LibJS: Add "Heap" and "Runtime" subdirectories

Let's try to keep LibJS tidy as it expands. :^)

Libraries/LibJS/Heap/Heap.cpp

@@ -0,0 +1,128 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/Badge.h>
+#include <AK/HashTable.h>
+#include <LibJS/Heap/Heap.h>
+#include <LibJS/Heap/HeapBlock.h>
+#include <LibJS/Interpreter.h>
+#include <LibJS/Runtime/Object.h>
+
+#define HEAP_DEBUG
+
+namespace JS {
+
+Heap::Heap(Interpreter& interpreter)
+    : m_interpreter(interpreter)
+{
+}
+
+Heap::~Heap()
+{
+}
+
+Cell* Heap::allocate_cell(size_t size)
+{
+    for (auto& block : m_blocks) {
+        if (size > block->cell_size())
+            continue;
+        if (auto* cell = block->allocate())
+            return cell;
+    }
+
+    auto block = HeapBlock::create_with_cell_size(*this, size);
+    auto* cell = block->allocate();
+    m_blocks.append(move(block));
+    return cell;
+}
+
+void Heap::collect_garbage()
+{
+    HashTable<Cell*> roots;
+    gather_roots(roots);
+    mark_live_cells(roots);
+    sweep_dead_cells();
+}
+
+void Heap::gather_roots(HashTable<Cell*>& roots)
+{
+    m_interpreter.gather_roots({}, roots);
+
+#ifdef HEAP_DEBUG
+    dbg() << "collect_roots:";
+    for (auto* root : roots) {
+        dbg() << "  + " << root;
+    }
+#endif
+}
+
+class MarkingVisitor final : public Cell::Visitor {
+public:
+    MarkingVisitor() {}
+
+    virtual void visit(Cell* cell)
+    {
+        if (cell->is_marked())
+            return;
+#ifdef HEAP_DEBUG
+        dbg() << "  ! " << cell;
+#endif
+        cell->set_marked(true);
+        cell->visit_children(*this);
+    }
+};
+
+void Heap::mark_live_cells(const HashTable<Cell*>& roots)
+{
+#ifdef HEAP_DEBUG
+    dbg() << "mark_live_cells:";
+#endif
+    MarkingVisitor visitor;
+    for (auto* root : roots)
+        visitor.visit(root);
+}
+
+void Heap::sweep_dead_cells()
+{
+#ifdef HEAP_DEBUG
+    dbg() << "sweep_dead_cells:";
+#endif
+    for (auto& block : m_blocks) {
+        block->for_each_cell([&](Cell* cell) {
+            if (cell->is_live()) {
+                if (!cell->is_marked()) {
+#ifdef HEAP_DEBUG
+                    dbg() << "  ~ " << cell;
+#endif
+                    block->deallocate(cell);
+                } else {
+                    cell->set_marked(false);
+                }
+            }
+        });
+    }
+}
+}