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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 "gc/Cell.h"
#include "js/Class.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;
// Allocator implementation functions. SpiderMonkey code outside this file
// should use:
//
// cx->newCell<T>(...)
//
// or optionally:
//
// cx->newCell<T, AllowGC::NoGC>(...)
//
// `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.
//
// The parameters will be passed to a type-specific function or constructor. For
// nursery-allocatable types, see e.g. the NewString, NewObject, and NewBigInt
// methods. For all other types, the parameters will be forwarded to the
// constructor.
class CellAllocator {
public:
template <typename T, js::AllowGC allowGC = CanGC, typename... Args>
static T* NewCell(JSContext* cx, Args&&... args);
private:
// Allocate a cell in the nursery, unless |heap| is Heap::Tenured or nursery
// allocation is disabled for |traceKind| in the current zone.
template <JS::TraceKind traceKind, AllowGC allowGC = CanGC>
static void* AllocNurseryOrTenuredCell(JSContext* cx, gc::AllocKind allocKind,
gc::Heap heap, AllocSite* site);
// Allocate a cell in the tenured heap.
template <AllowGC allowGC = CanGC>
static void* AllocTenuredCell(JSContext* cx, gc::AllocKind kind, size_t size);
// Allocate a string. Use cx->newCell<T>([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 T, AllowGC allowGC = CanGC, typename... Args>
static T* NewString(JSContext* cx, gc::Heap heap, Args&&... args) {
static_assert(std::is_base_of_v<JSString, T>);
gc::AllocKind kind = gc::MapTypeToAllocKind<T>::kind;
void* ptr = AllocNurseryOrTenuredCell<JS::TraceKind::String, allowGC>(
cx, kind, heap, nullptr);
if (!ptr) {
return nullptr;
}
return new (mozilla::KnownNotNull, ptr) T(std::forward<Args>(args)...);
}
template <typename T, AllowGC allowGC /* = CanGC */>
static T* NewBigInt(JSContext* cx, Heap heap) {
void* ptr = AllocNurseryOrTenuredCell<JS::TraceKind::BigInt, allowGC>(
cx, gc::AllocKind::BIGINT, heap, nullptr);
if (ptr) {
return new (mozilla::KnownNotNull, ptr) T();
}
return nullptr;
}
template <typename T, AllowGC allowGC = CanGC>
static T* NewObject(JSContext* cx, gc::AllocKind kind, gc::Heap heap,
const JSClass* clasp, gc::AllocSite* site = nullptr) {
MOZ_ASSERT(IsObjectAllocKind(kind));
MOZ_ASSERT_IF(heap != gc::Heap::Tenured && clasp->hasFinalize() &&
!clasp->isProxyObject(),
CanNurseryAllocateFinalizedClass(clasp));
void* cell = AllocNurseryOrTenuredCell<JS::TraceKind::Object, allowGC>(
cx, kind, heap, site);
if (!cell) {
return nullptr;
}
return new (mozilla::KnownNotNull, cell) T();
}
// Allocate all other kinds of GC thing.
template <typename T, AllowGC allowGC = CanGC, typename... Args>
static T* NewTenuredCell(JSContext* cx, Args&&... args) {
gc::AllocKind kind = gc::MapTypeToAllocKind<T>::kind;
void* cell = AllocTenuredCell<allowGC>(cx, kind, sizeof(T));
if (!cell) {
return nullptr;
}
return new (mozilla::KnownNotNull, cell) T(std::forward<Args>(args)...);
}
};
} // namespace gc
// This is the entry point for all allocation, though callers should still not
// use this directly. Use cx->newCell<T>(...) instead.
//
// 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.
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>);
// Objects. See the valid parameter list in NewObject, above.
if constexpr (std::is_base_of_v<JSObject, T>) {
return NewObject<T, allowGC>(cx, std::forward<Args>(args)...);
}
// BigInt
else if constexpr (std::is_base_of_v<JS::BigInt, T>) {
return NewBigInt<T, allowGC>(cx, std::forward<Args>(args)...);
}
// "Normal" strings (all of which can be nursery allocated). Atoms and
// external strings will fall through to the generic code below. All other
// strings go through NewString, which will forward the arguments to the
// appropriate string class's constructor.
else if constexpr (std::is_base_of_v<JSString, T> &&
!std::is_base_of_v<JSAtom, T> &&
!std::is_base_of_v<JSExternalString, T>) {
return NewString<T, 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 forwarded to the type's
// constructor.
return NewTenuredCell<T, allowGC>(cx, std::forward<Args>(args)...);
}
}
} // namespace js
#endif // gc_Allocator_h
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