https://github.com/python/cpython/commit/a3e8e7bbc3d39e9e6cfa5605df9524076176a041
commit: a3e8e7bbc3d39e9e6cfa5605df9524076176a041
branch: main
author: Kumar Aditya <[email protected]>
committer: kumaraditya303 <[email protected]>
date: 2024-11-08T12:51:11Z
summary:
GH-107803: use circular double linked list for tasks in `_asyncio` (#126577)
files:
M Modules/_asynciomodule.c
diff --git a/Modules/_asynciomodule.c b/Modules/_asynciomodule.c
index 214c18e966c4c1..58b57ae7a983c2 100644
--- a/Modules/_asynciomodule.c
+++ b/Modules/_asynciomodule.c
@@ -138,47 +138,18 @@ typedef struct {
/* Counter for autogenerated Task names */
uint64_t task_name_counter;
- /* Linked-list of all tasks which are instances of asyncio.Task or
subclasses
+ /* Circular linked-list of all tasks which are instances of asyncio.Task
or subclasses
of it. Third party tasks implementations which don't inherit from
asyncio.Task are tracked separately using the 'non_asyncio_tasks'
WeakSet.
- `tail` is used as a sentinel to mark the end of the linked-list. It
avoids one
+ `first` is used as a sentinel to mark the end of the linked-list. It
avoids one
branch in checking for empty list when adding a new task, the list is
- initialized with `head` pointing to `tail` to mark an empty list.
-
- Invariants:
- * When the list is empty:
- - asyncio_tasks.head == &asyncio_tasks.tail
- - asyncio_tasks.head->prev == NULL
- - asyncio_tasks.head->next == NULL
-
- * After adding the first task 'task1':
- - asyncio_tasks.head == task1
- - task1->next == &asyncio_tasks.tail
- - task1->prev == NULL
- - asyncio_tasks.tail.prev == task1
-
- * After adding a second task 'task2':
- - asyncio_tasks.head == task2
- - task2->next == task1
- - task2->prev == NULL
- - task1->prev == task2
- - asyncio_tasks.tail.prev == task1
-
- * After removing task 'task1':
- - asyncio_tasks.head == task2
- - task2->next == &asyncio_tasks.tail
- - task2->prev == NULL
- - asyncio_tasks.tail.prev == task2
-
- * After removing task 'task2', the list is empty:
- - asyncio_tasks.head == &asyncio_tasks.tail
- - asyncio_tasks.head->prev == NULL
- - asyncio_tasks.tail.prev == NULL
- - asyncio_tasks.tail.next == NULL
+ initialized with `head`, `head->next` and `head->prev` pointing to
`first`
+ to mark an empty list.
+
*/
struct {
- TaskObj tail;
+ TaskObj first;
TaskObj *head;
} asyncio_tasks;
@@ -1925,7 +1896,7 @@ register_task(asyncio_state *state, TaskObj *task)
{
ASYNCIO_STATE_LOCK(state);
assert(Task_Check(state, task));
- assert(task != &state->asyncio_tasks.tail);
+ assert(task != &state->asyncio_tasks.first);
if (task->next != NULL) {
// already registered
goto exit;
@@ -1934,8 +1905,10 @@ register_task(asyncio_state *state, TaskObj *task)
assert(state->asyncio_tasks.head != NULL);
task->next = state->asyncio_tasks.head;
+ task->prev = state->asyncio_tasks.head->prev;
+ state->asyncio_tasks.head->prev->next = task;
state->asyncio_tasks.head->prev = task;
- state->asyncio_tasks.head = task;
+
exit:
ASYNCIO_STATE_UNLOCK(state);
}
@@ -1951,7 +1924,7 @@ unregister_task(asyncio_state *state, TaskObj *task)
{
ASYNCIO_STATE_LOCK(state);
assert(Task_Check(state, task));
- assert(task != &state->asyncio_tasks.tail);
+ assert(task != &state->asyncio_tasks.first);
if (task->next == NULL) {
// not registered
assert(task->prev == NULL);
@@ -1959,12 +1932,7 @@ unregister_task(asyncio_state *state, TaskObj *task)
goto exit;
}
task->next->prev = task->prev;
- if (task->prev == NULL) {
- assert(state->asyncio_tasks.head == task);
- state->asyncio_tasks.head = task->next;
- } else {
- task->prev->next = task->next;
- }
+ task->prev->next = task->next;
task->next = NULL;
task->prev = NULL;
assert(state->asyncio_tasks.head != task);
@@ -3657,12 +3625,10 @@ _asyncio_all_tasks_impl(PyObject *module, PyObject
*loop)
Py_DECREF(eager_iter);
int err = 0;
ASYNCIO_STATE_LOCK(state);
- TaskObj *head = state->asyncio_tasks.head;
+ TaskObj *first = &state->asyncio_tasks.first;
+ TaskObj *head = state->asyncio_tasks.head->next;
Py_INCREF(head);
- assert(head != NULL);
- assert(head->prev == NULL);
- TaskObj *tail = &state->asyncio_tasks.tail;
- while (head != tail)
+ while (head != first)
{
if (add_one_task(state, tasks, (PyObject *)head, loop) < 0) {
Py_DECREF(tasks);
@@ -3875,9 +3841,12 @@ static int
module_exec(PyObject *mod)
{
asyncio_state *state = get_asyncio_state(mod);
- Py_SET_TYPE(&state->asyncio_tasks.tail, state->TaskType);
- _Py_SetImmortalUntracked((PyObject *)&state->asyncio_tasks.tail);
- state->asyncio_tasks.head = &state->asyncio_tasks.tail;
+
+ Py_SET_TYPE(&state->asyncio_tasks.first, state->TaskType);
+ _Py_SetImmortalUntracked((PyObject *)&state->asyncio_tasks.first);
+ state->asyncio_tasks.head = &state->asyncio_tasks.first;
+ state->asyncio_tasks.head->next = &state->asyncio_tasks.first;
+ state->asyncio_tasks.head->prev = &state->asyncio_tasks.first;
#define CREATE_TYPE(m, tp, spec, base) \
do { \
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