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author | Etienne Cordonnier <ecordonnier@snap.com> | 2023-02-01 15:19:00 +0100 |
---|---|---|
committer | Richard Purdie <richard.purdie@linuxfoundation.org> | 2023-02-04 17:03:15 +0000 |
commit | edb60ef6fd49764174d140ccae04fca65db131e0 (patch) | |
tree | 3945abb66359a2f0a35ada60f1d04aa5c1ff1106 /bitbake/lib/bb/siggen.py | |
parent | de41e1737b6014f651ad8beb08519b3ccbcc34d1 (diff) | |
download | poky-edb60ef6fd49764174d140ccae04fca65db131e0.tar.gz |
bitbake: siggen: Fix inefficient string concatenation
As discussed in https://stackoverflow.com/a/4435752/1710392 , CPython
has an optimization for statements in the form "a = a + b" or "a += b".
It seems that this line does not get optimized, because it has a form a = a + b + c:
data = data + "./" + f.split("/./")[1]
For that reason, it does a copy of data for each iteration, potentially copying megabytes
of data for each iteration.
Changing this line causes SignatureGeneratorBasic::get_taskhash to take 0.06 seconds
instead of 45 seconds on my test setup where SRC_URI points to a big directory.
Note that PEP8 recommends explicitely not to use this optimization which is specific to CPython:
"do not rely on CPython’s efficient implementation of in-place string concatenation for statements in the form a += b or a = a + b"
However, the PEP8 recommended form using "join()" also does not avoid the copy and takes 45 seconds in my test setup:
data = ''.join((data, "./", f.split("/./")[1]))
I have changed the other lines to also use += for consistency only, however those were in the form a = a + b
and were optimized already.
Co-authored-by: JJ Robertson <jrobertson@snap.com>
(Bitbake rev: 195750f2ca355e29d51219c58ecb2c1d83692717)
Signed-off-by: Etienne Cordonnier <ecordonnier@snap.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Diffstat (limited to 'bitbake/lib/bb/siggen.py')
-rw-r--r-- | bitbake/lib/bb/siggen.py | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/bitbake/lib/bb/siggen.py b/bitbake/lib/bb/siggen.py index 0e79404f76..26e0243b00 100644 --- a/bitbake/lib/bb/siggen.py +++ b/bitbake/lib/bb/siggen.py | |||
@@ -349,19 +349,19 @@ class SignatureGeneratorBasic(SignatureGenerator): | |||
349 | 349 | ||
350 | data = self.basehash[tid] | 350 | data = self.basehash[tid] |
351 | for dep in self.runtaskdeps[tid]: | 351 | for dep in self.runtaskdeps[tid]: |
352 | data = data + self.get_unihash(dep) | 352 | data += self.get_unihash(dep) |
353 | 353 | ||
354 | for (f, cs) in self.file_checksum_values[tid]: | 354 | for (f, cs) in self.file_checksum_values[tid]: |
355 | if cs: | 355 | if cs: |
356 | if "/./" in f: | 356 | if "/./" in f: |
357 | data = data + "./" + f.split("/./")[1] | 357 | data += "./" + f.split("/./")[1] |
358 | data = data + cs | 358 | data += cs |
359 | 359 | ||
360 | if tid in self.taints: | 360 | if tid in self.taints: |
361 | if self.taints[tid].startswith("nostamp:"): | 361 | if self.taints[tid].startswith("nostamp:"): |
362 | data = data + self.taints[tid][8:] | 362 | data += self.taints[tid][8:] |
363 | else: | 363 | else: |
364 | data = data + self.taints[tid] | 364 | data += self.taints[tid] |
365 | 365 | ||
366 | h = hashlib.sha256(data.encode("utf-8")).hexdigest() | 366 | h = hashlib.sha256(data.encode("utf-8")).hexdigest() |
367 | self.taskhash[tid] = h | 367 | self.taskhash[tid] = h |