Rollup merge of rust-lang#123811 - joboet:queue_em_up, r=ChrisDenton

Use queue-based `RwLock` on more platforms

This switches over Windows 7, SGX and Xous to the queue-based `RwLock` implementation added in rust-lang#110211, thereby fixing rust-lang#121949 for Windows 7 and partially resolving rust-lang#114581 on SGX. TEEOS can't currently be switched because it doesn't have a good thread parking implementation.

CC `@roblabla` `@raoulstrackx` `@xobs` Could you help me test this, please?
r? `@ChrisDenton` the Windows stuff should be familiar to you

library/std/src/sys/pal/sgx/libunwind_integration.rs

@@ -0,0 +1,46 @@
+//! The functions in this module are needed by libunwind. These symbols are named
+//! in pre-link args for the target specification, so keep that in sync.
+
+#![cfg(not(test))]
+
+use crate::sys::sync::RwLock;
+
+// Verify that the byte pattern libunwind uses to initialize an RwLock is
+// equivalent to the value of RwLock::new(). If the value changes,
+// `src/UnwindRustSgx.h` in libunwind needs to be changed too.
+const _: () = unsafe {
+    let bits_rust: usize = crate::mem::transmute(RwLock::new());
+    assert!(bits_rust == 0);
+};
+
+const EINVAL: i32 = 22;
+
+#[no_mangle]
+pub unsafe extern "C" fn __rust_rwlock_rdlock(p: *mut RwLock) -> i32 {
+    if p.is_null() {
+        return EINVAL;
+    }
+
+    // We cannot differentiate between reads an writes in unlock and therefore
+    // always use a write-lock. Unwinding isn't really in the hot path anyway.
+    unsafe { (*p).write() };
+    return 0;
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn __rust_rwlock_wrlock(p: *mut RwLock) -> i32 {
+    if p.is_null() {
+        return EINVAL;
+    }
+    unsafe { (*p).write() };
+    return 0;
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn __rust_rwlock_unlock(p: *mut RwLock) -> i32 {
+    if p.is_null() {
+        return EINVAL;
+    }
+    unsafe { (*p).write_unlock() };
+    return 0;
+}

library/std/src/sys/pal/sgx/mod.rs

@@ -17,6 +17,7 @@ pub mod fd;
 pub mod fs;
 #[path = "../unsupported/io.rs"]
 pub mod io;
+mod libunwind_integration;
 pub mod net;
 pub mod os;
 #[path = "../unsupported/pipe.rs"]

library/std/src/sys/pal/sgx/waitqueue/mod.rs

@@ -52,10 +52,6 @@ impl<T> WaitVariable<T> {
         WaitVariable { queue: WaitQueue::new(), lock: var }
     }
 
-    pub fn queue_empty(&self) -> bool {
-        self.queue.is_empty()
-    }
-
     pub fn lock_var(&self) -> &T {
         &self.lock
     }
@@ -68,7 +64,7 @@ impl<T> WaitVariable<T> {
 #[derive(Copy, Clone)]
 pub enum NotifiedTcs {
     Single(Tcs),
-    All { count: NonZero<usize> },
+    All { _count: NonZero<usize> },
 }
 
 /// An RAII guard that will notify a set of target threads as well as unlock
@@ -98,19 +94,6 @@ impl Default for WaitQueue {
     }
 }
 
-impl<'a, T> WaitGuard<'a, T> {
-    /// Returns which TCSes will be notified when this guard drops.
-    pub fn notified_tcs(&self) -> NotifiedTcs {
-        self.notified_tcs
-    }
-
-    /// Drop this `WaitGuard`, after dropping another `guard`.
-    pub fn drop_after<U>(self, guard: U) {
-        drop(guard);
-        drop(self);
-    }
-}
-
 impl<'a, T> Deref for WaitGuard<'a, T> {
     type Target = SpinMutexGuard<'a, WaitVariable<T>>;
 
@@ -141,10 +124,6 @@ impl WaitQueue {
         WaitQueue { inner: UnsafeList::new() }
     }
 
-    pub fn is_empty(&self) -> bool {
-        self.inner.is_empty()
-    }
-
     /// Adds the calling thread to the `WaitVariable`'s wait queue, then wait
     /// until a wakeup event.
     ///
@@ -253,7 +232,10 @@ impl WaitQueue {
             }
 
             if let Some(count) = NonZero::new(count) {
-                Ok(WaitGuard { mutex_guard: Some(guard), notified_tcs: NotifiedTcs::All { count } })
+                Ok(WaitGuard {
+                    mutex_guard: Some(guard),
+                    notified_tcs: NotifiedTcs::All { _count: count },
+                })
             } else {
                 Err(guard)
             }

library/std/src/sys/sync/rwlock/mod.rs

@@ -12,24 +12,20 @@ cfg_if::cfg_if! {
     ))] {
         mod futex;
         pub use futex::RwLock;
-    } else if #[cfg(target_family = "unix")] {
+    } else if #[cfg(any(
+        target_family = "unix",
+        all(target_os = "windows", target_vendor = "win7"),
+        all(target_vendor = "fortanix", target_env = "sgx"),
+        target_os = "xous",
+    ))] {
         mod queue;
         pub use queue::RwLock;
-    } else if #[cfg(all(target_os = "windows", target_vendor = "win7"))] {
-        mod windows7;
-        pub use windows7::RwLock;
-    } else if #[cfg(all(target_vendor = "fortanix", target_env = "sgx"))] {
-        mod sgx;
-        pub use sgx::RwLock;
     } else if #[cfg(target_os = "solid_asp3")] {
         mod solid;
         pub use solid::RwLock;
     } else if #[cfg(target_os = "teeos")] {
         mod teeos;
         pub use teeos::RwLock;
-    } else if #[cfg(target_os = "xous")] {
-        mod xous;
-        pub use xous::RwLock;
     } else {
         mod no_threads;
         pub use no_threads::RwLock;