From 2f4c016079727b96f51a602e86c16f7473a1f7a7 Mon Sep 17 00:00:00 2001
From: Suryakant Soni <suryakant.soni@coinbase.com>
Date: Tue, 13 May 2025 17:06:42 +0530
Subject: [PATCH] tokio:issue-6374-demo : demoing issue 2

---
 tokio/src/fs/file/tests.rs | 53 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/tokio/src/fs/file/tests.rs b/tokio/src/fs/file/tests.rs
index e824876c131..5316dd24ed6 100644
--- a/tokio/src/fs/file/tests.rs
+++ b/tokio/src/fs/file/tests.rs
@@ -976,3 +976,56 @@ fn busy_file_seek_error() {
     let mut t = task::spawn(file.seek(SeekFrom::Start(0)));
     assert_ready_err!(t.poll());
 }
+
+// issue 2 Demonstration
+#[test]
+fn open_write_old() {
+    let mut file = MockFile::default();
+    file.expect_inner_write()
+        .once()
+        .with(eq(HELLO))
+        .returning(|buf| Ok(buf.len()));
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+
+    assert_eq!(0, pool::len());
+
+    // This poll returns Ready even though the queued blocking write task hasn't run yet.`pool::run_one();` here
+    // This is the async contract violation we're fixing.
+    assert_ready_ok!(t.poll());
+
+    assert_eq!(1, pool::len());
+
+    pool::run_one();
+
+    assert!(!t.is_woken());
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+}
+#[test]
+fn open_write_new() {
+    let mut file = MockFile::default();
+    file.expect_inner_write()
+        .once()
+        .with(eq(HELLO))
+        .returning(|buf| Ok(buf.len()));
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+
+    // In the fixed code, this returns Pending because spawn_blocking hasn't completed yet.
+    // This assertion fails in the old (broken) code, because it incorrectly returns Ready too early.
+    assert_pending!(t.poll());
+    // running spawn task
+    pool::run_one();
+    assert!(t.is_woken());
+    // after spawn task is run - in the sequential polling iteration, ˝the poll status is set to ready
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+}