# ----------------------------------------------------------------------------
# pyglet
# Copyright (c) 2006-2008 Alex Holkner
# All rights reserved.
#
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# modification, are permitted provided that the following conditions
# are met:
#
# * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above copyright
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# the documentation and/or other materials provided with the
# distribution.
# * Neither the name of pyglet nor the names of its
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# derived from this software without specific prior written
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#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# ----------------------------------------------------------------------------
# $Id:$
'''Memory allocation algorithm for vertex arrays and buffers.
The region allocator is used to allocate vertex indices within a vertex
domain's multiple buffers. ("Buffer" refers to any abstract buffer presented
by `pyglet.graphics.vertexbuffer`.
The allocator will at times request more space from thebuffers.Thecurrent import
policy is to double the buffer size when there is not enough room to fulfil an
allocation. The buffer is never resized smaller.
The allocator maintains references to free space only; it is the caller's
responsibility to mantain the allocated regions.
'''
__docformat__ = 'restructuredtext'
__version__ = '$Id: $'
# Common cases:
# -regions will be the same size (instances of same object, e.g. sprites)
# -regions will not usually be resized (only exception is text)
# -alignment of 4 vertices (glyphs, sprites, images, ...)
#
# Optimise for:
# -keeping regions adjacent, reduce the number of entries in glMultiDrawArrays
# -finding large blocks of allocated regions quickly (for drawing)
# -finding block of unallocated space is the _uncommon_ case!
#
# Decisions:
# -don't over-allocate regions to any alignment -- this would require more
# work in finding the allocated spaces (for drawing) and would result in
# more entries in glMultiDrawArrays
# -don't move blocks when they truncate themselves. try not to allocate the
# space they freed too soon (they will likely need grow back into it later,
# and growing will usually require a reallocation).
# -allocator does not track individual allocated regions. Trusts caller
# to provide accurate (start, size) tuple, which completely describes
# a region from the allocator's point of view.
# -this means that compacting is probably not feasible, or would be hideously
# expensive
class AllocatorMemoryException(Exception):
'''The buffer is not large enough to fulfil an allocation.
Raised by `Allocator` methods when the operation failed due to lack of
buffer space. The buffer should be increased to at least
requested_capacity and then the operation retried (guaranteed to
pass second time).
'''
def __init__(self, requested_capacity):
self.requested_capacity = requested_capacity
class Allocator(object):
'''Buffer space allocation implementation.'''
def __init__(self, capacity):
'''Create an allocator for a buffer of the specified capacity.
:Parameters:
`capacity` : int
Maximum size of the buffer.
'''
self.capacity = capacity
# Allocated blocks. Start index and size in parallel lists.
#
# # = allocated, - = free
#
# 0 3 5 15 20 24 40
# |###--##########-----####----------------------|
#
# starts = [0, 5, 20]
# sizes = [3, 10, 4]
#
# To calculate free blocks:
# for i in range(0, len(starts)):
# free_start[i] = starts[i] + sizes[i]
# free_size[i] = starts[i+1] - free_start[i]
# free_size[i+1] = self.capacity - free_start[-1]
self.starts = []
self.sizes = []
def set_capacity(self, size):
'''Resize the maximum buffer size.
The capaity cannot be reduced.
:Parameters:
`size` : int
New maximum size of the buffer.
'''
assert size > self.capacity
self.capacity = size
def alloc(self, size):
'''Allocate memory in the buffer.
Raises `AllocatorMemoryException` if the allocation cannot be
fulfilled.
:Parameters:
`size` : int
Size of region to allocate.
:rtype: int
:return: Starting index of the allocated region.
'''
assert size > 0
# return start
# or raise AllocatorMemoryException
if not self.starts:
if size <= self.capacity:
self.starts.append(0)
self.sizes.append(size)
return 0
else:
raise AllocatorMemoryException(size)
# Allocate in a free space
free_start = self.starts[0] + self.sizes[0]
for i, (alloc_start, alloc_size) in \
enumerate(zip(self.starts[1:], self.sizes[1:])):
# Danger!
# i is actually index - 1 because of slicing above...
# starts[i] points to the block before this free space
# starts[i+1] points to the block after this free space, and is
# always valid.
free_size = alloc_start - free_start
if free_size == size:
# Merge previous block with this one (removing this free space)
self.sizes[i] += free_size + alloc_size
del self.starts[i+1]
del self.sizes[i+1]
return free_start
elif free_size > size:
# Increase size of previous block to intrude into this free
# space.
self.sizes[i] += size
return free_start
free_start = alloc_start + alloc_size
# Allocate at end of capacity
free_size = self.capacity - free_start
if free_size >= size:
self.sizes[-1] += size
return free_start
raise AllocatorMemoryException(self.capacity + size - free_size)
def realloc(self, start, size, new_size):
'''Reallocate a region of the buffer.
This is more efficient than separate `dealloc` and `alloc` calls, as
the region can often be resized in-place.
Raises `AllocatorMemoryException` if the allocation cannot be
fulfilled.
:Parameters:
`start` : int
Current starting index of the region.
`size` : int
Current size of the region.
`new_size` : int
New size of the region.
'''
assert size > 0 and new_size > 0
# return start
# or raise AllocatorMemoryException
# Truncation is the same as deallocating the tail cruft
if new_size < size:
self.dealloc(start + new_size, size - new_size)
return start
# Find which block it lives in
for i, (alloc_start, alloc_size) in \
enumerate(zip(*(self.starts, self.sizes))):
p = start - alloc_start
if p >= 0 and size <= alloc_size - p:
break
if not (p >= 0 and size <= alloc_size - p):
print zip(self.starts, self.sizes)
print start, size, new_size
print p, alloc_start, alloc_size
assert p >= 0 and size <= alloc_size - p, 'Region not allocated'
if size == alloc_size - p:
# Region is at end of block. Find how much free space is after
# it.
is_final_block = i == len(self.starts) - 1
if not is_final_block:
free_size = self.starts[i + 1] - (start + size)
else:
free_size = self.capacity - (start + size)
# TODO If region is an entire block being an island in free space,
# can possibly extend in both directions.
if free_size == new_size - size and not is_final_block:
# Merge block with next (region is expanded in place to
# exactly fill the free space)
self.sizes[i] += free_size + self.sizes[i + 1]
del self.starts[i + 1]
del self.sizes[i + 1]
return start
elif free_size > new_size - size:
# Expand region in place
self.sizes[i] += new_size - size
return start
# The block must be repositioned. Dealloc then alloc.
# But don't do this! If alloc fails, we've already silently dealloc'd
# the original block.
# self.dealloc(start, size)
# return self.alloc(new_size)
# It must be alloc'd first. We're not missing an optimisation
# here, because if freeing the block would've allowed for the block to
# be placed in the resulting free space, one of the above in-place
# checks would've found it.
result = self.alloc(new_size)
self.dealloc(start, size)
return result
def dealloc(self, start, size):
'''Free a region of the buffer.
:Parameters:
`start` : int
Starting index of the region.
`size` : int
Size of the region.
'''
assert size > 0
assert self.starts
# Find which block needs to be split
for i, (alloc_start, alloc_size) in \
enumerate(zip(*(self.starts, self.sizes))):
p = start - alloc_start
if p >= 0 and size <= alloc_size - p:
break
# Assert we left via the break
assert p >= 0 and size <= alloc_size - p, 'Region not allocated'
if p == 0 and size == alloc_size:
# Remove entire block
del self.starts[i]
del self.sizes[i]
elif p == 0:
# Truncate beginning of block
self.starts[i] += size
self.sizes[i] -= size
elif size == alloc_size - p:
# Truncate end of block
self.sizes[i] -= size
else:
# Reduce size of left side, insert block at right side
# $ = dealloc'd block, # = alloc'd region from same block
#
# <------8------>
# <-5-><-6-><-7->
# 1 2 3 4
# #####$$$$$#####
#
# 1 = alloc_start
# 2 = start
# 3 = start + size
# 4 = alloc_start + alloc_size
# 5 = start - alloc_start = p
# 6 = size
# 7 = {8} - ({5} + {6}) = alloc_size - (p + size)
# 8 = alloc_size
#
self.sizes[i] = p
self.starts.insert(i + 1, start + size)
self.sizes.insert(i + 1, alloc_size - (p + size))
def get_allocated_regions(self):
'''Get a list of (aggregate) allocated regions.
The result of this method is ``(starts, sizes)``, where ``starts`` is
a list of starting indices of the regions and ``sizes`` their
corresponding lengths.
:rtype: (list, list)
'''
# return (starts, sizes); len(starts) == len(sizes)
return (self.starts, self.sizes)
def get_fragmented_free_size(self):
'''Returns the amount of space unused, not including the final
free block.
:rtype: int
'''
if not self.starts:
return 0
# Variation of search for free block.
total_free = 0
free_start = self.starts[0] + self.sizes[0]
for i, (alloc_start, alloc_size) in \
enumerate(zip(self.starts[1:], self.sizes[1:])):
total_free += alloc_start - free_start
free_start = alloc_start + alloc_size
return total_free
def get_free_size(self):
'''Return the amount of space unused.
:rtype: int
'''
if not self.starts:
return self.capacity
free_end = self.capacity - (self.starts[-1] + self.sizes[-1])
return self.get_fragmented_free_size() + free_end
def get_usage(self):
'''Return fraction of capacity currently allocated.
:rtype: float
'''
return 1. - self.get_free_size() / float(self.capacity)
def get_fragmentation(self):
'''Return fraction of free space that is not expandable.
:rtype: float
'''
free_size = self.get_free_size()
if free_size == 0:
return 0.
return self.get_fragmented_free_size() / float(self.get_free_size())
def _is_empty(self):
return not self.starts
def __str__(self):
return 'allocs=' + repr(zip(self.starts, self.sizes))
def __repr__(self):
return '<%s %s>' % (self.__class__.__name__, str(self))
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