CS 4953 Special Studies in Computer Science:
Advanced Topics in Concurrency and Communication Fall 2003

The midterm exam will be open book - USP only.

It will cover the chapters that were discussed in class up to the exam:

• Chapter 9: Times and Timers
• Chapter 12: POSIX Threads
• Chapter 13:Thread Synchronization
• Chapter 14: Critical Sections and Semaphores
• Chapter 15: POSIX IPC
• Chapter 16: Producer Consumer Synchronization
• Chapter 18: Connection-Oriented Communication
• Chapter 20: Connectionless Communication and Multicast

• gettimeoffay uses struct timeval: seconds and microseconds since the epoch
• XSI uses struct timeval and struct itimerval: seconds and microseconds
• TMR uses struct timespec and struct itimerspec: seconds and nanoseconds
• Resoultion of timer expiration is not as good as that of getting the time.
• Absolute vs. relative time for periodic timers, timer drift

Chapter 12: POSIX Threads

• One parameter is passed, a pointer to whatever
• Make sure the values passed do not change before the thread can access them.
• A pointer is returned, but it cannot point to automatic storage of the thread.
• Must save the thread ID of each thread if you are going to join them.
• Look at Programs 12.7 and 12.8

Chapter 13: Thread Synchronization

• Mutex locks:
  • Usually statically allocated and initialized.
  • Use to protect short critical sections.
• Condition Variables: used with a mutex
  • pthread_cond_wait is always called in a loop.
  • May have spurious wake ups.
  • Look at Program 13.13.
• Signal Handling with threads:
  • Preferred method:
  • block all signals in all threads
  • dedicated thread that calls sigwait
  • Don't need to worry about async-signal safety
  • Look at Program 13.14

Chapter 14 POSIX:SEM semaphores unnamed and named

• unnamed semaphores:
  • usually used between threads of a single process
  • creation and initialization are done together
  • cannot easily be used between processes
• named semaphores:
  • may be used between processes or threads
  • creation and initialization are done together
  • fatal flaw: Cannot twll which ones exist

Chapter 15 POSIX:XSI IPC

• message queues, semaphores and shared memory
• start with a key: IPC_PRIVATE, ftok from path, directly
• use a get routine to get an ID.
• ipcs on the command line will list all
• ipcrm can be used to remove them
• trouble with semaphores: creation and initialization are separate operations.

Chapter 18: Connection-oriented communication

• UICI has three routines: u_open, u_accept, u_connect
• UICI name resolution: addr2name and name2addr
• 4 implementations of name resolution - some are thread safe

Chapter 20: Connectionless communication and multicast