[−][src]Crate multiqueue2
This crate provides a fast mpmc broadcast queue. It's based on the queue design from the LMAX Disruptor, with a few improvements:
-
It acts as a futures stream/sink, so you can set up high-performance pipelines
-
It can dynamically add/remove senders, and each stream can have multiple receivers
-
It has fast runtime fallbacks for when there's a single consumer and/or a single producer
-
It works on 32 bit systems without any performance or capability penalty
-
In most cases, one can view data written directly into the queue without copying it
In many cases, MultiQueue
will be a good replacement for channels and it's broadcast
capabilities can replace more complex concurrency systems with a single queue.
Queue Model:
MultiQueue
functions similarly to the LMAX Disruptor from a high level view.
There's an incoming FIFO data stream that is broadcast to a set of subscribers
as if there were multiple streams being written to.
There are two main differences:
-
MultiQueue
transparently supports switching between single and multiple producers. -
Each broadcast stream can be shared among multiple consumers.
The last part makes the model a bit confusing, since there's a difference between a stream of data and something consuming that stream. To make things worse, each consumer may not actually see each value on the stream. Instead, multiple consumers may act on a single stream each getting unique access to certain elements.
A helpful mental model may be to think about this as if each stream was really just an mpmc
queue that was getting pushed to, and the MultiQueue
structure just assembled a bunch
together behind the scenes. This isn't the case of course, but it's helpful for thinking.
An diagram that represents a general use case of the queue where each consumer has unique access to a stream is below - the # stand in for producers and @ stands in for the consumer of each stream, each with a label. The lines are meant to show the data flow through the queue.
. -> # @-1
. \ /
. -> -> -> @-2
. / \
. -> # @-3
This is a pretty standard broadcast queue setup - for each element sent in, it is seen on each stream by that's streams consumer.
However, in MultiQueue, each logical consumer might actually be demultiplexed across many actual consumers, like below.
. -> # @-1
. \ /
. -> -> -> @-2' (really @+@+@ each compete for a spot)
. / \
. -> # @-3
If this diagram is redrawn with each of the producers sending in a sequenced element (time goes left to right):
. t=1|t=2| t=3 | t=4|
. 1 -> # @-1 (1, 2)
. \ /
. -> 2 -> 1 -> -> @-2' (really @ (1) + @ (2) + @ (nothing yet))
. / \
. 2 -> # @-3 (1, 2)
If one imagines this as a webserver, the streams for @-1 and @-3 might be doing random webservery work like some logging or metrics gathering and can handle the workload completely on one core, @-2 is doing expensive work handling requests and is split into multiple workers dealing with the data stream.
MPMC Mode:
One might notice that the broadcast queue modes requires that a type be Clone, and the single-reader inplace variants require that a type be Sync as well. This is only required for broadcast queues and not normal mpmc queues, so there's an mpmc api as well. It doesn't require that a type be Clone or Sync for any api, and also moves items directly out of the queue instead of cloning them.
Futures Mode:
For both mpmc and broadcast, a futures mode is supported. The datastructures are quite similar to the normal ones, except they implement the Futures Sink/Stream traits for senders and receivers. This comes at a bit of a performance cost, which is why the futures types are separate
Usage:
From the receiving side, this behaves quite similarly to a channel receiver. The .recv function will block until data is available and then return the data.
For senders, there is only .try_send
(except for the futures sink, which can park),
This is due to performance and api reasons - you should handle backlog instead of just blocking.
Example: SPSC channel
extern crate multiqueue2 as multiqueue; use std::thread; let (send, recv) = multiqueue::mpmc_queue(10); let handle = thread::spawn(move || { for val in recv { println!("Got {}", val); } }); for i in 0..10 { send.try_send(i).unwrap(); } // Drop the sender to close the queue drop(send); handle.join(); // prints // Got 0 // Got 1 // Got 2 // etc
Example: SPSC broadcasting
extern crate multiqueue2 as multiqueue; use std::thread; let (send, recv) = multiqueue::broadcast_queue(4); let mut handles = vec![]; for i in 0..2 { // or n let cur_recv = recv.add_stream(); handles.push(thread::spawn(move || { for val in cur_recv { println!("Stream {} got {}", i, val); } })); } // Take notice that I drop the reader - this removes it from // the queue, meaning that the readers in the new threads // won't get starved by the lack of progress from recv recv.unsubscribe(); for i in 0..10 { // Don't do this busy loop in real stuff unless you're really sure loop { if send.try_send(i).is_ok() { break; } } } // Drop the sender to close the queue drop(send); for t in handles { t.join(); } // prints along the lines of // Stream 0 got 0 // Stream 0 got 1 // Stream 1 got 0 // Stream 0 got 2 // Stream 1 got 1 // etc
Example: SPMC broadcast
extern crate multiqueue2 as multiqueue; use std::thread; let (send, recv) = multiqueue::broadcast_queue(4); let mut handles = vec![]; for i in 0..2 { // or n let cur_recv = recv.add_stream(); for j in 0..2 { let stream_consumer = cur_recv.clone(); handles.push(thread::spawn(move || { for val in stream_consumer { println!("Stream {} consumer {} got {}", i, j, val); } })); } // cur_recv is dropped here } // Take notice that I drop the reader - this removes it from // the queue, meaning that the readers in the new threads // won't get starved by the lack of progress from recv recv.unsubscribe(); for i in 0..10 { // Don't do this busy loop in real stuff unless you're really sure loop { if send.try_send(i).is_ok() { break; } } } drop(send); for t in handles { t.join(); } // prints along the lines of // Stream 0 consumer 1 got 2 // Stream 0 consumer 0 got 0 // Stream 1 consumer 0 got 0 // Stream 0 consumer 1 got 1 // Stream 1 consumer 1 got 1 // Stream 1 consumer 0 got 2 // etc // some join mechanics here
Example: Usage menagerie
extern crate multiqueue2 as multiqueue; use std::thread; let (send, recv) = multiqueue::broadcast_queue(4); let mut handles = vec![]; // start like before for i in 0..2 { // or n let cur_recv = recv.add_stream(); for j in 0..2 { let stream_consumer = cur_recv.clone(); handles.push(thread::spawn(move || for val in stream_consumer { println!("Stream {} consumer {} got {}", i, j, val); } )); } // cur_recv is dropped here } // On this stream, since there's only one consumer, // the receiver can be made into a UniReceiver // which can view items inline in the queue let single_recv = recv.add_stream().into_single().unwrap(); handles.push(thread::spawn(move || for val in single_recv.iter_with(|item_ref| 10 * *item_ref) { println!("{}", val); } )); // Same as above, except this time we just want to iterate until the receiver is empty let single_recv_2 = recv.add_stream().into_single().unwrap(); handles.push(thread::spawn(move || for val in single_recv_2.try_iter_with(|item_ref| 10 * *item_ref) { println!("{}", val); } )); // Take notice that I drop the reader - this removes it from // the queue, meaning that the readers in the new threads // won't get starved by the lack of progress from recv recv.unsubscribe(); // Many senders to give all the receivers something for _ in 0..3 { let cur_send = send.clone(); handles.push(thread::spawn(move || for i in 0..10 { loop { if cur_send.try_send(i).is_ok() { break; } } } )); } drop(send); for t in handles { t.join(); }
Modules
wait | This module contains the waiting strategies used by the queue when there is no data left. Users should not find themselves directly accessing these except for construction unless a custom Wait is being written. |
Structs
BroadcastFutReceiver | This is the futures-compatible version of |
BroadcastFutSender | This is the futures-compatible version of |
BroadcastFutUniReceiver | This is the futures-compatible version of |
BroadcastReceiver | This class is the receiving half of the broadcast |
BroadcastSender | This class is the sending half of the broadcasting |
BroadcastUniReceiver | This class is similar to the receiver, except it ensures that there
is only one consumer for the stream it owns. This means that
one can safely view the data in-place with the recv_view method family
and avoid the cost of copying it. If there's only one receiver on a stream,
it can be converted into a |
MPMCFutReceiver | This is the futures-compatible version of |
MPMCFutSender | This is the futures-compatible version of |
MPMCFutUniReceiver | This is the futures-compatible version of |
MPMCReceiver | This is the receiving end of a standard mpmc view of the queue
It functions similarly to the |
MPMCSender | This class is the sending half of the mpmc |
MPMCUniReceiver | This is the receiving end of a standard mpmc view of the queue
for when it's statically know that there is only one receiver.
It functions similarly to the |
Functions
broadcast_fut_queue | Futures variant of broadcast_queue - datastructures implement Sink + Stream at a minor (~30 ns) performance cost to BlockingWait |
broadcast_fut_queue_with | |
broadcast_queue | Creates a ( |
broadcast_queue_with | Creates a ( |
mpmc_fut_queue | Futures variant of |
mpmc_queue | Creates a ( |
mpmc_queue_with |