From e90b72ec3082588b296956730bd2930cf8d5d671 Mon Sep 17 00:00:00 2001
From: Richard Qin <richard.qin.x@gmail.com>
Date: Fri, 10 Jul 2026 11:31:46 +0800
Subject: refactor: promote new architecture to repository root

Archive the deprecated implementation under lume-legacy, make the new kernel the default root-level build, and update repository entry points without changing kernel behavior.
---
 kernel/waitqueue.cc | 144 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 144 insertions(+)
 create mode 100644 kernel/waitqueue.cc

(limited to 'kernel/waitqueue.cc')

diff --git a/kernel/waitqueue.cc b/kernel/waitqueue.cc
new file mode 100644
index 0000000..9689417
--- /dev/null
+++ b/kernel/waitqueue.cc
@@ -0,0 +1,144 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/*
+ * WaitQueue — blocking synchronization implementation
+ *
+ * Two-phase wait protocol:
+ *
+ *   prepare_to_wait():  task → Sleeping, link into queue
+ *   [caller checks condition — if still false, calls schedule()]
+ *   finish_wait():      remove from queue, restore Runnable
+ *
+ * Legacy sleep() wraps the two-phase pattern for simple callers.
+ *
+ * wake_one()/wake_all(): dequeue waiters → Runnable, sched_enqueue()
+ *
+ * The internal spinlock protects the wait list only.
+ * schedule() is called AFTER releasing all spinlocks to avoid
+ * holding a lock across a context switch.
+ */
+
+#include <lume/waitqueue.h>
+#include <lume/task.h>
+#include <lume/sched.h>
+#include <lume/kprintf.h>
+#include <arch/cpu.h>
+
+/* ------------------------------------------------------------------ */
+/*  Two-phase wait API                                                 */
+/* ------------------------------------------------------------------ */
+
+void WaitQueue::prepare_to_wait(TaskControlBlock* task, TaskState new_state)
+{
+    LockGuard guard(lock_);
+
+    /* Set state BEFORE linking — this is the key to preventing lost wakeups.
+     * If wake_one fires between now and schedule(), it will set state back
+     * to Runnable, and schedule() will see Runnable and not block. */
+    task->state = new_state;
+
+    /* Only add to queue if not already linked (idempotent) */
+    if (task->run_link.next == &task->run_link) {
+        /* Link into wait queue tail */
+        list_node* node = &task->run_link;
+        node->prev = head_.prev;
+        node->next = &head_;
+        head_.prev->next = node;
+        head_.prev = node;
+    }
+}
+
+void WaitQueue::finish_wait(TaskControlBlock* task)
+{
+    LockGuard guard(lock_);
+
+    /* Remove from wait queue if still linked */
+    if (task->run_link.next != &task->run_link) {
+        list_node* node = &task->run_link;
+        node->prev->next = node->next;
+        node->next->prev = node->prev;
+        node->init();
+    }
+
+    /* Ensure task is Runnable (it may have been woken by wake_one/wake_all
+     * already, or it may never have slept if the condition was true). */
+    if (task->state == TaskState::Sleeping) {
+        task->state = TaskState::Runnable;
+    }
+}
+
+/* ------------------------------------------------------------------ */
+/*  Legacy convenience API                                             */
+/* ------------------------------------------------------------------ */
+
+void WaitQueue::sleep(Spinlock* external_lock)
+{
+    TaskControlBlock* curr = current_task();
+    if (!curr) {
+        if (external_lock) external_lock->release();
+        return;
+    }
+
+    /* Phase 1: add to queue, mark Sleeping */
+    prepare_to_wait(curr, TaskState::Sleeping);
+
+    /* Release external lock AFTER we are on the queue (critical ordering) */
+    if (external_lock) {
+        external_lock->release();
+    }
+
+    /* Phase 2: context switch away — will return here when woken */
+    schedule();
+
+    /* Phase 3: clean up */
+    finish_wait(curr);
+}
+
+/* ------------------------------------------------------------------ */
+/*  Wakeup                                                             */
+/* ------------------------------------------------------------------ */
+
+bool WaitQueue::wake_one()
+{
+    LockGuard guard(lock_);
+
+    if (head_.is_empty())
+        return false;
+
+    /* Dequeue the first (oldest) waiter */
+    list_node* node = head_.next;
+    node->prev->next = node->next;
+    node->next->prev = node->prev;
+    node->init();
+
+    TaskControlBlock* task =
+        list_entry<TaskControlBlock, &TaskControlBlock::run_link>(node);
+
+    task->state = TaskState::Runnable;
+    sched_enqueue(task);
+
+    return true;
+}
+
+int WaitQueue::wake_all()
+{
+    LockGuard guard(lock_);
+
+    int count = 0;
+    while (!head_.is_empty()) {
+        list_node* node = head_.next;
+        node->prev->next = node->next;
+        node->next->prev = node->prev;
+        node->init();
+
+        TaskControlBlock* task =
+            list_entry<TaskControlBlock, &TaskControlBlock::run_link>(node);
+
+        task->state = TaskState::Runnable;
+        sched_enqueue(task);
+        count++;
+    }
+
+    return count;
+}
-- 
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