zesterer / pollster

A minimal async executor that lets you block on a future

pancake

A personal C++ utility library for a variety of uses

What does it do?

pancake includes many pieces of boilerplate code that are common throughout my software including:

Why the name 'pancake'?

I don't know. I searched "random words" online and 'pancake' was the first thing I saw. I'm not very inventive when it comes to names.

pollster's Issues

How is this different from futures::executor::block_on ?

The functionality provided by this crate is identical to futures::executor::block_on .

I have the following natural questions that I feel deserve to be mentioned in the readme:

What are the differences between the two versions?
If I already depend on futures with the executor feature, is there any reason to prefer pollster over futures?
If pollster is preferred in that case, why isn't the futures version implemented through pollster?

I'm aware that the readme broaches this topic to some degree t but I feel that the futures crate version deserves special mention because it is not (?) a heavy weight executor part of a larger async framework.

Proc-Macro for `fn main` - à la `#[tokio::main]`

I know pollster tries to be as minimal as possible, but this would be very neat.
Is there any interest in hosting this as part of the official repo?

Deadlock

I had a quick look at it. It does have an unsafe without comment clarifying why it's guaranteed to be safe, which is unfortunate. On performance, it seems to be in the same league as async_std::task::block_on.

Now for the bad news, this deadlocks, and it doesn't on async_std::task::block_on, nor on futures::executor::block_on:

use
{
   std   :: { thread, sync::atomic::{ AtomicUsize, Ordering::SeqCst } } ,
   tokio :: { sync::mpsc                                              } ,
};


// queue size for the bounded channel, 16 is same as actix default size.
//
const BOUNDED : usize = 16;
const MESSAGES: usize = 100_000;


fn main()
{
   let (mut a_tx, mut a_rx) = mpsc::channel( BOUNDED );
   let (mut b_tx, mut b_rx) = mpsc::channel( BOUNDED );


   let thread_a = thread::spawn( move ||
   {
      pollster::block_on( async
      {
         while let Some( msg ) = a_rx.recv().await
         {
            b_tx.send( msg ).await.expect( "send on b" );
         }
      });
   });


   let thread_b = thread::spawn( move ||
   {
      pollster::block_on( async move
      {
         for _ in 0..MESSAGES
         {
            a_tx.send( () ).await.expect( "Send on a" );
         }
      });
   });


   pollster::block_on( async move
   {
      let sum = AtomicUsize::new(0);

      while sum.fetch_add( 1, SeqCst ) < MESSAGES
      {
         b_rx.recv().await;
      }

      assert_eq!( sum.load( SeqCst), MESSAGES + 1 );
   });


   thread_a.join().expect( "join thread_a" );
   thread_b.join().expect( "join thread_b" );
}

Some proper testing is in order I think. Good luck.

pollster 0.2.4 doesn't build on stable

Building a crate which indirectly depends on pollster suddenly started failing with the 0.2.4 release:

error[E0658]: use of unstable library feature 'wake_trait'
  --> /home/andrew/.cargo/registry/src/github.com-1ecc6299db9ec823/pollster-0.2.4/src/lib.rs:19:27
   |
19 |     task::{Context, Poll, Wake, Waker},
   |                           ^^^^
   |
   = note: see issue #69912 <https://github.com/rust-lang/rust/issues/69912> for more information

error[E0658]: use of unstable library feature 'wake_trait'
   --> /home/andrew/.cargo/registry/src/github.com-1ecc6299db9ec823/pollster-0.2.4/src/lib.rs:104:5
    |
104 | /     fn wake(self: Arc<Self>) {
105 | |         self.notify();
106 | |     }
    | |_____^
    |
    = note: see issue #69912 <https://github.com/rust-lang/rust/issues/69912> for more information

error[E0658]: use of unstable library feature 'wake_trait'
   --> /home/andrew/.cargo/registry/src/github.com-1ecc6299db9ec823/pollster-0.2.4/src/lib.rs:103:6
    |
103 | impl Wake for Signal {
    |      ^^^^
    |
    = note: see issue #69912 <https://github.com/rust-lang/rust/issues/69912> for more information

error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0658`.
error: could not compile `pollster`

Please yank 0.2.4 and release it as 0.3.0 instead, as this appears to be a breaking change..

Consider adding a LICENSE file

pollster's Cargo.toml specifies the license

pollster/Cargo.toml

Line 10 in 9cd9eed

license = "Apache-2.0/MIT"

but other tooling might not find this, e.g. github currently does not display a license button on the sidebar.