RGBCube/serenity
1
Fork 0
mirror of https://github.com/RGBCube/serenity synced 2025-05-28 08:45:09 +00:00
Code Issues Activity Actions

LibJS: Implement basic conservative garbage collection

Browse source 
We now scan the stack and CPU registers for potential pointers into the
GC heap, and include any valid Cell pointers in the set of roots.

This works pretty well but we'll also need to solve marking of things
passed to native functions, since those are currently in Vector<Value>
and the Vector storage is on the heap (not scanned.)
This commit is contained in:
Andreas Kling 2020-03-16 19:08:59 +01:00
parent ad92a1e4bc
commit ab404a2f88
3 changed files with 81 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

72
Libraries/LibJS/Heap/Heap.cpp
View file

@ -30,6 +30,9 @@
#include <LibJS/Heap/HeapBlock.h>
#include <LibJS/Interpreter.h>
#include <LibJS/Runtime/Object.h>
#include <serenity.h>
#include <setjmp.h>
#include <stdio.h>
#define HEAP_DEBUG
@ -71,14 +74,76 @@ void Heap::gather_roots(HashTable<Cell*>& roots)
{
m_interpreter.gather_roots({}, roots);
gather_conservative_roots(roots);
#ifdef HEAP_DEBUG
dbg() << "collect_roots:";
dbg() << "gather_roots:";
for (auto* root : roots) {
dbg() << " + " << root;
}
#endif
}
void Heap::gather_conservative_roots(HashTable<Cell*>& roots)
{
FlatPtr dummy;
#ifdef HEAP_DEBUG
dbg() << "gather_conservative_roots:";
#endif
jmp_buf buf;
setjmp(buf);
HashTable<FlatPtr> possible_pointers;
for (size_t i = 0; i < (sizeof(buf->regs) / sizeof(FlatPtr)); ++i)
possible_pointers.set(buf->regs[i]);
FlatPtr stack_base;
size_t stack_size;
if (get_stack_bounds(&stack_base, &stack_size) < 0) {
perror("get_stack_bounds");
ASSERT_NOT_REACHED();
}
FlatPtr stack_reference = reinterpret_cast<FlatPtr>(&dummy);
FlatPtr stack_top = stack_base + stack_size;
for (FlatPtr stack_address = stack_reference; stack_address < stack_top; stack_address += sizeof(FlatPtr)) {
auto data = *reinterpret_cast<FlatPtr*>(stack_address);
possible_pointers.set(data);
}
for (auto possible_pointer : possible_pointers) {
if (!possible_pointer)
continue;
#ifdef HEAP_DEBUG
dbg() << " ? " << (const void*)possible_pointer;
#endif
if (auto* cell = cell_from_possible_pointer(possible_pointer)) {
if (cell->is_live()) {
#ifdef HEAP_DEBUG
dbg() << " ?-> " << (const void*)cell;
#endif
roots.set(cell);
} else {
#ifdef HEAP_DEBUG
dbg() << " #-> " << (const void*)cell;
#endif
}
}
}
}
Cell* Heap::cell_from_possible_pointer(FlatPtr pointer)
{
auto* possible_heap_block = HeapBlock::from_cell(reinterpret_cast<const Cell*>(pointer));
if (m_blocks.find([possible_heap_block](auto& block) { return block.ptr() == possible_heap_block; }) == m_blocks.end())
return nullptr;
return possible_heap_block->cell_from_possible_pointer(pointer);
}
class MarkingVisitor final : public Cell::Visitor {
public:
MarkingVisitor() {}
@ -101,8 +166,11 @@ void Heap::mark_live_cells(const HashTable<Cell*>& roots)
dbg() << "mark_live_cells:";
#endif
MarkingVisitor visitor;
for (auto* root : roots)
for (auto* root : roots) {
if (!root)
continue;
visitor.visit(root);
}
}
void Heap::sweep_dead_cells()