Sleep: use timers and return context.Canceled in ctx.Done()

Signed-off-by: Juanjo Alvarez <[email protected]>

Author: Juanjo Alvarez

sql/expression/function/sleep.go

@@ -1,11 +1,11 @@
 package function
 
 import (
+	"context"
 	"fmt"
-	"time"
-
 	"github.com/src-d/go-mysql-server/sql"
 	"github.com/src-d/go-mysql-server/sql/expression"
+	"time"
 )
 
 // Sleep is a function that just waits for the specified number of seconds
@@ -37,10 +37,13 @@ func (s *Sleep) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 		return nil, err
 	}
 
+	t := time.NewTimer(time.Duration(child.(float64) * 1000) * time.Millisecond)
+	defer t.Stop()
+
 	select {
-	case <-time.After(time.Duration(child.(float64) * 1000) * time.Millisecond):
-		return 0, nil
 	case <-ctx.Done():
+		return 0, context.Canceled
+	case <-t.C:
 		return 0, nil
 	}
 }