Rollup merge of rust-lang#105695 - joboet:remove_generic_parker, r=m-ou-se

Replace generic thread parker with explicit no-op parker

With rust-lang#98391 merged, all platforms supporting threads now have their own parking implementations. Therefore, the generic implementation can be removed. On the remaining platforms (really just WASM without atomics), parking is not supported, so calls to `thread::park` now return instantly, which is [allowed by their API](https://doc.rust-lang.org/nightly/std/thread/fn.park.html). This is a change in behaviour, as spurious wakeups do not currently occur since all platforms guard against them. It is invalid to depend on this, but I'm still going to tag this as libs-api for confirmation.

```@rustbot``` label +T-libs +T-libs-api +A-atomic

r? rust-lang/libs

Author: Manishearth

library/std/src/sys/unsupported/mod.rs

@@ -22,6 +22,7 @@ pub mod thread;
 #[cfg(target_thread_local)]
 pub mod thread_local_dtor;
 pub mod thread_local_key;
+pub mod thread_parking;
 pub mod time;
 
 mod common;

library/std/src/sys/unsupported/thread_parking.rs

@@ -0,0 +1,11 @@
+use crate::pin::Pin;
+use crate::time::Duration;
+
+pub struct Parker {}
+
+impl Parker {
+    pub unsafe fn new_in_place(_parker: *mut Parker) {}
+    pub unsafe fn park(self: Pin<&Self>) {}
+    pub unsafe fn park_timeout(self: Pin<&Self>, _dur: Duration) {}
+    pub fn unpark(self: Pin<&Self>) {}
+}

library/std/src/sys/wasi/mod.rs

@@ -47,6 +47,8 @@ pub mod thread;
 pub mod thread_local_dtor;
 #[path = "../unsupported/thread_local_key.rs"]
 pub mod thread_local_key;
+#[path = "../unsupported/thread_parking.rs"]
+pub mod thread_parking;
 pub mod time;
 
 cfg_if::cfg_if! {

library/std/src/sys/wasm/mod.rs

@@ -70,6 +70,8 @@ cfg_if::cfg_if! {
         pub mod once;
         #[path = "../unsupported/thread.rs"]
         pub mod thread;
+        #[path = "../unsupported/thread_parking.rs"]
+        pub mod thread_parking;
     }
 }
 

library/std/src/sys_common/thread_parking/generic.rs

@@ -18,10 +18,7 @@ cfg_if::cfg_if! {
     ))] {
         mod id;
         pub use id::Parker;
-    } else if #[cfg(any(windows, target_family = "unix"))] {
-        pub use crate::sys::thread_parking::Parker;
     } else {
-        mod generic;
-        pub use generic::Parker;
+        pub use crate::sys::thread_parking::Parker;
     }
 }