Auto-set pad_token_id when the default is None and not set in the buffer config.

[yaochaorui]

Description

Background:
When using models like Llama where the default pad_token_id is None, the sampler_strategy could be incorrect if pad_token_id wasn't explicitly set in the config. Both Verl and vLLM automatically handle this during tokenizer loading by setting appropriate pad_token_id values.

Purpose:
Update the config after tokenizer loading to ensure the pad_token_id is properly set, making the sampler_strategy consistent and correct.

Changes made:

• Added config update logic after tokenizer loading to set pad_token_id when it's None in the original config
• Ensures sampler_strategy uses the correct pad_token_id that Verl/vLLM have automatically determined during tokenizer initialization
• Maintains alignment between our config and the actual tokenizer configuration

How to test:

1. Load a Llama tokenizer without specifying pad_token_id in the initial config
2. Verify that after tokenizer loading, the config is updated with the correct pad_token_id
3. Confirm that sampler_strategy works correctly with the updated config
4. Test with tokenizers that already have explicit pad_token_id to ensure no regression

Checklist

Please check the following items before code is ready to be reviewed.

• [x ] Code has passed all tests
• [x ] Docstrings have been added/updated in Google Style
• [x ] Code is ready for review

[gemini-code-assist]

Summary of Changes

Hello @yaochaorui, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses an issue where the sampler_strategy could be incorrect when using models like Llama, which default pad_token_id to None. It introduces logic to automatically set the pad_token_id in the configuration after tokenizer loading if it's not explicitly defined, ensuring consistency with the pad_token_id determined by the tokenizer itself (e.g., by Verl/vLLM). This change aims to maintain alignment between the internal configuration and the actual tokenizer setup, preventing potential issues with sampling.

Highlights

• Configuration Update: The system now automatically updates the pad_token_id in the global configuration if it's None when the tokenizer is loaded.
• Sampler Strategy Consistency: Ensures that the sampler_strategy correctly utilizes the pad_token_id that the tokenizer (e.g., from Verl/vLLM) has automatically determined.
• Config Alignment: Improves the alignment between the internal configuration and the actual tokenizer's settings.
• Logging: A warning message is now logged when the pad_token_id is automatically set.

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[gemini-code-assist]

Code Review

This pull request correctly addresses an issue where pad_token_id might not be set for certain models, causing inconsistencies. The proposed solution is to automatically set it from the tokenizer after it's loaded, which is a sensible approach.

My feedback focuses on making the implementation more robust and readable by adding a check to ensure the tokenizer's pad_token_id is not None before assignment and by improving the clarity of the corresponding warning message.

[yanxi-chen]

lgtm