From: Daniel Martí Date: Sun, 3 Mar 2019 15:30:24 +0000 (+0000) Subject: os/exec: preallocate for Cmd.childFiles X-Git-Tag: go1.13beta1~1243 X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=59712fd03d37c0d17cce9f6605a9cc87fa0d4870;p=gostls13.git os/exec: preallocate for Cmd.childFiles We're always going to add stdin, stdout, and stderr to childFiles, so its length will be at least three. The final length will be those three elements plus however many files were given via ExtraFiles. Allocate for that final length directly, saving two slice growth allocs in the common case where ExtraFiles is empty. name old time/op new time/op delta ExecEcho-8 435µs ± 0% 435µs ± 0% ~ (p=0.394 n=6+6) name old alloc/op new alloc/op delta ExecEcho-8 6.39kB ± 0% 6.37kB ± 0% -0.39% (p=0.002 n=6+6) name old allocs/op new allocs/op delta ExecEcho-8 36.0 ± 0% 34.0 ± 0% -5.56% (p=0.002 n=6+6) Change-Id: Ib702c0da1e43f0a55ed937af6d45fca6a170e8f3 Reviewed-on: https://go-review.googlesource.com/c/164898 Run-TryBot: Daniel Martí TryBot-Result: Gobot Gobot Reviewed-by: Brad Fitzpatrick --- diff --git a/src/os/exec/exec.go b/src/os/exec/exec.go index 7b2b2ebd92..30fd64a4b1 100644 --- a/src/os/exec/exec.go +++ b/src/os/exec/exec.go @@ -376,6 +376,7 @@ func (c *Cmd) Start() error { } } + c.childFiles = make([]*os.File, 0, 3+len(c.ExtraFiles)) type F func(*Cmd) (*os.File, error) for _, setupFd := range []F{(*Cmd).stdin, (*Cmd).stdout, (*Cmd).stderr} { fd, err := setupFd(c)