From 643e87a076bfb1b3e5fd65d2d79ff38f80e96bc2 Mon Sep 17 00:00:00 2001
From: Bananymous <bananymousosq@gmail.com>
Date: Thu, 3 Aug 2023 10:42:14 +0300
Subject: [PATCH] Kernel: Threads are deleted sooner and cleaner

We now delete threads when
    1. it is marked as Terminated and is the current thread
    2. it tries to start execution in Terminated state

This allows us to never have thread executing in Terminated state
---
 kernel/arch/x86_64/IDT.cpp | 14 +++++---------
 kernel/kernel/Syscall.cpp  |  6 +-----
 kernel/kernel/Thread.cpp   | 28 +++++++++++++++++++++++-----
 3 files changed, 29 insertions(+), 19 deletions(-)

diff --git a/kernel/arch/x86_64/IDT.cpp b/kernel/arch/x86_64/IDT.cpp
index 028fda268..0c2754390 100644
--- a/kernel/arch/x86_64/IDT.cpp
+++ b/kernel/arch/x86_64/IDT.cpp
@@ -201,13 +201,11 @@ namespace IDT
 			Kernel::panic("Unhandled exception");
 		}
 
-		// Don't continue exection when terminated
-		if (Kernel::Thread::current().state() == Kernel::Thread::State::Terminated)
-			Kernel::Scheduler::get().execute_current_thread();
-		
+		ASSERT(Kernel::Thread::current().state() != Kernel::Thread::State::Terminated);
+
 		if (from_userspace)
 		{
-			ASSERT(Kernel::Thread::current().state() != Kernel::Thread::State::Terminating);
+			ASSERT(Kernel::Thread::current().state() == Kernel::Thread::State::Executing);
 			Kernel::Thread::current().load_sse();
 		}
 	}
@@ -243,13 +241,11 @@ namespace IDT
 
 		Kernel::Scheduler::get().reschedule_if_idling();
 
-		// Don't continue exection when terminated
-		if (Kernel::Thread::current().state() == Kernel::Thread::State::Terminated)
-			Kernel::Scheduler::get().execute_current_thread();
+		ASSERT(Kernel::Thread::current().state() != Kernel::Thread::State::Terminated);
 
 		if (from_userspace)
 		{
-			ASSERT(Kernel::Thread::current().state() != Kernel::Thread::State::Terminating);
+			ASSERT(Kernel::Thread::current().state() == Kernel::Thread::State::Executing);
 			Kernel::Thread::current().load_sse();
 		}
 	}
diff --git a/kernel/kernel/Syscall.cpp b/kernel/kernel/Syscall.cpp
index 55406e5d4..de6137aa5 100644
--- a/kernel/kernel/Syscall.cpp
+++ b/kernel/kernel/Syscall.cpp
@@ -177,11 +177,7 @@ namespace Kernel
 
 		asm volatile("cli");
 
-		// Don't continue exection when terminated
-		if (Kernel::Thread::current().state() == Kernel::Thread::State::Terminated)
-			Kernel::Scheduler::get().execute_current_thread();
-
-		ASSERT(Kernel::Thread::current().state() != Kernel::Thread::State::Terminating);
+		ASSERT(Kernel::Thread::current().state() == Kernel::Thread::State::Executing);
 		Thread::current().load_sse();
 
 		if (ret.is_error())
diff --git a/kernel/kernel/Thread.cpp b/kernel/kernel/Thread.cpp
index 800c11349..d59b3fd2a 100644
--- a/kernel/kernel/Thread.cpp
+++ b/kernel/kernel/Thread.cpp
@@ -31,6 +31,9 @@ namespace Kernel
 	{
 		CriticalScope _;
 
+		// FIXME: this should not be a requirement
+		ASSERT(&thread == &Thread::current());
+
 		if (m_thread.state() == State::Executing || m_thread.m_terminate_blockers > 0)
 		{
 			m_thread.m_terminate_blockers++;
@@ -38,8 +41,11 @@ namespace Kernel
 		}
 
 		if (m_thread.state() == State::Terminating && m_thread.m_terminate_blockers == 0)
+		{
 			m_thread.m_state = State::Terminated;
-				
+			Scheduler::get().execute_current_thread();
+		}
+
 		while (true)
 			Scheduler::get().reschedule();
 	}
@@ -54,17 +60,29 @@ namespace Kernel
 			return;
 
 		if (m_thread.state() == State::Terminating && m_thread.m_terminate_blockers == 0)
+		{
 			m_thread.m_state = State::Terminated;
+			Scheduler::get().execute_current_thread();
+		}
 
-		while (true)
-			Scheduler::get().reschedule();
+		ASSERT_NOT_REACHED();
 	}
 
 	void Thread::set_terminating()
 	{
 		CriticalScope _;
-		m_state = m_terminate_blockers == 0 ? State::Terminated : State::Terminating;
-		Scheduler::get().unblock_thread(tid());
+		if (m_terminate_blockers == 0)
+		{
+			m_state = State::Terminated;
+			if (this == &Thread::current())
+				Scheduler::get().execute_current_thread();
+		}
+		else
+		{
+			m_state = State::Terminating;
+			if (this == &Thread::current())
+				Scheduler::get().unblock_thread(tid());
+		}
 	}
 
 	static pid_t s_next_tid = 1;