Kotlin Channels usage difference between Send and Offer

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Channels have two functions that allow us to send events into it. Send and offer.

I would like to understand better the difference between both.

I have some statements I wanna check are true.

  • Send is a suspend function. What will make my code(not the thread) wait for it to finish. So it keep running after the event inside send was complete/cancelled. OR it will be suspend only until I can queue the event/receive it?
  • This means that, if I use send from one channel to another, the first channel will be block until the second can receive/queue?
  • If I have a Rendezvous Channel and it is already running something (on suspend for example, waiting API) and I offer a new even. This will make offer throws exception? Cause the channel is not receiving?

If you know any other main difference I would be glad to know.

Thanks in advance

kotlin-coroutine-channel kotlin-coroutines kotlin channel
1 Answers

send suspends the coroutine it is invoked from while the channel being sent to is full.

send does not send from one channel to another one. When you invoke send you are sending an element to the channel. The channel then expects another block of code to invoke receive from a different coroutine.

In a RendezvousChannel the capacity is 0. This means that send always suspends waiting for a receive invocation from another coroutine. If you have invoked send on a RendezvousChannel and then use offer, offer will not throw an exception (it only does if the channel is closed), but rather it will return false if no balancing receive has been invoked on the RendezvousChannel after your initial send. This is because offer tries to immediately add the element to the channel if it doesn't violate its capacity restrictions.

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