improve the TaskGroup API

the TaskGroup now holds an Executor instead of passing it when calling
its spawn method

also, define a global executor `Executor<'static>` and use static
lifetime instead of a lifetime placeholder

This improvement simplify the code for spawning a new task. There is no
need to pass the executor around.

1 files changed, 28 insertions, 0 deletions

diff --git a/core/src/executor.rs b/core/src/executor.rs
new file mode 100644
index 0000000..136f6ea
--- /dev/null
+++ b/core/src/executor.rs
@@ -0,0 +1,28 @@
+
+
+/// Returns an estimate of the default amount of parallelism a program should use.
+/// see `std::thread::available_parallelism`
+fn available_parallelism() -> usize {
+    thread::available_parallelism()
+        .map(NonZeroUsize::get)
+        .unwrap_or(1)
+}
+
+/// Run a multi-threaded executor
+pub fn run_executor<T>(main_future: impl Future<Output = T>, ex: Executor<'_>) {
+    let (signal, shutdown) = channel::unbounded::<()>();
+
+    let num_threads = available_parallelism();
+
+    Parallel::new()
+        .each(0..(num_threads), |_| {
+            future::block_on(ex.run(shutdown.recv()))
+        })
+        // Run the main future on the current thread.
+        .finish(|| {
+            future::block_on(async {
+                main_future.await;
+                drop(signal);
+            })
+        });
+}