fixed lumiera_threadpool_destroy() by using LLIST_FOREACH

added some checks to lumiera_threadpool_release_thread(), maybe too much
modified thread_loop() to return a known value - 0
added checks to lumiera_thread_new()
added a check to lumiera_thread_destroy()
made lumiera_thread_destroy() unlink the thread from a pool list
updated test case to match new debug messages

src/backend/threadpool.c

@@ -65,16 +65,17 @@ lumiera_threadpool_init(void)
 void
 lumiera_threadpool_destroy(void)
 {
+  ECHO ("destroying threadpool");
   for (int i = 0; i < LUMIERA_THREADCLASS_COUNT; ++i)
     {
+      ECHO ("destroying individual pool #%d", i);
       // no locking is done at this point
-      LLIST_FOREACH(&threadpool.kind[i].pool, thread)
-        {
-          llist_unlink(thread);
-          lumiera_thread_delete((LumieraThread)thread);
-        }
-
+      ECHO ("number of threads in the pool=%d", llist_count(&threadpool.kind[i].pool));
+      LLIST_WHILE_HEAD(&threadpool.kind[i].pool, thread)
+        lumiera_thread_delete((LumieraThread)thread);
+      ECHO ("destroying the pool mutex");
       lumiera_mutex_destroy (&threadpool.kind[i].lock, &NOBUG_FLAG (threadpool));
+      ECHO ("pool mutex destroyed");
     }
 }
 
@@ -109,9 +110,11 @@ lumiera_threadpool_acquire_thread(enum lumiera_thread_class kind,
 void
 lumiera_threadpool_release_thread(LumieraThread thread)
 {
-  // TODO: do we need to check that index 'kind' is within range?
-  llist pool = threadpool.kind[thread->kind].pool;
-  llist_insert_head(&pool, &thread->node);
+  REQUIRE (thread, "invalid thread given");
+  REQUIRE (thread->kind < LUMIERA_THREADCLASS_COUNT, "thread belongs to an unknown pool kind: %d", thread->kind);
+  REQUIRE (llist_is_single(&thread->node), "thread already belongs to some list");
+  llist_insert_head(&threadpool.kind[thread->kind].pool, &thread->node);
+  REQUIRE (!llist_is_empty (&threadpool.kind[thread->kind].pool), "thread pool is still empty after insertion");
 }
 
 /*

src/backend/threads.c

@@ -55,7 +55,8 @@ struct lumiera_thread_mockup
 
 static void* thread_loop (void* arg)
 {
-  return arg;
+  (void)arg;
+  return 0;
 }
 
 #if 0
@@ -165,10 +166,12 @@ lumiera_thread_new (enum lumiera_thread_class kind,
   if (attr_once == PTHREAD_ONCE_INIT)
     pthread_once (&attr_once, thread_attr_init);
 
+  REQUIRE (kind < LUMIERA_THREADCLASS_COUNT, "invalid thread kind specified: %d", kind);
+  //REQUIRE (finished, "invalid finished flag passed");
+
   LumieraThread self = lumiera_malloc (sizeof (*self));
   llist_init(&self->node);
   self->finished = finished;
-  REQUIRE (kind < LUMIERA_THREADCLASS_COUNT, "invalid thread kind specified: %d", kind);
   self->kind = kind;
   self->state = LUMIERA_THREADSTATE_IDLE;
 
@@ -190,8 +193,11 @@ lumiera_thread_new (enum lumiera_thread_class kind,
 LumieraThread
 lumiera_thread_destroy (LumieraThread self)
 {
+  ECHO ("destroying thread");
+  REQUIRE (self, "trying to destroy an invalid thread");
+
   // TODO: stop the pthread
-  // TODO: empty the list/node?
+  llist_unlink(&self->node);
   //finished = NULL; // or free(finished)?
   lumiera_reccondition_destroy (self->finished, &NOBUG_FLAG(threads));
   //kind = 0;
@@ -202,6 +208,7 @@ lumiera_thread_destroy (LumieraThread self)
 void
 lumiera_thread_delete (LumieraThread self)
 {
+  ECHO ("deleting thread");
   lumiera_free (lumiera_thread_destroy (self));
 }
 

tests/30backend-threadpool.tests

@@ -13,5 +13,35 @@ err: releasing thread 1
 err: thread 1 has been released
 err: releasing thread 2
 err: thread 2 has been released
+err: destroying threadpool
+
+err: destroying individual pool #0
+err: number of threads in the pool=1
+err: deleting thread
+err: destroying thread
+err: destroying the pool mutex
+err: pool mutex destroyed
+
+err: destroying individual pool #1
+err: number of threads in the pool=0
+err: destroying the pool mutex
+err: pool mutex destroyed
+
+err: destroying individual pool #2
+err: number of threads in the pool=0
+err: destroying the pool mutex
+err: pool mutex destroyed
+
+err: destroying individual pool #3
+err: number of threads in the pool=0
+err: destroying the pool mutex
+err: pool mutex destroyed
+
+err: destroying individual pool #4
+err: number of threads in the pool=1
+err: deleting thread
+err: destroying thread
+err: destroying the pool mutex
+err: pool mutex destroyed
 END