Net2: Sets

Download Source in .tar.gz
Download Source in .zip

Part1: Introduction
Part2: Examples
Part3: Documentation
Part4: Sets

Sets are very useful in network programming because you often need to keep track of a number of sockets and/or IP addresses using operations like those on a logical set. These routines allow you to add an item to a set, test to see if an item is a member of a set, remove an item from a set, and to iterate over the contents of a set. I've also included code to send a message to each item in the set.

Most high level programming languages such as Java or C++ provide a set data type either as a built in part of the language or as part of a standard library. Net2 is written in C to make it as easy as possible to embedded it in other languages. C does not have a set data type so I decided to include code for handling sets in Net2. Then, I realized that many, if not most, Net2 users would not need them so I moved them into separate files (net2sets.c and net2sets.h) which you can use or ignore as you please. Most of the code for these functions is generated by a set of weird looking C macros in set.h. If you are new to C you might find the contents of set.h educational. It shows how we used to implement generic types before languages like C++ and Java came along. Or, at least this is how some of us did it when we couldn't use LISP.

This implementation of sets is efficient for sets with small numbers of items. But, it does set operations using iterative O(n/2) algorithms that may be too slow for handling very large sets.

Sample Code

The following code creates a SocketSet and initializes it. The example code then adds 1000 sockets to the set. After that it deletes all the even numbered sockets. Finally, it iterates over the set printing out all the sockets in no particular order. The complete program can be found in set.cpp.

int main(int argc, char **argv)
{
  int i;
  int j;

  SocketSet s;                       // declare the set
  initSocketSet(&s, 100);            // initialize it
  
  for (i = 0; i < 1000; i++)
  {
    addSocketSet(&s, &i);            // add members to the set
  }

  for (i = 0; i < 1000; i += 2)
  {
    delSocketSet(&s, &i);            // delete members from the set
  }

  for (j = firstSocketSet(&s, &i);   // get first member
       j != -1;                      // check for end of set
       j = nextSocketSet(&s, &i))    // get the next member 
  {
    printf("item = %d\n", i);        // print out the members
  }

  finitSocketSet(&s);                // free memory used by the set
}

Socket Sets

In Net2 a socket is represented as a small integer so the set operations take a pointer to a SocketSet structure and integers as parameters. To create a SocketSet declare a variable of type SocketSet or malloc() a structure of that type and then initialize it. The actual structure looks like:

typedef struct
{
  int itr;
  int last;
  int size;
  int *set;
} SocketSet;

int initSocketSet(SocketSet *s, int size);

Initializes a SocketSet structure for use by your program. You can't use the set until you initialized it. The size parameter tells you the initial size of the set. The set functions will allocate more memory to store the set if they need to. But, while the set will automatically grow beyond the size specified, it will not automatically shrink.