Promela: passing array to new proctype

I need to pass an array from parent process to child process in Promela but it is not allowing me to do so. Also, I have some constraints in making this array global, so can't do this also. How can this be done?

for e.g.:

proctype B(int hg)
{
 ..
}

proctype A()
{
    int hg[n];
    run B(hg);
}

Solution

The documentation of run says that:

DESCRIPTION The run operator takes as arguments the name of a previously declared proctype , and a possibly empty list of actual parameters that must match the number and types of the formal parameters of that proctype. [...]

The run operator must pass actual parameter values to the new process, if the proctype declaration specified a non-empty formal parameter list. Only message channels and instances of the basic data types can be passed as parameters. Arrays of variables cannot be passed.

[emphasis is mine]

You should consider using global variables instead.

In the following example, we enclose the array inside a user-defined structured data type --together with any other parameter which might be needed by the process--, and declare a global vector of such Records. Then, instead of directly passing around the array argument, we exchange the index of the Record containing the parameters for the other process.

#define m 10
#define n 10

typedef Record {
    int hg[n];
    // ...
    // other parameters
    // ... 
};

Record data[m];

active proctype A ()
{
    int idx = 1;

    data[idx].hg[0] = 12;

    // ...

    run B(idx);
}

proctype B (int idx)
{
    assert(data[idx].hg[0] == 12);

    data[idx].hg[0] = 17;

    // ...
}

This will allow you to generate a verifier:

~$ spin -search -bfs test.pml
...
State-vector 424 byte, depth reached 6, errors: 0
...

Alternatively, and only if you don't need to generate a verifier, you can simply pass-around your Record instance. e.g.

#define n 10

typedef Record {
    int hg[n];
    // ...
    // other parameters
    // ... 
};

active proctype A ()
{
    Record my_record;

    my_record.hg[0] = 12;

    // ...

    run B(my_record);
}

proctype B (Record data)
{
    assert(data.hg[0] == 12);

    data.hg[0] = 17;

    // ...
}

However, this only works in simulation mode and in particular it will not allow you to generate a verifier:

~$ spin -search -bfs test.pml
spin: test.pml:18, Error: hidden array in parameter data

In fact, the documentation of typedef explicitly mentions that

A typedef object can also be used as a parameter in a run statement, but in this case it may not contain any arrays.

[emphasis is mine]