iSpin LTL property evaluation only with activated "assertion violations"?

Question

I am trying to get used to iSpin/Promela. I am using:

Spin Version 6.4.3 -- 16 December 2014, iSpin Version 1.1.4 -- 27 November 2014, TclTk Version 8.6/8.6, Windows 8.1.

Here is an example where I try to use LTL. The verification of the LTL property should produce an error if the two steps in the for loop are non-atomic:

1   #define ten ((n !=10) && (finished == 2))
2   
3   int n = 0;
4   int finished = 0;
5   active [2] proctype P() {
6       //assert(_pid == 0 || _pid == 1);
7       
8           int t = 0;
9           byte j;
10          for (j : 1 .. 5) {
11              atomic {
12                  t = n;
13                  n = t+1;
14              }
15          }
16      finished = finished+1;
17  }
18  
19  ltl alwaysten {[] ! ten }

In the verification tap I just want to test the LTL property, so I disable all safety properties and activate "use claim". The claim name is "alwaysten".

But it seems that the LTL property is just evaluated if I activate "assertion violations". Why? A collegue is using iSpin v1.1.0 and he does not need to activate this? What am I doing wrong? I want to prove assertions and LTL properties independently...

Here is the trace:

pan: elapsed time 0.002 seconds
To replay the error-trail, goto Simulate/Replay and select "Run"
spin -a  1_2_ConcurrentCounters_8.pml
ltl alwaysten: [] (! (((n!=10)) && ((finished==2))))
C:/cygwin/bin/gcc -DMEMLIM=1024 -O2 -DXUSAFE -w -o pan pan.c
./pan -m10000  -E -a -N alwaysten
Pid: 6980
warning: only one claim defined, -N ignored

(Spin Version 6.4.3 -- 16 December 2014)
    + Partial Order Reduction

Full statespace search for:
    never claim             + (alwaysten)
    assertion violations    + (if within scope of claim)
    acceptance   cycles     + (fairness disabled)
    invalid end states  - (disabled by -E flag)

State-vector 36 byte, depth reached 57, errors: 0
      475 states, stored
      162 states, matched
      637 transitions (= stored+matched)
        0 atomic steps
hash conflicts:         0 (resolved)

Stats on memory usage (in Megabytes):
    0.024   equivalent memory usage for states (stored*(State-vector + overhead))
    0.291   actual memory usage for states
   64.000   memory used for hash table (-w24)
    0.343   memory used for DFS stack (-m10000)
   64.539   total actual memory usage


unreached in proctype P
    (0 of 13 states)
unreached in claim alwaysten
    _spin_nvr.tmp:8, state 10, "-end-"
    (1 of 10 states)

pan: elapsed time 0.001 seconds
No errors found -- did you verify all claims?

Answer 1

This is because your LTL is translated into a claim with an assert statement. See the following automaton.

So, without checking for assertion violations, no error can be found.

(A possible explanation of different behaviors: previous versions of Spin might translate this differently, perhaps using accept instead of assert.)