From 5d8dd090a925dc02b049917166e8f56d21dda1d9 Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Mon, 21 Apr 2025 14:01:38 +0300
Subject: [PATCH] LibC: Implement `pthread_once`

---
 userspace/libraries/LibC/include/pthread.h |  3 ++-
 userspace/libraries/LibC/pthread.cpp       | 16 ++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/userspace/libraries/LibC/include/pthread.h b/userspace/libraries/LibC/include/pthread.h
index 04318efa..ea656dcc 100644
--- a/userspace/libraries/LibC/include/pthread.h
+++ b/userspace/libraries/LibC/include/pthread.h
@@ -46,13 +46,14 @@ struct uthread
 #define PTHREAD_CREATE_JOINABLE			8
 #define PTHREAD_EXPLICIT_SCHED			9
 #define PTHREAD_INHERIT_SCHED			10
-#define PTHREAD_ONCE_INIT				17
 #define PTHREAD_PRIO_INHERIT			18
 #define PTHREAD_PRIO_NONE				19
 #define PTHREAD_PRIO_PROTECT			20
 #define PTHREAD_SCOPE_PROCESS			23
 #define PTHREAD_SCOPE_SYSTEM			24
 
+#define PTHREAD_ONCE_INIT				0
+
 #define PTHREAD_PROCESS_SHARED			0
 #define PTHREAD_PROCESS_PRIVATE			1
 
diff --git a/userspace/libraries/LibC/pthread.cpp b/userspace/libraries/LibC/pthread.cpp
index 2921c0ef..fb2da09d 100644
--- a/userspace/libraries/LibC/pthread.cpp
+++ b/userspace/libraries/LibC/pthread.cpp
@@ -312,6 +312,22 @@ pthread_t pthread_self(void)
 #endif
 }
 
+int pthread_once(pthread_once_t* once_control, void (*init_routine)(void))
+{
+	static_assert(PTHREAD_ONCE_INIT == 0);
+
+	pthread_once_t expected = 0;
+	if (BAN::atomic_compare_exchange(*once_control, expected, 1))
+	{
+		init_routine();
+		BAN::atomic_store(*once_control, 2);
+	}
+
+	while (BAN::atomic_load(*once_control) != 2)
+		sched_yield();
+	return 0;
+}
+
 int pthread_spin_destroy(pthread_spinlock_t* lock)
 {
 	(void)lock;