ring_buffer.c

/**
 * @file ring_buffer.c
 * @author Rafael Diniz
 * @date 12 Apr 2018
 * @brief Optimized ring-buffer implementation
 *
 * Optimized ring-buffer implementation
 *
 */

#include "ring_buffer.h"

void ring_buffer_create (struct ring_buffer *buffer, unsigned long order)
{
    char path[] = "/dev/shm/ring-buffer-XXXXXX";
    int file_descriptor;
    void *address;
    int status;

    file_descriptor = mkstemp (path);
    if (file_descriptor < 0)
        report_exceptional_condition ();

    status = unlink (path);
    if (status)
        report_exceptional_condition ();

    buffer->count_bytes = 1UL << order;
    buffer->write_offset_bytes = 0;
    buffer->read_offset_bytes = 0;

    status = ftruncate (file_descriptor, buffer->count_bytes);
    if (status)
	report_exceptional_condition ();
 
    buffer->address = mmap (NULL, buffer->count_bytes << 1, PROT_NONE,
			    MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
 
    if (buffer->address == MAP_FAILED)
	report_exceptional_condition ();
 
    address =
	mmap (buffer->address, buffer->count_bytes, PROT_READ | PROT_WRITE,
	      MAP_FIXED | MAP_SHARED, file_descriptor, 0);
 
    if (address != buffer->address)
	report_exceptional_condition ();
 
    address = mmap (buffer->address + buffer->count_bytes,
		    buffer->count_bytes, PROT_READ | PROT_WRITE,
		    MAP_FIXED | MAP_SHARED, file_descriptor, 0);
 
    if (address != buffer->address + buffer->count_bytes)
	report_exceptional_condition ();
 
    status = close (file_descriptor);
    if (status)
	report_exceptional_condition ();

}
 
void
ring_buffer_free (struct ring_buffer *buffer)
{
    int status;
 
    status = munmap (buffer->address, buffer->count_bytes << 1);
    if (status)
	report_exceptional_condition ();
}
 
void *
ring_buffer_write_address (struct ring_buffer *buffer)
{
    
  return buffer->address + buffer->write_offset_bytes;
}
 
void
ring_buffer_write_advance (struct ring_buffer *buffer,
                           unsigned long count_bytes)
{
  buffer->write_offset_bytes += count_bytes;
}
 
void *
ring_buffer_read_address (struct ring_buffer *buffer)
{
  return buffer->address + buffer->read_offset_bytes;
}
 
void
ring_buffer_read_advance (struct ring_buffer *buffer,
                          unsigned long count_bytes)
{
  buffer->read_offset_bytes += count_bytes;
 
  if (buffer->read_offset_bytes >= buffer->count_bytes)
    {
      buffer->read_offset_bytes -= buffer->count_bytes;
      buffer->write_offset_bytes -= buffer->count_bytes;
    }
}
 
unsigned long
ring_buffer_count_bytes (struct ring_buffer *buffer)
{
  return buffer->write_offset_bytes - buffer->read_offset_bytes;
}
 
unsigned long
ring_buffer_count_free_bytes (struct ring_buffer *buffer)
{
  return buffer->count_bytes - ring_buffer_count_bytes (buffer);
}
 
void
ring_buffer_clear (struct ring_buffer *buffer)
{
  buffer->write_offset_bytes = 0;
  buffer->read_offset_bytes = 0;
}