Synchronization and Access control

eXpOS assumes a single processor multi programming environment. This means that all processes exist concurrently in the machine and the OS time shares the machine between various processes. The OS specification requires that Round Robin scheduling is used with co-operative time-sharing. This is discussed in Section 6 . The OS does not provide any promise to the application program about the order in which processes will be executed.

However, application programs often need to stop and wait for another process to execute certain operations before proceeding. The OS provides system calls that allow user processes to synchronize execution.