Scheduler: Implement a find_by_pid function

kernel/include/thread/Scheduler.h

@@ -29,4 +29,6 @@ namespace Scheduler
     void reset_task(Task* task, ELFImage* new_image);
 
     void append_task(Task* task);
+
+    Task* find_by_pid(uint64_t pid);
 }

kernel/src/thread/Scheduler.cpp

@@ -33,6 +33,31 @@ extern "C" void idle_task_function();
 
 static uint64_t frequency;
 
+template <typename Callback> void sched_for_each_task(Callback callback)
+{
+    Task* task = base_task;
+    if (!task) return;
+    do {
+        bool will_continue = callback(task);
+        if (!will_continue) break;
+        task = task->next_task;
+    } while (task != base_task);
+}
+
+Task* Scheduler::find_by_pid(uint64_t pid)
+{
+    Task* result = nullptr;
+    sched_for_each_task([&](Task* task) {
+        if (task->id == pid)
+        {
+            result = task;
+            return false;
+        }
+        return true;
+    });
+    return result;
+}
+
 void Scheduler::append_task(Task* task)
 {
     if (!base_task)
@@ -295,17 +320,15 @@ void Scheduler::reap_tasks()
 
 static void sched_decrement_sleep_times()
 {
-    Task* task = base_task;
+    sched_for_each_task([](Task* task) {
-    if (!task) return;
-    do {
         if (task->task_sleep > 0)
         {
             task->task_sleep -= frequency;
             if (task->task_sleep < 0) task->task_sleep = 0;
         }
         if (task->task_sleep == 0 && task->state == task->Sleeping) task->state = task->Running;
-        task = task->next_task;
+        return true;
-    } while (task != base_task);
+    });
 }
 
 void Scheduler::task_tick(Context* context)