Struct blocking::Unblock

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pub struct Unblock<T> { /* private fields */ }
Expand description

Runs blocking I/O on a thread pool.

Blocking I/O must be isolated from async code. This type moves blocking I/O operations onto a special thread pool while exposing a familiar async interface.

This type implements traits Stream, AsyncRead, AsyncWrite, or AsyncSeek if the inner type implements Iterator, Read, Write, or Seek, respectively.

Caveats

Unblock is a low-level primitive, and as such it comes with some caveats.

For higher-level primitives built on top of Unblock, look into async-fs or async-process (on Windows).

Unblock communicates with I/O operations on the thread pool through a pipe. That means an async read/write operation simply receives/sends some bytes from/into the pipe. When in reading mode, the thread pool reads bytes from the I/O handle and forwards them into the pipe until it becomes full. When in writing mode, the thread pool reads bytes from the pipe and forwards them into the I/O handle.

Use Unblock::with_capacity() to configure the capacity of the pipe.

Reading

If you create an Unblock<Stdin>, read some bytes from it, and then drop it, a blocked read operation may keep hanging on the thread pool. The next attempt to read from stdin will lose bytes read by the hanging operation. This is a difficult problem to solve, so make sure you only use a single stdin handle for the duration of the entire program.

Writing

If writing data through the AsyncWrite trait, make sure to flush before dropping the Unblock handle or some buffered data might get lost.

Seeking

Because of buffering in the pipe, if Unblock wraps a File, a single read operation may move the file cursor farther than is the span of the operation. In fact, reading just keeps going in the background until the pipe gets full. Keep this mind when using AsyncSeek with relative offsets.

Examples

use blocking::Unblock;
use futures_lite::prelude::*;

let mut stdout = Unblock::new(std::io::stdout());
stdout.write_all(b"Hello world!").await?;
stdout.flush().await?;

Implementations§

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impl<T> Unblock<T>

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pub fn new(io: T) -> Unblock<T>

Wraps a blocking I/O handle into the async Unblock interface.

Examples
use blocking::Unblock;

let stdin = Unblock::new(std::io::stdin());
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pub fn with_capacity(cap: usize, io: T) -> Unblock<T>

Wraps a blocking I/O handle into the async Unblock interface with a custom buffer capacity.

When communicating with the inner Stream/Read/Write type from async code, data transferred between blocking and async code goes through a buffer of limited capacity. This constructor configures that capacity.

The default capacity is:

Examples
use blocking::Unblock;

let stdout = Unblock::with_capacity(64 * 1024, std::io::stdout());
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pub async fn get_mut(&mut self) -> &mut T

Gets a mutable reference to the blocking I/O handle.

This is an async method because the I/O handle might be on the thread pool and needs to be moved onto the current thread before we can get a reference to it.

Examples
use blocking::{unblock, Unblock};
use std::fs::File;

let file = unblock(|| File::create("file.txt")).await?;
let mut file = Unblock::new(file);

let metadata = file.get_mut().await.metadata()?;
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pub async fn with_mut<R, F>(&mut self, op: F) -> R
where F: FnOnce(&mut T) -> R + Send + 'static, R: Send + 'static, T: Send + 'static,

Performs a blocking operation on the I/O handle.

Examples
use blocking::{unblock, Unblock};
use std::fs::File;

let file = unblock(|| File::create("file.txt")).await?;
let mut file = Unblock::new(file);

let metadata = file.with_mut(|f| f.metadata()).await?;
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pub async fn into_inner(self) -> T

Extracts the inner blocking I/O handle.

This is an async method because the I/O handle might be on the thread pool and needs to be moved onto the current thread before we can extract it.

Examples
use blocking::{unblock, Unblock};
use futures_lite::prelude::*;
use std::fs::File;

let file = unblock(|| File::create("file.txt")).await?;
let file = Unblock::new(file);

let file = file.into_inner().await;

Trait Implementations§

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impl<T: Read + Send + 'static> AsyncRead for Unblock<T>

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fn poll_read( self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &mut [u8] ) -> Poll<Result<usize>>

Attempt to read from the AsyncRead into buf. Read more
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fn poll_read_vectored( self: Pin<&mut Self>, cx: &mut Context<'_>, bufs: &mut [IoSliceMut<'_>] ) -> Poll<Result<usize, Error>>

Attempt to read from the AsyncRead into bufs using vectored IO operations. Read more
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impl<T: Seek + Send + 'static> AsyncSeek for Unblock<T>

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fn poll_seek( self: Pin<&mut Self>, cx: &mut Context<'_>, pos: SeekFrom ) -> Poll<Result<u64>>

Attempt to seek to an offset, in bytes, in a stream. Read more
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impl<T: Write + Send + 'static> AsyncWrite for Unblock<T>

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fn poll_write( self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &[u8] ) -> Poll<Result<usize>>

Attempt to write bytes from buf into the object. Read more
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fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Attempt to flush the object, ensuring that any buffered data reach their destination. Read more
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fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>

Attempt to close the object. Read more
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fn poll_write_vectored( self: Pin<&mut Self>, cx: &mut Context<'_>, bufs: &[IoSlice<'_>] ) -> Poll<Result<usize, Error>>

Attempt to write bytes from bufs into the object using vectored IO operations. Read more
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impl<T: Debug> Debug for Unblock<T>

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl<T: Iterator + Send + 'static> Stream for Unblock<T>
where T::Item: Send + 'static,

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type Item = <T as Iterator>::Item

Values yielded by the stream.
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fn poll_next( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Option<T::Item>>

Attempt to pull out the next value of this stream, registering the current task for wakeup if the value is not yet available, and returning None if the stream is exhausted. Read more
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fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the stream. Read more

Auto Trait Implementations§

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impl<T> !RefUnwindSafe for Unblock<T>

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impl<T> Send for Unblock<T>
where T: Send,

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impl<T> Sync for Unblock<T>
where T: Sync,

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impl<T> Unpin for Unblock<T>

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impl<T> !UnwindSafe for Unblock<T>

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<R> AsyncReadExt for R
where R: AsyncRead + ?Sized,

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fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadFuture<'a, Self>
where Self: Unpin,

Reads some bytes from the byte stream. Read more
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fn read_vectored<'a>( &'a mut self, bufs: &'a mut [IoSliceMut<'a>] ) -> ReadVectoredFuture<'a, Self>
where Self: Unpin,

Like read(), except it reads into a slice of buffers. Read more
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fn read_to_end<'a>( &'a mut self, buf: &'a mut Vec<u8> ) -> ReadToEndFuture<'a, Self>
where Self: Unpin,

Reads the entire contents and appends them to a Vec. Read more
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fn read_to_string<'a>( &'a mut self, buf: &'a mut String ) -> ReadToStringFuture<'a, Self>
where Self: Unpin,

Reads the entire contents and appends them to a String. Read more
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fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadExactFuture<'a, Self>
where Self: Unpin,

Reads the exact number of bytes required to fill buf. Read more
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fn take(self, limit: u64) -> Take<Self>
where Self: Sized,

Creates an adapter which will read at most limit bytes from it. Read more
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fn bytes(self) -> Bytes<Self>
where Self: Sized,

Converts this AsyncRead into a Stream of bytes. Read more
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fn chain<R>(self, next: R) -> Chain<Self, R>
where R: AsyncRead, Self: Sized,

Creates an adapter which will chain this stream with another. Read more
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fn boxed_reader<'a>(self) -> Pin<Box<dyn AsyncRead + Send + 'a>>
where Self: Sized + Send + 'a,

Boxes the reader and changes its type to dyn AsyncRead + Send + 'a. Read more
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impl<S> AsyncSeekExt for S
where S: AsyncSeek + ?Sized,

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fn seek(&mut self, pos: SeekFrom) -> SeekFuture<'_, Self>
where Self: Unpin,

Seeks to a new position in a byte stream. Read more
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impl<W> AsyncWriteExt for W
where W: AsyncWrite + ?Sized,

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fn write<'a>(&'a mut self, buf: &'a [u8]) -> WriteFuture<'a, Self>
where Self: Unpin,

Writes some bytes into the byte stream. Read more
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fn write_vectored<'a>( &'a mut self, bufs: &'a [IoSlice<'a>] ) -> WriteVectoredFuture<'a, Self>
where Self: Unpin,

Like write(), except that it writes a slice of buffers. Read more
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fn write_all<'a>(&'a mut self, buf: &'a [u8]) -> WriteAllFuture<'a, Self>
where Self: Unpin,

Writes an entire buffer into the byte stream. Read more
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fn flush(&mut self) -> FlushFuture<'_, Self>
where Self: Unpin,

Flushes the stream to ensure that all buffered contents reach their destination. Read more
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fn close(&mut self) -> CloseFuture<'_, Self>
where Self: Unpin,

Closes the writer. Read more
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fn boxed_writer<'a>(self) -> Pin<Box<dyn AsyncWrite + Send + 'a>>
where Self: Sized + Send + 'a,

Boxes the writer and changes its type to dyn AsyncWrite + Send + 'a. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T> Instrument for T

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fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
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fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<S> StreamExt for S
where S: Stream + ?Sized,

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fn poll_next(&mut self, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>
where Self: Unpin,

A convenience for calling Stream::poll_next() on !Unpin types.
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fn next(&mut self) -> NextFuture<'_, Self>
where Self: Unpin,

Retrieves the next item in the stream. Read more
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fn try_next<T, E>(&mut self) -> TryNextFuture<'_, Self>
where Self: Stream<Item = Result<T, E>> + Unpin,

Retrieves the next item in the stream. Read more
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fn count(self) -> CountFuture<Self>
where Self: Sized,

Counts the number of items in the stream. Read more
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fn map<T, F>(self, f: F) -> Map<Self, F>
where Self: Sized, F: FnMut(Self::Item) -> T,

Maps items of the stream to new values using a closure. Read more
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fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
where Self: Sized, U: Stream, F: FnMut(Self::Item) -> U,

Maps items to streams and then concatenates them. Read more
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fn flatten(self) -> Flatten<Self>
where Self: Sized, Self::Item: Stream,

Concatenates inner streams. Read more
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fn then<F, Fut>(self, f: F) -> Then<Self, F, Fut>
where Self: Sized, F: FnMut(Self::Item) -> Fut, Fut: Future,

Maps items of the stream to new values using an async closure. Read more
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fn filter<P>(self, predicate: P) -> Filter<Self, P>
where Self: Sized, P: FnMut(&Self::Item) -> bool,

Keeps items of the stream for which predicate returns true. Read more
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fn filter_map<T, F>(self, f: F) -> FilterMap<Self, F>
where Self: Sized, F: FnMut(Self::Item) -> Option<T>,

Filters and maps items of the stream using a closure. Read more
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fn take(self, n: usize) -> Take<Self>
where Self: Sized,

Takes only the first n items of the stream. Read more
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fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P>
where Self: Sized, P: FnMut(&Self::Item) -> bool,

Takes items while predicate returns true. Read more
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fn skip(self, n: usize) -> Skip<Self>
where Self: Sized,

Skips the first n items of the stream. Read more
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fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>
where Self: Sized, P: FnMut(&Self::Item) -> bool,

Skips items while predicate returns true. Read more
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fn step_by(self, step: usize) -> StepBy<Self>
where Self: Sized,

Yields every stepth item. Read more
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fn chain<U>(self, other: U) -> Chain<Self, U>
where Self: Sized, U: Stream<Item = Self::Item>,

Appends another stream to the end of this one. Read more
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fn cloned<'a, T>(self) -> Cloned<Self>
where Self: Stream<Item = &'a T> + Sized, T: Clone + 'a,

Clones all items. Read more
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fn copied<'a, T>(self) -> Copied<Self>
where Self: Stream<Item = &'a T> + Sized, T: Copy + 'a,

Copies all items. Read more
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fn collect<C>(self) -> CollectFuture<Self, C>
where Self: Sized, C: Default + Extend<Self::Item>,

Collects all items in the stream into a collection. Read more
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fn try_collect<T, E, C>(self) -> TryCollectFuture<Self, C>
where Self: Stream<Item = Result<T, E>> + Sized, C: Default + Extend<T>,

Collects all items in the fallible stream into a collection. Read more
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fn partition<B, P>(self, predicate: P) -> PartitionFuture<Self, P, B>
where Self: Sized, B: Default + Extend<Self::Item>, P: FnMut(&Self::Item) -> bool,

Partitions items into those for which predicate is true and those for which it is false, and then collects them into two collections. Read more
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fn fold<T, F>(self, init: T, f: F) -> FoldFuture<Self, F, T>
where Self: Sized, F: FnMut(T, Self::Item) -> T,

Accumulates a computation over the stream. Read more
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fn try_fold<T, E, F, B>( &mut self, init: B, f: F ) -> TryFoldFuture<'_, Self, F, B>
where Self: Stream<Item = Result<T, E>> + Unpin + Sized, F: FnMut(B, T) -> Result<B, E>,

Accumulates a fallible computation over the stream. Read more
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fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>
where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option<B>,

Maps items of the stream to new values using a state value and a closure. Read more
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fn fuse(self) -> Fuse<Self>
where Self: Sized,

Fuses the stream so that it stops yielding items after the first None. Read more
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fn cycle(self) -> Cycle<Self>
where Self: Clone + Sized,

Repeats the stream from beginning to end, forever. Read more
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fn enumerate(self) -> Enumerate<Self>
where Self: Sized,

Enumerates items, mapping them to (index, item). Read more
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fn inspect<F>(self, f: F) -> Inspect<Self, F>
where Self: Sized, F: FnMut(&Self::Item),

Calls a closure on each item and passes it on. Read more
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fn nth(&mut self, n: usize) -> NthFuture<'_, Self>
where Self: Unpin,

Gets the nth item of the stream. Read more
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fn last(self) -> LastFuture<Self>
where Self: Sized,

Returns the last item in the stream. Read more
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fn find<P>(&mut self, predicate: P) -> FindFuture<'_, Self, P>
where Self: Unpin, P: FnMut(&Self::Item) -> bool,

Finds the first item of the stream for which predicate returns true. Read more
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fn find_map<F, B>(&mut self, f: F) -> FindMapFuture<'_, Self, F>
where Self: Unpin, F: FnMut(Self::Item) -> Option<B>,

Applies a closure to items in the stream and returns the first Some result. Read more
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fn position<P>(&mut self, predicate: P) -> PositionFuture<'_, Self, P>
where Self: Unpin, P: FnMut(Self::Item) -> bool,

Finds the index of the first item of the stream for which predicate returns true. Read more
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fn all<P>(&mut self, predicate: P) -> AllFuture<'_, Self, P>
where Self: Unpin, P: FnMut(Self::Item) -> bool,

Tests if predicate returns true for all items in the stream. Read more
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fn any<P>(&mut self, predicate: P) -> AnyFuture<'_, Self, P>
where Self: Unpin, P: FnMut(Self::Item) -> bool,

Tests if predicate returns true for any item in the stream. Read more
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fn for_each<F>(self, f: F) -> ForEachFuture<Self, F>
where Self: Sized, F: FnMut(Self::Item),

Calls a closure on each item of the stream. Read more
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fn try_for_each<F, E>(&mut self, f: F) -> TryForEachFuture<'_, Self, F>
where Self: Unpin, F: FnMut(Self::Item) -> Result<(), E>,

Calls a fallible closure on each item of the stream, stopping on first error. Read more
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fn zip<U>(self, other: U) -> Zip<Self, U>
where Self: Sized, U: Stream,

Zips up two streams into a single stream of pairs. Read more
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fn unzip<A, B, FromA, FromB>(self) -> UnzipFuture<Self, FromA, FromB>
where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Stream<Item = (A, B)> + Sized,

Collects a stream of pairs into a pair of collections. Read more
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fn or<S>(self, other: S) -> Or<Self, S>
where Self: Sized, S: Stream<Item = Self::Item>,

Merges with other stream, preferring items from self whenever both streams are ready. Read more
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fn race<S>(self, other: S) -> Race<Self, S>
where Self: Sized, S: Stream<Item = Self::Item>,

Merges with other stream, with no preference for either stream when both are ready. Read more
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fn boxed<'a>(self) -> Pin<Box<dyn Stream<Item = Self::Item> + Send + 'a>>
where Self: Send + Sized + 'a,

Boxes the stream and changes its type to dyn Stream + Send + 'a. Read more
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fn boxed_local<'a>(self) -> Pin<Box<dyn Stream<Item = Self::Item> + 'a>>
where Self: Sized + 'a,

Boxes the stream and changes its type to dyn Stream + 'a. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<S, T, E> TryStream for S
where S: Stream<Item = Result<T, E>> + ?Sized,

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type Ok = T

The type of successful values yielded by this future
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type Error = E

The type of failures yielded by this future
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fn try_poll_next( self: Pin<&mut S>, cx: &mut Context<'_> ) -> Poll<Option<Result<<S as TryStream>::Ok, <S as TryStream>::Error>>>

Poll this TryStream as if it were a Stream. Read more
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impl<T> WithSubscriber for T

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fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more
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fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more