android - Weird behavior with asynctask -

so coming across weird problem cant find explaination for. have async task in in dobackground method wait until variable set "wait" notified

private class testasynctask extends asynctask<void, object, boolean> {           @override         protected void onpreexecute() {               log.d("test1");         }          @override         protected boolean doinbackground(void... params) {                log.d("test2");                while (nextcardtoplay == null) {         wait();                     }                log.d("test3");        } } 

activity a:

protected void oncreate(){      = new testasynctask().execute(); }  protected void onpause(){     a.cancel() } 

so can see when activity starts, asynctask started. when activity closed asynctask supposed cancelled.

what noticed if open activity, close it, , reopen again asynctask created , in wait mode (never cancelled). no problem. whats confusing when start activity (while stale asynctask there), seems new asynctask started ( because logs onpreexecute called) doinbackground in nextasynctask not executed because test2 log not showing.

any idea why?

this behavior not @ weird if @ documentation, states asynctasks run on single background thread, i.e. sequentially. if want tasks run on parallel worker threads, use executeonexecutor() method instead of simple execute() , pass asynctask.thread_pool_executor parameter.