Instead of using sleep in time::advance, this fixes the root of the issue. When futures passed
to `Runtime::block_on` are woken, it bypassed all the machinery around advancing time. By
intercepting wakes in the time driver, we know when the block_on task is woken and skip
advancing time in that case.
Fixes#3837
Previously, `time::advance` would set the mocked clock forward the
requested amount, then yield. However, if there was no work ready to
perform immediately, this would result in advancing to the next expiring
sleep.
Now, `time::advance(...)` will unblock at the requested time. The
difference between `time::advance(...)` and `time::sleep(...)` is a bit
fuzzy. The main difference is `time::sleep(...)` operates on the current
task and `time::advance(...)` operates at the runtime level.
Fixes#3710
* sync: add `mpsc::Sender::{reserve_owned, try_reserve_owned}`
## Motivation
The `mpsc::Sender::reserve` method currently returns a permit that borrows
from the `Sender`. It would be nice to have a version of it that returns
an owned permit.
## Solution
This branch adds an `OwnedPermit` type and `Sender::{reserve_owned,
try_reserve_owned}` methods. Unlike the comparable methods on
`Semaphore`, these methods do *not* require an `Arc<Sender>` as the
receiver; this is because the sender internally reference counts the
channel and is already cheap to clone. Requiring an `Arc` would simply
add an unnecessary second layer of reference counting, which is not
ideal; instead, the documentation encourages the user to clone the
sender prior to calling `reserve_owned` when necessary.
Since these methods take the `Sender` by value, they also have the ability
to _return_ the `Sender` from a successful `OwnedPermit::send`. This
allows them to be used without additional clones. Essentially, this is a
very simple type-level encoding of the sender's state, with the
transitions
```
┌──────┐
┌───►│Sender├───┐
│ └──────┘ │
send reserve
│ ┌───────────┐ │
└─┤OwnedPermit│◄┘
└───────────┘
```
Additionally, I added an `OwnedPermit::release`, which returns the
`Sender` and releases the permit *without* sending a message.
Closes#3688
Signed-off-by: Eliza Weisman <[email protected]>
Simply exposes the number of available permits of the semaphore.
This makes some kinds of bookkeeping easier without having to manually keep counts using atomics.
Fixes#2642
Diggory Blake