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A question:  I have several coroutines (~100) sending a message to a channel. This channel reads the messages in a  `for( message in myChannel){ ... }` loop.  I can see, via logging, that the events are being send and I see that they are read in the for loop. However, all except for one of the sending coroutines do not continue and keep being stuck in the suspended state.
Any idea what could cause this ?
Adding a buffer to the channel seems to help,  but I would like to know what causes my issue ?

The <https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.channels/-channel/index.html|channel docs> say:
&gt; The `Channel(capacity)` factory function is used to create channels of different kinds depending on the value of the `capacity` integer:
&gt; • When `capacity` is 0 — it creates a _rendezvous_ channel. This channel does not have any buffer at all. An element is transferred from the sender to the receiver only when <https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.channels/-channel/send.html|send> and <https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.channels/-channel/receive.html|receive> invocations meet in time (rendezvous), so *<https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.channels/-channel/send.html|send> suspends until another coroutine invokes <https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.channels/-channel/receive.html|receive>*, and <https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.channels/-channel/receive.html|receive> suspends until another coroutine invokes <https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.channels/-channel/send.html|send>.
(bold added)

In `RENDEZVOUS` mode, “Send suspends until another coroutine invokes receive”

And if you look at the <https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.channels/-channel.html|docs> for the `Channel()` function, you’ll see the default capacity is `RENDEZVOUS`.

the messages *are* received,  but the sending coroutines remains suspended

Are all the threads blocked somehow? If not, I’m not sure what’s going on

Can you share some code that reproduces the issue? As <@U0KMMQA20> suggested it might be due to thread starvation. For instance if what you do in the loop blocks the thread

Are you sending messages back to the original source 'actor' (ie process that puts messages into the source Channel)? A circular graph of actors can cause locks.

<@UBXMWAA69> <@U0KMMQA20> <@U010JQZ3FRC> <@U72C3TBDH> Sorry for not posting sooner. I have found the cause and the solution of my problem.
The cause was Ktor. The client starts blocking after a certain number of calls. I was running a test in which I did 100 simultaneous  calls using  Ktor's 2.0 `testApplication` function.

The solution was to configure the client to use the CIO engine

```val client = createClient {
                engine { CIO }
                install(WebSockets)
            }```