fix submission race condition

conf/constants.go

@@ -1,12 +1,21 @@
 package conf
 
+import "github.com/mdg-iitr/Codephile/models/types"
+
 const (
 	CODECHEF   = "codechef"
 	CODEFORCES = "codeforces"
 	HACKERRANK = "hackerrank"
 	SPOJ       = "spoj"
 )
 
+var (
+	codechefSubMutex   = types.SubmissionMutex{Website: CODECHEF}
+	codeforcesSubMutex = types.SubmissionMutex{Website: CODECHEF}
+	hackerrankSubMutex = types.SubmissionMutex{Website: CODECHEF}
+	spojSubMutex       = types.SubmissionMutex{Website: CODECHEF}
+)
+
 var ValidSites = []string{HACKERRANK, CODECHEF, CODEFORCES, SPOJ}
 
 func IsSiteValid(s string) bool {
@@ -17,4 +26,17 @@ func IsSiteValid(s string) bool {
 	}
 	return false
 }
-
+func GetMutexForWebsiteSubmission(site string) *types.SubmissionMutex {
+	switch site {
+	case CODECHEF:
+		return &codechefSubMutex
+	case CODEFORCES:
+		return &codeforcesSubMutex
+	case HACKERRANK:
+		return &hackerrankSubMutex
+	case SPOJ:
+		return &spojSubMutex
+	default:
+		return nil
+	}
+}

models/submission.go

@@ -16,6 +16,11 @@ import (
 func AddSubmissions(uid bson.ObjectId, site string) error {
 	sess := db.NewUserCollectionSession()
 	defer sess.Close()
+	// Since each website submission can be allowed to fetch
+	// concurrently, so a different mutex for each website
+	mutex := GetMutexForWebsiteSubmission(site)
+	mutex.Lock()
+	defer mutex.Unlock()
 	coll := sess.Collection
 	var user types.User
 	err := coll.FindId(uid).Select(bson.M{"handle": 1, "lastfetched": 1}).One(&user)

models/types/submission.go

@@ -1,6 +1,7 @@
 package types
 
 import (
+	"sync"
 	"time"
 )
 
@@ -22,3 +23,8 @@ type CodeforcesSubmissions struct {
 	Status string                   `json:"status"`
 	Result []map[string]interface{} `json:"result"`
 }
+
+type SubmissionMutex struct {
+	Website string
+	sync.Mutex
+}