Stan Math Library  2.11.0
reverse mode automatic differentiation
stack_alloc.hpp
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1 #ifndef STAN_MATH_MEMORY_STACK_ALLOC_HPP
2 #define STAN_MATH_MEMORY_STACK_ALLOC_HPP
3 
4 // TODO(Bob): <cstddef> replaces this ifdef in C++11, until then this
5 // is best we can do to get safe pointer casts to uints.
6 #include <stdint.h>
8 #include <cstdlib>
9 #include <cstddef>
10 #include <sstream>
11 #include <stdexcept>
12 #include <vector>
13 
14 namespace stan {
15 
16  namespace math {
17 
29  template <typename T>
30  bool is_aligned(T* ptr, unsigned int bytes_aligned) {
31  return (reinterpret_cast<uintptr_t>(ptr) % bytes_aligned) == 0U;
32  }
33 
34 
35  namespace {
36  const size_t DEFAULT_INITIAL_NBYTES = 1 << 16; // 64KB
37 
38 
39  // FIXME: enforce alignment
40  // big fun to inline, but only called twice
41  inline char* eight_byte_aligned_malloc(size_t size) {
42  char* ptr = static_cast<char*>(malloc(size));
43  if (!ptr) return ptr; // malloc failed to alloc
44  if (!is_aligned(ptr, 8U)) {
45  std::stringstream s;
46  s << "invalid alignment to 8 bytes, ptr="
47  << reinterpret_cast<uintptr_t>(ptr)
48  << std::endl;
49  throw std::runtime_error(s.str());
50  }
51  return ptr;
52  }
53  }
54 
74  class stack_alloc {
75  private:
76  std::vector<char*> blocks_; // storage for blocks,
77  // may be bigger than cur_block_
78  std::vector<size_t> sizes_; // could store initial & shift for others
79  size_t cur_block_; // index into blocks_ for next alloc
80  char* cur_block_end_; // ptr to cur_block_ptr_ + sizes_[cur_block_]
81  char* next_loc_; // ptr to next available spot in cur
82  // block
83  // next three for keeping track of nested allocations on top of stack:
84  std::vector<size_t> nested_cur_blocks_;
85  std::vector<char*> nested_next_locs_;
86  std::vector<char*> nested_cur_block_ends_;
87 
88 
97  char* move_to_next_block(size_t len) {
98  char* result;
99  ++cur_block_;
100  // Find the next block (if any) containing at least len bytes.
101  while ((cur_block_ < blocks_.size()) && (sizes_[cur_block_] < len))
102  ++cur_block_;
103  // Allocate a new block if necessary.
104  if (unlikely(cur_block_ >= blocks_.size())) {
105  // New block should be max(2*size of last block, len) bytes.
106  size_t newsize = sizes_.back() * 2;
107  if (newsize < len)
108  newsize = len;
109  blocks_.push_back(eight_byte_aligned_malloc(newsize));
110  if (!blocks_.back())
111  throw std::bad_alloc();
112  sizes_.push_back(newsize);
113  }
114  result = blocks_[cur_block_];
115  // Get the object's state back in order.
116  next_loc_ = result + len;
117  cur_block_end_ = result + sizes_[cur_block_];
118  return result;
119  }
120 
121  public:
131  explicit stack_alloc(size_t initial_nbytes = DEFAULT_INITIAL_NBYTES) :
132  blocks_(1, eight_byte_aligned_malloc(initial_nbytes)),
133  sizes_(1, initial_nbytes),
134  cur_block_(0),
135  cur_block_end_(blocks_[0] + initial_nbytes),
136  next_loc_(blocks_[0]) {
137  if (!blocks_[0])
138  throw std::bad_alloc(); // no msg allowed in bad_alloc ctor
139  }
140 
148  // free ALL blocks
149  for (size_t i = 0; i < blocks_.size(); ++i)
150  if (blocks_[i])
151  free(blocks_[i]);
152  }
153 
166  inline void* alloc(size_t len) {
167  // Typically, just return and increment the next location.
168  char* result = next_loc_;
169  next_loc_ += len;
170  // Occasionally, we have to switch blocks.
171  if (unlikely(next_loc_ >= cur_block_end_))
172  result = move_to_next_block(len);
173  return reinterpret_cast<void*>(result);
174  }
175 
184  template <typename T>
185  inline
186  T* alloc_array(size_t n) {
187  return static_cast<T*>(alloc(n * sizeof(T)));
188  }
189 
190 
197  inline void recover_all() {
198  cur_block_ = 0;
199  next_loc_ = blocks_[0];
200  cur_block_end_ = next_loc_ + sizes_[0];
201  }
202 
207  inline void start_nested() {
208  nested_cur_blocks_.push_back(cur_block_);
209  nested_next_locs_.push_back(next_loc_);
210  nested_cur_block_ends_.push_back(cur_block_end_);
211  }
212 
216  inline void recover_nested() {
217  if (unlikely(nested_cur_blocks_.empty()))
218  recover_all();
219 
220  cur_block_ = nested_cur_blocks_.back();
221  nested_cur_blocks_.pop_back();
222 
223  next_loc_ = nested_next_locs_.back();
224  nested_next_locs_.pop_back();
225 
226  cur_block_end_ = nested_cur_block_ends_.back();
227  nested_cur_block_ends_.pop_back();
228  }
229 
235  inline void free_all() {
236  // frees all BUT the first (index 0) block
237  for (size_t i = 1; i < blocks_.size(); ++i)
238  if (blocks_[i])
239  free(blocks_[i]);
240  sizes_.resize(1);
241  blocks_.resize(1);
242  recover_all();
243  }
244 
255  size_t bytes_allocated() {
256  size_t sum = 0;
257  for (size_t i = 0; i <= cur_block_; ++i) {
258  sum += sizes_[i];
259  }
260  return sum;
261  }
262  };
263 
264  }
265 }
266 #endif
fvar< T > sum(const std::vector< fvar< T > > &m)
Return the sum of the entries of the specified standard vector.
Definition: sum.hpp:20
~stack_alloc()
Destroy this memory allocator.
void recover_nested()
recover memory back to the last start_nested call.
#define unlikely(x)
Definition: likely.hpp:9
void free_all()
Free all memory used by the stack allocator other than the initial block allocation back to the syste...
void recover_all()
Recover all the memory used by the stack allocator.
size_t bytes_allocated()
Return number of bytes allocated to this instance by the heap.
T * alloc_array(size_t n)
Allocate an array on the arena of the specified size to hold values of the specified template paramet...
int size(const std::vector< T > &x)
Return the size of the specified standard vector.
Definition: size.hpp:17
void start_nested()
Store current positions before doing nested operation so can recover back to start.
bool is_aligned(T *ptr, unsigned int bytes_aligned)
Return true if the specified pointer is aligned on the number of bytes.
Definition: stack_alloc.hpp:30
stack_alloc(size_t initial_nbytes=DEFAULT_INITIAL_NBYTES)
Construct a resizable stack allocator initially holding the specified number of bytes.
An instance of this class provides a memory pool through which blocks of raw memory may be allocated ...
Definition: stack_alloc.hpp:74
void * alloc(size_t len)
Return a newly allocated block of memory of the appropriate size managed by the stack allocator...

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