1. A computer system comprising: a cache unit; and a first processing unit, arranged to run a first program thread, and perform an instruction to store information of a signal change event into the cache unit through a cache stashing operation, wherein the signal change event is initiated by the first program thread for alerting a second program thread; wherein when the first program thread initiates the signal change event before the second program thread performs an instruction to acquire the information of the signal change event, the information of the signal change event is stored into the cache unit through the cache stashing operation, where the information of the signal change event is not acquired by the second program thread before the information of the signal change event is stored into the cache unit by the cache stashing operation; wherein when the first program thread initiates the signal change event at the time the second program thread initiates the instruction to acquire the information of the signal change event, the information of the signal change event is not stored into the cache unit through the cache stashing operation; and wherein when the second program thread performs the instruction to acquire the information of the signal change event before the first program thread initiates the signal change event, the information of the signal change event is acquired by the second program thread at the time the first program thread initiates the signal change event, or is acquired by the second program thread after the information of the signal change event is stored into the cache unit by the cache stashing operation.