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slozier
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Oct 24, 2026
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Looks good to me! Thanks!
| SetTarget(target); | ||
| Thread.MemoryBarrier(); | ||
| while (context.EnableTracing != tracing) { | ||
| tracing = context.EnableTracing; |
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Lots of reading context.EnableTracing (and another one at the top of UpdateDelegate). Any chance of things getting out of sync (seems unlikely but doesn't hurt to ask).
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The bug: switching tracing on or off (
sys.settrace) updates the target of every code object, but other writers of the target are not synchronized with that switch: the adaptive compiler's completion callbacks, the background precompile of class bodies, compilation on first use inMakeClassandFunctionCode.Call, and -X:Debugfunction definitions.A delegate built for the previous mode could thus become the target after the switch and stay until the next one, e.g. a class body that runs untraced while tracing is on.
These writers now set the target through
FunctionCode.PublishTarget, which skips a delegate built for a mode that is no longer current (it stays in its cache for when the mode switches back) and checks the mode again after setting the target, repeating the switch's update if the mode changed meanwhile.SetTracechanges the mode with an interlocked operation, so the new mode is visible before any code is updated for it.Under
-X:Debugthis also fixes functions defined while tracing is on, which always got their normal delegate and were not traced.