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Commitcfccd8a

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Merge pull request#28831 from tacaswell/fix/better_fm_cache
Improve the cache when getting font metrics
2 parentsea40d72 +94d6fc8 commitcfccd8a

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2 files changed

+119
-11
lines changed

2 files changed

+119
-11
lines changed

‎lib/matplotlib/tests/test_text.py‎

Lines changed: 38 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,6 @@
11
fromdatetimeimportdatetime
2+
importgc
3+
importinspect
24
importio
35
importwarnings
46

@@ -874,14 +876,21 @@ def test_pdf_chars_beyond_bmp():
874876

875877
@needs_usetex
876878
deftest_metrics_cache():
877-
mpl.text._get_text_metrics_with_cache_impl.cache_clear()
879+
# dig into the signature to get the mutable default used as a cache
880+
renderer_cache=inspect.signature(
881+
mpl.text._get_text_metrics_function
882+
).parameters['_cache'].default
883+
884+
renderer_cache.clear()
878885

879886
fig=plt.figure()
880887
fig.text(.3,.5,"foo\nbar")
881888
fig.text(.3,.5,"foo\nbar",usetex=True)
882889
fig.text(.5,.5,"foo\nbar",usetex=True)
883890
fig.canvas.draw()
884891
renderer=fig._get_renderer()
892+
assertrendererinrenderer_cache
893+
885894
ys= {}# mapping of strings to where they were drawn in y with draw_tex.
886895

887896
defcall(*args,**kwargs):
@@ -897,12 +906,39 @@ def call(*args, **kwargs):
897906
# get incorrectly reused by the first TeX string.
898907
assertlen(ys["foo"])==len(ys["bar"])==1
899908

900-
info=mpl.text._get_text_metrics_with_cache_impl.cache_info()
909+
info=renderer_cache[renderer].cache_info()
901910
# Every string gets a miss for the first layouting (extents), then a hit
902911
# when drawing, but "foo\nbar" gets two hits as it's drawn twice.
903912
assertinfo.hits>info.misses
904913

905914

915+
deftest_metrics_cache2():
916+
# dig into the signature to get the mutable default used as a cache
917+
renderer_cache=inspect.signature(
918+
mpl.text._get_text_metrics_function
919+
).parameters['_cache'].default
920+
gc.collect()
921+
renderer_cache.clear()
922+
923+
defhelper():
924+
fig,ax=plt.subplots()
925+
fig.draw_without_rendering()
926+
# show we hit the outer cache
927+
assertlen(renderer_cache)==1
928+
func=renderer_cache[fig.canvas.get_renderer()]
929+
cache_info=func.cache_info()
930+
# show we hit the inner cache
931+
assertcache_info.currsize>0
932+
assertcache_info.currsize==cache_info.misses
933+
assertcache_info.hits>cache_info.misses
934+
plt.close(fig)
935+
936+
helper()
937+
gc.collect()
938+
# show the outer cache has a lifetime tied to the renderer (via the figure)
939+
assertlen(renderer_cache)==0
940+
941+
906942
deftest_annotate_offset_fontsize():
907943
# Test that offset_fontsize parameter works and uses accurate values
908944
fig,ax=plt.subplots()

‎lib/matplotlib/text.py‎

Lines changed: 81 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -64,17 +64,89 @@ def _get_textbox(text, renderer):
6464

6565
def_get_text_metrics_with_cache(renderer,text,fontprop,ismath,dpi):
6666
"""Call ``renderer.get_text_width_height_descent``, caching the results."""
67-
# Cached based on a copy of fontprop so that later in-place mutations of
68-
# the passed-in argument do not mess up the cache.
69-
return_get_text_metrics_with_cache_impl(
70-
weakref.ref(renderer),text,fontprop.copy(),ismath,dpi)
7167

68+
# hit the outer cache layer and get the function to compute the metrics
69+
# for this renderer instance
70+
get_text_metrics=_get_text_metrics_function(renderer)
71+
# call the function to compute the metrics and return
72+
#
73+
# We pass a copy of the fontprop because FontProperties is both mutable and
74+
# has a `__hash__` that depends on that mutable state. This is not ideal
75+
# as it means the hash of an object is not stable over time which leads to
76+
# very confusing behavior when used as keys in dictionaries or hashes.
77+
returnget_text_metrics(text,fontprop.copy(),ismath,dpi)
7278

73-
@functools.lru_cache(4096)
74-
def_get_text_metrics_with_cache_impl(
75-
renderer_ref,text,fontprop,ismath,dpi):
76-
# dpi is unused, but participates in cache invalidation (via the renderer).
77-
returnrenderer_ref().get_text_width_height_descent(text,fontprop,ismath)
79+
80+
def_get_text_metrics_function(input_renderer,_cache=weakref.WeakKeyDictionary()):
81+
"""
82+
Helper function to provide a two-layered cache for font metrics
83+
84+
85+
To get the rendered size of a size of string we need to know:
86+
- what renderer we are using
87+
- the current dpi of the renderer
88+
- the string
89+
- the font properties
90+
- is it math text or not
91+
92+
We do this as a two-layer cache with the outer layer being tied to a
93+
renderer instance and the inner layer handling everything else.
94+
95+
The outer layer is implemented as `.WeakKeyDictionary` keyed on the
96+
renderer. As long as someone else is holding a hard ref to the renderer
97+
we will keep the cache alive, but it will be automatically dropped when
98+
the renderer is garbage collected.
99+
100+
The inner layer is provided by an lru_cache with a large maximum size (such
101+
that we expect very few cache misses in actual use cases). As the
102+
dpi is mutable on the renderer, we need to explicitly include it as part of
103+
the cache key on the inner layer even though we do not directly use it (it is
104+
used in the method call on the renderer).
105+
106+
This function takes a renderer and returns a function that can be used to
107+
get the font metrics.
108+
109+
Parameters
110+
----------
111+
input_renderer : maplotlib.backend_bases.RendererBase
112+
The renderer to set the cache up for.
113+
114+
_cache : dict, optional
115+
We are using the mutable default value to attach the cache to the function.
116+
117+
In principle you could pass a different dict-like to this function to inject
118+
a different cache, but please don't. This is an internal function not meant to
119+
be reused outside of the narrow context we need it for.
120+
121+
There is a possible race condition here between threads, we may need to drop the
122+
mutable default and switch to a threadlocal variable in the future.
123+
124+
"""
125+
if (_text_metrics:=_cache.get(input_renderer,None))isNone:
126+
# We are going to include this in the closure we put as values in the
127+
# cache. Closing over a hard-ref would create an unbreakable reference
128+
# cycle.
129+
renderer_ref=weakref.ref(input_renderer)
130+
131+
# define the function locally to get a new lru_cache per renderer
132+
@functools.lru_cache(4096)
133+
# dpi is unused, but participates in cache invalidation (via the renderer).
134+
def_text_metrics(text,fontprop,ismath,dpi):
135+
# this should never happen under normal use, but this is a better error to
136+
# raise than an AttributeError on `None`
137+
if (local_renderer:=renderer_ref())isNone:
138+
raiseRuntimeError(
139+
"Trying to get text metrics for a renderer that no longer exists. "
140+
"This should never happen and is evidence of a bug elsewhere."
141+
)
142+
# do the actual method call we need and return the result
143+
returnlocal_renderer.get_text_width_height_descent(text,fontprop,ismath)
144+
145+
# stash the function for later use.
146+
_cache[input_renderer]=_text_metrics
147+
148+
# return the inner function
149+
return_text_metrics
78150

79151

80152
@_docstring.interpd

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