chore(cbus): add `Send` bound to callback for `tarantool::cbus::Message` (close #165)

Summary

• chore(cbus): add Send bound to callback for tarantool::cbus::Message (close #165 (closed))

cc @d.rodionov @gmoshkin @e-ivkov please review it too

Ensure that

• New code is covered by tests
• API is documented
• Changelog is up to date
• Version is bumped in the appropriate Cargo.toml files

tarantool/src/cbus/mod.rs

@@ -56,7 +56,9 @@ use crate::ffi;
 use crate::ffi::tarantool::{
     cbus_endpoint_delete, cbus_endpoint_new, cbus_loop, lcpipe_delete, lcpipe_new, lcpipe_push_now,
 };
+use crate::fiber::Cond;
 use std::ffi::CString;
+use std::ops::Deref;
 use std::os::raw::c_void;
 use std::ptr;
 
@@ -96,7 +98,7 @@ pub struct Message<T> {
 
 impl<F> Message<F>
 where
-    F: FnOnce() + 'static,
+    F: FnOnce() + Send + 'static,
 {
     unsafe fn trampoline(msg: *mut c_void) {
         let msg = msg.cast::<Self>();
@@ -203,6 +205,25 @@ impl Drop for LCPipe {
     }
 }
 
+/// This is a wrapper over a [`Cond`] for sending it between threads.
+///
+/// # Safety.
+/// `UnsafeCond` must be dereference and dropped only at TX thread, drop this structure
+/// in non-TX thread will lead to application crash.
+struct UnsafeCond(Cond);
+
+impl Deref for UnsafeCond {
+    type Target = Cond;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+unsafe impl Send for UnsafeCond {}
+
+unsafe impl Sync for UnsafeCond {}
+
 #[cfg(feature = "internal_test")]
 mod tests {
     use crate::cbus;