An Introduction to Programming with Threads

• A thread is a single sequential flow of control. Multiple threads execute within a single address space.
• Concurrency can be achieved through the use of a lightweight multi-threading facility. Concurrency is good for multiple processors; driving slow devices such as disks, networks, terminals, and printers; dealing with human users; building a distributed system with shared network servers; and reducing the latency of operations.
• A multi-threading facility has four major mechanisms:
  • Thread creation (Fork)
  • Mutual exclusion or critical section (Mutex)
  • Condition variables (Wait, Signal, Broadcast)
  • Alerts
• Mutex
  • When to use:
    • To protect mutable data that will be accessed concurrently. Mutex synchronizes access through serialization.
    • Think of the mutex as protecting the invariant of the associated data.
  • Problems:
    • Cheating
    • Deadlock
    • Poor performance through lock conflicts
• Condition Variable
  • When to use:
    • When you want to schedule the way in which multiple threads access some shared resource, and the simple one-at-a-time mutual exclusion provided by mutexes is not sufficient.
  • Problems:
    • Spurious wake-ups
    • Spurious lock conflicts
    • Starvation
    • Deadlock
• Other problems: If you have significantly more threads ready to run than there are processors, you will usually find that your performance degrades.