Bump tokio from 0.2.4 to 0.2.6

[dependabot-preview]

Bumps tokio from 0.2.4 to 0.2.6.

Release notes

Sourced from tokio's releases.

Tokio v0.2.6

This release fixes an API regression introduced as part of v0.2.5.

Fixes

• fs::File::seek API regression (#1991).

Tokio v0.2.5

Includes new APIs, utilities, and fixes. Some highlights:

tokio::sync::broadcast

A multi-producer, multi-consumer channel where each sent value is sent to all consumers (fan-out). The channel is bounded and when consumers lag, they will receive an error indicating they have lagged too far behind.

use tokio::sync::broadcast;
#[tokio::main]
async fn main() {
let (tx, mut rx1) = broadcast::channel(16);
let mut rx2 = tx.subscribe();
tokio::spawn(async move {
    assert_eq!(rx1.recv().await.unwrap(), 10);
    assert_eq!(rx1.recv().await.unwrap(), 20);
});
tokio::spawn(async move {
assert_eq!(rx2.recv().await.unwrap(), 10);
assert_eq!(rx2.recv().await.unwrap(), 20);
});
tx.send(10).unwrap();
tx.send(20).unwrap();

}

Senders never block. When the channel is full, the oldest value still held by the channel is overwritten. This tends to be the desired behavior in order to prevent slow consumers from blocking the entire system. However, you can use a Semaphore (also added in this release) to ensure that all consumers see all messages.

tokio::sync::Semaphore

A counting synchronization primitive. It is used to limit a critical section to 1 or more concurrent tasks. For example, assume we wish to limit the number of in-flight database queries, we could do something like:

struct MyDbClient {
    db: MyDbHandle,
    semaphore: tokio::sync:Semaphore,
}
async fn query(client: &MyDbClient, query: Query) -> QueryResult {
let _permit = client.semaphore.acquire().await;
</tr></table> ... (truncated)

Commits

• 248bf21 prepare v0.2.6 release (#1995)
• 93ab70a fs: add deprecated fs::File::seek fn (#1991)
• 58b5abd update connect example (#1787)
• 2d78cfe chore: prepare v0.2.5 release (#1984)
• 4c64586 stream: add next and map utility fn (#1962)
• b0836ec sync: encapsulate TryLockError variants (#1980)
• 0c0f682 Improve runtime threading options docs
• b24ad9f rt: add configuration for core threads and max threads (#1977)
• 7c010ed sync: add broadcast channel (#1943)
• 42c942d Fix ROADMAP link (#1981)
• Additional commits viewable in compare view

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