1. A method for determining a vulnerability of program code to soft errors, comprising: by a computing device, performing operations for: from corresponding instructions for each of two or more threads in multi-threaded program code, identifying instructions that perform predetermined accesses of one or more architectural structures; based on executing the program code, determining a time for which the program code is exposed to soft errors due to predetermined accesses performed by the identified instructions; and using the time for which the program code is exposed to soft errors to determine the vulnerability of the program code to soft errors.