1# 2# Module which supports allocation of memory from an mmap 3# 4# multiprocessing/heap.py 5# 6# Copyright (c) 2006-2008, R Oudkerk 7# Licensed to PSF under a Contributor Agreement. 8# 9 10import bisect 11from collections import defaultdict 12import mmap 13import os 14import sys 15import tempfile 16import threading 17 18from .context import reduction, assert_spawning 19from . import util 20 21__all__ = ['BufferWrapper'] 22 23# 24# Inheritable class which wraps an mmap, and from which blocks can be allocated 25# 26 27if sys.platform == 'win32': 28 29 import _winapi 30 31 class Arena(object): 32 """ 33 A shared memory area backed by anonymous memory (Windows). 34 """ 35 36 _rand = tempfile._RandomNameSequence() 37 38 def __init__(self, size): 39 self.size = size 40 for i in range(100): 41 name = 'pym-%d-%s' % (os.getpid(), next(self._rand)) 42 buf = mmap.mmap(-1, size, tagname=name) 43 if _winapi.GetLastError() == 0: 44 break 45 # We have reopened a preexisting mmap. 46 buf.close() 47 else: 48 raise FileExistsError('Cannot find name for new mmap') 49 self.name = name 50 self.buffer = buf 51 self._state = (self.size, self.name) 52 53 def __getstate__(self): 54 assert_spawning(self) 55 return self._state 56 57 def __setstate__(self, state): 58 self.size, self.name = self._state = state 59 # Reopen existing mmap 60 self.buffer = mmap.mmap(-1, self.size, tagname=self.name) 61 # XXX Temporarily preventing buildbot failures while determining 62 # XXX the correct long-term fix. See issue 23060 63 #assert _winapi.GetLastError() == _winapi.ERROR_ALREADY_EXISTS 64 65else: 66 67 class Arena(object): 68 """ 69 A shared memory area backed by a temporary file (POSIX). 70 """ 71 72 if sys.platform == 'linux': 73 _dir_candidates = ['/dev/shm'] 74 else: 75 _dir_candidates = [] 76 77 def __init__(self, size, fd=-1): 78 self.size = size 79 self.fd = fd 80 if fd == -1: 81 # Arena is created anew (if fd != -1, it means we're coming 82 # from rebuild_arena() below) 83 self.fd, name = tempfile.mkstemp( 84 prefix='pym-%d-'%os.getpid(), 85 dir=self._choose_dir(size)) 86 os.unlink(name) 87 util.Finalize(self, os.close, (self.fd,)) 88 os.ftruncate(self.fd, size) 89 self.buffer = mmap.mmap(self.fd, self.size) 90 91 def _choose_dir(self, size): 92 # Choose a non-storage backed directory if possible, 93 # to improve performance 94 for d in self._dir_candidates: 95 st = os.statvfs(d) 96 if st.f_bavail * st.f_frsize >= size: # enough free space? 97 return d 98 return util.get_temp_dir() 99 100 def reduce_arena(a): 101 if a.fd == -1: 102 raise ValueError('Arena is unpicklable because ' 103 'forking was enabled when it was created') 104 return rebuild_arena, (a.size, reduction.DupFd(a.fd)) 105 106 def rebuild_arena(size, dupfd): 107 return Arena(size, dupfd.detach()) 108 109 reduction.register(Arena, reduce_arena) 110 111# 112# Class allowing allocation of chunks of memory from arenas 113# 114 115class Heap(object): 116 117 # Minimum malloc() alignment 118 _alignment = 8 119 120 _DISCARD_FREE_SPACE_LARGER_THAN = 4 * 1024 ** 2 # 4 MB 121 _DOUBLE_ARENA_SIZE_UNTIL = 4 * 1024 ** 2 122 123 def __init__(self, size=mmap.PAGESIZE): 124 self._lastpid = os.getpid() 125 self._lock = threading.Lock() 126 # Current arena allocation size 127 self._size = size 128 # A sorted list of available block sizes in arenas 129 self._lengths = [] 130 131 # Free block management: 132 # - map each block size to a list of `(Arena, start, stop)` blocks 133 self._len_to_seq = {} 134 # - map `(Arena, start)` tuple to the `(Arena, start, stop)` block 135 # starting at that offset 136 self._start_to_block = {} 137 # - map `(Arena, stop)` tuple to the `(Arena, start, stop)` block 138 # ending at that offset 139 self._stop_to_block = {} 140 141 # Map arenas to their `(Arena, start, stop)` blocks in use 142 self._allocated_blocks = defaultdict(set) 143 self._arenas = [] 144 145 # List of pending blocks to free - see comment in free() below 146 self._pending_free_blocks = [] 147 148 # Statistics 149 self._n_mallocs = 0 150 self._n_frees = 0 151 152 @staticmethod 153 def _roundup(n, alignment): 154 # alignment must be a power of 2 155 mask = alignment - 1 156 return (n + mask) & ~mask 157 158 def _new_arena(self, size): 159 # Create a new arena with at least the given *size* 160 length = self._roundup(max(self._size, size), mmap.PAGESIZE) 161 # We carve larger and larger arenas, for efficiency, until we 162 # reach a large-ish size (roughly L3 cache-sized) 163 if self._size < self._DOUBLE_ARENA_SIZE_UNTIL: 164 self._size *= 2 165 util.info('allocating a new mmap of length %d', length) 166 arena = Arena(length) 167 self._arenas.append(arena) 168 return (arena, 0, length) 169 170 def _discard_arena(self, arena): 171 # Possibly delete the given (unused) arena 172 length = arena.size 173 # Reusing an existing arena is faster than creating a new one, so 174 # we only reclaim space if it's large enough. 175 if length < self._DISCARD_FREE_SPACE_LARGER_THAN: 176 return 177 blocks = self._allocated_blocks.pop(arena) 178 assert not blocks 179 del self._start_to_block[(arena, 0)] 180 del self._stop_to_block[(arena, length)] 181 self._arenas.remove(arena) 182 seq = self._len_to_seq[length] 183 seq.remove((arena, 0, length)) 184 if not seq: 185 del self._len_to_seq[length] 186 self._lengths.remove(length) 187 188 def _malloc(self, size): 189 # returns a large enough block -- it might be much larger 190 i = bisect.bisect_left(self._lengths, size) 191 if i == len(self._lengths): 192 return self._new_arena(size) 193 else: 194 length = self._lengths[i] 195 seq = self._len_to_seq[length] 196 block = seq.pop() 197 if not seq: 198 del self._len_to_seq[length], self._lengths[i] 199 200 (arena, start, stop) = block 201 del self._start_to_block[(arena, start)] 202 del self._stop_to_block[(arena, stop)] 203 return block 204 205 def _add_free_block(self, block): 206 # make block available and try to merge with its neighbours in the arena 207 (arena, start, stop) = block 208 209 try: 210 prev_block = self._stop_to_block[(arena, start)] 211 except KeyError: 212 pass 213 else: 214 start, _ = self._absorb(prev_block) 215 216 try: 217 next_block = self._start_to_block[(arena, stop)] 218 except KeyError: 219 pass 220 else: 221 _, stop = self._absorb(next_block) 222 223 block = (arena, start, stop) 224 length = stop - start 225 226 try: 227 self._len_to_seq[length].append(block) 228 except KeyError: 229 self._len_to_seq[length] = [block] 230 bisect.insort(self._lengths, length) 231 232 self._start_to_block[(arena, start)] = block 233 self._stop_to_block[(arena, stop)] = block 234 235 def _absorb(self, block): 236 # deregister this block so it can be merged with a neighbour 237 (arena, start, stop) = block 238 del self._start_to_block[(arena, start)] 239 del self._stop_to_block[(arena, stop)] 240 241 length = stop - start 242 seq = self._len_to_seq[length] 243 seq.remove(block) 244 if not seq: 245 del self._len_to_seq[length] 246 self._lengths.remove(length) 247 248 return start, stop 249 250 def _remove_allocated_block(self, block): 251 arena, start, stop = block 252 blocks = self._allocated_blocks[arena] 253 blocks.remove((start, stop)) 254 if not blocks: 255 # Arena is entirely free, discard it from this process 256 self._discard_arena(arena) 257 258 def _free_pending_blocks(self): 259 # Free all the blocks in the pending list - called with the lock held. 260 while True: 261 try: 262 block = self._pending_free_blocks.pop() 263 except IndexError: 264 break 265 self._add_free_block(block) 266 self._remove_allocated_block(block) 267 268 def free(self, block): 269 # free a block returned by malloc() 270 # Since free() can be called asynchronously by the GC, it could happen 271 # that it's called while self._lock is held: in that case, 272 # self._lock.acquire() would deadlock (issue #12352). To avoid that, a 273 # trylock is used instead, and if the lock can't be acquired 274 # immediately, the block is added to a list of blocks to be freed 275 # synchronously sometimes later from malloc() or free(), by calling 276 # _free_pending_blocks() (appending and retrieving from a list is not 277 # strictly thread-safe but under CPython it's atomic thanks to the GIL). 278 if os.getpid() != self._lastpid: 279 raise ValueError( 280 "My pid ({0:n}) is not last pid {1:n}".format( 281 os.getpid(),self._lastpid)) 282 if not self._lock.acquire(False): 283 # can't acquire the lock right now, add the block to the list of 284 # pending blocks to free 285 self._pending_free_blocks.append(block) 286 else: 287 # we hold the lock 288 try: 289 self._n_frees += 1 290 self._free_pending_blocks() 291 self._add_free_block(block) 292 self._remove_allocated_block(block) 293 finally: 294 self._lock.release() 295 296 def malloc(self, size): 297 # return a block of right size (possibly rounded up) 298 if size < 0: 299 raise ValueError("Size {0:n} out of range".format(size)) 300 if sys.maxsize <= size: 301 raise OverflowError("Size {0:n} too large".format(size)) 302 if os.getpid() != self._lastpid: 303 self.__init__() # reinitialize after fork 304 with self._lock: 305 self._n_mallocs += 1 306 # allow pending blocks to be marked available 307 self._free_pending_blocks() 308 size = self._roundup(max(size, 1), self._alignment) 309 (arena, start, stop) = self._malloc(size) 310 real_stop = start + size 311 if real_stop < stop: 312 # if the returned block is larger than necessary, mark 313 # the remainder available 314 self._add_free_block((arena, real_stop, stop)) 315 self._allocated_blocks[arena].add((start, real_stop)) 316 return (arena, start, real_stop) 317 318# 319# Class wrapping a block allocated out of a Heap -- can be inherited by child process 320# 321 322class BufferWrapper(object): 323 324 _heap = Heap() 325 326 def __init__(self, size): 327 if size < 0: 328 raise ValueError("Size {0:n} out of range".format(size)) 329 if sys.maxsize <= size: 330 raise OverflowError("Size {0:n} too large".format(size)) 331 block = BufferWrapper._heap.malloc(size) 332 self._state = (block, size) 333 util.Finalize(self, BufferWrapper._heap.free, args=(block,)) 334 335 def create_memoryview(self): 336 (arena, start, stop), size = self._state 337 return memoryview(arena.buffer)[start:start+size] 338