feature(fiber): fiber name is set from caller source location

this adds some overhead when creating fibers as now the compiler passes
an additional implicit parameter to the fiber creation functions which
also call a function for getting the location info.

However at some point in the future these functions will become `const`
which means that the overhead will disappear automatically.

The allocations required for `format` won't probably disappear as soon
though :(

Author: gmoshkin

tarantool/src/fiber.rs

@@ -338,7 +338,11 @@ macro_rules! inner_spawn {
     ($self:expr, $invocation:tt) => {
         {
             let Self { name, attr, f } = $self;
-            let name = name.unwrap_or_else(|| "<rust>".into());
+            let name = if let Some(name) = name {
+                name
+            } else {
+                impl_details::fiber_name_from_caller()
+            };
             Ok(Fyber::$invocation(name, f, attr.as_ref())?.spawn())
         }
     };
@@ -355,6 +359,7 @@ where
     /// to the new fiber immediately.
     ///
     /// See the [`start`] free function for more details.
+    #[track_caller]
     pub fn start(self) -> Result<C::JoinHandle> {
         inner_spawn!(self, immediate)
     }
@@ -370,6 +375,7 @@ where
     /// In the future we are planning to add a correct implementation.
     ///
     /// See the [`defer`] free function for more details.
+    #[track_caller]
     pub fn defer(self) -> Result<C::JoinHandle> {
         inner_spawn!(self, deferred)
     }
@@ -498,8 +504,11 @@ where
         Self { callee }
     }
 
+    #[track_caller]
     pub fn spawn(self) -> Result<C::JoinHandle> {
         let Self { callee } = self;
+        let name = impl_details::fiber_name_from_caller();
+
         let fiber_ref = unsafe {
             let l = ffi::luaT_state();
             lua::lua_getglobal(l, c_ptr!("require"));
@@ -520,6 +529,17 @@ where
             impl_details::guarded_pcall(l, 2, 0)
                 .map_err(|e| panic!("{}", e))
                 .unwrap();
+
+            lua::lua_getfield(l, -1, c_ptr!("name"));
+            lua::lua_pushvalue(l, -2);
+            lua::lua_pushlstring(l, name.as_ptr() as _, name.len());
+            impl_details::guarded_pcall(l, 2, 0)
+                .map_err(|e| {
+                    // Pop the fiber module and fiber instance from the stack
+                    lua::lua_pop(l, 2);
+                    e
+                })?;
+
             let fiber_ref = lua::luaL_ref(l, lua::LUA_REGISTRYINDEX);
             // pop the fiber module from the stack
             lua::lua_pop(l, 1);
@@ -752,6 +772,12 @@ mod impl_details {
             0
         }
     }
+
+    #[track_caller]
+    pub(super) fn fiber_name_from_caller() -> String {
+        let loc = std::panic::Location::caller();
+        format!("<rust:{}:{}:{}>", loc.file(), loc.line(), loc.column())
+    }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -1170,6 +1196,7 @@ impl TrampolineArgs for VaList {
 /// This will create a fiber using default parameters of [`Builder`], if you
 /// want to specify the stack size or the name of the thread, use this API
 /// instead.
+#[track_caller]
 pub fn start<'f, F, T>(f: F) -> JoinHandle<'f, T>
 where
     F: FnOnce() -> T,
@@ -1188,6 +1215,7 @@ where
 /// should always be used instead of the latter.
 ///
 /// For more details see: [`start`]
+#[track_caller]
 pub fn start_proc<'f, F>(f: F) -> UnitJoinHandle<'f>
 where
     F: FnOnce(),
@@ -1207,6 +1235,7 @@ where
 ///
 /// The new fiber can be joined by calling [`LuaJoinHandle::join`] method on
 /// it's join handle.
+#[track_caller]
 pub fn defer<'f, F, T>(f: F) -> LuaJoinHandle<'f, T>
 where
     F: FnOnce() -> T,
@@ -1226,6 +1255,7 @@ where
 /// it's join handle.
 ///
 /// This is an optimized version [`defer`]`<F, ()>`.
+#[track_caller]
 pub fn defer_proc<'f, F>(f: F) -> LuaUnitJoinHandle<'f>
 where
     F: FnOnce(),

tests/src/fiber/mod.rs

@@ -468,3 +468,26 @@ pub fn lifetime() {
     // }.join();
 }
 
+fn fiber_name() -> String {
+    let lua = tarantool::lua_state();
+    lua.eval("return require 'fiber'.name()").unwrap()
+}
+
+pub fn name() {
+    let name = fiber::start(fiber_name).join();
+    assert_eq!(name, format!("<rust:{}:{}:{}>", file!(), line!() - 1, 16));
+
+    let (tx, rx) = Rc::new(Cell::new(None)).into_clones();
+    fiber::start_proc(|| tx.set(Some(fiber_name()))).join();
+    let expected = format!("<rust:{}:{}:{}>", file!(), line!() - 1, 5);
+    assert_eq!(rx.take().unwrap(), expected);
+
+    let name = fiber::defer(fiber_name).join();
+    assert_eq!(name, format!("<rust:{}:{}:{}>", file!(), line!() - 1, 16));
+
+    let (tx, rx) = Rc::new(Cell::new(None)).into_clones();
+    fiber::defer_proc(|| tx.set(Some(fiber_name()))).join();
+    let expected = format!("<rust:{}:{}:{}>", file!(), line!() - 1, 5);
+    assert_eq!(rx.take().unwrap(), expected);
+}
+

tests/src/lib.rs

@@ -382,6 +382,7 @@ fn run_tests(cfg: TestConfig) -> Result<bool, io::Error> {
                 fiber::deferred_with_cond,
                 fiber::lua_thread,
                 fiber::lifetime,
+                fiber::name,
 
                 fiber::channel::send_self,
                 fiber::channel::send_full,