Rollup merge of rust-lang#125800 - fortanix:raoul/rte-99-fix_mut_static_task_queue, r=jethrogb

Fix `mut` static task queue in SGX target

[PR 125046](rust-lang#125046) prevents mutable references to statics with `#[linkage]`. Such a construct was used with the tests for the `x86_64-fortanix-unknown-sgx` target. This PR fixes this and cleans up code a bit in 5 steps. Each step passes CI:

- The `mut` static is removed, and `Task` explicitly implements `Send`
- Renaming of the `task_queue::lock` function
- Pass function for `Thread` as `Send` to `Thread::imp` and update when `Packet<'scope, T>` implements `Sync`
- Storing `Task::p` as a type that implements `Send`
- Letting the compiler auto implement `Send` for `Task`

cc: ``@jethrogb``

Author: matthiaskrgr

std/src/sys/pal/sgx/thread.rs

@@ -15,7 +15,7 @@ pub use self::task_queue::JoinNotifier;
 
 mod task_queue {
     use super::wait_notify;
-    use crate::sync::{Mutex, MutexGuard, Once};
+    use crate::sync::{Mutex, MutexGuard};
 
     pub type JoinHandle = wait_notify::Waiter;
 
@@ -28,12 +28,12 @@ mod task_queue {
     }
 
     pub(super) struct Task {
-        p: Box<dyn FnOnce()>,
+        p: Box<dyn FnOnce() + Send>,
         done: JoinNotifier,
     }
 
     impl Task {
-        pub(super) fn new(p: Box<dyn FnOnce()>) -> (Task, JoinHandle) {
+        pub(super) fn new(p: Box<dyn FnOnce() + Send>) -> (Task, JoinHandle) {
             let (done, recv) = wait_notify::new();
             let done = JoinNotifier(Some(done));
             (Task { p, done }, recv)
@@ -45,18 +45,12 @@ mod task_queue {
         }
     }
 
-    #[cfg_attr(test, linkage = "available_externally")]
-    #[export_name = "_ZN16__rust_internals3std3sys3sgx6thread15TASK_QUEUE_INITE"]
-    static TASK_QUEUE_INIT: Once = Once::new();
     #[cfg_attr(test, linkage = "available_externally")]
     #[export_name = "_ZN16__rust_internals3std3sys3sgx6thread10TASK_QUEUEE"]
-    static mut TASK_QUEUE: Option<Mutex<Vec<Task>>> = None;
+    static TASK_QUEUE: Mutex<Vec<Task>> = Mutex::new(Vec::new());
 
     pub(super) fn lock() -> MutexGuard<'static, Vec<Task>> {
-        unsafe {
-            TASK_QUEUE_INIT.call_once(|| TASK_QUEUE = Some(Default::default()));
-            TASK_QUEUE.as_ref().unwrap().lock().unwrap()
-        }
+        TASK_QUEUE.lock().unwrap()
     }
 }
 
@@ -101,7 +95,7 @@ pub mod wait_notify {
 
 impl Thread {
     // unsafe: see thread::Builder::spawn_unchecked for safety requirements
-    pub unsafe fn new(_stack: usize, p: Box<dyn FnOnce()>) -> io::Result<Thread> {
+    pub unsafe fn new(_stack: usize, p: Box<dyn FnOnce() + Send>) -> io::Result<Thread> {
         let mut queue_lock = task_queue::lock();
         unsafe { usercalls::launch_thread()? };
         let (task, handle) = task_queue::Task::new(p);

std/src/thread/mod.rs

@@ -561,7 +561,8 @@ impl Builder {
         let main = Box::new(main);
         // SAFETY: dynamic size and alignment of the Box remain the same. See below for why the
         // lifetime change is justified.
-        let main = unsafe { Box::from_raw(Box::into_raw(main) as *mut (dyn FnOnce() + 'static)) };
+        let main =
+            unsafe { Box::from_raw(Box::into_raw(main) as *mut (dyn FnOnce() + Send + 'static)) };
 
         Ok(JoinInner {
             // SAFETY:
@@ -1544,7 +1545,7 @@ struct Packet<'scope, T> {
 // The type `T` should already always be Send (otherwise the thread could not
 // have been created) and the Packet is Sync because all access to the
 // `UnsafeCell` synchronized (by the `join()` boundary), and `ScopeData` is Sync.
-unsafe impl<'scope, T: Sync> Sync for Packet<'scope, T> {}
+unsafe impl<'scope, T: Send> Sync for Packet<'scope, T> {}
 
 impl<'scope, T> Drop for Packet<'scope, T> {
     fn drop(&mut self) {