UNIX-POSIX

C programs that rely on POSIX standards

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Signals and interrupts

• Signals are a limited form of inter-process communication (IPC)

• Used in Unix, Unix-like, and other POSIX-compliant operating systems

• Signal is an asynchronous notification sent to a process or to a specific thread within the same process in order to notify it of an event that occurred

• When a signal is sent, the operating system interrupts the target process' normal flow of execution to deliver the signal

  • If the process has previously registered a signal handler, that routine is executed
  • Otherwise, the default signal handler is executed

#include <signal.h>

int sighold(int sig);
int sigignore(int sig);
int sigpause(int sig);
int sigrelse(int sig);
void (*sigset(int sig, void (*disp)(int)))(int);

Examples

1. Prime numbers

   • SIGALRM, SIGINT
   • Pause program and periodically print status

2. Signal handler

   • SIGUSR1, SIGUSR2
   • Handle and keep track of multiple signals with different priority

3. Signal generator

   • Generate signals for handler

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Multiprocessing and multithreading

• A thread of execution is the smallest sequence of programmed instructions that can be managed independently by a scheduler, part of the operating system

• A thread is a component of a process

• Multiple threads can exist within one process, executing concurrently and sharing resources such as memory, while different processes do not share these resources

• The threads of a process share its executable code and the values of its dynamically allocated variables and non-thread-local global variables at any given time

Take a loook at: https://computing.llnl.gov/tutorials/pthreads/

Examples

Threads

Processes

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Synchronization

1. Lamport and Dekker algorithms
2. Atomic operations (TAS)
3. Semaphores
4. Mutex
5. Monitor