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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 17:02:57 +0000 |
commit | 195750f2ca355e29d51219c58ecb2c1d83692717 (patch) | |
tree | 463c354bf8789bf6545f771a0c52587cbd61fabb | |
parent | 22be2dbd8e70322239f70e53ace2a552425e3665 (diff) | |
download | bitbake-195750f2ca355e29d51219c58ecb2c1d83692717.tar.gz |
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>
Signed-off-by: Etienne Cordonnier <ecordonnier@snap.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
-rw-r--r-- | lib/bb/siggen.py | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/lib/bb/siggen.py b/lib/bb/siggen.py index 0e79404f7..26e0243b0 100644 --- a/lib/bb/siggen.py +++ b/lib/bb/siggen.py @@ -349,19 +349,19 @@ class SignatureGeneratorBasic(SignatureGenerator): data = self.basehash[tid] for dep in self.runtaskdeps[tid]: - data = data + self.get_unihash(dep) + data += self.get_unihash(dep) for (f, cs) in self.file_checksum_values[tid]: if cs: if "/./" in f: - data = data + "./" + f.split("/./")[1] - data = data + cs + data += "./" + f.split("/./")[1] + data += cs if tid in self.taints: if self.taints[tid].startswith("nostamp:"): - data = data + self.taints[tid][8:] + data += self.taints[tid][8:] else: - data = data + self.taints[tid] + data += self.taints[tid] h = hashlib.sha256(data.encode("utf-8")).hexdigest() self.taskhash[tid] = h |