3 Building and running user programs

User programs can be run on each simulated node. Each user program is run as a separate user process as shown in Figure 1.

All user programs used with the simulator must be linked against the user libraries we provide (see the template Makefile for more details). There are two important issues regarding user programs:

1. Use Main() instead of main(). The entry point of a user program is actually in the simulator, not the code you write. After the simulator is done with the necessary initializations, it invokes your Main() function. The Main() function is exactly the same as main(); that is, the usual argc and argv are still there.
2. User programs must be run with ``-n i'' as the first argument. This argument is to specify that this user program should be run on node i. Note that the Main() function will not get this argument (i.e. the simulator will strip this argument before passing the arguments to Main()).
3. You should close all open sockets before returning from Main(). If you forget to close an open socket, the simulator will not close it for you and future invocations of your program might fail.