Can thread t return
Can thread t return result?
Get pending operation.
Does t have an operation pending?
Add that op is invoked by t (destructive).
The number of states.
Give new ThreadStates object corresponding to t doing op producing res (non-destructive).
Log that t fired op and returned (destructive).
Log that t fired op and returned (non-destructive).
Create new ThreadStates corresponding to op being invoked by t.
Create new ThreadStates corresponding to op being invoked by t. (Non-destructive.)
Give new ThreadStates object corresponding to t having returned (non-destructive).
Give new ThreadStates object corresponding to t having returned result (non-destructive).
Log that t returns result (destructive).
Number of pending operations.
Each object of this class records the states of each thread within a configuration