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LibJS+js+test-js: Add GC debug mode that keeps cells "alive" as zombies

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This patch adds a `-z` option to js and test-js. When run in this mode,
garbage cells are never actually destroyed. We instead keep them around
in a special zombie state.

This allows us to validate that zombies don't get marked in future GC
scans (since there were not supposed to be any more references!) :^)

Cells get notified when they become a zombie (via did_become_zombie())
and this is used by WeakContainer cells to deregister themselves from
the heap.
This commit is contained in:
Andreas Kling 2021-09-11 16:44:40 +02:00
parent 57371f7608
commit c364520c24
10 changed files with 33 additions and 1 deletions
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14
Userland/Libraries/LibJS/Heap/Heap.cpp
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@ -183,6 +183,13 @@ public:
if (cell.is_marked())
return;
dbgln_if(HEAP_DEBUG, " ! {}", &cell);
if (cell.state() == Cell::State::Zombie) {
dbgln("BUG! Marking a zombie cell, {} @ {:p}", cell.class_name(), &cell);
cell.vm().dump_backtrace();
VERIFY_NOT_REACHED();
}
cell.set_marked(true);
cell.visit_edges(*this);
}
@ -223,7 +230,12 @@ void Heap::sweep_dead_cells(bool print_report, const Core::ElapsedTimer& measure
dbgln_if(HEAP_DEBUG, " ~ {}", cell);
if (should_store_swept_cells)
swept_cells.append(cell);
block.deallocate(cell);
if (m_zombify_dead_cells) {
cell->set_state(Cell::State::Zombie);
cell->did_become_zombie();
} else {
block.deallocate(cell);
}
++collected_cells;
collected_cell_bytes += block.cell_size();
} else {