401 lines
14 KiB
Python
401 lines
14 KiB
Python
# ----------------------------------------------------------------------------
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# pyglet
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# Copyright (c) 2006-2008 Alex Holkner
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# Copyright (c) 2008-2020 pyglet contributors
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# All rights reserved.
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#
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# Redistribution and use in source and binary forms, with or without
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# modification, are permitted provided that the following conditions
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# are met:
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#
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# * Redistributions of source code must retain the above copyright
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# notice, this list of conditions and the following disclaimer.
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# * Redistributions in binary form must reproduce the above copyright
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# notice, this list of conditions and the following disclaimer in
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# the documentation and/or other materials provided with the
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# distribution.
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# * Neither the name of pyglet nor the names of its
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# contributors may be used to endorse or promote products
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# derived from this software without specific prior written
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# permission.
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#
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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# COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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# POSSIBILITY OF SUCH DAMAGE.
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# ----------------------------------------------------------------------------
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"""Memory allocation algorithm for vertex arrays and buffers.
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The region allocator is used to allocate vertex indices within a vertex
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domain's multiple buffers. ("Buffer" refers to any abstract buffer presented
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by :py:mod:`pyglet.graphics.vertexbuffer`.
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The allocator will at times request more space from the buffers. The current
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policy is to double the buffer size when there is not enough room to fulfil an
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allocation. The buffer is never resized smaller.
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The allocator maintains references to free space only; it is the caller's
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responsibility to maintain the allocated regions.
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"""
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# Common cases:
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# -regions will be the same size (instances of same object, e.g. sprites)
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# -regions will not usually be resized (only exception is text)
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# -alignment of 4 vertices (glyphs, sprites, images, ...)
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#
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# Optimise for:
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# -keeping regions adjacent, reduce the number of entries in glMultiDrawArrays
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# -finding large blocks of allocated regions quickly (for drawing)
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# -finding block of unallocated space is the _uncommon_ case!
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#
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# Decisions:
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# -don't over-allocate regions to any alignment -- this would require more
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# work in finding the allocated spaces (for drawing) and would result in
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# more entries in glMultiDrawArrays
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# -don't move blocks when they truncate themselves. try not to allocate the
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# space they freed too soon (they will likely need grow back into it later,
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# and growing will usually require a reallocation).
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# -allocator does not track individual allocated regions. Trusts caller
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# to provide accurate (start, size) tuple, which completely describes
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# a region from the allocator's point of view.
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# -this means that compacting is probably not feasible, or would be hideously
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# expensive
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class AllocatorMemoryException(Exception):
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"""The buffer is not large enough to fulfil an allocation.
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Raised by `Allocator` methods when the operation failed due to
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lack of buffer space. The buffer should be increased to at least
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requested_capacity and then the operation retried (guaranteed to
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pass second time).
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"""
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def __init__(self, requested_capacity):
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self.requested_capacity = requested_capacity
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class Allocator:
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"""Buffer space allocation implementation."""
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__slots__ = 'capacity', 'starts', 'sizes'
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def __init__(self, capacity):
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"""Create an allocator for a buffer of the specified capacity.
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:Parameters:
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`capacity` : int
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Maximum size of the buffer.
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"""
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self.capacity = capacity
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# Allocated blocks. Start index and size in parallel lists.
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#
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# # = allocated, - = free
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#
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# 0 3 5 15 20 24 40
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# |###--##########-----####----------------------|
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#
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# starts = [0, 5, 20]
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# sizes = [3, 10, 4]
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#
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# To calculate free blocks:
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# for i in range(0, len(starts)):
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# free_start[i] = starts[i] + sizes[i]
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# free_size[i] = starts[i+1] - free_start[i]
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# free_size[i+1] = self.capacity - free_start[-1]
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self.starts = []
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self.sizes = []
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def set_capacity(self, size):
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"""Resize the maximum buffer size.
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The capaity cannot be reduced.
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:Parameters:
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`size` : int
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New maximum size of the buffer.
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"""
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assert size > self.capacity
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self.capacity = size
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def alloc(self, size):
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"""Allocate memory in the buffer.
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Raises `AllocatorMemoryException` if the allocation cannot be
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fulfilled.
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:Parameters:
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`size` : int
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Size of region to allocate.
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:rtype: int
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:return: Starting index of the allocated region.
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"""
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assert size >= 0
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if size == 0:
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return 0
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# Return start, or raise AllocatorMemoryException
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if not self.starts:
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if size <= self.capacity:
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self.starts.append(0)
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self.sizes.append(size)
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return 0
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else:
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raise AllocatorMemoryException(size)
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# Restart from zero if space exists
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if self.starts[0] > size:
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self.starts.insert(0, 0)
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self.sizes.insert(0, size)
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return 0
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# Allocate in a free space
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free_start = self.starts[0] + self.sizes[0]
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for i, (alloc_start, alloc_size) in enumerate(zip(self.starts[1:], self.sizes[1:])):
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# Danger!
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# i is actually index - 1 because of slicing above...
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# starts[i] points to the block before this free space
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# starts[i+1] points to the block after this free space, and is always valid.
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free_size = alloc_start - free_start
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if free_size == size:
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# Merge previous block with this one (removing this free space)
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self.sizes[i] += free_size + alloc_size
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del self.starts[i+1]
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del self.sizes[i+1]
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return free_start
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elif free_size > size:
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# Increase size of previous block to intrude into this free
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# space.
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self.sizes[i] += size
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return free_start
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free_start = alloc_start + alloc_size
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# Allocate at end of capacity
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free_size = self.capacity - free_start
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if free_size >= size:
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self.sizes[-1] += size
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return free_start
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raise AllocatorMemoryException(self.capacity + size - free_size)
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def realloc(self, start, size, new_size):
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"""Reallocate a region of the buffer.
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This is more efficient than separate `dealloc` and `alloc` calls, as
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the region can often be resized in-place.
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Raises `AllocatorMemoryException` if the allocation cannot be
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fulfilled.
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:Parameters:
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`start` : int
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Current starting index of the region.
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`size` : int
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Current size of the region.
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`new_size` : int
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New size of the region.
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"""
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assert size >= 0 and new_size >= 0
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if new_size == 0:
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if size != 0:
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self.dealloc(start, size)
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return 0
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elif size == 0:
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return self.alloc(new_size)
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# return start, or raise AllocatorMemoryException
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# Truncation is the same as deallocating the tail cruft
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if new_size < size:
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self.dealloc(start + new_size, size - new_size)
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return start
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# Find which block it lives in
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for i, (alloc_start, alloc_size) in enumerate(zip(*(self.starts, self.sizes))):
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p = start - alloc_start
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if p >= 0 and size <= alloc_size - p:
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break
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if not (p >= 0 and size <= alloc_size - p):
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print(list(zip(self.starts, self.sizes)))
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print(start, size, new_size)
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print(p, alloc_start, alloc_size)
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assert p >= 0 and size <= alloc_size - p, 'Region not allocated'
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if size == alloc_size - p:
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# Region is at end of block. Find how much free space is after it.
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is_final_block = i == len(self.starts) - 1
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if not is_final_block:
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free_size = self.starts[i + 1] - (start + size)
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else:
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free_size = self.capacity - (start + size)
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# TODO If region is an entire block being an island in free space,
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# can possibly extend in both directions.
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if free_size == new_size - size and not is_final_block:
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# Merge block with next (region is expanded in place to
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# exactly fill the free space)
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self.sizes[i] += free_size + self.sizes[i + 1]
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del self.starts[i + 1]
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del self.sizes[i + 1]
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return start
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elif free_size > new_size - size:
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# Expand region in place
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self.sizes[i] += new_size - size
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return start
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# The block must be repositioned. Dealloc then alloc.
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# But don't do this! If alloc fails, we've already silently dealloc'd
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# the original block.
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# self.dealloc(start, size)
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# return self.alloc(new_size)
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# It must be alloc'd first. We're not missing an optimisation
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# here, because if freeing the block would've allowed for the block to
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# be placed in the resulting free space, one of the above in-place
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# checks would've found it.
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result = self.alloc(new_size)
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self.dealloc(start, size)
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return result
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def dealloc(self, start, size):
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"""Free a region of the buffer.
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:Parameters:
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`start` : int
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Starting index of the region.
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`size` : int
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Size of the region.
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"""
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assert size >= 0
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if size == 0:
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return
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assert self.starts
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# Find which block needs to be split
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for i, (alloc_start, alloc_size) in enumerate(zip(*(self.starts, self.sizes))):
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p = start - alloc_start
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if p >= 0 and size <= alloc_size - p:
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break
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# Assert we left via the break
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assert p >= 0 and size <= alloc_size - p, 'Region not allocated'
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if p == 0 and size == alloc_size:
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# Remove entire block
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del self.starts[i]
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del self.sizes[i]
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elif p == 0:
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# Truncate beginning of block
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self.starts[i] += size
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self.sizes[i] -= size
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elif size == alloc_size - p:
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# Truncate end of block
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self.sizes[i] -= size
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else:
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# Reduce size of left side, insert block at right side
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# $ = dealloc'd block, # = alloc'd region from same block
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#
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# <------8------>
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# <-5-><-6-><-7->
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# 1 2 3 4
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# #####$$$$$#####
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#
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# 1 = alloc_start
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# 2 = start
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# 3 = start + size
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# 4 = alloc_start + alloc_size
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# 5 = start - alloc_start = p
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# 6 = size
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# 7 = {8} - ({5} + {6}) = alloc_size - (p + size)
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# 8 = alloc_size
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#
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self.sizes[i] = p
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self.starts.insert(i + 1, start + size)
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self.sizes.insert(i + 1, alloc_size - (p + size))
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def get_allocated_regions(self):
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"""Get a list of (aggregate) allocated regions.
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The result of this method is ``(starts, sizes)``, where ``starts`` is
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a list of starting indices of the regions and ``sizes`` their
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corresponding lengths.
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:rtype: (list, list)
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"""
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# return (starts, sizes); len(starts) == len(sizes)
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return self.starts, self.sizes
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def get_fragmented_free_size(self):
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"""Returns the amount of space unused, not including the final
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free block.
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:rtype: int
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"""
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if not self.starts:
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return 0
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# Variation of search for free block.
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total_free = 0
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free_start = self.starts[0] + self.sizes[0]
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for i, (alloc_start, alloc_size) in enumerate(zip(self.starts[1:], self.sizes[1:])):
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total_free += alloc_start - free_start
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free_start = alloc_start + alloc_size
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return total_free
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def get_free_size(self):
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"""Return the amount of space unused.
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:rtype: int
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"""
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if not self.starts:
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return self.capacity
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free_end = self.capacity - (self.starts[-1] + self.sizes[-1])
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return self.get_fragmented_free_size() + free_end
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def get_usage(self):
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"""Return fraction of capacity currently allocated.
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:rtype: float
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"""
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return 1. - self.get_free_size() / float(self.capacity)
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def get_fragmentation(self):
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"""Return fraction of free space that is not expandable.
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:rtype: float
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"""
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free_size = self.get_free_size()
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if free_size == 0:
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return 0.
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return self.get_fragmented_free_size() / float(self.get_free_size())
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def __str__(self):
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return 'allocs=' + repr(list(zip(self.starts, self.sizes)))
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def __repr__(self):
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return '<%s %s>' % (self.__class__.__name__, str(self))
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