Micro optimization in Tag Cache

Removed defer from the simple Tag Cache lock & unlock and reduced
execution time for even single field validation by almost 100ns
from 254ns/op to 163ns/op .. Not badd for such a simple modification
and this effect ripples throughout struct validation.

```go
$ go test -cpu=4 -bench=. -benchmem=true
PASS
BenchmarkFieldSuccess-4                            	10000000 163 ns/op	       0 B/op	       0 allocs/op
BenchmarkFieldFailure-4                            	 2000000 673 ns/op	     400 B/op	       4 allocs/op
BenchmarkFieldDiveSuccess-4                        	  500000 3019 ns/op	     480 B/op	      27 allocs/op
BenchmarkFieldDiveFailure-4                        	  500000 3553 ns/op	     880 B/op	      31 allocs/op
BenchmarkFieldCustomTypeSuccess-4                  	 5000000 347 ns/op	      32 B/op	       2 allocs/op
BenchmarkFieldCustomTypeFailure-4                  	 2000000 645 ns/op	     400 B/op	       4 allocs/op
BenchmarkFieldOrTagSuccess-4                       	 1000000 1177 ns/op	      16 B/op	       1 allocs/op
BenchmarkFieldOrTagFailure-4                       	 1000000 1093 ns/op	     432 B/op	       6 allocs/op
BenchmarkStructLevelValidationSuccess-4            	 2000000 702 ns/op	     160 B/op	       6 allocs/op
BenchmarkStructLevelValidationFailure-4            	 1000000 1279 ns/op	     592 B/op	      11 allocs/op
BenchmarkStructSimpleCustomTypeSuccess-4           	 1000000 1010 ns/op	      80 B/op	       5 allocs/op
BenchmarkStructSimpleCustomTypeFailure-4           	 1000000 1544 ns/op	     624 B/op	      11 allocs/op
BenchmarkStructPartialSuccess-4                    	 1000000 1249 ns/op	     400 B/op	      11 allocs/op
BenchmarkStructPartialFailure-4                    	 1000000 1797 ns/op	     816 B/op	      16 allocs/op
BenchmarkStructExceptSuccess-4                     	 2000000 927 ns/op	     368 B/op	       9 allocs/op
BenchmarkStructExceptFailure-4                     	 1000000 1259 ns/op	     400 B/op	      11 allocs/op
BenchmarkStructSimpleCrossFieldSuccess-4           	 1000000 1076 ns/op	     128 B/op	       6 allocs/op
BenchmarkStructSimpleCrossFieldFailure-4           	 1000000 1623 ns/op	     560 B/op	      11 allocs/op
BenchmarkStructSimpleCrossStructCrossFieldSuccess-4	 1000000 1582 ns/op	     176 B/op	       9 allocs/op
BenchmarkStructSimpleCrossStructCrossFieldFailure-4	 1000000 2139 ns/op	     608 B/op	      14 allocs/op
BenchmarkStructSimpleSuccess-4                     	 1000000 1040 ns/op	      48 B/op	       3 allocs/op
BenchmarkStructSimpleFailure-4                     	 1000000 1683 ns/op	     624 B/op	      11 allocs/op
BenchmarkStructSimpleSuccessParallel-4             	 5000000 356 ns/op	      48 B/op	       3 allocs/op
BenchmarkStructSimpleFailureParallel-4             	 2000000 831 ns/op	     624 B/op	      11 allocs/op
BenchmarkStructComplexSuccess-4                    	  200000 6738 ns/op	     512 B/op	      30 allocs/op
BenchmarkStructComplexFailure-4                    	  200000 11387 ns/op	    3415 B/op	      72 allocs/op
BenchmarkStructComplexSuccessParallel-4            	  500000 2330 ns/op	     512 B/op	      30 allocs/op
BenchmarkStructComplexFailureParallel-4            	  300000 4857 ns/op	    3416 B/op	      72 allocs/op
```

```go
$ go test -cpu=4 -bench=. -benchmem=true
PASS
BenchmarkFieldSuccess-4                            	 5000000 254 ns/op	       0 B/op	       0 allocs/op
BenchmarkFieldFailure-4                            	 2000000 779 ns/op	     400 B/op	       4 allocs/op
BenchmarkFieldDiveSuccess-4                        	  500000 3451 ns/op	     480 B/op	      27 allocs/op
BenchmarkFieldDiveFailure-4                        	  300000 3954 ns/op	     880 B/op	      31 allocs/op
BenchmarkFieldCustomTypeSuccess-4                  	 3000000 451 ns/op	      32 B/op	       2 allocs/op
BenchmarkFieldCustomTypeFailure-4                  	 2000000 751 ns/op	     400 B/op	       4 allocs/op
BenchmarkFieldOrTagSuccess-4                       	 1000000 1312 ns/op	      16 B/op	       1 allocs/op
BenchmarkFieldOrTagFailure-4                       	 1000000 1206 ns/op	     432 B/op	       6 allocs/op
BenchmarkStructLevelValidationSuccess-4            	 2000000 829 ns/op	     160 B/op	       6 allocs/op
BenchmarkStructLevelValidationFailure-4            	 1000000 1403 ns/op	     592 B/op	      11 allocs/op
BenchmarkStructSimpleCustomTypeSuccess-4           	 1000000 1238 ns/op	      80 B/op	       5 allocs/op
BenchmarkStructSimpleCustomTypeFailure-4           	 1000000 1771 ns/op	     624 B/op	      11 allocs/op
BenchmarkStructPartialSuccess-4                    	 1000000 1399 ns/op	     400 B/op	      11 allocs/op
BenchmarkStructPartialFailure-4                    	 1000000 1926 ns/op	     816 B/op	      16 allocs/op
BenchmarkStructExceptSuccess-4                     	 2000000 930 ns/op	     368 B/op	       9 allocs/op
BenchmarkStructExceptFailure-4                     	 1000000 1381 ns/op	     400 B/op	      11 allocs/op
BenchmarkStructSimpleCrossFieldSuccess-4           	 1000000 1253 ns/op	     128 B/op	       6 allocs/op
BenchmarkStructSimpleCrossFieldFailure-4           	 1000000 1849 ns/op	     560 B/op	      11 allocs/op
BenchmarkStructSimpleCrossStructCrossFieldSuccess-4	 1000000 1902 ns/op	     176 B/op	       9 allocs/op
BenchmarkStructSimpleCrossStructCrossFieldFailure-4	  500000 2453 ns/op	     608 B/op	      14 allocs/op
BenchmarkStructSimpleSuccess-4                     	 1000000 1182 ns/op	      48 B/op	       3 allocs/op
BenchmarkStructSimpleFailure-4                     	 1000000 1842 ns/op	     624 B/op	      11 allocs/op
BenchmarkStructSimpleSuccessParallel-4             	 5000000 342 ns/op	      48 B/op	       3 allocs/op
BenchmarkStructSimpleFailureParallel-4             	 2000000 665 ns/op	     624 B/op	      11 allocs/op
BenchmarkStructComplexSuccess-4                    	  200000 7924 ns/op	     512 B/op	      30 allocs/op
BenchmarkStructComplexFailure-4                    	  100000 12605 ns/op	    3415 B/op	      72 allocs/op
BenchmarkStructComplexSuccessParallel-4            	 1000000 2421 ns/op	     512 B/op	      30 allocs/op
BenchmarkStructComplexFailureParallel-4            	  300000 4234 ns/op	    3416 B/op	      72 allocs/op
```

Author: joeybloggs

README.md

@@ -310,34 +310,34 @@ Benchmarks
 ```go
 $ go test -cpu=4 -bench=. -benchmem=true
 PASS
-BenchmarkFieldSuccess-4                            	 5000000	       254 ns/op	       0 B/op	       0 allocs/op
-BenchmarkFieldFailure-4                            	 2000000	       779 ns/op	     400 B/op	       4 allocs/op
-BenchmarkFieldDiveSuccess-4                        	  500000	      3451 ns/op	     480 B/op	      27 allocs/op
-BenchmarkFieldDiveFailure-4                        	  300000	      3954 ns/op	     880 B/op	      31 allocs/op
-BenchmarkFieldCustomTypeSuccess-4                  	 3000000	       451 ns/op	      32 B/op	       2 allocs/op
-BenchmarkFieldCustomTypeFailure-4                  	 2000000	       751 ns/op	     400 B/op	       4 allocs/op
-BenchmarkFieldOrTagSuccess-4                       	 1000000	      1312 ns/op	      16 B/op	       1 allocs/op
-BenchmarkFieldOrTagFailure-4                       	 1000000	      1206 ns/op	     432 B/op	       6 allocs/op
-BenchmarkStructLevelValidationSuccess-4            	 2000000	       829 ns/op	     160 B/op	       6 allocs/op
-BenchmarkStructLevelValidationFailure-4            	 1000000	      1403 ns/op	     592 B/op	      11 allocs/op
-BenchmarkStructSimpleCustomTypeSuccess-4           	 1000000	      1238 ns/op	      80 B/op	       5 allocs/op
-BenchmarkStructSimpleCustomTypeFailure-4           	 1000000	      1771 ns/op	     624 B/op	      11 allocs/op
-BenchmarkStructPartialSuccess-4                    	 1000000	      1399 ns/op	     400 B/op	      11 allocs/op
-BenchmarkStructPartialFailure-4                    	 1000000	      1926 ns/op	     816 B/op	      16 allocs/op
-BenchmarkStructExceptSuccess-4                     	 2000000	       930 ns/op	     368 B/op	       9 allocs/op
-BenchmarkStructExceptFailure-4                     	 1000000	      1381 ns/op	     400 B/op	      11 allocs/op
-BenchmarkStructSimpleCrossFieldSuccess-4           	 1000000	      1253 ns/op	     128 B/op	       6 allocs/op
-BenchmarkStructSimpleCrossFieldFailure-4           	 1000000	      1849 ns/op	     560 B/op	      11 allocs/op
-BenchmarkStructSimpleCrossStructCrossFieldSuccess-4	 1000000	      1902 ns/op	     176 B/op	       9 allocs/op
-BenchmarkStructSimpleCrossStructCrossFieldFailure-4	  500000	      2453 ns/op	     608 B/op	      14 allocs/op
-BenchmarkStructSimpleSuccess-4                     	 1000000	      1182 ns/op	      48 B/op	       3 allocs/op
-BenchmarkStructSimpleFailure-4                     	 1000000	      1842 ns/op	     624 B/op	      11 allocs/op
-BenchmarkStructSimpleSuccessParallel-4             	 5000000	       342 ns/op	      48 B/op	       3 allocs/op
-BenchmarkStructSimpleFailureParallel-4             	 2000000	       665 ns/op	     624 B/op	      11 allocs/op
-BenchmarkStructComplexSuccess-4                    	  200000	      7924 ns/op	     512 B/op	      30 allocs/op
-BenchmarkStructComplexFailure-4                    	  100000	     12605 ns/op	    3415 B/op	      72 allocs/op
-BenchmarkStructComplexSuccessParallel-4            	 1000000	      2421 ns/op	     512 B/op	      30 allocs/op
-BenchmarkStructComplexFailureParallel-4            	  300000	      4234 ns/op	    3416 B/op	      72 allocs/op
+BenchmarkFieldSuccess-4                            	10000000	       163 ns/op	       0 B/op	       0 allocs/op
+BenchmarkFieldFailure-4                            	 2000000	       673 ns/op	     400 B/op	       4 allocs/op
+BenchmarkFieldDiveSuccess-4                        	  500000	      3019 ns/op	     480 B/op	      27 allocs/op
+BenchmarkFieldDiveFailure-4                        	  500000	      3553 ns/op	     880 B/op	      31 allocs/op
+BenchmarkFieldCustomTypeSuccess-4                  	 5000000	       347 ns/op	      32 B/op	       2 allocs/op
+BenchmarkFieldCustomTypeFailure-4                  	 2000000	       645 ns/op	     400 B/op	       4 allocs/op
+BenchmarkFieldOrTagSuccess-4                       	 1000000	      1177 ns/op	      16 B/op	       1 allocs/op
+BenchmarkFieldOrTagFailure-4                       	 1000000	      1093 ns/op	     432 B/op	       6 allocs/op
+BenchmarkStructLevelValidationSuccess-4            	 2000000	       702 ns/op	     160 B/op	       6 allocs/op
+BenchmarkStructLevelValidationFailure-4            	 1000000	      1279 ns/op	     592 B/op	      11 allocs/op
+BenchmarkStructSimpleCustomTypeSuccess-4           	 1000000	      1010 ns/op	      80 B/op	       5 allocs/op
+BenchmarkStructSimpleCustomTypeFailure-4           	 1000000	      1544 ns/op	     624 B/op	      11 allocs/op
+BenchmarkStructPartialSuccess-4                    	 1000000	      1249 ns/op	     400 B/op	      11 allocs/op
+BenchmarkStructPartialFailure-4                    	 1000000	      1797 ns/op	     816 B/op	      16 allocs/op
+BenchmarkStructExceptSuccess-4                     	 2000000	       927 ns/op	     368 B/op	       9 allocs/op
+BenchmarkStructExceptFailure-4                     	 1000000	      1259 ns/op	     400 B/op	      11 allocs/op
+BenchmarkStructSimpleCrossFieldSuccess-4           	 1000000	      1076 ns/op	     128 B/op	       6 allocs/op
+BenchmarkStructSimpleCrossFieldFailure-4           	 1000000	      1623 ns/op	     560 B/op	      11 allocs/op
+BenchmarkStructSimpleCrossStructCrossFieldSuccess-4	 1000000	      1582 ns/op	     176 B/op	       9 allocs/op
+BenchmarkStructSimpleCrossStructCrossFieldFailure-4	 1000000	      2139 ns/op	     608 B/op	      14 allocs/op
+BenchmarkStructSimpleSuccess-4                     	 1000000	      1040 ns/op	      48 B/op	       3 allocs/op
+BenchmarkStructSimpleFailure-4                     	 1000000	      1683 ns/op	     624 B/op	      11 allocs/op
+BenchmarkStructSimpleSuccessParallel-4             	 5000000	       356 ns/op	      48 B/op	       3 allocs/op
+BenchmarkStructSimpleFailureParallel-4             	 2000000	       831 ns/op	     624 B/op	      11 allocs/op
+BenchmarkStructComplexSuccess-4                    	  200000	      6738 ns/op	     512 B/op	      30 allocs/op
+BenchmarkStructComplexFailure-4                    	  200000	     11387 ns/op	    3415 B/op	      72 allocs/op
+BenchmarkStructComplexSuccessParallel-4            	  500000	      2330 ns/op	     512 B/op	      30 allocs/op
+BenchmarkStructComplexFailureParallel-4            	  300000	      4857 ns/op	    3416 B/op	      72 allocs/op
 ```
 
 How to Contribute

validator.go

@@ -69,15 +69,15 @@ type tagCacheMap struct {
 
 func (s *tagCacheMap) Get(key string) (*cachedTag, bool) {
 	s.lock.RLock()
-	defer s.lock.RUnlock()
 	value, ok := s.m[key]
+	s.lock.RUnlock()
 	return value, ok
 }
 
 func (s *tagCacheMap) Set(key string, value *cachedTag) {
 	s.lock.Lock()
-	defer s.lock.Unlock()
 	s.m[key] = value
+	s.lock.Unlock()
 }
 
 // StructLevel contains all of the information and helper methods