From perldoc threads v1.75:

$thr->error() Threads are executed in an "eval" context. This method will return "undef" if the thread terminates normally. Otherwise, it returns the value of $@ associated with the thread's execution status in its "eval" context.

and you might want to look at

 threads->create({'exit' => 'thread_only'}, ...)
 This overrides the default behavior of "exit()" inside the newly crea
+ted thread only.
...... with this setting, calling "exit()" causes only the thread to t
+erminate
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