From 2ca5d105b00353d3f3aa4da023e405b0550117d0 Mon Sep 17 00:00:00 2001
From: Sameer Ajmani <sameer@golang.org>
Date: Mon, 6 Feb 2017 13:21:57 -0500
Subject: [PATCH] os/user: cache the result of user.Current
This has a notable impact on systems with very large passwd files.
Before:
BenchmarkCurrent-12 30000 42546 ns/op
After:
BenchmarkCurrent-12 20000000 77.5 ns/op
Saved in perf dashboard:
https://perf.golang.org/search?q=upload:20170206.1
Fixes #11625
Change-Id: Iebc9bf122cc64a4cab24ac06843c7b2bc450ded9
Reviewed-on: https://go-review.googlesource.com/36391
Reviewed-by: Ian Lance Taylor <iant@golang.org>
---
src/os/user/lookup.go | 22 +++++++++++++++++++++-
src/os/user/user_test.go | 6 ++++++
2 files changed, 27 insertions(+), 1 deletion(-)
diff --git a/src/os/user/lookup.go b/src/os/user/lookup.go
index 3b4421badd5..2243a25788a 100644
--- a/src/os/user/lookup.go
+++ b/src/os/user/lookup.go
@@ -4,20 +4,40 @@
package user
+import "sync"
+
// Current returns the current user.
func Current() (*User, error) {
- return current()
+ cache.Do(func() { cache.u, cache.err = current() })
+ if cache.err != nil {
+ return nil, cache.err
+ }
+ u := *cache.u // copy
+ return &u, nil
+}
+
+// cache of the current user
+var cache struct {
+ sync.Once
+ u *User
+ err error
}
// Lookup looks up a user by username. If the user cannot be found, the
// returned error is of type UnknownUserError.
func Lookup(username string) (*User, error) {
+ if u, err := Current(); err == nil && u.Username == username {
+ return u, err
+ }
return lookupUser(username)
}
// LookupId looks up a user by userid. If the user cannot be found, the
// returned error is of type UnknownUserIdError.
func LookupId(uid string) (*User, error) {
+ if u, err := Current(); err == nil && u.Uid == uid {
+ return u, err
+ }
return lookupUserId(uid)
}
diff --git a/src/os/user/user_test.go b/src/os/user/user_test.go
index 9d8d94d8dae..73e8ed8de73 100644
--- a/src/os/user/user_test.go
+++ b/src/os/user/user_test.go
@@ -31,6 +31,12 @@ func TestCurrent(t *testing.T) {
}
}
+func BenchmarkCurrent(b *testing.B) {
+ for i := 0; i < b.N; i++ {
+ Current()
+ }
+}
+
func compare(t *testing.T, want, got *User) {
if want.Uid != got.Uid {
t.Errorf("got Uid=%q; want %q", got.Uid, want.Uid)
--
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