multithreading - Scala Play thread -

i'm using scala / play2 framework / mongodb (reactivemongo) have function in request doing : find maximum value in collection, increase maximum number random, , save new value collection, , return new value.

def generatecode():future[string] = {   // find maximum   maximum = future[].... map { maxvalue =>       // increase maxvalue       newvalue = maxvalue + random       // save database   } } 

the problem want code 1 thread run @ time. because if 2 thread run same time, value con conflicted. example: thread 1: read max = 100, thread 2 read max = 100 thread 1: increase max = 105, thread 2 increase max = 102 thread 1: save 105 db, thread 2 save 102 db

finally maximum in db 102, in should 105. how can ?

as rule reactivemongo api , operations on future require implicit executioncontext in scope. can define single threaded execution context , use in class defined generatecode() method , in class call reactivemongo api.

import java.util.concurrent.executors  implicit val ec: executioncontext = executioncontext.fromexecutor(executors.newsinglethreadexecutor()) 

you can pass ec explicitly methods require implicit executioncontext. need make sure whole chain of asynchronous method calls uses same single threaded execution context.