Explanation of Code

I am having trouble seeing what this code is doing. I keep getting flag[i] as the only on going into the critical section, which obviously means I am missing something! This isnt homework and I didn't write this code, we are discussing it in class, but I need a better understanding of what is going on! Please explain! Thanks!

So all elements of flag are initially idle, and inital value of turn is between 0 and n-1 (this is what is throwing me off I think.) The processes share:

Code:

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enum pstate {idle, want_int, in_cs};
pstate flag[n];
int turn;

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Code:

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do {
    while(TRUE){
        flag[i] - want_in;
        j = turn;
   
        while( j != i){
                if (flag[j] != idle)
                    j = turn;
                else
                    j = (j + 1) % n;
                }

        flag[i] = in_cs;
        j = 0;

        while ((j<n) && (j == i || flag[j] != in_cs))
              j++;

        if ((j >=n) && (turn == i || flag[turn] == idle))
              break;
}

//critical section

j = (turn + 1) % n;

while (flag[j] == idle)
      j = (j + 1) % n;

turn = j;
flag[i]= idle;

//remainder section

} while (TRUE)

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Is this all the code, you are missing some stuff. Also the last line ends the do and should just contain the '}'. Where is turn assigned a value? j = turn; just reserves a space in memory and does not guarantee an initial value of 0. try declaring turn similar to the following:

Code:

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int turn = 0;

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Also, what parts do you understand? mabye a debugger or deskchecking it might help...

Code:

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        flag[i] - want_in;

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This is probably a typo: It doesn't do anything [well, in theory, it calculates flag[i] - want_in and then throws away the result - but that is "doing nothing"].

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Mats