Scheduler: Don't search threads spawned before the current thread to find children

Children will always be spawned later (and thus have a higher PID) than their parent.

kernel/src/sys/exit.cpp

@@ -7,7 +7,10 @@ Result<u64> sys_exit(Registers*, SyscallArgs args)
 
     Thread* current = Scheduler::current();
 
-    Scheduler::for_each_child((pid_t)current->id, [](Thread* child) { child->parent_id = 1; });
+    Scheduler::for_each_child(current, [](Thread* child) {
+        child->parent_id = 1;
+        return true;
+    });
 
     current->status = status;
     current->state = ThreadState::Exited;

kernel/src/sys/waitpid.cpp

@@ -27,11 +27,11 @@ Result<u64> sys_waitpid(Registers*, SyscallArgs args)
     }
     else if (pid == -1)
     {
-        if (!Scheduler::has_children((pid_t)current->id)) return err(ECHILD);
+        if (!Scheduler::has_children(current)) return err(ECHILD);
 
         Option<Thread*> child;
 
-        while (child = Scheduler::find_exited_child((pid_t)current->id), !child.has_value())
+        while (child = Scheduler::find_exited_child(current), !child.has_value())
         {
             if (options & WNOHANG) return err(EAGAIN);
             kernel_sleep(10);

kernel/src/thread/Scheduler.cpp

@@ -249,12 +249,13 @@ namespace Scheduler
 
         g_current->ticks_left--;
 
-        g_threads.for_each([](Thread* thread) {
+        for (auto* const thread : g_threads)
+        {
             if (thread->state == ThreadState::Sleeping)
             {
                 if (--thread->sleep_ticks_left == 0) thread->state = ThreadState::Runnable;
             }
-        });
+        }
 
         if (!g_current->ticks_left) switch_task(regs);
     }
@@ -276,30 +277,37 @@ namespace Scheduler
 
     Option<Thread*> find_by_pid(pid_t pid)
     {
-        Option<Thread*> result;
+        for (auto* const thread : g_threads)
+        {
+            if (thread->id == (u64)pid && thread->state != ThreadState::Dying) return thread;
+        }
 
-        g_threads.for_each([&](Thread* thread) {
+        return {};
-            if (thread->id == (u64)pid && thread->state != ThreadState::Dying) result = thread;
+    }
+
+    bool has_children(Thread* thread)
+    {
+        bool result { false };
+
+        for_each_child(thread, [&](Thread*) {
+            result = true;
+            return false;
         });
 
         return result;
     }
 
-    bool has_children(pid_t pid)
+    Option<Thread*> find_exited_child(Thread* thread)
-    {
-        bool result { false };
-
-        for_each_child(pid, [&](Thread*) { result = true; });
-
-        return result;
-    }
-
-    Option<Thread*> find_exited_child(pid_t pid)
     {
         Option<Thread*> result;
 
-        for_each_child(pid, [&](Thread* child) {
+        for_each_child(thread, [&](Thread* child) {
-            if (!result.has_value() && child->state == ThreadState::Exited) result = child;
+            if (!result.has_value() && child->state == ThreadState::Exited)
+            {
+                result = child;
+                return false;
+            }
+            return true;
         });
 
         return result;

kernel/src/thread/Scheduler.h

@@ -29,16 +29,21 @@ namespace Scheduler
 
     Option<Thread*> find_by_pid(pid_t pid);
 
-    template <typename Callback> void for_each_child(pid_t pid, Callback callback)
+    template <typename Callback> void for_each_child(Thread* thread, Callback callback)
     {
-        g_threads.for_each([&](Thread* thread) {
+        for (Thread* current = thread; current; current = g_threads.next(current).value_or(nullptr))
-            if (thread->parent_id == (u64)pid) callback(thread);
+        {
-        });
+            if (current && current->parent_id == thread->id)
+            {
+                bool should_continue = callback(current);
+                if (!should_continue) return;
+            }
+        }
     }
 
-    bool has_children(pid_t pid);
+    bool has_children(Thread* thread);
 
-    Option<Thread*> find_exited_child(pid_t pid);
+    Option<Thread*> find_exited_child(Thread* thread);
 }
 
 extern "C" void kernel_yield();

libluna/include/luna/LinkedList.h

@@ -210,6 +210,47 @@ template <typename T> class LinkedList
         return m_count;
     }
 
+    struct LinkedListIterator
+    {
+        typedef T* PtrT;
+
+      private:
+        LinkedListIterator(PtrT ptr, LinkedList<T>& list) : m_ptr(ptr), m_list(list)
+        {
+        }
+
+        PtrT m_ptr;
+        LinkedList<T>& m_list;
+
+      public:
+        PtrT& operator*()
+        {
+            return m_ptr;
+        }
+
+        void operator++()
+        {
+            m_ptr = m_list.next(m_ptr).value_or(nullptr);
+        }
+
+        bool operator!=(LinkedListIterator& other)
+        {
+            return m_ptr != other.m_ptr || &m_list != &other.m_list;
+        }
+
+        friend class LinkedList<T>;
+    };
+
+    LinkedListIterator begin()
+    {
+        return { (T*)m_start_node, *this };
+    }
+
+    LinkedListIterator end()
+    {
+        return { nullptr, *this };
+    }
+
   private:
     Node* m_start_node = nullptr;
     Node* m_end_node = nullptr;