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The prefix computation for onepass was incorrectly returning
complete=true when it encountered a beginning-of-text empty width match
(^) in the middle of an expression.
Fix by returning complete only when the prefix is followed by $ and then
an accepting state.
Fixes #11175.
Change-Id: Ie9c4cf5f76c1d2c904a6fb2f016cedb265c19fde
Reviewed-on: https://go-review.googlesource.com/16200
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
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This helps users who wish to use separate Regexps in each goroutine to
avoid lock contention. Previously they had to parse the expression
multiple times to achieve this.
I used variants of the included benchmark to evaluate this change. I
used the arguments -benchtime 20s -cpu 1,2,4,8,16 on a machine with 16
hardware cores.
Comparing a single shared Regexp vs. copied Regexps, we can see that
lock contention causes huge slowdowns at higher levels of parallelism.
The copied version shows the expected linear speedup.
name old time/op new time/op delta
MatchParallel 366ns ± 0% 370ns ± 0% +1.09% (p=0.000 n=10+8)
MatchParallel-2 324ns ±28% 184ns ± 1% -43.37% (p=0.000 n=10+10)
MatchParallel-4 352ns ± 5% 93ns ± 1% -73.70% (p=0.000 n=9+10)
MatchParallel-8 480ns ± 3% 46ns ± 0% -90.33% (p=0.000 n=9+8)
MatchParallel-16 510ns ± 8% 24ns ± 6% -95.36% (p=0.000 n=10+8)
I also compared a modified version of Regexp that has no mutex and a
single machine (the "RegexpForSingleGoroutine" rsc mentioned in
https://github.com/golang/go/issues/8232#issuecomment-66096128).
In this next test, I compared using N copied Regexps vs. N separate
RegexpForSingleGoroutines. This shows that, even for this relatively
simple regex, avoiding the lock entirely would only buy about 10-12%
further improvement.
name old time/op new time/op delta
MatchParallel 370ns ± 0% 322ns ± 0% -12.97% (p=0.000 n=8+8)
MatchParallel-2 184ns ± 1% 162ns ± 1% -11.60% (p=0.000 n=10+10)
MatchParallel-4 92.7ns ± 1% 81.1ns ± 2% -12.43% (p=0.000 n=10+10)
MatchParallel-8 46.4ns ± 0% 41.8ns ±10% -9.78% (p=0.000 n=8+10)
MatchParallel-16 23.7ns ± 6% 20.6ns ± 1% -13.14% (p=0.000 n=8+8)
Updates #8232.
Change-Id: I15201a080c363d1b44104eafed46d8df5e311902
Reviewed-on: https://go-review.googlesource.com/16110
Reviewed-by: Russ Cox <rsc@golang.org>
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Regular expressions involving a (x){0} term are
simplified by removing this term from the
expression, just before the expression is compiled.
The number of subexpressions is evaluated before
the simplification. The number of capture instructions
in the compiled expressions is not necessarily in line
with the number of subexpressions.
When the ReplaceAll(String) methods are used, a number
of capture slots (nmatch) is evaluated as 2*(s+1)
(s being the number of subexpressions).
In some case, it can be higher than the number of capture
instructions evaluated at compile time, resulting in a
panic when the internal slices of regexp.machine
are resized to this value.
Fixed by capping the number of capture slots to the number
of capture instructions.
I must say I do not really see the benefits of setting
nmatch lower than re.prog.NumCap using this 2*(s+1) formula,
so perhaps this can be further simplified.
Fixes #11178
Fixes #11176
Change-Id: I21415e8ef2dd5f2721218e9a679f7f6bfb76ae9b
Reviewed-on: https://go-review.googlesource.com/14013
Reviewed-by: Russ Cox <rsc@golang.org>
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Fixes #10319
Change-Id: I96015b0e1dff30a72de11fea3837638b5c672891
Reviewed-on: https://go-review.googlesource.com/8501
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
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The stack blowout can no longer happen,
but we can still test that too-complex regexps
are rejected.
Replacement for CL 162770043.
LGTM=iant, r
R=r, iant
CC=bradfitz, golang-codereviews
https://golang.org/cl/162860043
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Preparation was in CL 134570043.
This CL contains only the effect of 'hg mv src/pkg/* src'.
For more about the move, see golang.org/s/go14nopkg.
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