commit d2a958f4227460aa0d6b42c2b3a24ad01ed3d388
author Mazdak Farrokhzad <twingoow@gmail.com> Fri Mar 22 19:31:27 2019 +0100
committer GitHub <noreply@github.com> Fri Mar 22 19:31:27 2019 +0100
tree 64a37ec8b26af12b57e5150252e462118c1d6ffc
parent 28644cd9fafe92fb8ce14e15cada77b9757afc1a
parent c1d9191fa576c600775b4fbb90a3d09ca5e0fa0b

Rollup merge of #59291 - SimonSapin:nonzero-thread-id, r=alexcrichton

Make Option<ThreadId> no larger than ThreadId, with NonZeroU64

src/libstd/thread/mod.rs

diff --git a/src/libstd/thread/mod.rs b/src/libstd/thread/mod.rs
index 08f0aa2..d856f9b 100644
--- a/src/libstd/thread/mod.rs
+++ b/src/libstd/thread/mod.rs
@@ -163,6 +163,7 @@
 use crate::fmt;
 use crate::io;
 use crate::mem;
+use crate::num::NonZeroU64;
 use crate::panic;
 use crate::panicking;
 use crate::str;
@@ -1036,7 +1037,7 @@
 /// [`Thread`]: ../../std/thread/struct.Thread.html
 #[stable(feature = "thread_id", since = "1.19.0")]
 #[derive(Eq, PartialEq, Clone, Copy, Hash, Debug)]
-pub struct ThreadId(u64);
+pub struct ThreadId(NonZeroU64);
 
 impl ThreadId {
     // Generate a new unique thread ID.
@@ -1044,7 +1045,7 @@
         // We never call `GUARD.init()`, so it is UB to attempt to
         // acquire this mutex reentrantly!
         static GUARD: mutex::Mutex = mutex::Mutex::new();
-        static mut COUNTER: u64 = 0;
+        static mut COUNTER: u64 = 1;
 
         unsafe {
             let _guard = GUARD.lock();
@@ -1058,7 +1059,7 @@
             let id = COUNTER;
             COUNTER += 1;
 
-            ThreadId(id)
+            ThreadId(NonZeroU64::new(id).unwrap())
         }
     }
 }
@@ -1484,9 +1485,10 @@
 mod tests {
     use super::Builder;
     use crate::any::Any;
+    use crate::mem;
     use crate::sync::mpsc::{channel, Sender};
     use crate::result;
-    use crate::thread;
+    use crate::thread::{self, ThreadId};
     use crate::time::Duration;
     use crate::u32;
 
@@ -1717,6 +1719,11 @@
     }
 
     #[test]
+    fn test_size_of_option_thread_id() {
+        assert_eq!(mem::size_of::<Option<ThreadId>>(), mem::size_of::<ThreadId>());
+    }
+
+    #[test]
     fn test_thread_id_equal() {
         assert!(thread::current().id() == thread::current().id());
     }