From f6a78b3516193a7f987df940e88e29ef2473ca98 Mon Sep 17 00:00:00 2001
From: Martin Eyben <martin.eyben@enseirb-matmeca.fr>
Date: Tue, 25 Mar 2025 10:35:02 +0100
Subject: [PATCH] feat: add deadlock verification

---
 src/thread/thread.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/thread/thread.c b/src/thread/thread.c
index 70a8425..cc825ac 100644
--- a/src/thread/thread.c
+++ b/src/thread/thread.c
@@ -9,6 +9,7 @@
 #include <sys/queue.h>
 #include <ucontext.h>
 #include <valgrind/valgrind.h>
+#include <errno.h>
 
 #define FINISHED 0x1
 #define IS_FINISHED(entry) (entry->status & FINISHED)
@@ -49,7 +50,7 @@ static struct context_entry* running = NULL;
 
 int thread_yield(void)
 {
-    TRACE("thread_yield");
+    //TRACE("thread_yield");
     if (TAILQ_EMPTY(&head)) {
         return 0;
     }
@@ -140,10 +141,20 @@ int thread_join(thread_t thread, void** retval)
     TRACE("Join thread %p", thread);
     struct context_entry* entry = thread;
     // Check if the target is not already waited by another
-    if (IS_WAITED(entry) || IS_WAITING(entry) && GET_WAITED_THREAD(entry) == running) {
+    if (IS_WAITED(entry)) {
         return -1;
     }
 
+    // Check if there is a deadlock
+    struct context_entry* parent = thread;
+    while (IS_WAITING(parent)) {
+      if (GET_WAITED_THREAD(parent) == running) {
+        TRACE("Deadlock detected");
+        return EDEADLK;
+      }
+      parent = GET_WAITED_THREAD(parent);
+    }
+
     if (!IS_FINISHED(entry)) {
         // Use status to be in waiting state
         running->status |= WAITING;
@@ -152,6 +163,8 @@ int thread_join(thread_t thread, void** retval)
         entry->status |= WAITED;
         // Use retvalue to share which thread is currently waiting for this thread
         entry->retvalue = running;
+
+        DBG("%p is waiting for %p", running, entry);
         do {
             thread_yield();
         } while (!IS_FINISHED(entry));