tpl/partials: Fix cache locking

To make sure a cached partial is ony executed  exactly once.

Performance same:

```bash
name                         old time/op    new time/op    delta
TemplateParamsKeysToLower-4    17.2µs ± 0%    16.5µs ± 0%   ~     (p=1.000 n=1+1)
Partial-4                      18.6µs ± 0%    19.4µs ± 0%   ~     (p=1.000 n=1+1)
PartialCached-4                64.2ns ± 0%    63.7ns ± 0%   ~     (p=1.000 n=1+1)

name                         old alloc/op   new alloc/op   delta
TemplateParamsKeysToLower-4    2.66kB ± 0%    2.66kB ± 0%   ~     (all equal)
Partial-4                      1.31kB ± 0%    1.31kB ± 0%   ~     (all equal)
PartialCached-4                 0.00B          0.00B        ~     (all equal)

name                         old allocs/op  new allocs/op  delta
TemplateParamsKeysToLower-4      92.0 ± 0%      92.0 ± 0%   ~     (all equal)
Partial-4                        41.0 ± 0%      41.0 ± 0%   ~     (all equal)
```

diff --git a/tpl/partials/partials.go b/tpl/partials/partials.go
index d3a75edadcea5cc5175566717ac8617d5694d479..d999041be163ef8fbbb50af01128ff2e058d3d16 100644 (file)
--- a/tpl/partials/partials.go
+++ b/tpl/partials/partials.go
@@ -110,27 +110,30 @@ func (ns *Namespace) IncludeCached(name string, context interface{}, variant ...
        return ns.getOrCreate(key, name, context)
 }
 
-func (ns *Namespace) getOrCreate(key, name string, context interface{}) (p interface{}, err error) {
-       var ok bool
+func (ns *Namespace) getOrCreate(key, name string, context interface{}) (interface{}, error) {
 
        ns.cachedPartials.RLock()
-       p, ok = ns.cachedPartials.p[key]
+       p, ok := ns.cachedPartials.p[key]
        ns.cachedPartials.RUnlock()
 
        if ok {
-               return
+               return p, nil
        }
 
        ns.cachedPartials.Lock()
-       if p, ok = ns.cachedPartials.p[key]; !ok {
-               ns.cachedPartials.Unlock()
-               p, err = ns.Include(name, context)
+       defer ns.cachedPartials.Unlock()
 
-               ns.cachedPartials.Lock()
-               ns.cachedPartials.p[key] = p
+       // Double-check.
+       if p, ok = ns.cachedPartials.p[key]; ok {
+               return p, nil
+       }
 
+       p, err := ns.Include(name, context)
+       if err != nil {
+               return nil, err
        }
-       ns.cachedPartials.Unlock()
 
-       return
+       ns.cachedPartials.p[key] = p
+
+       return p, nil
 }