hi guys, im trying to write a program that would simulate a process scheduling algorithm and would seek to avoid deadlocks. this is how it should look like:
shell> program file.dat 5
where program is my program that i will explain shortly, file.dat is a data file which i will access, and 5 is a number of processes 0-4(example)
i got the first part of inputting the command line variables, now the problem is i have to detect a deadlock in a system so the file.dat would be something like this:
332
010753
200322
302902
211222
002433
where 332 is the AVAILABLE resources in the system
each of the other rows is process 0 - 4, where (010 | 753) 010 is the ALLOCATED resouces and 753 is the MAX resource vector. so only 3 resouces exist A B C, so this is what it looks like:
ALLOCATED
A B C
P0 0 1 0
P1 2 0 0
P2 3 0 2
P3 2 1 1
P4 0 0 2
MAX
A B C
7 5 3
3 2 2
9 0 2
2 2 2
4 3 3
NEED (max-allocated)
A B C
7 4 3
1 2 2
6 0 0
0 1 1
4 3 1
AVAILABLE
A B C
3 3 2
the output has to determine whether the system is in a safe state i.e. whether it can determine a sequence to run processes without causing a deadlock, so the above snapshot of a system, a safe state would exist when we have a sequence like this:
P1 -> P3 -> P4 -> P2 -> P0
P1 goes because its NEED vector is closest and less than the AVAILABLE vector i.e. 3 2 2 < 3 3 2, runs and gives back its allocated resources to the AVAILABLE pool, so the AVAILABLE vector is now 6 5 4
P3 would be the next process because its needs are the next lowest... and so on.
so when the program can determine that there is such a sequence, then its in a safe state.
if anyone has ideas, id really appreciate it, thanx, -mike
