Concepts of parallel processing

Various concepts have developed that help us understand the complexities of parallel processing.

• Synchronization: Any constraint on the order in which operations are carried out with the implication that the operations belong to different processes.
• Concurrent Processes: Whenever the first operation of one process is started before the last operation of some other process is completed.
• Simultaneous Processes: When the operations of several processes can occur during the same moment of time. Notice that simultaneous processes are concurrent processes, but the opposite is not necessarily the case.
• Mutual Exclusion: When, for the purpose of exclusively using a shared resource, one process blocks the further progress of other concurrent processes that require the use of the same resource.
• Critical Region: A set of operations within a process that invoke mutual exclusion. This implies that most of a process does not operate within a critical region.
• Lock: An implementation of mutual exclusion in which a shared resource is explicitly identified.
• Mutual exclusion is necessary when:
  • A shared resource can be used by only one process at a time and
  • Access to a shared resource must be granted to one of several concurrent processes within a finite time and
  • A process must release a shared resource within a finite time.
• Deadlock: A state where some processes fail to terminate because they are waiting on (shared) resources that are being held by each other. See Table 1.