doc: document `from_std` functions panic (#2056)

Document that conversion from `std` types must be done from within
the Tokio runtime context.

1 files changed, 16 insertions, 0 deletions

diff --git a/tokio/src/net/tcp/stream.rs b/tokio/src/net/tcp/stream.rs
index d35f1620..f32a6c4a 100644
--- a/tokio/src/net/tcp/stream.rs
+++ b/tokio/src/net/tcp/stream.rs
@@ -139,6 +139,22 @@ impl TcpStream {
     ///     Ok(())
     /// }
     /// ```
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called
+    /// from a future driven by a tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Handle::enter`](crate::runtime::Handle::enter) function.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called
+    /// from a future driven by a tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Handle::enter`](crate::runtime::Handle::enter) function.
     pub fn from_std(stream: net::TcpStream) -> io::Result<TcpStream> {
         let io = mio::net::TcpStream::from_stream(stream)?;
         let io = PollEvented::new(io)?;