Kernel: Move all tasks-related code to the Tasks subdirectory

Kernel/Tasks/ProcessGroup.h

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2020-2023, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/IntrusiveList.h>
+#include <AK/RefPtr.h>
+#include <Kernel/Forward.h>
+#include <Kernel/Library/ListedRefCounted.h>
+#include <Kernel/Library/LockWeakable.h>
+#include <Kernel/Locking/SpinlockProtected.h>
+#include <Kernel/UnixTypes.h>
+
+namespace Kernel {
+
+class ProcessGroup
+    : public ListedRefCounted<ProcessGroup, LockType::Spinlock>
+    , public LockWeakable<ProcessGroup> {
+
+    AK_MAKE_NONMOVABLE(ProcessGroup);
+    AK_MAKE_NONCOPYABLE(ProcessGroup);
+
+public:
+    ~ProcessGroup();
+
+    static ErrorOr<NonnullRefPtr<ProcessGroup>> create_if_unused_pgid(ProcessGroupID);
+    static ErrorOr<NonnullRefPtr<ProcessGroup>> find_or_create(ProcessGroupID);
+    static RefPtr<ProcessGroup> from_pgid(ProcessGroupID);
+
+    ProcessGroupID const& pgid() const { return m_pgid; }
+
+private:
+    ProcessGroup(ProcessGroupID pgid)
+        : m_pgid(pgid)
+    {
+    }
+
+    ProcessGroupID m_pgid;
+
+    mutable IntrusiveListNode<ProcessGroup> m_list_node;
+
+public:
+    using AllInstancesList = IntrusiveList<&ProcessGroup::m_list_node>;
+    static SpinlockProtected<AllInstancesList, LockRank::None>& all_instances();
+};
+
+}