#
# Module which supports allocation of memory from an mmap
#
# multiprocessing/heap.py
#
# Copyright (c) 2006-2008, R Oudkerk
# Licensed to PSF under a Contributor Agreement.
#

import bisect
from collections import defaultdict
import mmap
import os
import sys
import tempfile
import threading

from .context import reduction, assert_spawning
from . import util

__all__ = ['BufferWrapper']

#
# Inheritable class which wraps an mmap, and from which blocks can be allocated
#

if sys.platform == 'win32':

 import _winapi

 class Arena(object):
 """
 A shared memory area backed by anonymous memory (Windows).
 """

 _rand = tempfile._RandomNameSequence()

 def __init__(self, size):
 self.size = size
 for i in range(100):
 name = 'pym-%d-%s' % (os.getpid(), next(self._rand))
 buf = mmap.mmap(-1, size, tagname=name)
 if _winapi.GetLastError() == 0:
 break
 # We have reopened a preexisting mmap.
 buf.close()
 else:
 raise FileExistsError('Cannot find name for new mmap')
 self.name = name
 self.buffer = buf
 self._state = (self.size, self.name)

 def __getstate__(self):
 assert_spawning(self)
 return self._state

 def __setstate__(self, state):
 self.size, self.name = self._state = state
 # Reopen existing mmap
 self.buffer = mmap.mmap(-1, self.size, tagname=self.name)
 # XXX Temporarily preventing buildbot failures while determining
 # XXX the correct long-term fix. See issue 23060
 #assert _winapi.GetLastError() == _winapi.ERROR_ALREADY_EXISTS

else:

 class Arena(object):
 """
 A shared memory area backed by a temporary file (POSIX).
 """

 if sys.platform == 'linux':
 _dir_candidates = ['/dev/shm']
 else:
 _dir_candidates = []

 def __init__(self, size, fd=-1):
 self.size = size
 self.fd = fd
 if fd == -1:
 # Arena is created anew (if fd != -1, it means we're coming
 # from rebuild_arena() below)
 self.fd, name = tempfile.mkstemp(
 prefix='pym-%d-'%os.getpid(),
 dir=self._choose_dir(size))
 os.unlink(name)
 util.Finalize(self, os.close, (self.fd,))
 os.ftruncate(self.fd, size)
 self.buffer = mmap.mmap(self.fd, self.size)

 def _choose_dir(self, size):
 # Choose a non-storage backed directory if possible,
 # to improve performance
 for d in self._dir_candidates:
 st = os.statvfs(d)
 if st.f_bavail * st.f_frsize >= size: # enough free space?
 return d
 return util.get_temp_dir()

 def reduce_arena(a):
 if a.fd == -1:
 raise ValueError('Arena is unpicklable because '
 'forking was enabled when it was created')
 return rebuild_arena, (a.size, reduction.DupFd(a.fd))

 def rebuild_arena(size, dupfd):
 return Arena(size, dupfd.detach())

 reduction.register(Arena, reduce_arena)

#
# Class allowing allocation of chunks of memory from arenas
#

class Heap(object):

 # Minimum malloc() alignment
 _alignment = 8

 _DISCARD_FREE_SPACE_LARGER_THAN = 4 * 1024 ** 2 # 4 MB
 _DOUBLE_ARENA_SIZE_UNTIL = 4 * 1024 ** 2

 def __init__(self, size=mmap.PAGESIZE):
 self._lastpid = os.getpid()
 self._lock = threading.Lock()
 # Current arena allocation size
 self._size = size
 # A sorted list of available block sizes in arenas
 self._lengths = []

 # Free block management:
 # - map each block size to a list of `(Arena, start, stop)` blocks
 self._len_to_seq = {}
 # - map `(Arena, start)` tuple to the `(Arena, start, stop)` block
 # starting at that offset
 self._start_to_block = {}
 # - map `(Arena, stop)` tuple to the `(Arena, start, stop)` block
 # ending at that offset
 self._stop_to_block = {}

 # Map arenas to their `(Arena, start, stop)` blocks in use
 self._allocated_blocks = defaultdict(set)
 self._arenas = []

 # List of pending blocks to free - see comment in free() below
 self._pending_free_blocks = []

 # Statistics
 self._n_mallocs = 0
 self._n_frees = 0

 @staticmethod
 def _roundup(n, alignment):
 # alignment must be a power of 2
 mask = alignment - 1
 return (n + mask) & ~mask

 def _new_arena(self, size):
 # Create a new arena with at least the given *size*
 length = self._roundup(max(self._size, size), mmap.PAGESIZE)
 # We carve larger and larger arenas, for efficiency, until we
 # reach a large-ish size (roughly L3 cache-sized)
 if self._size < self._DOUBLE_ARENA_SIZE_UNTIL:
 self._size *= 2
 util.info('allocating a new mmap of length %d', length)
 arena = Arena(length)
 self._arenas.append(arena)
 return (arena, 0, length)

 def _discard_arena(self, arena):
 # Possibly delete the given (unused) arena
 length = arena.size
 # Reusing an existing arena is faster than creating a new one, so
 # we only reclaim space if it's large enough.
 if length < self._DISCARD_FREE_SPACE_LARGER_THAN:
 return
 blocks = self._allocated_blocks.pop(arena)
 assert not blocks
 del self._start_to_block[(arena, 0)]
 del self._stop_to_block[(arena, length)]
 self._arenas.remove(arena)
 seq = self._len_to_seq[length]
 seq.remove((arena, 0, length))
 if not seq:
 del self._len_to_seq[length]
 self._lengths.remove(length)

 def _malloc(self, size):
 # returns a large enough block -- it might be much larger
 i = bisect.bisect_left(self._lengths, size)
 if i == len(self._lengths):
 return self._new_arena(size)
 else:
 length = self._lengths[i]
 seq = self._len_to_seq[length]
 block = seq.pop()
 if not seq:
 del self._len_to_seq[length], self._lengths[i]

 (arena, start, stop) = block
 del self._start_to_block[(arena, start)]
 del self._stop_to_block[(arena, stop)]
 return block

 def _add_free_block(self, block):
 # make block available and try to merge with its neighbours in the arena
 (arena, start, stop) = block

 try:
 prev_block = self._stop_to_block[(arena, start)]
 except KeyError:
 pass
 else:
 start, _ = self._absorb(prev_block)

 try:
 next_block = self._start_to_block[(arena, stop)]
 except KeyError:
 pass
 else:
 _, stop = self._absorb(next_block)

 block = (arena, start, stop)
 length = stop - start

 try:
 self._len_to_seq[length].append(block)
 except KeyError:
 self._len_to_seq[length] = [block]
 bisect.insort(self._lengths, length)

 self._start_to_block[(arena, start)] = block
 self._stop_to_block[(arena, stop)] = block

 def _absorb(self, block):
 # deregister this block so it can be merged with a neighbour
 (arena, start, stop) = block
 del self._start_to_block[(arena, start)]
 del self._stop_to_block[(arena, stop)]

 length = stop - start
 seq = self._len_to_seq[length]
 seq.remove(block)
 if not seq:
 del self._len_to_seq[length]
 self._lengths.remove(length)

 return start, stop

 def _remove_allocated_block(self, block):
 arena, start, stop = block
 blocks = self._allocated_blocks[arena]
 blocks.remove((start, stop))
 if not blocks:
 # Arena is entirely free, discard it from this process
 self._discard_arena(arena)

 def _free_pending_blocks(self):
 # Free all the blocks in the pending list - called with the lock held.
 while True:
 try:
 block = self._pending_free_blocks.pop()
 except IndexError:
 break
 self._add_free_block(block)
 self._remove_allocated_block(block)

 def free(self, block):
 # free a block returned by malloc()
 # Since free() can be called asynchronously by the GC, it could happen
 # that it's called while self._lock is held: in that case,
 # self._lock.acquire() would deadlock (issue #12352). To avoid that, a
 # trylock is used instead, and if the lock can't be acquired
 # immediately, the block is added to a list of blocks to be freed
 # synchronously sometimes later from malloc() or free(), by calling
 # _free_pending_blocks() (appending and retrieving from a list is not
 # strictly thread-safe but under CPython it's atomic thanks to the GIL).
 if os.getpid() != self._lastpid:
 raise ValueError(
 "My pid ({0:n}) is not last pid {1:n}".format(
 os.getpid(),self._lastpid))
 if not self._lock.acquire(False):
 # can't acquire the lock right now, add the block to the list of
 # pending blocks to free
 self._pending_free_blocks.append(block)
 else:
 # we hold the lock
 try:
 self._n_frees += 1
 self._free_pending_blocks()
 self._add_free_block(block)
 self._remove_allocated_block(block)
 finally:
 self._lock.release()

 def malloc(self, size):
 # return a block of right size (possibly rounded up)
 if size < 0:
 raise ValueError("Size {0:n} out of range".format(size))
 if sys.maxsize <= size:
 raise OverflowError("Size {0:n} too large".format(size))
 if os.getpid() != self._lastpid:
 self.__init__() # reinitialize after fork
 with self._lock:
 self._n_mallocs += 1
 # allow pending blocks to be marked available
 self._free_pending_blocks()
 size = self._roundup(max(size, 1), self._alignment)
 (arena, start, stop) = self._malloc(size)
 real_stop = start + size
 if real_stop < stop:
 # if the returned block is larger than necessary, mark
 # the remainder available
 self._add_free_block((arena, real_stop, stop))
 self._allocated_blocks[arena].add((start, real_stop))
 return (arena, start, real_stop)

#
# Class wrapping a block allocated out of a Heap -- can be inherited by child process
#

class BufferWrapper(object):

 _heap = Heap()

 def __init__(self, size):
 if size < 0:
 raise ValueError("Size {0:n} out of range".format(size))
 if sys.maxsize <= size:
 raise OverflowError("Size {0:n} too large".format(size))
 block = BufferWrapper._heap.malloc(size)
 self._state = (block, size)
 util.Finalize(self, BufferWrapper._heap.free, args=(block,))

 def create_memoryview(self):
 (arena, start, stop), size = self._state
 return memoryview(arena.buffer)[start:start+size]