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kotlinkotlinx.coroutines

Couldn't receive few messages using kotlin channel


I have below kotlin coroutine code.

    import kotlinx.coroutines.*
    import kotlinx.coroutines.channels.*

    fun main() = runBlocking {

        val channel =  Channel<Int>()
        val job = launch {
            for(x in 1..5) {
                println("sending $x")
                channel.send(x)
            }

            channel.close()
        }

        for (y in channel) {
            // if (!channel.isClosedForReceive && !channel.isClosedForSend)
            println( "received ${channel.receive()} isClosedForSend ${channel.isClosedForSend} isClosedForReceive ${channel.isClosedForReceive}  " )
        }
        job.join()
    }

The output of the above program is (which is missing few elements at receive end) -

sending 1
sending 2
received 2 isClosedForSend false isClosedForReceive false  
sending 3
sending 4
received 4 isClosedForSend false isClosedForReceive false  
sending 5

If I unncomment the line if (!channel.isClosedForReceive && !channel.isClosedForSend), I get same output with exception.

    sending 1
    sending 2
    received 2 isClosedForSend false isClosedForReceive false  
    sending 3
    sending 4
    received 4 isClosedForSend false isClosedForReceive false  
    sending 5
    Exception in thread "main" kotlinx.coroutines.channels.ClosedReceiveChannelException: Channel was closed
        at kotlinx.coroutines.channels.Closed.getReceiveException(AbstractChannel.kt:1081)
        at kotlinx.coroutines.channels.AbstractChannel.receiveResult(AbstractChannel.kt:577)
        at kotlinx.coroutines.channels.AbstractChannel.receive(AbstractChannel.kt:570)

How can I get the correct output without any exception?


Solution

  • You can just write

    for (y in channel) {
        println(y)
    }