macOS build: protoc-gen-grpc killed by signal 9 during oblib_grpc code generation

Summary

On macOS (arm64), parallel make fails while generating gRPC C++ stubs under deps/oblib/src/grpc/. protoc invokes protoc-gen-grpc (grpc_cpp_plugin), which is terminated with signal 9 (SIGKILL).

Error output

--grpc_out: protoc-gen-grpc: Plugin killed by signal 9.
make[2]: *** [.../deps/oblib/src/grpc/example.grpc.pb.cc] Error 1
make[2]: *** Waiting for unfinished jobs....
--grpc_out: protoc-gen-grpc: Plugin killed by signal 9.
make[2]: *** [.../deps/oblib/src/grpc/logservice.grpc.pb.cc] Error 1
make[1]: *** [deps/oblib/src/grpc/CMakeFiles/oblib_grpc.dir/all] Error 2
make: *** [all] Error 2

Build was around 10–15% when this happened (oblib_lib_extra had already built).

Environment

Codegen is configured in deps/oblib/src/grpc/CMakeLists.txt (non-Windows: protoc --grpc_out=... --plugin=protoc-gen-grpc=${_GRPC_CPP_PLUGIN}).

Possible causes (for investigation)

1. OOM under parallel make -jN — multiple concurrent protoc / grpc_cpp_plugin processes; SIGKILL is typical for memory pressure on macOS.
2. macOS security — plugin process killed when run as protoc subprocess (verify with manual protoc invocation).
3. Toolchain mismatch — bundled grpc_cpp_plugin vs protoc version (usually a different error, still worth checking).
4. Missing serialization of gRPC codegen — parallel add_custom_command outputs for several .proto files.

Suggested next steps

• Reproduce with make -j1 targeting oblib_grpc only.
• Run the exact failing protoc line from the build log manually; watch memory in Activity Monitor.
• On Apple platforms, consider serializing proto/gRPC generation (JOB_POOLS / single job pool) or documenting safe -j limits.
• If OOM: reduce default parallelism for codegen on macOS or pre-generate checked-in stubs for dev builds (policy TBD).

Context

Reported from a local fork build on Apple Silicon; tracking here before a fix PR.

Start with deps/oblib/src/grpc/CMakeLists.txt and the oblib_grpc target. Reproduce with make -j1, then run the exact failing protoc command while monitoring memory and checking the bundled grpc_cpp_plugin; done means identifying the cause and making or documenting a reliable macOS parallel-build fix.