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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef gc_Allocator_h
#define gc_Allocator_h
#include "mozilla/OperatorNewExtensions.h"
#include <stdint.h>
#include "gc/AllocKind.h"
#include "js/TypeDecls.h"
namespace js {
// [SMDOC] AllowGC template parameter
//
// AllowGC is a template parameter for functions that support both with and
// without GC operation.
//
// The CanGC variant of the function can trigger a garbage collection, and
// should set a pending exception on failure.
//
// The NoGC variant of the function cannot trigger a garbage collection, and
// should not set any pending exception on failure. This variant can be called
// in fast paths where the caller has unrooted pointers. The failure means we
// need to perform GC to allocate an object. The caller can fall back to a slow
// path that roots pointers before calling a CanGC variant of the function,
// without having to clear a pending exception.
enum AllowGC { NoGC = 0, CanGC = 1 };
namespace gc {
class AllocSite;
struct Cell;
class TenuredCell;
// `friend` js::gc::CellAllocator in a subtype T of Cell in order to allow it to
// be allocated with cx->newCell<T>(...). The friend declaration will allow
// calling T's constructor.
class CellAllocator {
template <AllowGC allowGC = CanGC>
static gc::Cell* AllocateStringCell(JSContext* cx, gc::AllocKind kind,
size_t size, gc::InitialHeap heap);
// Allocate a string. Use cx->newCell<StringT>([heap]).
//
// Use for nursery-allocatable strings. Returns a value cast to the correct
// type. Non-nursery-allocatable strings will go through the fallback
// tenured-only allocation path.
template <typename StringT, AllowGC allowGC = CanGC, typename... Args>
static StringT* AllocateString(JSContext* cx, gc::InitialHeap heap,
Args&&... args) {
static_assert(std::is_base_of_v<JSString, StringT>);
gc::AllocKind kind = gc::MapTypeToAllocKind<StringT>::kind;
gc::Cell* cell =
AllocateStringCell<allowGC>(cx, kind, sizeof(StringT), heap);
if (!cell) {
return nullptr;
}
return new (mozilla::KnownNotNull, cell)
StringT(std::forward<Args>(args)...);
}
public:
template <typename T, js::AllowGC allowGC = CanGC, typename... Args>
static T* NewCell(JSContext* cx, Args&&... args);
};
namespace detail {
// Allocator implementation functions. SpiderMonkey code outside this file
// should use
//
// cx->newCell<T>(...)
//
// or optionally
//
// cx->newCell<T, AllowGC::NoGC>(...)
//
// The parameters will be passed to a type-specific function or constructor. For
// nursery-allocatable types, see eg AllocateString, AllocateObject, and
// AllocateBigInt below. For all other types, the parameters will be
// forwarded to the constructor.
template <AllowGC allowGC = CanGC>
gc::TenuredCell* AllocateTenuredImpl(JSContext* cx, gc::AllocKind kind,
size_t size);
// Allocate a JSObject. Use cx->newCell<ObjectT>(kind, ...).
//
// Parameters support various optimizations. If dynamic slots are requested they
// will be allocated and the pointer stored directly in |NativeObject::slots_|.
template <AllowGC allowGC = CanGC>
JSObject* AllocateObject(JSContext* cx, gc::AllocKind kind,
size_t nDynamicSlots, gc::InitialHeap heap,
const JSClass* clasp, gc::AllocSite* site = nullptr);
// Allocate a BigInt. Use cx->newCell<BigInt>(heap).
//
// Use for nursery-allocatable BigInt.
template <AllowGC allowGC = CanGC>
JS::BigInt* AllocateBigInt(JSContext* cx, gc::InitialHeap heap);
} // namespace detail
} // namespace gc
// This is the entry point for all allocation, though callers should still not
// use this directly. Use cx->newCell<T>(...) instead.
template <typename T, AllowGC allowGC, typename... Args>
T* gc::CellAllocator::NewCell(JSContext* cx, Args&&... args) {
static_assert(std::is_base_of_v<gc::Cell, T>);
if constexpr (std::is_base_of_v<JSString, T> &&
!std::is_base_of_v<JSAtom, T> &&
!std::is_base_of_v<JSExternalString, T>) {
return AllocateString<T, allowGC>(cx, std::forward<Args>(args)...);
} else if constexpr (std::is_base_of_v<JS::BigInt, T>) {
return gc::detail::AllocateBigInt<allowGC>(cx, args...);
} else if constexpr (std::is_base_of_v<JSObject, T>) {
return static_cast<T*>(
gc::detail::AllocateObject<allowGC>(cx, std::forward<Args>(args)...));
} else {
// Allocate a new tenured GC thing that's not nursery-allocatable. Use
// cx->newCell<T>(...), where the parameters are prefixed with a cx
// parameter and forwarded to the type's constructor.
//
// After a successful allocation the caller must fully initialize the thing
// before calling any function that can potentially trigger GC. This will
// ensure that GC tracing never sees junk values stored in the partially
// initialized thing.
gc::AllocKind kind = gc::MapTypeToAllocKind<T>::kind;
gc::TenuredCell* cell =
gc::detail::AllocateTenuredImpl<allowGC>(cx, kind, sizeof(T));
if (!cell) {
return nullptr;
}
return new (mozilla::KnownNotNull, cell) T(std::forward<Args>(args)...);
}
}
} // namespace js
#endif // gc_Allocator_h
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