Problem with monitors in C-- - Programmers Heaven

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Problem with monitors in C--

IamBMFIamBMF Posts: 3Member
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:

[code]
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
[/code]

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?

Comments

  • LundinLundin Posts: 3,711Member
    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.
  • IamBMFIamBMF Posts: 3Member
    [link=http://inside.mines.edu/fs_home/tcamp/baci/]This is their website.[/link]

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

    [code]
    main()
    {
    cobegin
    {
    method1();
    method2();
    }
    } // main
    [/code]

    to:

    [code]
    main()
    {
    method1();
    method2();
    } // main
    [/code]

    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.
  • IamBMFIamBMF Posts: 3Member
    It works now.

    [code]
    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[/code]

    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.


  • LundinLundin Posts: 3,711Member
    That language appears to be quite obscure :)
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