Fix race between GC and case object construction#211
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jrincayc merged 3 commits intojrincayc:masterfrom Mar 31, 2025
Merged
Fix race between GC and case object construction#211jrincayc merged 3 commits intojrincayc:masterfrom
jrincayc merged 3 commits intojrincayc:masterfrom
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Does a partial GC before constructing new case objects to ensure there are enough free nodes to finish construction and add it to a root node before the GC runs again. Case objects must be marked twice so if the GC runs after a new case is allocated but before it is added to the hash table AND a root AND the pointer isn't found on the stack, eg because it was optimized out, then the GC may free the cases. I was concerned this would have a negative performance impact... It actually improved unit test performance by 10-20%. ¯\_(ツ)_/¯
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Adds too much performance overhead. Need more performant fix. |
Contributor
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Ok I fixed the performance regression. There's really only one place this hazard occurs, in one call to cons(). So we just pre-allocate that cons, and then mutate it, avoiding calls to newnode() until the case obj is linked back to it's containing object. |
jrincayc
reviewed
Mar 29, 2025
globals.h
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| void do_gc(BOOLEAN full); |
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Does a partial GC before constructing new case objects to ensure there are enough free nodes to finish construction and add it to a root node before the GC runs again.
Case objects must be marked twice so if the GC runs after a new case is allocated but before it is added to the hash table AND a root AND the pointer isn't found on the stack, eg because it was optimized out, then the GC may free the cases.
I was concerned this would have a negative performance impact...
It actually improved unit test performance by 10-20%.And it does. It's way slow. I'm not sure how I produced the "improvement".
So we probably want to find a more performant fix.