Initial QSfera import

Server/vendor/github.com/longsleep/go-metrics/timing/timing.go

@@ -0,0 +1,69 @@
+package timing
+
+import (
+	"context"
+	"time"
+)
+
+// key is an unexported type for keys defined in this package.
+type key int
+
+// elapsedKey is the key for elapsedRecord which holds start end elapsed time
+// in Contexts.
+const elapsedKey key = 0
+
+type elapsedRecord struct {
+	start   time.Time
+	elapsed time.Duration
+	done    chan bool
+	cancel  context.CancelFunc
+}
+
+// NewContext returns a new Context that carries the start time and calls the
+// provided stopped function then the created Context is cancelled. The stopped
+// function can be nil in which case nothing is called.
+func NewContext(parent context.Context, stopped func(elapsed time.Duration)) context.Context {
+	ctx, cancel := context.WithCancel(parent)
+	recordPtr := &elapsedRecord{
+		start:  time.Now(),
+		done:   make(chan bool),
+		cancel: cancel,
+	}
+	ctx = context.WithValue(ctx, elapsedKey, recordPtr)
+	go func() {
+		<-ctx.Done()
+		recordPtr.elapsed = time.Since(recordPtr.start)
+		close(recordPtr.done)
+		if stopped != nil {
+			stopped(recordPtr.elapsed)
+		}
+	}()
+
+	return ctx
+}
+
+// StartFromContext returns the start time from the provided Context.
+func StartFromContext(ctx context.Context) time.Time {
+	return ctx.Value(elapsedKey).(*elapsedRecord).start
+}
+
+// ElapsedFromContext returns the elapsed time from the provided Context. If the
+// provided context is not yet cancelled the duration from now since start is
+// returned.
+func ElapsedFromContext(ctx context.Context) time.Duration {
+	elapsed := ctx.Value(elapsedKey).(*elapsedRecord).elapsed
+	if elapsed > 0 {
+		return elapsed
+	}
+
+	return time.Since(StartFromContext(ctx))
+}
+
+// CancelContext cancels the provided Context if it carries start time.
+func CancelContext(ctx context.Context) {
+	recordPtr := ctx.Value(elapsedKey).(*elapsedRecord)
+	if recordPtr != nil {
+		recordPtr.cancel()
+		<-recordPtr.done // Wait until done is complete.
+	}
+}