1. A computer-implemented method of executing an instruction sequence with a recursive function call of a plurality of threads within a thread group in a Single-Instruction-Multiple-Threads (SIMT) system, the method comprising: providing each of the threads a function call counter (FCC), an active mask, an execution mask and a per-thread program counter (PTPC), wherein the PTPC for a specific thread indicates a target in the instruction sequence for the specific thread to be active; executing the instruction sequence with the recursive function call by the threads in the thread group according to a program counter (PC) indicating a target that all of the threads will jump to for subsequent execution, and upon executing the recursive function call, for each thread, setting the active mask according to the PTPC and the target indicated by the PC, determining the FCC when entering to or returning from a first iteration of the recursive function call, setting the execution mask according to the FCC and the active mask, and determining whether an execution result of the recursive function call takes effects according to the execution mask, wherein, for each thread, the execution result of the recursive function call in each iteration takes effect if the execution mask is set to a predetermined value and the execution result does not take effect if the execution mask is not set to the predetermined value.