Function send_signal_first 

pub fn send_signal_first(
    task: &Task,
    task_state: TaskWriteGuard<'_>,
    signal_info: SignalInfo,
)

Enqueues signal_info at the front of task’s signal queue and wakes task.

Callers must not hold ThreadGroupMutableStateLock, as delivering SIGKILL or waking the thread group acquires the target thread group’s write lock.