synchronise access to database statements

src/main/scala/lc/Main.scala

@@ -5,12 +5,15 @@ import java.io.ByteArrayInputStream
 import java.util.concurrent._
 import java.util.UUID
 import java.sql.{Blob, ResultSet}
+import java.util.concurrent.atomic.AtomicInteger
 
 case class Size(height: Int, width: Int)
 case class Parameters(level: String, media: String, input_type: String, size: Option[Size])
 case class Id(id: String)
 case class Answer(answer: String, id: String)
 
+case class ProviderSecret(provider: String, secret: String)
+
 class Captcha(throttle: Int) extends DBConn {
 
   val stmt = getConn()
@@ -55,13 +58,17 @@ class Captcha(throttle: Int) extends DBConn {
     }
   }
 
+  private val uniqueIntCount = new AtomicInteger()
+
   def generateChallenge(param: Parameters): String = {
   	//TODO: eval params to choose a provider
   	val providerMap = getProvider()
   	val provider = providers(providerMap)
     val challenge = provider.returnChallenge()
     val blob = new ByteArrayInputStream(challenge.content)
-    val token = scala.util.Random.nextInt(10000).toString
+    // val token = scala.util.Random.nextInt(100000).toString
+    val token = uniqueIntCount.incrementAndGet().toString
+    insertPstmt.synchronized {
       insertPstmt.setString(1, token)
       insertPstmt.setString(2, provider.getId)
       insertPstmt.setString(3, challenge.secret)
@@ -69,6 +76,7 @@ class Captcha(throttle: Int) extends DBConn {
       insertPstmt.setString(5, challenge.contentType)
       insertPstmt.setBlob(6, blob)
       insertPstmt.executeUpdate()
+    }
     token
   }
 
@@ -91,35 +99,43 @@ class Captcha(throttle: Int) extends DBConn {
   }
 
   def getChallenge(param: Parameters): Id = {
+    val idOpt = stmt.synchronized {
       val rs = stmt.executeQuery("SELECT token FROM challenge WHERE solved=FALSE ORDER BY RAND() LIMIT 1")
-    val id = if(rs.next()){
+      if(rs.next()) {
-      rs.getString("token")
+        Some(rs.getString("token"))
       } else {
-      generateChallenge(param)
+        None
       }
+    }
+    val id = idOpt.getOrElse(generateChallenge(param))
     val uuid = getUUID(id)
     Id(uuid)
   }
 
   def getUUID(id: String): String = {
     val uuid = UUID.randomUUID().toString
+    mapPstmt.synchronized {
       mapPstmt.setString(1,uuid)
       mapPstmt.setString(2,id)
       mapPstmt.executeUpdate()
+    }
     uuid
   }
 
   def checkAnswer(answer: Answer): Boolean = {
+    val psOpt:Option[ProviderSecret] = selectPstmt.synchronized {
       selectPstmt.setString(1, answer.id)
       val rs: ResultSet = selectPstmt.executeQuery()
       if (rs.first()) {
         val secret = rs.getString("secret")
         val provider = rs.getString("provider")
-      providers(provider).checkAnswer(secret, answer.answer)
+        Some(ProviderSecret(provider, secret))
       } else {
-      false
+        None
       }
     }
+    psOpt.map(ps => providers(ps.provider).checkAnswer(ps.secret, answer.answer)).getOrElse(false)
+  }
 
   def getHash(email: String): Int = {
     val secret = ""