1/*
2 * Copyright (C) 2016 Apple Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
14 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
15 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
17 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
18 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
19 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
20 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
21 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
22 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
23 * THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#pragma once
27
28#include "VM.h"
29
30namespace JSC {
31
32class JSCell;
33class SlotVisitor;
34class VM;
35
36// Note that if all you're doing is calling LazyProperty::get(), it's completely safe to bitcast
37// this LazyProperty<JSCell, JSCell>.
38template<typename OwnerType, typename ElementType>
39class LazyProperty {
40public:
41 struct Initializer {
42 Initializer(OwnerType* owner, LazyProperty& property)
43 : vm(*Heap::heap(owner)->vm())
44 , owner(owner)
45 , property(property)
46 {
47 }
48
49 void set(ElementType* value) const;
50
51 VM& vm;
52 OwnerType* owner;
53 LazyProperty& property;
54 };
55
56private:
57 typedef ElementType* (*FuncType)(const Initializer&);
58
59public:
60 LazyProperty()
61 {
62 }
63
64 // Tell the property to run the given callback next time someone tries to get the value
65 // using get(). The passed callback must be stateless. For example:
66 //
67 // property.initLater(
68 // [] (const LazyProperty<Foo, Bar>::Initializer& init) {
69 // init.set(...things...);
70 // });
71 //
72 // This method is always inlineable and should always compile to a store of a constant
73 // pointer no matter how complicated the callback is.
74 template<typename Func>
75 void initLater(const Func&);
76
77 // This lazily initializes the property. Note that this gracefully supports recursive calls.
78 // If this gets called while the property is being initialized, it will simply return null.
79 ElementType* get(const OwnerType* owner) const
80 {
81 ASSERT(!isCompilationThread());
82 return getInitializedOnMainThread(owner);
83 }
84
85 ElementType* getConcurrently() const
86 {
87 uintptr_t pointer = m_pointer;
88 if (pointer & lazyTag)
89 return nullptr;
90 return bitwise_cast<ElementType*>(pointer);
91 }
92
93 ElementType* getInitializedOnMainThread(const OwnerType* owner) const
94 {
95 if (UNLIKELY(m_pointer & lazyTag)) {
96 ASSERT(!isCompilationThread());
97 FuncType func = *bitwise_cast<FuncType*>(m_pointer & ~(lazyTag | initializingTag));
98 return func(Initializer(const_cast<OwnerType*>(owner), *const_cast<LazyProperty*>(this)));
99 }
100 return bitwise_cast<ElementType*>(m_pointer);
101 }
102
103 void setMayBeNull(VM&, const OwnerType* owner, ElementType*);
104 void set(VM&, const OwnerType* owner, ElementType*);
105
106 void visit(SlotVisitor&);
107
108 void dump(PrintStream&) const;
109
110private:
111 template<typename Func>
112 static ElementType* callFunc(const Initializer&);
113
114 static const uintptr_t lazyTag = 1;
115 static const uintptr_t initializingTag = 2;
116
117 uintptr_t m_pointer { 0 };
118};
119
120// It's valid to bitcast any LazyProperty to LazyCellProperty if you're just going to call get()
121// or getConcurrently().
122typedef LazyProperty<JSCell, JSCell> LazyCellProperty;
123
124} // namespace JSC
125