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@@ -0,0 +1,102 @@
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+package metrics
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+
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+import (
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+ "fmt"
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+ "reflect"
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+ "sync"
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+)
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+
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+// DuplicateMetric is the error returned by Registry.Register when a metric
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+// already exists. If you mean to Register that metric you must first
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+// Unregister the existing metric.
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+type DuplicateMetric string
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+
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+func (err DuplicateMetric) Error() string {
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+ return fmt.Sprintf("duplicate metric: %s", string(err))
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+}
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+
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+type Registry interface {
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+ // Call the given function for each registered metric.
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+ Each(func(string, interface{}))
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+
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+ // Get the metric by the given name or nil if none is registered.
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+ Get(string) interface{}
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+
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+ // Gets an existing metric or registers the given one.
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+ // The interface can be the metric to register if not found in registry,
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+ // or a function returning the metric for lazy instantiation.
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+ GetOrRegister(string, interface{}) interface{}
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+
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+ // Register the given metric under the given name.
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+ Register(string, interface{}) error
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+}
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+
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+// The standard implementation of a Registry is a mutex-protected map
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+// of names to metrics.
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+type StandardRegistry struct {
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+ metrics map[string]interface{}
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+ mutex sync.Mutex
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+}
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+
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+// Create a new registry.
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+func NewRegistry() Registry {
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+ return &StandardRegistry{metrics: make(map[string]interface{})}
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+}
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+
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+// Call the given function for each registered metric.
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+func (r *StandardRegistry) Each(f func(string, interface{})) {
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+ for name, i := range r.registered() {
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+ f(name, i)
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+ }
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+}
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+
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+// Get the metric by the given name or nil if none is registered.
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+func (r *StandardRegistry) Get(name string) interface{} {
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+ r.mutex.Lock()
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+ defer r.mutex.Unlock()
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+ return r.metrics[name]
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+}
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+
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+// Gets an existing metric or creates and registers a new one. Threadsafe
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+// alternative to calling Get and Register on failure.
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+// The interface can be the metric to register if not found in registry,
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+// or a function returning the metric for lazy instantiation.
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+func (r *StandardRegistry) GetOrRegister(name string, i interface{}) interface{} {
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+ r.mutex.Lock()
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+ defer r.mutex.Unlock()
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+ if metric, ok := r.metrics[name]; ok {
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+ return metric
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+ }
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+ if v := reflect.ValueOf(i); v.Kind() == reflect.Func {
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+ i = v.Call(nil)[0].Interface()
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+ }
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+ r.register(name, i)
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+ return i
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+}
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+
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+// Register the given metric under the given name. Returns a DuplicateMetric
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+// if a metric by the given name is already registered.
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+func (r *StandardRegistry) Register(name string, i interface{}) error {
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+ r.mutex.Lock()
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+ defer r.mutex.Unlock()
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+ return r.register(name, i)
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+}
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+
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+func (r *StandardRegistry) register(name string, i interface{}) error {
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+ if _, ok := r.metrics[name]; ok {
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+ return DuplicateMetric(name)
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+ }
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+
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+ r.metrics[name] = i
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+ return nil
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+}
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+
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+func (r *StandardRegistry) registered() map[string]interface{} {
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+ metrics := make(map[string]interface{}, len(r.metrics))
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+ r.mutex.Lock()
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+ defer r.mutex.Unlock()
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+ for name, i := range r.metrics {
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+ metrics[name] = i
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+ }
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+ return metrics
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+}
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