From 1643f7b4cca88faa47d1fc7ea0fe7f77160076f8 Mon Sep 17 00:00:00 2001
From: Drew Galbraith <dgalbraith33@gmail.com>
Date: Thu, 2 Nov 2023 22:36:48 -0700
Subject: [PATCH] [Zion] Update FIXME in threading.

---
 zion/object/thread.cpp | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/zion/object/thread.cpp b/zion/object/thread.cpp
index 286d731..f9c7629 100644
--- a/zion/object/thread.cpp
+++ b/zion/object/thread.cpp
@@ -69,7 +69,7 @@ void Thread::Exit() {
 #endif
   state_ = FINISHED;
   process_.CheckState();
-  while (!blocked_threads_.size() == 0) {
+  while (blocked_threads_.size() != 0) {
     auto thread = blocked_threads_.PopFront();
     thread->SetState(Thread::RUNNABLE);
     gScheduler->Enqueue(thread);
@@ -78,7 +78,16 @@ void Thread::Exit() {
 }
 
 void Thread::Wait() {
-  // FIXME: We need synchronization code here.
+  // TODO: We need synchronization code here.
+  // Race condition is for A waiting on B.
+  // 1. A checks if B is finished.
+  // 2. Context Switch A -> B
+  // 3. B finishes.
+  // 4. Context Switch B -> A
+  // 5. A forever blocks on B.
+  if (state_ == Thread::FINISHED) {
+    return;
+  }
   auto thread = gScheduler->CurrentThread();
   thread->SetState(Thread::BLOCKED);
   blocked_threads_.PushBack(thread);