Windows: Fallback for overlapped I/O

Try waiting on the file handle once. If that fails then give up.

library/std/src/sys/windows/c.rs

@@ -326,7 +326,9 @@ union IO_STATUS_BLOCK_union {
 }
 impl Default for IO_STATUS_BLOCK_union {
     fn default() -> Self {
-        Self { Pointer: ptr::null_mut() }
+        let mut this = Self { Pointer: ptr::null_mut() };
+        this.Status = STATUS_PENDING;
+        this
     }
 }
 #[repr(C)]
@@ -335,6 +337,16 @@ pub struct IO_STATUS_BLOCK {
     u: IO_STATUS_BLOCK_union,
     pub Information: usize,
 }
+impl IO_STATUS_BLOCK {
+    pub fn status(&self) -> NTSTATUS {
+        // SAFETY: If `self.u.Status` was set then this is obviously safe.
+        // If `self.u.Pointer` was set then this is the equivalent to converting
+        // the pointer to an integer, which is also safe.
+        // Currently the only safe way to construct `IO_STATUS_BLOCK` outside of
+        // this module is to call the `default` method, which sets the `Status`.
+        unsafe { self.u.Status }
+    }
+}
 
 pub type LPOVERLAPPED_COMPLETION_ROUTINE = unsafe extern "system" fn(
     dwErrorCode: DWORD,

library/std/src/sys/windows/handle.rs

@@ -248,6 +248,13 @@ impl Handle {
             offset.map(|n| n as _).as_ref(),
             None,
         );
+
+        let status = if status == c::STATUS_PENDING {
+            c::WaitForSingleObject(self.as_raw_handle(), c::INFINITE);
+            io_status.status()
+        } else {
+            status
+        };
         match status {
             // If the operation has not completed then abort the process.
             // Doing otherwise means that the buffer and stack may be written to
@@ -291,6 +298,12 @@ impl Handle {
                 None,
             )
         };
+        let status = if status == c::STATUS_PENDING {
+            unsafe { c::WaitForSingleObject(self.as_raw_handle(), c::INFINITE) };
+            io_status.status()
+        } else {
+            status
+        };
         match status {
             // If the operation has not completed then abort the process.
             // Doing otherwise means that the buffer may be read and the stack