Buffered Channel with overflow capacity doesn't raise

[askn]

I wanted to test out Buffered Channels but seems like the capacity option is not being used. This code compiles but it just locks the process without any output.

ch = Channel::Buffered(Int32).new(2)
ch.send 7
ch.send 5
ch.send 6
ch.send 2

loop {
  puts "Yo"
  ch.receive
}

[asterite]

Yes, that's the expected behaviour. Once you try to send the third number it blocks the current coroutine, which is the main and only one, because the capacity is 2.

What you probably want is this:

ch = Channel::Buffered(Int32).new(2)

# Send messages in a different coroutine: if `send` blocks, it will block just this couroutine
spawn do
  ch.send 7
  ch.send 5
  ch.send 6
  ch.send 2
end

# This is on the main coroutine. `receive` blocks until it gets messages from `send`, 
# and now it works because two coroutines are communicating
loop {
  puts "Yo"
  ch.receive
}

[askn]

I thought that it should raise an exception if the capacity is full or over like in Go e.g http://play.golang.org/p/94yoBGi0Zz

[asterite]

In Go it panics because the runtime detects that there's a deadlock. We can do the same, but right now it's not done. In a way, both programs crash: Go with panic, Crystal hangs forever.

[jhass]

The exception seems to be because of a deadlock, not because the channel is full. We might do deadlock detection in the future, but that's a separate topic.

Edit: Ah, too slow.

[jhass]

Closing, please open a separate issue if you want deadlock detection.