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

Kernel/Tasks/WorkQueue.h

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Error.h>
+#include <AK/IntrusiveList.h>
+#include <Kernel/Forward.h>
+#include <Kernel/Locking/SpinlockProtected.h>
+#include <Kernel/Tasks/WaitQueue.h>
+
+namespace Kernel {
+
+extern WorkQueue* g_io_work;
+extern WorkQueue* g_ata_work;
+
+class WorkQueue {
+    AK_MAKE_NONCOPYABLE(WorkQueue);
+    AK_MAKE_NONMOVABLE(WorkQueue);
+
+public:
+    static void initialize();
+
+    ErrorOr<void> try_queue(void (*function)(void*), void* data = nullptr, void (*free_data)(void*) = nullptr)
+    {
+        auto item = new (nothrow) WorkItem; // TODO: use a pool
+        if (!item)
+            return Error::from_errno(ENOMEM);
+        item->function = [function, data, free_data] {
+            function(data);
+            if (free_data)
+                free_data(data);
+        };
+        do_queue(*item);
+        return {};
+    }
+
+    template<typename Function>
+    ErrorOr<void> try_queue(Function function)
+    {
+        auto item = new (nothrow) WorkItem; // TODO: use a pool
+        if (!item)
+            return Error::from_errno(ENOMEM);
+        item->function = Function(function);
+        do_queue(*item);
+        return {};
+    }
+
+private:
+    explicit WorkQueue(StringView);
+
+    struct WorkItem {
+    public:
+        IntrusiveListNode<WorkItem> m_node;
+        Function<void()> function;
+    };
+
+    void do_queue(WorkItem&);
+
+    RefPtr<Thread> m_thread;
+    WaitQueue m_wait_queue;
+    SpinlockProtected<IntrusiveList<&WorkItem::m_node>, LockRank::None> m_items {};
+};
+
+}