Fix race condition in script reload causing null pointer crash #1031
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When pressing 'apply' to reload a script, the code had a critical thread-safety issue: multiple threads were executing Lua operations on the same lua_State concurrently without proper synchronization. The race condition occurred because: 1. UI thread would load/compile new script WITHOUT holding the lock 2. Audio thread could be running script->process() at the same time 3. Both threads manipulate the same Lua stack -> corruption 4. This caused DSPScriptPosition userdata to become invalid 5. Accessing position methods (bar(), beat(), etc.) would crash with null pointer dereference The fix moves the ScopedLock acquisition to the very beginning of loadScript(), ensuring ALL Lua operations are serialized: - Script loading and compilation - DSPScript construction - Script preparation - Pointer swap - Old script cleanup (release, cleanup, destructor) This prevents any concurrent Lua state access. The tradeoff is a brief audio dropout during script reload, which is acceptable for this operation. Fixes crash: Access violation reading location 0x0000000000000000 in DSPScriptPosition::_bar() and DSPScriptPosition::_beat() 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
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Member
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This looks reasonable thanks! But I can't merge until the CLA is signed: #1031 (comment) |
Contributor
Author
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Signed (FYI the host this occured in was Maschine) |
Member
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Awesome. thanks! |
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When pressing 'apply' to reload a script, the code had a thread-safety issue: multiple threads were executing Lua operations on the same lua_State concurrently without proper synchronization.
The race condition occurred because:
The fix moves the ScopedLock acquisition to the very beginning of loadScript(), ensuring ALL Lua operations are serialized:
This prevents any concurrent Lua state access. The tradeoff is a brief audio dropout during script reload, which is acceptable for this operation.
Fixes crash: Access violation reading location 0x0000000000000000 in DSPScriptPosition::_bar() and DSPScriptPosition::_beat()
🤖 Generated with Claude Code