Kernel: Add Semaphore to block threads

kernel/Makefile

@@ -57,6 +57,7 @@ kernel/PIT.o					\
 kernel/Process.o				\
 kernel/RTC.o					\
 kernel/Scheduler.o				\
+kernel/Semaphore.o				\
 kernel/Serial.o					\
 kernel/Shell.o					\
 kernel/SpinLock.o				\

kernel/include/kernel/Input/PS2Keyboard.h

@@ -4,6 +4,7 @@
 #include <kernel/Input/KeyEvent.h>
 #include <kernel/Input/PS2Controller.h>
 #include <kernel/Input/PS2Keymap.h>
+#include <kernel/Semaphore.h>
 
 namespace Kernel::Input
 {
@@ -60,6 +61,8 @@ namespace Kernel::Input
 
 		State m_state { State::Normal };
 
+		Semaphore m_semaphore;
+
 		BAN::String m_name;
 
 	public:

kernel/include/kernel/Scheduler.h

@@ -2,6 +2,7 @@
 
 #include <BAN/LinkedList.h>
 #include <BAN/Memory.h>
+#include <kernel/Semaphore.h>
 #include <kernel/Thread.h>
 
 namespace Kernel
@@ -21,6 +22,9 @@ namespace Kernel
 		void set_current_thread_sleeping(uint64_t);
 		[[noreturn]] void set_current_thread_done();
 
+		void block_current_thread(Semaphore*);
+		void unblock_threads(Semaphore*);
+
 		BAN::RefPtr<Thread> current_thread();
 
 	private:
@@ -47,9 +51,18 @@ namespace Kernel
 			uint64_t wake_time;
 		};
 
+		struct BlockingThread
+		{
+			BlockingThread(const BAN::RefPtr<Thread>& thread, Semaphore* semaphore) : thread(thread), semaphore(semaphore) {}
+			BAN::RefPtr<Thread> thread;
+			Semaphore* semaphore;
+			uint8_t padding[sizeof(uint64_t) - sizeof(Semaphore*)];
+		};
+
 		BAN::RefPtr<Thread> m_idle_thread;
 		BAN::LinkedList<ActiveThread> m_active_threads;
 		BAN::LinkedList<SleepingThread> m_sleeping_threads;
+		BAN::LinkedList<BlockingThread> m_blocking_threads;
 
 		BAN::LinkedList<ActiveThread>::iterator m_current_thread;
 

kernel/include/kernel/Semaphore.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <kernel/SpinLock.h>
+
+namespace Kernel
+{
+
+	class Semaphore
+	{
+	public:
+		void block();
+		void unblock();
+		bool is_blocked() const { return m_blocked; }
+
+	private:
+		void set_blocked(bool blocked) { m_blocked = blocked; }
+
+	private:
+		bool m_blocked { false };
+
+		friend class Scheduler;
+	};
+
+}

kernel/kernel/Input/PS2Keyboard.cpp

@@ -211,8 +211,9 @@ namespace Kernel::Input
 			m_event_queue.pop();
 		}
 		m_event_queue.push(event);
-	}
 
+		m_semaphore.unblock();
+	}
 
 	void PS2Keyboard::update_leds()
 	{
@@ -231,14 +232,20 @@ namespace Kernel::Input
 		if (size < sizeof(KeyEvent))
 			return BAN::Error::from_errno(ENOBUFS);
 
-		while (m_event_queue.empty())
-			PIT::sleep(1);
+		while (true)
+		{
+			if (m_event_queue.empty())
+				m_semaphore.block();
 
-		CriticalScope _;
-		*(KeyEvent*)buffer = m_event_queue.front();
-		m_event_queue.pop();
+			CriticalScope _;
+			if (m_event_queue.empty())
+				continue;
 
-		return sizeof(KeyEvent);
+			*(KeyEvent*)buffer = m_event_queue.front();
+			m_event_queue.pop();
+
+			return sizeof(KeyEvent);
+		}
 	}
 
 }

kernel/kernel/Scheduler.cpp

@@ -211,4 +211,58 @@ namespace Kernel
 		ASSERT_NOT_REACHED();
 	}
 
+#pragma GCC push_options
+#pragma GCC optimize("O0")
+	void Scheduler::block_current_thread(Semaphore* semaphore)
+	{
+		VERIFY_STI();
+		DISABLE_INTERRUPTS();
+
+		ASSERT(m_current_thread);
+
+		auto blocking = m_current_thread->thread;
+
+		if (save_current_thread())
+		{
+			ENABLE_INTERRUPTS();
+			return;
+		}
+		remove_and_advance_current_thread();
+
+		// This should work as we released enough memory from active thread
+		static_assert(sizeof(ActiveThread) == sizeof(BlockingThread));
+		MUST(m_blocking_threads.emplace_back(blocking, semaphore));
+		blocking.clear();
+
+		semaphore->m_blocked = true;
+
+		execute_current_thread();
+		ASSERT_NOT_REACHED();
+	}
+#pragma GCC pop_options
+	
+	void Scheduler::unblock_threads(Semaphore* semaphore)
+	{
+		Kernel::CriticalScope critical;
+
+		for (auto it = m_blocking_threads.begin(); it != m_blocking_threads.end();)
+		{
+			if (it->semaphore == semaphore)
+			{
+				auto thread = it->thread;
+				it = m_blocking_threads.remove(it);
+
+				// This should work as we released enough memory from active thread
+				static_assert(sizeof(ActiveThread) == sizeof(BlockingThread));
+				MUST(m_active_threads.emplace_back(thread));
+			}
+			else
+			{
+				it++;
+			}
+		}
+
+		semaphore->m_blocked = false;
+	}
+
 }

kernel/kernel/Semaphore.cpp

@@ -0,0 +1,20 @@
+#include <kernel/LockGuard.h>
+#include <kernel/Scheduler.h>
+#include <kernel/Semaphore.h>
+
+namespace Kernel
+{
+
+	void Semaphore::block()
+	{
+		Scheduler::get().block_current_thread(this);
+	}
+
+	void Semaphore::unblock()
+	{
+		if (!m_blocked)
+			return;
+		Scheduler::get().unblock_threads(this);
+	}
+
+}