From 52f5bb6bd24b9ee08aa4f707faf84f34f735f2de Mon Sep 17 00:00:00 2001
From: Dibyamartanda Samanta <dibyaxp@noreply.codingworkshop.git>
Date: Mon, 15 Jul 2024 10:32:15 +0200
Subject: [PATCH] [NTOSKRNL:KE] Implemented Slim Futex

Implemented Exceptionally Fast, yet simple Mutex ,exclusive to Alcyone called Slim Futex.
Functions implemented
*KeInitializeSlimFutex
*KeAcquireSlimFutex
*KeReleaseSlimFutex
*KeIsSlimFutexHeld
*KeIsSlimFutexLocked
---
 NTOSKRNL/KE/slimfutex.cpp | 145 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 145 insertions(+)
 create mode 100644 NTOSKRNL/KE/slimfutex.cpp

diff --git a/NTOSKRNL/KE/slimfutex.cpp b/NTOSKRNL/KE/slimfutex.cpp
new file mode 100644
index 0000000..60cc3f4
--- /dev/null
+++ b/NTOSKRNL/KE/slimfutex.cpp
@@ -0,0 +1,145 @@
+/*
+ * PROJECT: Alcyone System Kernel
+ * LICENSE: BSD Clause 3
+ * PURPOSE: Slim Futex 
+ * NT KERNEL: 5.11.9360
+ * COPYRIGHT:  2023-2029 Dibymartanda Samanta <>
+ */ 
+
+#include <ntoskrnl.h>
+#define NTDEBUG
+
+extern "C"
+
+typedef struct _KE_SLIM_FUTEX {
+    volatile LONG Value;
+} KE_SLIM_FUTEX, *PKE_SLIM_FUTEX;
+
+/* IS_HELD_BIT: Indicates if the futex is currently held.
+   HAS_PARKED_BIT : Indicates if there are any parked (waiting) threads. */
+constexpr ULONG IS_HELD_BIT = 1;
+constexpr ULONG HAS_PARKED_BIT = 2; 
+
+NTSTATUS
+KeAcquireSlimFutexSlow(
+    _Inout_ PKE_SLIM_FUTEX Futex
+)
+{
+    NTSTATUS Status;
+    LARGE_INTEGER Timeout;
+    Timeout.QuadPart = -50000; // 5ms
+
+    for (;;) {
+        LONG CurrentValue = Futex->Value;
+        if (!(CurrentValue & IS_HELD_BIT)) {
+            if (InterlockedCompareExchange(&Futex->Value, CurrentValue | IS_HELD_BIT, CurrentValue) == CurrentValue) {
+                return STATUS_SUCCESS;
+            }
+            continue;
+        }
+
+        if (!(CurrentValue & HAS_PARKED_BIT)) {
+            if (InterlockedCompareExchange(&Futex->Value, CurrentValue | HAS_PARKED_BIT, CurrentValue) != CurrentValue) {
+                continue;
+            }
+        }
+
+        Status = KeWaitForSingleObject(Futex, Executive, KernelMode, FALSE, &Timeout);
+        if (!NT_SUCCESS(Status) && Status != STATUS_TIMEOUT) {
+            return Status;
+        }
+    }
+}
+
+NTSTATUS
+KeReleaseSlimFutexSlow(
+    _Inout_ PKE_SLIM_FUTEX Futex
+)
+{
+    LONG OldValue;
+    do {
+        OldValue = Futex->Value;
+        LONG NewValue = OldValue & ~IS_HELD_BIT;
+        if (OldValue & HAS_PARKED_BIT)
+            NewValue &= ~HAS_PARKED_BIT;
+        if (InterlockedCompareExchange(&Futex->Value, NewValue, OldValue) == OldValue) {
+            if (OldValue & HAS_PARKED_BIT) {
+                KeSetEvent((PRKEVENT)Futex, IO_NO_INCREMENT, FALSE);
+            }
+            return STATUS_SUCCESS;
+        }
+    } while (TRUE);
+}
+
+/*Exported Function*/ 
+
+/* Initializes PKE_SLIM_FUTEX  Pointer*/ 
+NTSTATUS
+KeInitializeSlimFutex(
+    _Out_ PKE_SLIM_FUTEX Futex
+)
+{
+    Futex->Value = 0;
+    return STATUS_SUCCESS;
+}
+
+/* Attempts to acquire the slim futex, return STATUS_SUCCESS  if succeeds */  
+NTSTATUS
+KeAcquireSlimFutex(
+    _Inout_ PKE_SLIM_FUTEX Futex
+)
+{
+    if (InterlockedCompareExchange(&Futex->Value, IS_HELD_BIT, 0) == 0) {
+        // Futex acquired!
+        return STATUS_SUCCESS;
+    }
+
+    return KeAcquireSlimFutexSlow(Futex);
+}
+
+/*TRUE if the futex is successfully acquired, FALSE otherwise*/
+
+BOOLEAN
+KeTryAcquireSlimFutex(
+    _Inout_ PKE_SLIM_FUTEX Futex
+)
+{
+    for (;;) {
+        LONG CurrentValue = Futex->Value;
+        if (CurrentValue & IS_HELD_BIT)
+            return FALSE;
+        if (InterlockedCompareExchange(&Futex->Value, CurrentValue | IS_HELD_BIT, CurrentValue) == CurrentValue)
+            return TRUE;
+    }
+}
+
+/* Releases the slim futex*/
+NTSTATUS
+KeReleaseSlimFutex(
+    _Inout_ PKE_SLIM_FUTEX Futex
+)
+{
+    if (InterlockedCompareExchange(&Futex->Value, 0, IS_HELD_BIT) == IS_HELD_BIT) {
+        // Futex released and nobody was waiting!
+        return STATUS_SUCCESS;
+    }
+
+    return KeReleaseSlimFutexSlow(Futex);
+}
+
+/* Return TRUE if provided Slim Futex is held , else false */
+BOOLEAN
+KeIsSlimFutexHeld(
+    _In_ PKE_SLIM_FUTEX Futex
+)
+{
+    return (Futex->Value & IS_HELD_BIT) != 0;
+}
+/* Return true  if Futex Locked, else return False */
+BOOLEAN
+KeIsSlimFutexLocked(
+    _In_ PKE_SLIM_FUTEX Futex
+)
+{
+    return KeIsSlimFutexHeld(Futex);
+}