BroadcastChan: Closable, fair, single-wakeup, broadcast channels
A closable, fair, single-wakeup channel that avoids the 0 reader space leak
that Control.Concurrent.Chan
from base suffers from.
The Chan
type from Control.Concurrent.Chan
consists of both a read and
write end combined into a single value. This means there is always at least 1
read end for a Chan
, which keeps any values written to it alive. This is a
problem for applications/libraries that want to have a channel that can have
zero listeners.
Suppose we have an library that produces events and we want to let users
register to receive events. If we use a channel and write all events to it, we
would like to drop and garbage collect any events that take place when there
are 0 listeners. The always present read end of Chan
from base makes this
impossible. We end up with a Chan
that forever accumulates more and more
events that will never get removed, resulting in a memory leak.
BroadcastChan
splits channels into separate read and write ends. Any message
written to a a channel with no existing read end is immediately dropped so it
can be garbage collected. Once a read end is created, all messages written to
the channel will be accessible to that read end.
Once all read ends for a channel have disappeared and been garbage collected,
the channel will return to dropping messages as soon as they are written.
Why should I use BroadcastChan
over Control.Concurrent.Chan
?
BroadcastChan
is closable,
BroadcastChan
has no 0 reader space leak,
BroadcastChan
has comparable or better performance.
Why should I use BroadcastChan
over various (closable) STM channels?
BroadcastChan
is single-wakeup,
BroadcastChan
is fair,
BroadcastChan
performs better under contention.