macOS: benchmark run can hang indefinitely with default multiprocessing/data loader settings #1

Description

On macOS, benchmark_runner may hang indefinitely during benchmark run when using default runtime settings.
The process reaches the benchmark phase but does not make progress for several minutes (or longer), and no explicit error is raised.

Environment

• OS: macOS (Apple Silicon)
• Python: 3.11
• benchmark-runner: v0.0.2
  Backend: OpenAI-compatible HTTP endpoint
  Data: synthetic (prompt_tokens=...,output_tokens=...)

Reproduction

python -m benchmark_runner.main benchmark run \
  --target http://<server>:<port> \
  --sample-requests 0 \
  --output-dir .cache \
  --outputs full.json \
  --processor <local_tokenizer_path> \
  --data prompt_tokens=8192,output_tokens=100 \
  --profile constant \
  --rate 1 \
  --max-requests 10

Expected behavior

Benchmark starts and either: progresses normally, or fails fast with a clear error.

Actual behavior

The command appears stuck/hung (often at the benchmark stage) without completion or explicit failure.