Fix GC compaction crashes - #806
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This commit fixes crashes that can occur after garbage collection compaction, and adds a test for it (the test fails before the fix, and succeeds afterwards). Without this commit, GC compaction can lead to crashes. Ruby 2.7+ supports GC compaction (GC.compact), which can move objects in memory to reduce fragmentation. The rb_redcarpet_rndr struct stores Ruby VALUE references (link_attributes, self, base_class) as raw C pointers. When compaction moves these objects, the pointers become stale, causing segfaults or "T_IMEMO" errors on next use. This commit fixes this problem in the standard Ruby way. It registers a dcompact callback via Ruby's TypedData API. When GC compaction runs, Ruby calls this callback, allowing us to update each VALUE pointer using rb_gc_location() to its new address. The callback is conditionally compiled only when rb_gc_location is available (Ruby 2.7+), maintaining backward compatibility. Co-authored-by: David A. Wheeler <dwheeler@dwheeler.com> Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: David A. Wheeler <dwheeler@dwheeler.com>
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This commit fixes crashes that can occur after garbage collection compaction, and adds a test for it (the test fails before the fix, and succeeds afterwards). Without this commit, GC compaction can lead to crashes.
Ruby 2.7+ supports GC compaction (GC.compact), which can move objects in memory to reduce fragmentation. The rb_redcarpet_rndr struct stores Ruby VALUE references (link_attributes, self, base_class) as raw C pointers. When compaction moves these objects, the pointers become stale, causing segfaults or "T_IMEMO" errors on next use.
This commit fixes this problem in the standard Ruby way. It registers a dcompact callback via Ruby's TypedData API. When GC compaction runs, Ruby calls this callback, allowing us to update each VALUE pointer using rb_gc_location() to its new address. The callback is conditionally compiled only when rb_gc_location is available (Ruby 2.7+), maintaining backward compatibility.