std: use ptr::dangling_mut() in thread locals and related code

Author: bluss

src/libstd/io/lazy.rs

@@ -37,7 +37,7 @@ impl<T: Send + Sync + 'static> Lazy<T> {
             let ptr = self.ptr.get();
             let ret = if ptr.is_null() {
                 Some(self.init())
-            } else if ptr as usize == 1 {
+            } else if ptr == ptr::dangling_mut() {
                 None
             } else {
                 Some((*ptr).clone())
@@ -55,7 +55,7 @@ impl<T: Send + Sync + 'static> Lazy<T> {
         let registered = sys_common::at_exit(move || {
             self.lock.lock();
             let ptr = self.ptr.get();
-            self.ptr.set(1 as *mut _);
+            self.ptr.set(ptr::dangling_mut());
             self.lock.unlock();
             drop(Box::from_raw(ptr))
         });

src/libstd/lib.rs

@@ -301,6 +301,7 @@
 #![feature(placement_in_syntax)]
 #![feature(placement_new_protocol)]
 #![feature(prelude_import)]
+#![feature(ptr_dangling)]
 #![feature(rand)]
 #![feature(raw)]
 #![feature(repr_align)]

src/libstd/sys_common/thread_local.rs

@@ -36,7 +36,7 @@
 //! ```ignore (cannot-doctest-private-modules)
 //! let key = Key::new(None);
 //! assert!(key.get().is_null());
-//! key.set(1 as *mut u8);
+//! key.set(std::ptr::dangling_mut::<u8>());
 //! assert!(!key.get().is_null());
 //!
 //! drop(key); // deallocate this TLS slot.
@@ -50,7 +50,7 @@
 //!
 //! unsafe {
 //!     assert!(KEY.get().is_null());
-//!     KEY.set(1 as *mut u8);
+//!     KEY.set(std::ptr::dangling_mut::<u8>());
 //! }
 //! ```
 
@@ -81,7 +81,7 @@ use sys_common::mutex::Mutex;
 ///
 /// unsafe {
 ///     assert!(KEY.get().is_null());
-///     KEY.set(1 as *mut u8);
+///     KEY.set(std::ptr::dangling_mut::<u8>());
 /// }
 /// ```
 pub struct StaticKey {
@@ -110,7 +110,7 @@ pub struct StaticKey {
 ///
 /// let key = Key::new(None);
 /// assert!(key.get().is_null());
-/// key.set(1 as *mut u8);
+/// key.set(std::ptr::dangling_mut::<u8>());
 /// assert!(!key.get().is_null());
 ///
 /// drop(key); // deallocate this TLS slot.

src/libstd/thread/local.rs

@@ -492,7 +492,7 @@ pub mod os {
         pub unsafe fn get(&'static self) -> Option<&'static UnsafeCell<Option<T>>> {
             let ptr = self.os.get() as *mut Value<T>;
             if !ptr.is_null() {
-                if ptr as usize == 1 {
+                if ptr == ptr::dangling_mut() {
                     return None
                 }
                 return Some(&(*ptr).value);
@@ -520,7 +520,7 @@ pub mod os {
         // before we return from the destructor ourselves.
         let ptr = Box::from_raw(ptr as *mut Value<T>);
         let key = ptr.key;
-        key.os.set(1 as *mut u8);
+        key.os.set(ptr::dangling_mut());
         drop(ptr);
         key.os.set(ptr::null_mut());
     }