Expand description
Lock-free Bounded Non-Blocking Pub-Sub Queue
This is a publish subscribe pattern queue, where the publisher is never blocked by slow subscribers. The side effect is that slow subscribers will miss messages. The intended use-case are high throughput streams where receiving the latest message is prioritized over receiving the entire stream. Market Data Feeds, Live Streams, etc….
The underlying data-structure is a vector of Arc(s) eliminating the use of copies.
Features
- Lock-Free Write/Read - Lock-Free for Publisher and Lock-Free for Subscribers.
- Bounded - Constant size of memory used, max is
sizeof(MsgObject)*(queue_size + sub_cnt + 1). This is an edge-case where each subscriber is holding a ref to an object while the publisher has published a full length of queue in the mean time. - Non-Blocking - The queue never blocks the publisher, slow subscribers miss data proportinal to their speed.
- Pub-Sub - Every Subscriber that can keep up with the Publisher will recieve all the data the Publisher publishes.
sync/async- both interfaces are provided, as well as a bare queue implementation without the thread synchronisation ,and futures logic.- std::sync::mpsc like interface - The API is modeled after the standard library mpsc queue, channel function are used to create a tuple of (Publisher, Subscriber), while the Clone trait on Subscriber creates additional subscribers to the same Publisher.
sync::Publisher, async::Publisher, and BarePublisher are used to broadcast data to
sync::Subscriber, async::Subscriber, and BareSubscriber pools. Subscribers are
clone-able such that many threads, or futures, can receive data simultaneously. The only
limitation is that Subscribers have to keep up with the frequency of the Publisher. If a
Subscriber is slow it will drop data.
Disconnection
The broadcast and receive operations on channels will all return a Result
indicating whether the operation succeeded or not. An unsuccessful operation
is normally indicative of the other half of a channel having “hung up” by
being dropped in its corresponding thread.
Once half of a channel has been deallocated, most operations can no longer
continue to make progress, so Err will be returned. Many applications
will continue to unwrap the results returned from this module,
instigating a propagation of failure among threads if one unexpectedly dies.
Examples
Simple bare usage
extern crate bus_queue;
use bus_queue::bare_channel;
fn main() {
let (tx, rx) = bare_channel(10);
(1..15).for_each(|x| tx.broadcast(x).unwrap());
let received: Vec<i32> = rx.map(|x| *x).collect();
// Test that only the last 10 elements are in the received list.
let expected: Vec<i32> = (5..15).collect();
assert_eq!(expected, received);
}Simple synchronous usage
extern crate bus_queue;
use bus_queue::sync;
fn main() {
// Create a sync channel
let (tx, rx) = sync::channel(10);
// spawn tx thread, broadcast all and drop publisher.
let tx_t = std::thread::spawn(move || {
(1..15).for_each(|x| tx.broadcast(x).unwrap());
});
// small sleep for the tx thread to send and close, before rx thread is called
std::thread::sleep(std::time::Duration::from_millis(100));
// spawn rx thread to get all the items left in the buffer
let rx_t = std::thread::spawn(move || {
let received: Vec<i32> = rx.map(|x| *x).collect();
// Test that only the last 10 elements are in the received list.
let expected: Vec<i32> = (5..15).collect();
assert_eq!(received, expected);
});
tx_t.join().unwrap();
rx_t.join().unwrap();
}Simple asynchronous usage
extern crate bus_queue;
extern crate futures;
extern crate tokio;
use bus_queue::async;
use futures::*;
use tokio::runtime::Runtime;
fn main() {
let mut rt = Runtime::new().unwrap();
let (tx, rx) = async::channel(10);
let sent: Vec<i32> = (1..15).collect();
let publisher = stream::iter_ok(sent)
.forward(tx)
.and_then(|(_, mut sink)| sink.close())
.map_err(|_| ())
.map(|_| ());
rt.spawn(publisher);
let received: Vec<i32> = rt.block_on(rx.map(|x| *x).collect()).unwrap();
// Test that only the last 10 elements are in the received list.
let expected: Vec<i32> = (5..15).collect();
assert_eq!(expected, received);
}Modules
Structs
Sender::send or SyncSender::send
function on channels.Enums
recv_timeout
unable to return data when called. This can occur with both a channel and
a sync_channel.try_recv could
not return data when called. This can occur with both a channel and
a sync_channel.