Closable, fair, single-wakeup channel type that avoids 0 reader space leaks.

WARNING: While the code in this library should be fairly stable and production, the API is something I'm still working on. API changes will follow the PVP, but expect breaking API changes in future versions!

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.

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.