1/*
2 This file is part of the KDE libraries
3
4 SPDX-FileCopyrightText: 1999 Waldo Bastian <bastian@kde.org>
5 SPDX-FileCopyrightText: 2002 Michael Matz <matz@kde.org>
6
7 SPDX-License-Identifier: LGPL-2.0-or-later
8*/
9//----------------------------------------------------------------------------
10//
11// KDE Memory Allocator
12
13#ifndef KZONEALLOCATOR_P_H
14#define KZONEALLOCATOR_P_H
15
16#include <cstddef> // size_t
17
18template<typename T>
19class QList;
20
21/*!
22 * Memory allocator for large groups of small objects.
23 * This should be used for large groups of objects that are created and
24 * destroyed together. When used carefully for this purpose it is faster
25 * and more memory efficient than malloc. Additionally to a usual obstack
26 * like allocator you can also free the objects individually. Because it
27 * does no compaction it still is faster than malloc()/free(). Depending
28 * on the exact usage pattern that might come at the expense of some
29 * memory though.
30 *
31 * \internal
32 */
33class KZoneAllocator
34{
35public:
36 /*!
37 * Creates a KZoneAllocator object.
38 * \a _blockSize Size in bytes of the blocks requested from malloc.
39 */
40 explicit KZoneAllocator(unsigned long _blockSize = 8 * 1024);
41
42 /*!
43 * Destructs the ZoneAllocator and free all memory allocated by it.
44 */
45 ~KZoneAllocator();
46
47 KZoneAllocator(const KZoneAllocator &) = delete;
48 KZoneAllocator &operator=(const KZoneAllocator &) = delete;
49
50 /*!
51 * Allocates a memory block.
52 * \a _size Size in bytes of the memory block. Memory is aligned to
53 * the size of a pointer.
54 */
55 void *allocate(size_t _size);
56
57 /*!
58 * Gives back a block returned by allocate() to the zone
59 * allocator, and possibly deallocates the block holding it (when it's
60 * empty). The first deallocate() after many allocate() calls
61 * (or the first at all) builds an internal data structure for speeding
62 * up deallocation. The consistency of that structure is maintained
63 * from then on (by allocate() and deallocate()) unless many
64 * more objects are allocated without any intervening deallocation, in
65 * which case it's thrown away and rebuilt at the next deallocate().
66 *
67 * The effect of this is, that such initial deallocate() calls take
68 * more time then the normal calls, and that after this list is built, i.e.
69 * generally if deallocate() is used at all, also allocate() is a
70 * little bit slower. This means, that if you want to squeeze out the last
71 * bit performance you would want to use KZoneAllocator as an obstack, i.e.
72 * just use the functions allocate() and free_since(). All the
73 * remaining memory is returned to the system if the zone allocator
74 * is destroyed.
75 * \a ptr Pointer as returned by allocate().
76 */
77 void deallocate(void *ptr);
78
79 /*!
80 * Deallocate many objects at once.
81 * free_since() deallocates all objects allocated after \a ptr,
82 * \e including \a ptr itself.
83 *
84 * The intended use is something along the lines of:
85 * \code
86 * KZoneAllocator alloc(8192);
87 * void *remember_me = alloc.allocate(0);
88 * for (int i = 0; i < 1000; i++)
89 * do_something_with (alloc.allocate(12));
90 * alloc.free_since (remember_me);
91 * \endcode
92 * Note, that we don't need to remember all the pointers to the 12-byte
93 * objects for freeing them. The free_since() does deallocate them
94 * all at once.
95 * \a ptr Pointer as returned by allocate(). It acts like
96 * a kind of mark of a certain position in the stack of all objects,
97 * off which you can throw away everything above that mark.
98 */
99 void free_since(void *ptr);
100
101protected:
102 /*! A single chunk of memory from the heap. \internal */
103 class MemBlock;
104 /*!< A list of chunks. \internal */
105 typedef QList<MemBlock *> MemList;
106 void addBlock(MemBlock *b);
107 void delBlock(MemBlock *b);
108 void insertHash(MemBlock *b);
109 void initHash();
110
111private:
112 class Private;
113 Private *const d;
114};
115
116#endif
117

source code of kcompletion/src/kzoneallocator_p.h