MPD  0.20.15
SliceBuffer.hxx
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19 
20 #ifndef MPD_SLICE_BUFFER_HXX
21 #define MPD_SLICE_BUFFER_HXX
22 
23 #include "HugeAllocator.hxx"
24 #include "Compiler.h"
25 
26 #include <utility>
27 #include <new>
28 
29 #include <assert.h>
30 #include <stddef.h>
31 
36 template<typename T>
37 class SliceBuffer {
38  union Slice {
39  Slice *next;
40 
41  T value;
42  };
43 
47  const unsigned n_max;
48 
54  unsigned n_initialized;
55 
59  unsigned n_allocated;
60 
61  Slice *const data;
62 
66  Slice *available;
67 
68  size_t CalcAllocationSize() const {
69  return n_max * sizeof(Slice);
70  }
71 
72 public:
73  SliceBuffer(unsigned _count)
74  :n_max(_count), n_initialized(0), n_allocated(0),
75  data((Slice *)HugeAllocate(CalcAllocationSize())),
76  available(nullptr) {
77  assert(n_max > 0);
78  }
79 
81  /* all slices must be freed explicitly, and this
82  assertion checks for leaks */
83  assert(n_allocated == 0);
84 
85  HugeFree(data, CalcAllocationSize());
86  }
87 
88  SliceBuffer(const SliceBuffer &other) = delete;
89  SliceBuffer &operator=(const SliceBuffer &other) = delete;
90 
91  unsigned GetCapacity() const {
92  return n_max;
93  }
94 
95  bool IsEmpty() const {
96  return n_allocated == 0;
97  }
98 
99  bool IsFull() const {
100  return n_allocated == n_max;
101  }
102 
103  template<typename... Args>
104  T *Allocate(Args&&... args) {
105  assert(n_initialized <= n_max);
106  assert(n_allocated <= n_initialized);
107 
108  if (available == nullptr) {
109  if (n_initialized == n_max) {
110  /* out of (internal) memory, buffer is full */
111  assert(n_allocated == n_max);
112  return nullptr;
113  }
114 
115  available = &data[n_initialized++];
116  available->next = nullptr;
117  }
118 
119  /* allocate a slice */
120  T *value = &available->value;
121  available = available->next;
122  ++n_allocated;
123 
124  /* construct the object */
125  return ::new((void *)value) T(std::forward<Args>(args)...);
126  }
127 
128  void Free(T *value) {
129  assert(n_initialized <= n_max);
130  assert(n_allocated > 0);
131  assert(n_allocated <= n_initialized);
132 
133  Slice *slice = reinterpret_cast<Slice *>(value);
134  assert(slice >= data && slice < data + n_max);
135 
136  /* destruct the object */
137  value->~T();
138 
139  /* insert the slice in the "available" linked list */
140  slice->next = available;
141  available = slice;
142  --n_allocated;
143 
144  /* give memory back to the kernel when the last slice
145  was freed */
146  if (n_allocated == 0) {
147  HugeDiscard(data, CalcAllocationSize());
148  n_initialized = 0;
149  available = nullptr;
150  }
151  }
152 };
153 
154 #endif
bool IsFull() const
Definition: SliceBuffer.hxx:99
SliceBuffer(unsigned _count)
Definition: SliceBuffer.hxx:73
bool IsEmpty() const
Definition: SliceBuffer.hxx:95
void Free(T *value)
static void HugeDiscard(void *, size_t) noexcept
unsigned GetCapacity() const
Definition: SliceBuffer.hxx:91
SliceBuffer & operator=(const SliceBuffer &other)=delete
This class pre-allocates a certain number of objects, and allows callers to allocate and free these o...
Definition: SliceBuffer.hxx:37
static void HugeFree(void *_p, size_t) noexcept
T * Allocate(Args &&... args)
static gcc_malloc void * HugeAllocate(size_t size)