sync: move CancellationToken to tokio-util (#2721)

* sync: move CancellationToken to tokio-util

The `CancellationToken` utility is only available with the
`tokio_unstable` flag. This was done as the API is not final, but it
adds friction for users.

This patch moves `CancellationToken` to tokio-util where it is generally
available. The tokio-util crate does not have any constraints on
breaking change releases.

* fix clippy

* clippy again

tokio-util/src/sync/tests/loom_cancellation_token.rs

@@ -0,0 +1,155 @@
+use crate::sync::CancellationToken;
+
+use loom::{future::block_on, thread};
+use tokio_test::assert_ok;
+
+#[test]
+fn cancel_token() {
+    loom::model(|| {
+        let token = CancellationToken::new();
+        let token1 = token.clone();
+
+        let th1 = thread::spawn(move || {
+            block_on(async {
+                token1.cancelled().await;
+            });
+        });
+
+        let th2 = thread::spawn(move || {
+            token.cancel();
+        });
+
+        assert_ok!(th1.join());
+        assert_ok!(th2.join());
+    });
+}
+
+#[test]
+fn cancel_with_child() {
+    loom::model(|| {
+        let token = CancellationToken::new();
+        let token1 = token.clone();
+        let token2 = token.clone();
+        let child_token = token.child_token();
+
+        let th1 = thread::spawn(move || {
+            block_on(async {
+                token1.cancelled().await;
+            });
+        });
+
+        let th2 = thread::spawn(move || {
+            token2.cancel();
+        });
+
+        let th3 = thread::spawn(move || {
+            block_on(async {
+                child_token.cancelled().await;
+            });
+        });
+
+        assert_ok!(th1.join());
+        assert_ok!(th2.join());
+        assert_ok!(th3.join());
+    });
+}
+
+#[test]
+fn drop_token_no_child() {
+    loom::model(|| {
+        let token = CancellationToken::new();
+        let token1 = token.clone();
+        let token2 = token.clone();
+
+        let th1 = thread::spawn(move || {
+            drop(token1);
+        });
+
+        let th2 = thread::spawn(move || {
+            drop(token2);
+        });
+
+        let th3 = thread::spawn(move || {
+            drop(token);
+        });
+
+        assert_ok!(th1.join());
+        assert_ok!(th2.join());
+        assert_ok!(th3.join());
+    });
+}
+
+#[test]
+fn drop_token_with_childs() {
+    loom::model(|| {
+        let token1 = CancellationToken::new();
+        let child_token1 = token1.child_token();
+        let child_token2 = token1.child_token();
+
+        let th1 = thread::spawn(move || {
+            drop(token1);
+        });
+
+        let th2 = thread::spawn(move || {
+            drop(child_token1);
+        });
+
+        let th3 = thread::spawn(move || {
+            drop(child_token2);
+        });
+
+        assert_ok!(th1.join());
+        assert_ok!(th2.join());
+        assert_ok!(th3.join());
+    });
+}
+
+#[test]
+fn drop_and_cancel_token() {
+    loom::model(|| {
+        let token1 = CancellationToken::new();
+        let token2 = token1.clone();
+        let child_token = token1.child_token();
+
+        let th1 = thread::spawn(move || {
+            drop(token1);
+        });
+
+        let th2 = thread::spawn(move || {
+            token2.cancel();
+        });
+
+        let th3 = thread::spawn(move || {
+            drop(child_token);
+        });
+
+        assert_ok!(th1.join());
+        assert_ok!(th2.join());
+        assert_ok!(th3.join());
+    });
+}
+
+#[test]
+fn cancel_parent_and_child() {
+    loom::model(|| {
+        let token1 = CancellationToken::new();
+        let token2 = token1.clone();
+        let child_token = token1.child_token();
+
+        let th1 = thread::spawn(move || {
+            drop(token1);
+        });
+
+        let th2 = thread::spawn(move || {
+            token2.cancel();
+        });
+
+        let th3 = thread::spawn(move || {
+            child_token.cancel();
+        });
+
+        assert_ok!(th1.join());
+        assert_ok!(th2.join());
+        assert_ok!(th3.join());
+    });
+}

tokio-util/src/sync/tests/mod.rs

@@ -0,0 +1 @@
+