Hello, I started studying BACI recently and I am having some trouble with monitors.
I know this is not strictly C/C++ but I did not know where to post this. I hope someone can help.

I made a very simple application that shows what my problem is:

monitor monSimple
{
    int variable;
   
    void method1()
    {
        cout << "method1: variable = " << variable << endl;
        variable++;
        cout << "method1: variable = " << variable << endl;
    }
   
    void method2()
    {
        cout << "method2: variable = " << variable << endl;
        variable++;
        cout << "method2: variable = " << variable << endl;
    }
    
    init
    {
        variable = 0;
    }
    
} //monitor


main()
{
    cobegin 
    {
        method1();
        method2();
    }
} // main

I expect the output to be:

method1: variable = 0
method1: variable = 1
method2: variable = 1
method2: variable = 2

or

method2: variable = 0
method2: variable = 1
method1: variable = 1
method1: variable = 2.

However, the real output is either:

method1: variable = 0
method1: variable = 2407
method2: variable = 0
method2: variable = 2607

or:

method2: variable = 0
method2: variable = 2607
method1: variable = 0
method1: variable = 2407.

What am I doing wrong?

This is the first time I hear of this "BACI". While I have no idea of the syntax, my guess is that the variable isn't initialized to zero properly.

This is their website.

In case it helps, if the main is changed from:

main()
{
    cobegin 
    {
        method1();
        method2();
    }
} // main

to:

main()
{
   method1();
   method2();
} // main

Then it outputs the 'expected' result (and the value in the init block initializes the variable properly in this case). I think this proves the monitor's code right. There could be some interference between cobegin and monitor.

A monitor is a block so that functions on it will only execute one at a time, basically. Ideal for mutual exclusion problems.
A cobegin a block whose functions will be executed concurrently. For example, you don't know which of the functions will be executed first.

Calling monitor functions inside a cobegin block, I am just trying to make a program where any of the monitor functions may be called first, but only one is running at a time.

It works now.

monitor monSimple
{
    int variable;
   
    void method1()
    {
        cout << "method1: variable = " << variable << endl;
        variable++;
        cout << "method1: variable = " << variable << endl;
    }
   
    void method2()
    {
        cout << "method2: variable = " << variable << endl;
        variable++;
        cout << "method2: variable = " << variable << endl;
    }
    
    init
    {
        variable = 0;
    }
    
} //monitor


void method1aux()
{
    method1();
}

void method2aux()
{
    method2();
}

main()
{
    cobegin 
    {
        method1aux();
        method2aux();
    }
} // main

Apparently you can't call monitor functions directly from inside a cobegin block (which is something I found by trial and error, it's not in the documentation as far as I can see). So I just enclosed the calls in auxiliary functions and it works.

That language appears to be quite obscure :)