Gatling Feeders - creating new instances - scala

Question

The following code works as expected, for each iteration the next value from the valueFeed is popped and written to the output.csv file
class TestSimulation extends Simulation {
val valueFeed = csv("input.csv")
val writer = {
val fos = new java.io.FileOutputStream("output.csv")
new java.io.PrintWriter(fos, true)
}
val scn = scenario("Test Sim")
.repeat(2) {
feed(valueFeed)
.exec(session => {
writer.println(session("value").as[String])
session
})
}
setUp(scn.inject(constantUsersPerSec(1) during (10 seconds)))
}
When feed creation is inlined in the feed method the behaviour is still exactly the same
class TestSimulation extends Simulation {
val writer = {
val fos = new java.io.FileOutputStream("output.csv")
new java.io.PrintWriter(fos, true)
}
val scn = scenario("Test Sim")
.repeat(2) {
feed(csv("input.csv"))
.exec(session => {
writer.println(session("value").as[String])
session
})
}
setUp(scn.inject(constantUsersPerSec(1) during (10 seconds)))
}
Since the feed creation is not extracted I would not expect each iteration to be using the same feed but creating it's own feed instance.
Why then is it the behaviour implies the same feed is being used and the first value from the input file not always written to the output?
Example input file (data truncated, tested with more lines to prevent empty feeder exception):
value
1
2
3
4
5

Answer 1

Because csv(...) is in fact FeederBuilder which is called once to produce the feeder to be used within the scenario.

Answer 2

The gatling DSL defines builders - these are executed only once at startup, so even when you inline you get a feeder shared between all users as the same (and only) builder is used to create all the users.
if you want to have each user have its own copy of the data, you can't use the .feed method, but you can get all the records and use other looping constructs to iterate through them
val records = csv("foo.csv").records
foreach(records, "record") {
exec(flattenMapIntoAttributes("${record}"))
}