mirror of
https://github.com/anthropics/claude-code-sdk-python.git
synced 2025-12-23 09:19:52 +00:00
2d67166cae
## TL;DR
Adds a write lock to `SubprocessCLITransport` to prevent concurrent
writes from parallel subagents.
---
## Overview
When multiple subagents run in parallel and invoke MCP tools, the CLI
sends concurrent `control_request` messages. Each handler tries to write
a response back to the subprocess stdin at the same time. Trio's
`TextSendStream` isn't thread-safe for concurrent access, so this causes
`BusyResourceError`.
This PR adds an `anyio.Lock` around all write operations (`write()`,
`end_input()`, and the stdin-closing part of `close()`). The lock
serializes concurrent writes so they happen one at a time. The `_ready`
flag is now set inside the lock during `close()` to prevent a TOCTOU
race where `write()` checks `_ready`, then `close()` sets it and closes
the stream before `write()` actually sends data.
---
## Call Flow
```mermaid
flowchart TD
A["write()<br/>subprocess_cli.py:505"] --> B["acquire _write_lock<br/>subprocess_cli.py:507"]
B --> C["check _ready & stream<br/>subprocess_cli.py:509"]
C --> D["_stdin_stream.send()<br/>subprocess_cli.py:523"]
E["close()<br/>subprocess_cli.py:458"] --> F["acquire _write_lock<br/>subprocess_cli.py:478"]
F --> G["set _ready = False<br/>subprocess_cli.py:479"]
G --> H["close _stdin_stream<br/>subprocess_cli.py:481"]
I["end_input()<br/>subprocess_cli.py:531"] --> J["acquire _write_lock<br/>subprocess_cli.py:533"]
J --> K["close _stdin_stream<br/>subprocess_cli.py:535"]
```
|
||
|---|---|---|
| .. | ||
| conftest.py | ||
| test_changelog.py | ||
| test_client.py | ||
| test_errors.py | ||
| test_integration.py | ||
| test_message_parser.py | ||
| test_sdk_mcp_integration.py | ||
| test_streaming_client.py | ||
| test_subprocess_buffering.py | ||
| test_tool_callbacks.py | ||
| test_transport.py | ||
| test_types.py | ||