A processor includes an instruction pipeline. The pipeline can be operated alternatively in a multi-thread mode and in a single-thread mode. In the multi-thread mode, the instruction pipeline processes multiple threads in an interleaved or simultaneous manner. In the single-thread mode, the pipeline processes a single thread. The instruction pipeline comprises multiple functional units, each of which is reserved for one thread among the multiple threads when the pipeline is in the multi-thread mode and reserved for one context layer among multiple context layers when the instruction pipeline is in the single-thread mode.