Refactor convolution-nchw kernels create functions.

PiperOrigin-RevId: 817650789

Author: qukhan

src/pthreads.c

@@ -432,7 +432,7 @@ static uint32_t thread_wrap_up(struct pthreadpool* threadpool,
   return curr_active_threads;
 }
 
-static void* thread_main(void* arg);
+static int thread_main(void* arg);
 
 static void ensure_num_threads(struct pthreadpool* threadpool,
                                uint32_t thread_id) {
@@ -476,7 +476,7 @@ static void ensure_num_threads(struct pthreadpool* threadpool,
   }
 }
 
-static void* thread_main(void* arg) {
+static int thread_main(void* arg) {
   // Unpack the argument, i.e. extract the pointer to the `pthreadpool` from the
   // provided pointer to this thread's `thread_info`.
   struct thread_info* thread = (struct thread_info*)arg;
@@ -558,7 +558,7 @@ static void* thread_main(void* arg) {
   // Release our hold on the threadpool.
   pthreadpool_release(threadpool);
 
-  return NULL;
+  return 0;
 }
 
 static size_t get_num_cpus() {

src/threadpool-atomics.h

@@ -85,7 +85,7 @@ static inline void pthreadpool_cond_broadcast(pthreadpool_cond_t* cond) {
   pthread_cond_broadcast(cond);
 }
 static inline void pthreadpool_thread_create(pthreadpool_thread_t* thread,
-                                             void*(fun)(void*), void* arg) {
+                                             int(fun)(void*), void* arg) {
   pthread_create(thread, NULL, fun, arg);
 }
 static inline void pthreadpool_thread_join(pthreadpool_thread_t thread,