gh-103793: Defer formatting task name (#103767)

The default task name is "Task-<counter>" (if no name is passed in during Task creation).
This is initialized in `Task.__init__` (C impl) using string formatting, which can be quite slow.
Actually using the task name in real world code is not very common, so this is wasted init.

Let's defer this string formatting to the first time the name is read (in `get_name` impl),
so we don't need to pay the string formatting cost if the task name is never read.

We don't change the order in which tasks are assigned numbers (if they are) --
the number is set on task creation, as a PyLong instead of a formatted string.

Co-authored-by: Łukasz Langa <lukasz@langa.pl>

4 files changed, 29 insertions, 2 deletions

diff --git a/Doc/whatsnew/3.12.rst b/Doc/whatsnew/3.12.rst
index 908cf3bb36..f4ee30b0d4 100644
--- a/Doc/whatsnew/3.12.rst
+++ b/Doc/whatsnew/3.12.rst
@@ -610,6 +610,9 @@ Optimizations
   replacement strings containing group references by 2--3 times.
   (Contributed by Serhiy Storchaka in :gh:`91524`.)
 
+* Speed up :class:`asyncio.Task` creation by deferring expensive string formatting.
+  (Contributed by Itamar O in :gh:`103793`.)
+
 
 CPython bytecode changes
 ========================
diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py
index 31622c9147..6e8a51ce25 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -399,6 +399,18 @@ class BaseTaskTests:
         self.loop.run_until_complete(t1)
         self.loop.run_until_complete(t2)
 
+    def test_task_set_name_pylong(self):
+        # test that setting the task name to a PyLong explicitly doesn't
+        # incorrectly trigger the deferred name formatting logic
+        async def notmuch():
+            return 123
+
+        t = self.new_task(self.loop, notmuch(), name=987654321)
+        self.assertEqual(t.get_name(), '987654321')
+        t.set_name(123456789)
+        self.assertEqual(t.get_name(), '123456789')
+        self.loop.run_until_complete(t)
+
     def test_task_repr_name_not_str(self):
         async def notmuch():
             return 123
diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-04-24-14-38-16.gh-issue-103793.kqoH6Q.rst b/Misc/NEWS.d/next/Core and Builtins/2023-04-24-14-38-16.gh-issue-103793.kqoH6Q.rst
new file mode 100644
index 0000000000..c48348798e
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2023-04-24-14-38-16.gh-issue-103793.kqoH6Q.rst
@@ -0,0 +1,3 @@
+Optimized asyncio Task creation by deferring expensive string formatting
+(task name generation) from Task creation to the first time ``get_name`` is
+called. This makes asyncio benchmarks up to 5% faster.
diff --git a/Modules/_asynciomodule.c b/Modules/_asynciomodule.c
index 2476dca6f5..82dbc08732 100644
--- a/Modules/_asynciomodule.c
+++ b/Modules/_asynciomodule.c
@@ -2069,8 +2069,10 @@ _asyncio_Task___init___impl(TaskObj *self, PyObject *coro, PyObject *loop,
     Py_XSETREF(self->task_coro, coro);
 
     if (name == Py_None) {
-        name = PyUnicode_FromFormat("Task-%" PRIu64,
-                                    ++state->task_name_counter);
+        // optimization: defer task name formatting
+        // store the task counter as PyLong in the name
+        // for deferred formatting in get_name
+        name = PyLong_FromUnsignedLongLong(++state->task_name_counter);
     } else if (!PyUnicode_CheckExact(name)) {
         name = PyObject_Str(name);
     } else {
@@ -2449,6 +2451,13 @@ _asyncio_Task_get_name_impl(TaskObj *self)
 /*[clinic end generated code: output=0ecf1570c3b37a8f input=a4a6595d12f4f0f8]*/
 {
     if (self->task_name) {
+        if (PyLong_CheckExact(self->task_name)) {
+            PyObject *name = PyUnicode_FromFormat("Task-%S", self->task_name);
+            if (name == NULL) {
+                return NULL;
+            }
+            Py_SETREF(self->task_name, name);
+        }
         return Py_NewRef(self->task_name);
     }