feat(retool): add local thread pool execution mode for tool calls

[xiaohong42]

verl-project/verl#5646 (comment)

[gemini-code-assist]

Summary of Changes

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This pull request enhances the tool execution capabilities by introducing a local thread pool execution mode as an alternative to the existing Ray-based system. This change provides greater flexibility in how tools are run, allowing for execution without a full Ray setup. The core logic now dynamically switches between execution backends based on a new configuration parameter, and tool results are standardized using a dedicated ToolResponse type.

Highlights

• New Local Thread Pool Execution Mode: Introduced a new execution mode for tool calls that utilizes a local thread pool via asyncio.run_in_executor, providing an alternative to the existing Ray-based execution.
• Configurable Execution Backend: The execute method in retool.py was modified to conditionally use either the Ray execution pool or the new local thread pool, controlled by a new configuration flag.
• Standardized Tool Response Type: The return type of the execute method was updated to ToolResponse, ensuring consistent handling and typing of tool results.
• New Configuration Option: A use_ray_execution_pool boolean option was added to sandbox_fusion_tool_config.yaml to allow users to specify their preferred execution environment.

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[gemini-code-assist]

Code Review

This pull request introduces a new local thread pool execution mode for tool calls, which is a valuable addition for environments where Ray might not be suitable. The implementation correctly uses run_in_executor for running blocking code in an async context. However, a significant issue has been identified: the use of a blocking semaphore within an async function. This will block the event loop, potentially causing severe performance degradation. I have provided a comment with a suggested fix to use a non-blocking asyncio.Semaphore.