If this is executed in a single core, that core will then interleave between the three threads, each time filtering some of the words before switching to the next one. This interleaving process is called context switching.

Context switching adds overhead to the overall process, because it requires saving the state of the current thread and then loading the state of the next one. This overhead makes it likely that this multi-threaded implementation of isPalindrome() will take longer in a single-core machine when compared to the sequential implementation seen before. This happens because the sequential implementation will have one core do all the work but will avoid the context switch.