Module mq_queue

Queues that participate in the memory quota system

Wraps a communication channel, such as [futures::channel::mpsc], tracks the memory use of the queue, and participates in the memory quota system.

Each item in the queue must know its memory cost, and provide it via HasMemoryCost.

New queues are created by calling the new_mq method on a ChannelSpec, for example MpscSpec or MpscUnboundedSpec.

The ends implement [Stream] and [Sink]. If the underlying channel’s sender is Clone, for example with an MPSC queue, the returned sender is also Clone.

Note that the Sender and Receiver only hold weak references to the Account. Ie, the queue is not the accountholder. The caller should keep a separate copy of the account.

Example

use tor_memquota::{MemoryQuotaTracker, HasMemoryCost, EnabledToken};
use tor_rtcompat::{DynTimeProvider, PreferredRuntime};
use tor_memquota::mq_queue::{MpscSpec, ChannelSpec as _};

#[derive(Debug)]
struct Message(String);
impl HasMemoryCost for Message {
    fn memory_cost(&self, _: EnabledToken) -> usize { self.0.len() }
}

let runtime = PreferredRuntime::create().unwrap();
let time_prov = DynTimeProvider::new(runtime.clone());
let config  = tor_memquota::Config::builder().max(1024*1024*1024).build().unwrap();
let trk = MemoryQuotaTracker::new(&runtime, config).unwrap();
let account = trk.new_account(None).unwrap();

let (tx, rx) = MpscSpec { buffer: 10 }.new_mq::<Message>(time_prov, &account)?;

Caveat

The memory use tracking is based on external observations, i.e., items inserted and removed.

How well this reflects the actual memory use of the channel depends on the channel’s implementation.

For example, if the channel uses a single contiguous buffer containing the unboxed items, and that buffer doesn’t shrink, then the memory tracking can be based on an underestimate. (This is significantly mitigated if the bulk of the memory use for each item is separately boxed.)

Structs

MpscSpec

Specification for a (bounded) MPSC channel

MpscUnboundedSpec

Specification for an unbounded MPSC channel

Receiver

Receiver for a channel that participates in the memory quota system

Sender

Sender for a channel that participates in the memory quota system

Enums

CollapseReason

Argument to CollapseCallback: why are we collapsing?

SendError

Error returned when trying to write to a Sender

Traits

ChannelSpec

Specification for a communication channel

Type Aliases

CollapseCallback

Callback passed to Receiver::register_collapse_hook