From cf500b301ee3f518ea391ea21e39853b7e7a37c8 Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Sun, 26 Jul 2026 20:33:10 +0200
Subject: kapi: implement a simple, tracked mutex

---
 kernel/CMakeLists.txt                   |  1 +
 kernel/kapi/tracked_mutex.cpp           | 55 +++++++++++++++++++++++++++++++++
 kernel/kernel/test_support/kapi/cpu.cpp |  7 +++++
 3 files changed, 63 insertions(+)
 create mode 100644 kernel/kapi/tracked_mutex.cpp

(limited to 'kernel')

diff --git a/kernel/CMakeLists.txt b/kernel/CMakeLists.txt
index d22ad107..a97c1e4a 100644
--- a/kernel/CMakeLists.txt
+++ b/kernel/CMakeLists.txt
@@ -24,6 +24,7 @@ target_sources("kernel_lib" PRIVATE
     "kapi/interrupts.cpp"
     "kapi/memory.cpp"
     "kapi/system.cpp"
+    "kapi/tracked_mutex.cpp"
 
     # Kernel-defined KSTD Implementation
     "kstd/os.cpp"
diff --git a/kernel/kapi/tracked_mutex.cpp b/kernel/kapi/tracked_mutex.cpp
new file mode 100644
index 00000000..6608169c
--- /dev/null
+++ b/kernel/kapi/tracked_mutex.cpp
@@ -0,0 +1,55 @@
+#include <kapi/tracked_mutex.hpp>
+
+#include <kapi/cpu.hpp>
+#include <kapi/system.hpp>
+
+#include <atomic>
+
+namespace kapi
+{
+
+  auto tracked_mutex::lock() -> void
+  {
+    auto self = kapi::cpu::current_id();
+    auto expected = kapi::cpu::invalid_id;
+
+    while (!m_owner.compare_exchange_weak(expected, self, std::memory_order::acquire, std::memory_order::relaxed))
+    {
+      if (expected == self)
+      {
+        system::panic("[OS] CPU {} tried to reacquire a mutex it already holds!", self);
+      }
+      expected = kapi::cpu::invalid_id;
+    }
+  }
+
+  auto tracked_mutex::try_lock() -> bool
+  {
+    auto self = kapi::cpu::current_id();
+    auto expected = kapi::cpu::invalid_id;
+
+    if (m_owner.compare_exchange_strong(expected, self, std::memory_order::acquire, std::memory_order::relaxed))
+    {
+      return true;
+    }
+
+    if (expected == self)
+    {
+      system::panic("[OS] CPU {} tried to reacquire a mutex it already holds!", self);
+    }
+
+    return false;
+  }
+
+  auto tracked_mutex::unlock() -> void
+  {
+    auto self = kapi::cpu::current_id();
+    auto expected = self;
+
+    if (!m_owner.compare_exchange_strong(expected, kapi::cpu::invalid_id, std::memory_order::release))
+    {
+      system::panic("[OS] CPU {} released a mutex it did not hold!", self);
+    }
+  }
+
+}  // namespace kapi
\ No newline at end of file
diff --git a/kernel/kernel/test_support/kapi/cpu.cpp b/kernel/kernel/test_support/kapi/cpu.cpp
index 5d956331..a82dc348 100644
--- a/kernel/kernel/test_support/kapi/cpu.cpp
+++ b/kernel/kernel/test_support/kapi/cpu.cpp
@@ -3,7 +3,9 @@
 #include <kapi/cpu.hpp>
 
 #include <atomic>
+#include <functional>
 #include <stdexcept>
+#include <thread>
 
 namespace
 {
@@ -34,6 +36,11 @@ namespace kapi::cpu
     return true;
   }
 
+  auto current_id() -> id
+  {
+    return id{.value = std::hash<std::thread::id>{}(std::this_thread::get_id())};
+  }
+
 }  // namespace kapi::cpu
 
 namespace kernel::tests::cpu
-- 
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