_CHANNEL_MANAGER_CLASS_NAME configuration key, defaulting to PooledChannelManager. This allows for easy swapping or customization of channel management strategies. (src/main/java/emissary/grpc/GrpcRoutingPlace.java) [1] [2]

• Updated JavaDoc and documentation references in both GrpcConnectionPlace and GrpcRoutingPlace to point to ChannelManager for channel configuration, replacing references to the deprecated ConnectionFactory. (src/main/java/emissary/grpc/GrpcConnectionPlace.java, src/main/java/emissary/grpc/GrpcRoutingPlace.java) [1] [2]

Simplification and Cleanup

• Removed all usage of Apache Commons Pool and the associated ConnectionFactory and PoolException classes from GrpcRoutingPlace, simplifying the code and reducing dependencies. (src/main/java/emissary/grpc/GrpcRoutingPlace.java) [1] [2] [3] [4]

• Refactored internal lookup and invocation logic in GrpcRoutingPlace to use the new invokerTable and getInvoker() method, streamlining how gRPC calls are routed and executed. (src/main/java/emissary/grpc/GrpcRoutingPlace.java) [1] [2] [3]

These changes collectively modernize the gRPC connection infrastructure, making it more modular, configurable, and easier to extend or maintain.

[fbruton]

Attached is a patch to replace reflection with a factory design pattern. Any class subclass without the proper method signature will throw a compile error.
0001-replace-reflection-with-a-factory.patch

[rcameronm]

I've been using this reflection pattern for awhile. Should I make some new tickets to change them to this factory design pattern as well?

[fbruton]

I recommend it. It will improve maintainability.