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mirror of https://github.com/golang/go synced 2024-11-21 21:34:40 -07:00

syscall: cache environment variables on Plan 9.

This can drastically reduce the number of system
calls made by programs that repeatedly query the
environment.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5599054
This commit is contained in:
Anthony Martin 2012-01-31 18:14:02 -08:00
parent 82555d7b40
commit 1583931bcf

View File

@ -6,69 +6,123 @@
package syscall
import "errors"
import (
"errors"
"sync"
)
func Getenv(key string) (value string, found bool) {
if len(key) == 0 {
return "", false
}
f, e := Open("/env/"+key, O_RDONLY)
if e != nil {
return "", false
}
defer Close(f)
var (
// envOnce guards initialization by copyenv, which populates env.
envOnce sync.Once
l, _ := Seek(f, 0, 2)
Seek(f, 0, 0)
// envLock guards env.
envLock sync.RWMutex
// env maps from an environment variable to its value.
env map[string]string
)
func readenv(key string) (string, error) {
fd, err := Open("/env/"+key, O_RDONLY)
if err != nil {
return "", err
}
defer Close(fd)
l, _ := Seek(fd, 0, 2)
Seek(fd, 0, 0)
buf := make([]byte, l)
n, e := Read(f, buf)
if e != nil {
return "", false
n, err := Read(fd, buf)
if err != nil {
return "", err
}
if n > 0 && buf[n-1] == 0 {
buf = buf[:n-1]
}
return string(buf), true
return string(buf), nil
}
func writeenv(key, value string) error {
fd, err := Create("/env/"+key, O_RDWR, 0666)
if err != nil {
return err
}
defer Close(fd)
_, err = Write(fd, []byte(value))
return err
}
func copyenv() {
env = make(map[string]string)
fd, err := Open("/env", O_RDONLY)
if err != nil {
return
}
defer Close(fd)
files, err := readdirnames(fd)
if err != nil {
return
}
for _, key := range files {
v, err := readenv(key)
if err != nil {
continue
}
env[key] = v
}
}
func Getenv(key string) (value string, found bool) {
envOnce.Do(copyenv)
if len(key) == 0 {
return "", false
}
envLock.RLock()
defer envLock.RUnlock()
v, ok := env[key]
if !ok {
return "", false
}
return v, true
}
func Setenv(key, value string) error {
envOnce.Do(copyenv)
if len(key) == 0 {
return errors.New("bad arg in system call")
return errors.New("zero length key")
}
f, e := Create("/env/"+key, O_RDWR, 0666)
if e != nil {
return e
}
defer Close(f)
envLock.Lock()
defer envLock.Unlock()
_, e = Write(f, []byte(value))
err := writeenv(key, value)
if err != nil {
return err
}
env[key] = value
return nil
}
func Clearenv() {
envOnce.Do(copyenv) // prevent copyenv in Getenv/Setenv
envLock.Lock()
defer envLock.Unlock()
env = make(map[string]string)
RawSyscall(SYS_RFORK, RFCENVG, 0, 0)
}
func Environ() []string {
env := make([]string, 0, 100)
f, e := Open("/env", O_RDONLY)
if e != nil {
panic(e)
envOnce.Do(copyenv)
envLock.RLock()
defer envLock.RUnlock()
a := make([]string, len(env))
i := 0
for k, v := range env {
a[i] = k + "=" + v
i++
}
defer Close(f)
names, e := readdirnames(f)
if e != nil {
panic(e)
}
for _, k := range names {
if v, ok := Getenv(k); ok {
env = append(env, k+"="+v)
}
}
return env[0:len(env)]
return a
}