poll.h Library

I learned about the <poll.h> library. The purpose of this library is to function as an event listener. The library includes a function that waits for a set of file descriptors to become ready for I/O operations (input, output). I used this library in parallel with a thread where I monitor a GPIO pin for events triggered by pressing a push-button on my Raspberry Pi board. When the push button is pressed and the voltage increases, the interrupt is triggered and will activate or deactivate an LED based on a defined function I created.

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The pollfd structure is used to store information about a file descriptor.

• The first argument is the file descriptor.
• The second argument is the events the file descriptor is interested in.
• The third argument is the events that have occurred.

The poll() function is used to wait for a set of file descriptors to become ready for I/O operations.

• The first argument is a pointer to an array of pollfd structures.
• The second argument is the number of elements in the array.
• The third argument is the timeout in milliseconds.
• The function returns the number of file descriptors ready for I/O operations, or -1 if an error occurs.

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Simple implementation of the poll library:

#include <poll.h>
 
int main()
{
  struct pollfd fds[1];
 
  fds[0].fd = open("/sys/class/gpio/gpio6/value", O_RDWR);
  fds[0].events = POLLPRI;
  fds[0].revents = 0;
 
  int myPoll = poll(fds, 0, 5000);
 
  if (myPoll < 0)
  {
    // the poll couldn't start
  }
  
  else if (myPoll == 0)
  {
    // the poll timed out!
  }
  
  else
  {
    // do something
  }
  
  return 0;
}

Here is the documentation for the poll.h library