configurable dynamic stream concurrency scalar

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/utils/stream/broadband.rs

@@ -7,9 +7,7 @@ use futures::{
 	Future,
 };
 
-use super::ReadyExt;
-
-const WIDTH: usize = 32;
+use super::{automatic_width, ReadyExt};
 
 /// Concurrency extensions to augment futures::StreamExt. broad_ combinators
 /// produce out-of-order
@@ -95,7 +93,7 @@ where
 		Fut: Future<Output = bool> + Send,
 	{
 		self.map(f)
-			.buffer_unordered(n.into().unwrap_or(WIDTH))
+			.buffer_unordered(n.into().unwrap_or_else(automatic_width))
 			.ready_all(identity)
 	}
 
@@ -107,7 +105,7 @@ where
 		Fut: Future<Output = bool> + Send,
 	{
 		self.map(f)
-			.buffer_unordered(n.into().unwrap_or(WIDTH))
+			.buffer_unordered(n.into().unwrap_or_else(automatic_width))
 			.ready_any(identity)
 	}
 
@@ -120,7 +118,7 @@ where
 		U: Send,
 	{
 		self.map(f)
-			.buffer_unordered(n.into().unwrap_or(WIDTH))
+			.buffer_unordered(n.into().unwrap_or_else(automatic_width))
 			.ready_filter_map(identity)
 	}
 
@@ -132,6 +130,7 @@ where
 		Fut: Future<Output = U> + Send,
 		U: Send,
 	{
-		self.map(f).buffer_unordered(n.into().unwrap_or(WIDTH))
+		self.map(f)
+			.buffer_unordered(n.into().unwrap_or_else(automatic_width))
 	}
 }

src/core/utils/stream/mod.rs

@@ -19,3 +19,32 @@ pub use tools::Tools;
 pub use try_broadband::TryBroadbandExt;
 pub use try_ready::TryReadyExt;
 pub use wideband::WidebandExt;
+
+/// Stream concurrency factor; this is a live value.
+static WIDTH: std::sync::atomic::AtomicUsize = std::sync::atomic::AtomicUsize::new(32);
+
+/// Practicable limits on the stream width
+pub const WIDTH_LIMIT: (usize, usize) = (1, 1024);
+
+/// Sets the live concurrency factor. The first return value is the previous
+/// width which was replaced. The second return value is the value which was set
+/// after any applied limits.
+pub fn set_width(width: usize) -> (usize, usize) {
+	use std::sync::atomic::Ordering;
+
+	let width = width.clamp(WIDTH_LIMIT.0, WIDTH_LIMIT.1);
+	(WIDTH.swap(width, Ordering::Relaxed), width)
+}
+
+/// Used by stream operations where the concurrency factor hasn't been manually
+/// supplied by the caller (most uses). Instead we provide a default value which
+/// is adjusted at startup for the specific system and also dynamically.
+#[inline]
+pub fn automatic_width() -> usize {
+	use std::sync::atomic::Ordering;
+
+	let width = WIDTH.load(Ordering::Relaxed);
+	debug_assert!(width >= WIDTH_LIMIT.0, "WIDTH should not be zero");
+	debug_assert!(width <= WIDTH_LIMIT.1, "WIDTH is probably too large");
+	width
+}

src/core/utils/stream/try_broadband.rs

@@ -2,10 +2,9 @@
 
 use futures::{TryFuture, TryStream, TryStreamExt};
 
+use super::automatic_width;
 use crate::Result;
 
-const WIDTH: usize = 32;
-
 /// Concurrency extensions to augment futures::TryStreamExt. broad_ combinators
 /// produce out-of-order
 pub trait TryBroadbandExt<T, E>
@@ -49,6 +48,6 @@ where
 		Fut: TryFuture<Ok = U, Error = E, Output = Result<U, E>> + Send,
 	{
 		self.map_ok(f)
-			.try_buffer_unordered(n.into().unwrap_or(WIDTH))
+			.try_buffer_unordered(n.into().unwrap_or_else(automatic_width))
 	}
 }

src/core/utils/stream/wideband.rs

@@ -7,9 +7,7 @@ use futures::{
 	Future,
 };
 
-use super::ReadyExt;
-
-const WIDTH: usize = 32;
+use super::{automatic_width, ReadyExt};
 
 /// Concurrency extensions to augment futures::StreamExt. wideband_ combinators
 /// produce in-order.
@@ -66,7 +64,7 @@ where
 		U: Send,
 	{
 		self.map(f)
-			.buffered(n.into().unwrap_or(WIDTH))
+			.buffered(n.into().unwrap_or_else(automatic_width))
 			.ready_filter_map(identity)
 	}
 
@@ -78,6 +76,7 @@ where
 		Fut: Future<Output = U> + Send,
 		U: Send,
 	{
-		self.map(f).buffered(n.into().unwrap_or(WIDTH))
+		self.map(f)
+			.buffered(n.into().unwrap_or_else(automatic_width))
 	}
 }