From 379dca552ca91d22ee007b42f93803ad3dc2b274 Mon Sep 17 00:00:00 2001
From: hozan23 <hozan23@proton.me>
Date: Wed, 20 Mar 2024 15:20:21 +0100
Subject: core: add the option to create a new task group without providing an
 executor & remove GlobalExecutor type

---
 core/Cargo.toml                   |  2 ++
 core/src/async_util/executor.rs   | 30 ++++++++++++++++++++++++
 core/src/async_util/mod.rs        |  2 ++
 core/src/async_util/task_group.rs | 48 ++++++++++++++++++++++++++++++++++++---
 core/src/lib.rs                   |  9 --------
 5 files changed, 79 insertions(+), 12 deletions(-)
 create mode 100644 core/src/async_util/executor.rs

(limited to 'core')

diff --git a/core/Cargo.toml b/core/Cargo.toml
index 7e7e511..c8e2b8d 100644
--- a/core/Cargo.toml
+++ b/core/Cargo.toml
@@ -16,6 +16,8 @@ rand = "0.8.5"
 thiserror = "1.0.58"
 dirs = "5.0.1"
 async-task = "4.7.0"
+async-lock = "3.3.0"
+async-process = "2.1.0"
 
 ed25519-dalek = { version = "2.1.1", features = ["rand_core"], optional = true}
 
diff --git a/core/src/async_util/executor.rs b/core/src/async_util/executor.rs
new file mode 100644
index 0000000..3e7aa06
--- /dev/null
+++ b/core/src/async_util/executor.rs
@@ -0,0 +1,30 @@
+use std::{panic::catch_unwind, sync::Arc, thread};
+
+use async_lock::OnceCell;
+use smol::Executor as SmolEx;
+
+static GLOBAL_EXECUTOR: OnceCell<Arc<smol::Executor<'_>>> = OnceCell::new();
+
+/// A pointer to an Executor
+pub type Executor<'a> = Arc<SmolEx<'a>>;
+
+/// Returns a single-threaded global executor
+pub(crate) fn global_executor() -> Executor<'static> {
+    fn init_executor() -> Executor<'static> {
+        let ex = smol::Executor::new();
+        thread::Builder::new()
+            .spawn(|| loop {
+                catch_unwind(|| {
+                    smol::block_on(global_executor().run(smol::future::pending::<()>()))
+                })
+                .ok();
+            })
+            .expect("cannot spawn executor thread");
+        // Prevent spawning another thread by running the process driver on this
+        // thread. see https://github.com/smol-rs/smol/blob/master/src/spawn.rs
+        ex.spawn(async_process::driver()).detach();
+        Arc::new(ex)
+    }
+
+    GLOBAL_EXECUTOR.get_or_init_blocking(init_executor).clone()
+}
diff --git a/core/src/async_util/mod.rs b/core/src/async_util/mod.rs
index c871bad..2916118 100644
--- a/core/src/async_util/mod.rs
+++ b/core/src/async_util/mod.rs
@@ -1,6 +1,7 @@
 mod backoff;
 mod condvar;
 mod condwait;
+mod executor;
 mod select;
 mod task_group;
 mod timeout;
@@ -8,6 +9,7 @@ mod timeout;
 pub use backoff::Backoff;
 pub use condvar::CondVar;
 pub use condwait::CondWait;
+pub use executor::Executor;
 pub use select::{select, Either};
 pub use task_group::{TaskGroup, TaskResult};
 pub use timeout::timeout;
diff --git a/core/src/async_util/task_group.rs b/core/src/async_util/task_group.rs
index 7129af2..0fb4855 100644
--- a/core/src/async_util/task_group.rs
+++ b/core/src/async_util/task_group.rs
@@ -2,9 +2,7 @@ use std::{future::Future, sync::Arc, sync::Mutex};
 
 use async_task::FallibleTask;
 
-use crate::Executor;
-
-use super::{select, CondWait, Either};
+use super::{executor::global_executor, select, CondWait, Either, Executor};
 
 /// TaskGroup is a group of spawned tasks.
 ///
@@ -35,6 +33,19 @@ pub struct TaskGroup<'a> {
     executor: Executor<'a>,
 }
 
+impl TaskGroup<'static> {
+    /// Creates a new task group without providing an executor
+    ///
+    /// This will Spawn a task onto a global executor (single-threaded by default).
+    pub fn new_without_executor() -> Self {
+        Self {
+            tasks: Mutex::new(Vec::new()),
+            stop_signal: Arc::new(CondWait::new()),
+            executor: global_executor(),
+        }
+    }
+}
+
 impl<'a> TaskGroup<'a> {
     /// Creates a new task group
     pub fn new(executor: Executor<'a>) -> Self {
@@ -191,4 +202,35 @@ mod tests {
             group.cancel().await;
         }));
     }
+
+    #[test]
+    fn test_task_group_without_executor() {
+        smol::block_on(async {
+            let group = Arc::new(TaskGroup::new_without_executor());
+
+            group.spawn(future::ready(0), |res| async move {
+                assert!(matches!(res, TaskResult::Completed(0)));
+            });
+
+            group.spawn(future::pending::<()>(), |res| async move {
+                assert!(matches!(res, TaskResult::Cancelled));
+            });
+
+            let groupc = group.clone();
+            group.spawn(
+                async move {
+                    groupc.spawn(future::pending::<()>(), |res| async move {
+                        assert!(matches!(res, TaskResult::Cancelled));
+                    });
+                },
+                |res| async move {
+                    assert!(matches!(res, TaskResult::Completed(_)));
+                },
+            );
+
+            // Do something
+            smol::Timer::after(std::time::Duration::from_millis(50)).await;
+            group.cancel().await;
+        });
+    }
 }
diff --git a/core/src/lib.rs b/core/src/lib.rs
index 442b642..ae88188 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -18,13 +18,4 @@ pub mod pubsub;
 /// Collects common cryptographic tools
 pub mod crypto;
 
-use smol::Executor as SmolEx;
-use std::sync::Arc;
-
-/// A pointer to an Executor
-pub type Executor<'a> = Arc<SmolEx<'a>>;
-
-/// A Global Executor
-pub type GlobalExecutor = Arc<SmolEx<'static>>;
-
 use error::Result;
-- 
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