Add embassy multi-thread feature, use it in sunsetc

Now sunsetc runs with a threaded executor instead of a LocalSet,
to test multi-thread.

async/Cargo.toml

@@ -50,3 +50,6 @@ embedded-io-adapters = { version = "0.6", features = ["tokio-1"] }
 simplelog = "0.12"
 # for simplelog
 time = { version = "0.3", features = ["local-offset"] }
+
+sunset-embassy = { version = "0.2", path = "../embassy", features = ["multi-thread"] }
+critical-section = { version = "1.1", features = ["std"] }

async/examples/sunsetc.rs

@@ -26,14 +26,7 @@ use time::UtcOffset;
 #[tokio::main]
 async fn real_main(tz: UtcOffset) -> Result<()> {
     let args = parse_args(tz)?;
-
-    // TODO: currently we just run it all on a single thread.
-    // Running with tokio's normal multiple threads works fine
-    // if we change SunsetRawMutex to a CriticalSectionMutex
-    // (or something wrapping std::sync::Mutex).
-    // Need to figure how to make it configurable.
-    let local = tokio::task::LocalSet::new();
-    let exit_code = local.run_until(run(args)).await?;
+    let exit_code = run(args).await?;
     std::process::exit(exit_code)
 }
 
@@ -73,11 +66,16 @@ async fn run(args: Args) -> Result<i32> {
         want_pty = false
     }
 
-    let ssh_task = spawn_local(async move {
+    // Sunset will work fine on a non-threaded executor (such as Tokio LocalSet).
+    // sunset-embassy's "multi-thread" feature is not required in that case.
+    // sunsetc example here uses the normal threaded scheduler in order to test the
+    // "multi-thread" feature (and as a more "default" example).
+    let ssh_task = tokio::task::spawn(async move {
         let mut rxbuf = Zeroizing::new(vec![0; 3000]);
         let mut txbuf = Zeroizing::new(vec![0; 3000]);
         let ssh = SSHClient::new(&mut rxbuf, &mut txbuf)?;
 
+        // CmdlineClient implements the session logic for a commandline SSH client.
         let mut app = CmdlineClient::new(
             args.username.as_ref().unwrap(),
             &args.host,

async/src/cmdline_client.rs

@@ -372,6 +372,7 @@ enum EscapeAction {
     Suspend,
 }
 
+/// Handles ~. escape sequences in an interactive shell.
 #[derive(Debug)]
 enum Escaper {
     Idle,

embassy/Cargo.toml

@@ -19,6 +19,12 @@ sunset = { version = "0.2.0", path = "../", features = ["embedded-io"] }
 log = { version = "0.4" }
 
 [features]
+# Use a critical-section mutex to lock state. This feature must be enabled
+# to run on executors that require futures to be Send (such as default Tokio).
+# The application should depend on critical-section "std" feature.
+# When multi-thread is disabled locking overhead is avoided.
+multi-thread = []
+
 # Remove any use of `unsafe`. This currently requires
 # nightly and -Zpolonius (not ready yet)
 try-polonius = []

embassy/src/embassy_sunset.rs

@@ -7,7 +7,8 @@ use core::sync::atomic::AtomicBool;
 use core::sync::atomic::Ordering::{Relaxed, SeqCst};
 
 use embassy_sync::waitqueue::WakerRegistration;
-use embassy_sync::blocking_mutex::raw::NoopRawMutex;
+#[allow(unused_imports)]
+use embassy_sync::blocking_mutex::raw::{NoopRawMutex,CriticalSectionRawMutex};
 use embassy_sync::mutex::{Mutex, MutexGuard};
 use embassy_sync::signal::Signal;
 use embassy_futures::select::select;
@@ -23,11 +24,10 @@ use sunset::{error, ChanData, ChanHandle, ChanNum, Error, Result, Runner};
 use sunset::config::MAX_CHANNELS;
 use sunset::event::Event;
 
-// For now we only support single-threaded executors.
-// In future this could be behind a cfg to allow different
-// RawMutex for std executors or other situations.
+#[cfg(feature = "multi-thread")]
+pub type SunsetRawMutex = CriticalSectionRawMutex;
+#[cfg(not(feature = "multi-thread"))]
 pub type SunsetRawMutex = NoopRawMutex;
-// pub type SunsetRawMutex = CriticalSectionRawMutex;
 
 pub type SunsetMutex<T> = Mutex<SunsetRawMutex, T>;