Package expvar provides a standardized interface to public variables, such as operation counters in servers. It exposes these variables via HTTP at /debug/vars in JSON format.
Operations to set or modify these public variables are atomic.
In addition to adding the HTTP handler, this package registers the following variables:
cmdline os.Args memstats runtime.Memstats
The package is sometimes only imported for the side effect of registering its HTTP handler and the above variables. To use it this way, link this package into your program:
import _ "expvar"
func Do(f func(KeyValue))
Do calls f for each exported variable. The global variable map is locked during the iteration, but existing entries may be concurrently updated.
func Handler() http.Handler
Handler returns the expvar HTTP Handler.
This is only needed to install the handler in a non-standard location.
func Publish(name string, v Var)
Publish declares a named exported variable. This should be called from a package's init function when it creates its Vars. If the name is already registered then this will log.Panic.
Float is a 64-bit float variable that satisfies the Var interface.
type Float struct {
// contains filtered or unexported fields
} func NewFloat(name string) *Float
func (v *Float) Add(delta float64)
Add adds delta to v.
func (v *Float) Set(value float64)
Set sets v to value.
func (v *Float) String() string
func (v *Float) Value() float64
Func implements Var by calling the function and formatting the returned value using JSON.
type Func func() interface{} func (f Func) String() string
func (f Func) Value() interface{} Int is a 64-bit integer variable that satisfies the Var interface.
type Int struct {
// contains filtered or unexported fields
} func NewInt(name string) *Int
func (v *Int) Add(delta int64)
func (v *Int) Set(value int64)
func (v *Int) String() string
func (v *Int) Value() int64
KeyValue represents a single entry in a Map.
type KeyValue struct {
Key string
Value Var
} Map is a string-to-Var map variable that satisfies the Var interface.
type Map struct {
// contains filtered or unexported fields
} func NewMap(name string) *Map
func (v *Map) Add(key string, delta int64)
Add adds delta to the *Int value stored under the given map key.
func (v *Map) AddFloat(key string, delta float64)
AddFloat adds delta to the *Float value stored under the given map key.
func (v *Map) Do(f func(KeyValue))
Do calls f for each entry in the map. The map is locked during the iteration, but existing entries may be concurrently updated.
func (v *Map) Get(key string) Var
func (v *Map) Init() *Map
Init removes all keys from the map.
func (v *Map) Set(key string, av Var)
func (v *Map) String() string
String is a string variable, and satisfies the Var interface.
type String struct {
// contains filtered or unexported fields
} func NewString(name string) *String
func (v *String) Set(value string)
func (v *String) String() string
String implements the Val interface. To get the unquoted string use Value.
func (v *String) Value() string
Var is an abstract type for all exported variables.
type Var interface {
// String returns a valid JSON value for the variable.
// Types with String methods that do not return valid JSON
// (such as time.Time) must not be used as a Var.
String() string
} func Get(name string) Var
Get retrieves a named exported variable. It returns nil if the name has not been registered.
© Google, Inc.
Licensed under the Creative Commons Attribution License 3.0.
https://golang.org/pkg/expvar/