ExtractPthread.Action
uniquely identifies the function call ** created/defined by `fun_ctx` function
type t =
| Call of fun_call_id
| Assign of string * string
| Cond of string
| ThreadCreate of thread
| ThreadJoin of thread_id
| ThreadExit
| MutexInit of mutex_id
| MutexLock of mutex_id
| MutexUnlock of mutex_id
| CondVarInit of cond_var_id
| CondVarBroadcast of cond_var_id
| CondVarSignal of cond_var_id
| CondVarWait of cond_wait
| Nop
ADT of all possible edge actions types