Nonblocking mail_receive, fix proc_kill scheduling issues

kernel/syscall/syscall.c

@@ -274,6 +274,35 @@ DEFINE_SYSCALL (sys_mail_receive) {
   return SYSRESULT (ST_OK);
 }
 
+/* int mail_receive_nonblock (void* recv_mesg, size_t mesg_size) */
+DEFINE_SYSCALL (sys_mail_receive_nonblock) {
+  uint64_t fp;
+
+  uintptr_t uvaddr_mesg = a1;
+  size_t mesg_size = (size_t)a2;
+
+  spin_lock (&proc->lock, &fp);
+  struct procgroup* procgroup = proc->procgroup;
+  spin_unlock (&proc->lock, fp);
+
+  void* mesg = sys_get_user_buffer (procgroup, uvaddr_mesg, mesg_size);
+
+  if (mesg == NULL)
+    return SYSRESULT (-ST_BAD_ADDRESS_SPACE);
+
+  struct proc_resource* mail_resource = proc_find_resource (procgroup, 0);
+
+  if (mail_resource == NULL)
+    return SYSRESULT (-ST_NOT_FOUND);
+
+  bool r = proc_mail_receive_nonblock (proc, &mail_resource->u.mail, rctx, mesg, mesg_size);
+
+  if (r)
+    return SYSRESULT (ST_OK);
+  else
+    return SYSRESULT (-ST_TRY_AGAIN);
+}
+
 /* int device_do (int device_id, int cmd, void* a1, void* a2, void* a3, void* a4) */
 DEFINE_SYSCALL (sys_device_do) {
   uint64_t fpg, fd, fp;
@@ -1025,6 +1054,7 @@ static syscall_handler_func_t handler_table[] = {
     [SYS_ENV_GET] = &sys_env_get,
     [SYS_EXEC_PARTIAL] = &sys_exec_partial,
     [SYS_EXEC_PARTIAL_FINI] = &sys_exec_partial_fini,
+    [SYS_MAIL_RECEIVE_NONBLOCK] = &sys_mail_receive_nonblock,
 };
 
 syscall_handler_func_t syscall_find_handler (int syscall_num) {