1 /*
2  *  Copyright (c) 2021, The OpenThread Authors.
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9  *  2. Redistributions in binary form must reproduce the above copyright
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14  *     derived from this software without specific prior written permission.
15  *
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27  */
28 
29 /**
30  * @file
31  *   This file includes definitions for `Heap::Allocatable`.
32  */
33 
34 #ifndef HEAP_ALLOCATABLE_HPP_
35 #define HEAP_ALLOCATABLE_HPP_
36 
37 #include "openthread-core-config.h"
38 
39 #include "common/code_utils.hpp"
40 #include "common/error.hpp"
41 #include "common/heap.hpp"
42 #include "common/new.hpp"
43 
44 namespace ot {
45 namespace Heap {
46 
47 /**
48  * This template class defines a `Heap::Allocatable` object.
49  *
50  * `Heap::Allocatable` provides methods to allocate and free instances of `Type` on heap.
51  *
52  * Users of this class should follow CRTP-style inheritance, i.e., the `Type` class itself should inherit from
53  * `Allocatable<Type>`.
54  *
55  * The `Type` class destructor is used when `Free()` is called. The destructor frees any heap allocated data members
56  * that are stored in a `Type` instance (e.g., `Heap::String`, `Heap::Data`, etc).
57  *
58  */
59 template <class Type> class Allocatable
60 {
61 public:
62     /**
63      * This static method allocates a new instance of `Type` on heap and initializes it using `Type` constructor.
64      *
65      * The `Type` class MUST have a constructor `Type(Args...)` which is invoked upon allocation of new `Type` to
66      * initialize it.
67      *
68      * @param[in] aArgs   A set of arguments to pass to the `Type` constructor of the allocated `Type` instance.
69      *
70      * @returns A pointer to the newly allocated instance or `nullptr` if it fails to allocate.
71      *
72      */
Allocate(Args &&...aArgs)73     template <typename... Args> static Type *Allocate(Args &&...aArgs)
74     {
75         void *buf = Heap::CAlloc(1, sizeof(Type));
76 
77         return (buf != nullptr) ? new (buf) Type(static_cast<Args &&>(aArgs)...) : nullptr;
78     }
79 
80     /**
81      * This static method allocates a new instance of `Type` on heap and initializes it using `Type::Init()` method.
82      *
83      * The `Type` class MUST have a default constructor (with no arguments) which is invoked upon allocation of new
84      * `Type` instance. It MUST also provide an `Error Init(Args...)` method to initialize the instance. If any `Error`
85      * other than `kErrorNone` is returned the initialization is considered failed.
86      *
87      * @param[in] aArgs   A set of arguments to initialize the allocated `Type` instance.
88      *
89      * @returns A pointer to the newly allocated instance or `nullptr` if it fails to allocate or initialize.
90      *
91      */
AllocateAndInit(Args &&...aArgs)92     template <typename... Args> static Type *AllocateAndInit(Args &&...aArgs)
93     {
94         void *buf    = Heap::CAlloc(1, sizeof(Type));
95         Type *object = nullptr;
96 
97         VerifyOrExit(buf != nullptr);
98 
99         object = new (buf) Type();
100 
101         if (object->Init(static_cast<Args &&>(aArgs)...) != kErrorNone)
102         {
103             object->Free();
104             object = nullptr;
105         }
106 
107     exit:
108         return object;
109     }
110 
111     /**
112      * This method frees the `Type` instance.
113      *
114      * The instance MUST be heap allocated using either `Allocate()` or `AllocateAndInit()`.
115      *
116      * The `Free()` method invokes the `Type` destructor before releasing the allocated heap buffer for the instance.
117      * This ensures that any heap allocated member variables in `Type` are freed before the `Type` instance itself is
118      * freed.
119      *
120      */
Free(void)121     void Free(void)
122     {
123         static_cast<Type *>(this)->~Type();
124         Heap::Free(this);
125     }
126 
127 protected:
128     Allocatable(void) = default;
129 };
130 
131 } // namespace Heap
132 } // namespace ot
133 
134 #endif // HEAP_ALLOCATABLE_HPP_
135