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LibJS: Keep track of PrimitiveStrings and share them

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VM now has a string cache which tracks all live PrimitiveStrings and
reuses an existing one if possible. This drastically reduces the number
of GC-allocated strings in many real-word situations.
This commit is contained in:
Andreas Kling 2021-10-02 01:36:57 +02:00
parent ba6e4c7ae1
commit f290c59dd8
3 changed files with 13 additions and 1 deletions
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1
Userland/Libraries/LibJS/Heap/Heap.cpp
View file

@ -52,6 +52,7 @@ Heap::Heap(VM& vm)
Heap::~Heap()
{
vm().string_cache().clear();
collect_garbage(CollectionType::CollectEverything);
}

10
Userland/Libraries/LibJS/Runtime/PrimitiveString.cpp
View file

@ -25,6 +25,7 @@ PrimitiveString::PrimitiveString(Utf16String string)
PrimitiveString::~PrimitiveString()
{
vm().string_cache().remove(m_utf8_string);
}
String const& PrimitiveString::string() const
@ -90,7 +91,14 @@ PrimitiveString* js_string(Heap& heap, String string)
return &heap.vm().single_ascii_character_string(ch);
}
return heap.allocate_without_global_object<PrimitiveString>(move(string));
auto& string_cache = heap.vm().string_cache();
auto it = string_cache.find(string);
if (it == string_cache.end()) {
auto* new_string = heap.allocate_without_global_object<PrimitiveString>(string);
string_cache.set(move(string), new_string);
return new_string;
}
return it->value;
}
PrimitiveString* js_string(VM& vm, String string)

3
Userland/Libraries/LibJS/Runtime/VM.h
View file

@ -81,6 +81,7 @@ public:
Symbol* get_global_symbol(const String& description);
HashMap<String, PrimitiveString*>& string_cache() { return m_string_cache; }
PrimitiveString& empty_string() { return *m_empty_string; }
PrimitiveString& single_ascii_character_string(u8 character)
{
@ -294,6 +295,8 @@ private:
Exception* m_exception { nullptr };
HashMap<String, PrimitiveString*> m_string_cache;
Heap m_heap;
Vector<Interpreter*> m_interpreters;