mirror of https://github.com/golang/go.git
cf26fbb1f6
When one has a []byte on hand, but desires to call the Parse functions,
the conversion from []byte to string would allocate.
var b []byte = ...
v, err := strconv.ParseXXX(string(b), ...)
This changes it such that the input string never escapes from
any of the Parse functions. Together with the compiler optimization
where the compiler stack allocates any string smaller than 32B
this makes most valid inputs for strconv.ParseXXX(string(b), ...)
not require an allocation for the input string.
For example, the longest int64 or uint64 encoded in decimal is 20B.
Also, the longest decimal formatting of a float64 in appendix B
of RFC 8785 is 25B.
Previously, this was not possible since the input leaked to the error,
which causes the prover to give up and instead heap copy the []byte.
We fix this by copying the input string in the error case.
The advantage of this change is that you can now call strconv.ParseXXX
with a []byte without allocations (most times) in the non-error case.
The detriment is that the error-case now has an extra allocation.
We should optimize for the non-error path, rather than the error path.
The effects of this change is transitively seen through packages
that must use strconv.ParseXXX on a []byte such as "encoding/json":
name old time/op new time/op delta
UnmarshalFloat64 186ns 157ns -15.89% (p=0.000 n=10+10)
name old alloc/op new alloc/op delta
UnmarshalFloat64 148B 144B -2.70% (p=0.000 n=10+10)
name old allocs/op new allocs/op delta
UnmarshalFloat64 2.00 1.00 -50.00% (p=0.000 n=10+10)
In order for "encoding/json" to benefit, there needs to be a
small change made to how "encoding/json" calls strconv.ParseXXX.
That will be a future change.
Credit goes to Jeff Wendling for a similar patch.
Fixes #42429
Change-Id: I512d6927f965f82e95bd7ec14a28a587f23b7203
Reviewed-on: https://go-review.googlesource.com/c/go/+/345488
Reviewed-by: Martin Möhrmann <martin@golang.org>
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Auto-Submit: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
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| archive | ||
| bufio | ||
| builtin | ||
| bytes | ||
| cmd | ||
| compress | ||
| container | ||
| context | ||
| crypto | ||
| database/sql | ||
| debug | ||
| embed | ||
| encoding | ||
| errors | ||
| expvar | ||
| flag | ||
| fmt | ||
| go | ||
| hash | ||
| html | ||
| image | ||
| index/suffixarray | ||
| internal | ||
| io | ||
| log | ||
| math | ||
| mime | ||
| net | ||
| os | ||
| path | ||
| plugin | ||
| reflect | ||
| regexp | ||
| runtime | ||
| sort | ||
| strconv | ||
| strings | ||
| sync | ||
| syscall | ||
| testdata | ||
| testing | ||
| text | ||
| time | ||
| unicode | ||
| unsafe | ||
| vendor | ||
| Make.dist | ||
| README.vendor | ||
| all.bash | ||
| all.bat | ||
| all.rc | ||
| bootstrap.bash | ||
| buildall.bash | ||
| clean.bash | ||
| clean.bat | ||
| clean.rc | ||
| cmp.bash | ||
| go.mod | ||
| go.sum | ||
| make.bash | ||
| make.bat | ||
| make.rc | ||
| race.bash | ||
| race.bat | ||
| run.bash | ||
| run.bat | ||
| run.rc | ||
README.vendor
Vendoring in std and cmd
========================
The Go command maintains copies of external packages needed by the
standard library in the src/vendor and src/cmd/vendor directories.
In GOPATH mode, imports of vendored packages are resolved to these
directories following normal vendor directory logic
(see golang.org/s/go15vendor).
In module mode, std and cmd are modules (defined in src/go.mod and
src/cmd/go.mod). When a package outside std or cmd is imported
by a package inside std or cmd, the import path is interpreted
as if it had a "vendor/" prefix. For example, within "crypto/tls",
an import of "golang.org/x/crypto/cryptobyte" resolves to
"vendor/golang.org/x/crypto/cryptobyte". When a package with the
same path is imported from a package outside std or cmd, it will
be resolved normally. Consequently, a binary may be built with two
copies of a package at different versions if the package is
imported normally and vendored by the standard library.
Vendored packages are internally renamed with a "vendor/" prefix
to preserve the invariant that all packages have distinct paths.
This is necessary to avoid compiler and linker conflicts. Adding
a "vendor/" prefix also maintains the invariant that standard
library packages begin with a dotless path element.
The module requirements of std and cmd do not influence version
selection in other modules. They are only considered when running
module commands like 'go get' and 'go mod vendor' from a directory
in GOROOT/src.
Maintaining vendor directories
==============================
Before updating vendor directories, ensure that module mode is enabled.
Make sure GO111MODULE=off is not set ('on' or 'auto' should work).
Requirements may be added, updated, and removed with 'go get'.
The vendor directory may be updated with 'go mod vendor'.
A typical sequence might be:
cd src
go get -d golang.org/x/net@latest
go mod tidy
go mod vendor
Use caution when passing '-u' to 'go get'. The '-u' flag updates
modules providing all transitively imported packages, not only
the module providing the target package.
Note that 'go mod vendor' only copies packages that are transitively
imported by packages in the current module. If a new package is needed,
it should be imported before running 'go mod vendor'.