Merge pull request #951 from mglagla/try-current

add task::try_current

Author: yoshuawuyts

src/task/current.rs

@@ -23,6 +23,26 @@ use crate::task::{Task, TaskLocalsWrapper};
 /// # })
 /// ```
 pub fn current() -> Task {
-    TaskLocalsWrapper::get_current(|t| t.task().clone())
-        .expect("`task::current()` called outside the context of a task")
+    try_current().expect("`task::current()` called outside the context of a task")
 }
+
+/// Returns a handle to the current task if called within the context of a task created by [`block_on`],
+/// [`spawn`], or [`Builder::spawn`], otherwise returns `None`.
+///
+/// [`block_on`]: fn.block_on.html
+/// [`spawn`]: fn.spawn.html
+/// [`Builder::spawn`]: struct.Builder.html#method.spawn
+///
+/// # Examples
+///
+/// ```
+/// use async_std::task;
+///
+/// match task::try_current() {
+///     Some(t) => println!("The name of this task is {:?}", t.name()),
+///     None    => println!("Not inside a task!"),
+/// }
+/// ```
+pub fn try_current() -> Option<Task> {
+    TaskLocalsWrapper::get_current(|t| t.task().clone())
+}

src/task/mod.rs

@@ -133,7 +133,7 @@ cfg_std! {
 cfg_default! {
     pub use block_on::block_on;
     pub use builder::Builder;
-    pub use current::current;
+    pub use current::{current, try_current};
     pub use task::Task;
     pub use task_id::TaskId;
     pub use join_handle::JoinHandle;