// A state is safe iff there exists a safe sequence of grants that are sufficient 
// to allow all threads to eventually receive their maximum resource needs.

bool
ResourceMgr::isSafe() {
    int j;
    int toBeAvail[] = copy avail[];
    int need[][] = max[][] - alloc[][];  // need[i][j] is initialized to 
                                         // max[i][j] - alloc[i][j]
    bool finish[] = [false, false, false, ...]; // finish[j] is true
                                         // if thread j is guaranteed to finish

    while (true) {
        j = any threadID such that:
             (finish[j] == false) && forall i: need[i][j] <= toBeAvail[i];
        if (no such j exists) {
            if (forall j: finish[j] == true) {
                return true;
            } else {
                return false;
            }
        } else {  // Thread j will eventually finish and return its 
                  // current allocation to the pool.
            finish[j] = true;
            forall i:  toBeAvail[i] = toBeAvail[i] + alloc[i][j];
        }
    }
}

// Hypothetically grant request and see if resulting state is safe.

bool 
ResourceMgr::wouldBeSafe(int resourceID, int threadID) {  
    bool result = false;       

    avail[resourceID]--;
    alloc[resourceID][threadID]++;
    if (isSafe()) {
        result = true;
    }
    avail[resourceID]++;
    alloc[resourceID][threadID]--;
    return result;
}