libpollcat/src/pollcat.c

/** Wrapper structure for poll()
 *
 *  This file is part of the Pollcat Library.
 *  Copyright (C) 2022 Expatria Technologies Inc.
 *  Contact: Morgan Hughes <morgan@expatria.ca>
 *
 *  The Pollcat Library is free software: you can redistribute it and/or modify it under
 *  the terms of the the GNU Lesser General Public License as published by the Free
 *  Software Foundation; either version 3 of the License, or (at your option) any later
 *  version.
 *
 *  This program is distributed in the hope that it will be useful, but WITHOUT ANY
 *  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
 *  PARTICULAR PURPOSE.  See the GNU General Public License for more details.
 *
 *  You should have received copies of the GNU General Public License and the GNU Lesser
 *  General Public License along with the Pollcat Library.  If not, see
 *  https://www.gnu.org/licenses/
 *
 *  vim:ts=4:noexpandtab
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <poll.h>

#include <pollcat.h>
#include "private.h"


static struct pollfd *pollcat_list = NULL;
static size_t         pollcat_size = 0;
static size_t         pollcat_used = 0;
static int            pollcat_last = -1;


static int pollcat_time_current = -1;

/** Optional function to call on fatal error; if unset an assert()-style message will be
 *  printed on stderr and abort() called.
 */
typedef void (* pollcat_assert_f) (const char *file, int line, const char *mesg);
pollcat_assert_f pollcat_assert_func = NULL;

/** Base timeout for wrapped poll() calls in milliseconds; pollcat_time_reduce() may be
 *  called to reduce this on a per-loop basis to improve latency of things like timers.
 *  The default is POLLCAT_TIME_BASE.
 */
int pollcat_time_base = POLLCAT_TIME_BASE;

/** Minimum timeout for wrapped poll() calls in milliseconds; pollcat_time_reduce() will
 *  not reduce the per-loop timeout below this value. The default is POLLCAT_TIME_MINIMUM.
 */
int pollcat_time_minimum = POLLCAT_TIME_MINIMUM;

/** Initial size of the pollfd array. The default is POLLCAT_SIZE_INITIAL.
 */
size_t pollcat_size_initial = POLLCAT_SIZE_INITIAL;

/** Incremental size of the pollfd array. The default is POLLCAT_SIZE_INCREMENT.
 */
size_t pollcat_size_increment = POLLCAT_SIZE_INCREMENT;


/** Cleanup function and atexit flag */
static int pollcat_exit = 0;
static void pollcat_done (void)
{
	free(pollcat_list);
	pollcat_list = NULL;
	pollcat_size = 0;
	pollcat_used = 0;
	pollcat_last = -1;
}

/** Init function */
static void pollcat_init (void)
{
    /* Register cleanup */
	if ( !pollcat_exit )
	{
		atexit(pollcat_done);
		pollcat_exit = 1;
	}

	if ( pollcat_list )
		return;

	if ( pollcat_size_initial < 1 )
		pollcat_size_initial = 1;
	if ( pollcat_size_increment < 1 )
		pollcat_size_increment = 1;

	pollcat_list = malloc(pollcat_size_initial * sizeof(struct pollfd));
	memset(pollcat_list, 0xFF, pollcat_size_initial * sizeof(struct pollfd));
	POLLCAT_ASSERT(pollcat_list != NULL);

	pollcat_size = pollcat_size_initial;
	pollcat_used = 0;
	pollcat_last = -1;

	pollcat_time_current = pollcat_time_base;
}

/** Binary search compare function */
static int pollcat_comp (const void *va, const void *vb)
{
	const struct pollfd *pa = (const struct pollfd *)va;
	const struct pollfd *pb = (const struct pollfd *)vb;

	POLLCAT_ASSERT(va != NULL);
	POLLCAT_ASSERT(vb != NULL);

	return pa->fd - pb->fd;
}

/** Binary search function */
static struct pollfd *pollcat_search (int fd)
{
	struct pollfd  key = { 0 };
	struct pollfd *ret;

	if ( pollcat_used < 1 )
		return NULL;

	/* Check cached index first */
	if ( pollcat_last > -1 && pollcat_last < pollcat_used
	  && pollcat_list[pollcat_last].fd == fd )
		return &pollcat_list[pollcat_last];

	/* Do binary search and cache result */
	key.fd = fd;
	ret = bsearch(&key, pollcat_list, pollcat_used, sizeof(struct pollfd), pollcat_comp);
	pollcat_last = ret ? ret - pollcat_list : -1;
	return ret;
}


/** Add an FD to the poll array and set the events requested
 *
 *  \param  fd      File descriptor
 *  \param  events  Bitmap of events from poll.h, such as POLLIN
 */
void pollcat_fd_add (int fd, short int events)
{
	struct pollfd *pfd;

	/* Auto init, no-return if failed */
	pollcat_init();

	/* Update existing if found */
	if ( (pfd = pollcat_search(fd)) )
	{
		pfd->events = events;
		return;
	}

	/* Grow list if full */
	if ( pollcat_used == pollcat_size )
	{
		size_t new = pollcat_size + pollcat_size_increment;
		pfd = malloc(new * sizeof(struct pollfd));
		POLLCAT_ASSERT(pfd != NULL);

		memcpy(pfd, pollcat_list, pollcat_size * sizeof(struct pollfd));
		memset(pfd + pollcat_size, 0xFF, pollcat_size_increment * sizeof(struct pollfd));
		free(pollcat_list);
		pollcat_list  = pfd;
		pollcat_size += pollcat_size_increment;
	}

	/* Add new entry and increment used */
	pollcat_list[pollcat_used].fd     = fd;
	pollcat_list[pollcat_used].events = events;
	pollcat_used++;

	/* Re-sort list */
	qsort(pollcat_list, pollcat_used, sizeof(struct pollfd), pollcat_comp);
}


/** Get request bits of an FD in the poll array
 *
 *  \param  fd  File descriptor
 *
 *  \return bitmap on success, <0 if not found
 */
short int pollcat_events_get (int fd)
{
	struct pollfd *pfd;

	/* Auto init, no-return if failed */
	pollcat_init();

	if ( !(pfd = pollcat_search(fd)) )
		return -1;

	return pfd->events;
}


/** Set request bits on an FD in the poll array
 *
 *  \param  fd      File descriptor
 *  \param  events  Bitmap of events from poll.h, such as POLLIN
 */
void pollcat_events_set (int fd, short int events)
{
	struct pollfd *pfd;

	/* Auto init, no-return if failed */
	pollcat_init();

	if ( !(pfd = pollcat_search(fd)) )
		return;

	pfd->events = events;
}


/** Get result bits of an FD in the poll array
 *
 *  \param  fd  File descriptor
 *
 *  \return bitmap on success, 0 on error
 */
short int pollcat_revents (int fd)
{
	struct pollfd *pfd;

	/* Auto init, no-return if failed */
	pollcat_init();

	if ( !(pfd = pollcat_search(fd)) )
		return 0;

	return pfd->revents;
}


/** Remove an FD from the poll array
 *
 *  \param  fd  File descriptor
 */
void pollcat_fd_remove (int fd)
{
	struct pollfd *pfd;

	/* Auto init, no-return if failed */
	pollcat_init();

	if ( !(pfd = pollcat_search(fd)) )
		return;

	/* Last entry in list is cheap */
	if ( 1 == pollcat_used )
	{
		pollcat_used--;
		pollcat_last = -1;
		return;
	}

	/* Decrement used and move last entry into vacant slot */
	pollcat_used--;
	pfd->fd     = pollcat_list[pollcat_used].fd;
	pfd->events = pollcat_list[pollcat_used].events;
	memset(&pollcat_list[pollcat_used], 0xFF, sizeof(struct pollfd));

	/* Re-sort list */
	qsort(pollcat_list, pollcat_used, sizeof(struct pollfd), pollcat_comp);
}


/** Reduce the current timeout
 *
 *  \param  time  New timeout in milliseconds
 */
void pollcat_time_reduce (int time)
{
	if ( time < pollcat_time_current )
		pollcat_time_current = time;
}


/** Wraps the system poll() command using the internal pollfd array and timeout
 *
 *  \return as per poll(), <0 on error
 */
int pollcat_poll (void)
{
	int ret;

	/* Auto init, no-return if failed */
	pollcat_init();

	if ( pollcat_time_current < pollcat_time_minimum )
		pollcat_time_current = pollcat_time_minimum;

	ret = poll(pollcat_list, pollcat_used, pollcat_time_current);
	pollcat_time_current = pollcat_time_base;

	return ret;
}

#if POLLCAT_DEBUG
static const char *pollcat_bits (short int  events)
{
	static char  buff[20] = { 0 };
	char        *ins = buff;

	*ins++ = events & POLLIN    ? 'I' : '_';
	*ins++ = events & POLLPRI   ? 'P' : '_';
	*ins++ = events & POLLOUT   ? 'O' : '_';
#ifdef POLLRDHUP
	*ins++ = events & POLLRDHUP ? 'R' : '_';
#endif
	*ins++ = events & POLLERR   ? 'E' : '_';
	*ins++ = events & POLLHUP   ? 'H' : '_';
	*ins++ = events & POLLNVAL  ? 'N' : '_';
#ifdef POLLMSG
	*ins++ = events & POLLMSG   ? 'M' : '_';
#endif
#ifdef _XOPEN_SOURCE
	*ins++ = ',';
	*ins++ = 'R';
	*ins++ = events & POLLRDNORM ? 'N' : '_';
	*ins++ = events & POLLRDBAND ? 'B' : '_';
	*ins++ = ',';
	*ins++ = 'W';
	*ins++ = events & POLLWRNORM ? 'N' : '_';
	*ins++ = events & POLLWRBAND ? 'B' : '_';
#endif

	return buff;
}
#endif

void pollcat_dump (FILE *fp)
{
#if POLLCAT_DEBUG
	int i;

	if ( !fp && stderr )
		fp = stderr;
	if ( !fp && stdout )
		fp = stdout;
	if ( !fp )
		return;

	fprintf(fp, "pollcat: list %p, used %zu / size %zu\n",
	        pollcat_list, pollcat_used, pollcat_size);

	fprintf(fp, "fd  events    revents   path\n");
	for ( i = 0; i < pollcat_used; i++ )
	{
		char  path[256];
		char  link[256];

		snprintf(path, sizeof(path), "/proc/self/fd/%d", pollcat_list[i].fd);
		memset(link, 0, sizeof(link));
		if ( readlink(path, link, sizeof(link) - 1) < 0 )
			snprintf(link, sizeof(link), "err:%s", strerror(errno));

		fprintf(fp, "%2d  %-8s  ", pollcat_list[i].fd,
		        pollcat_bits(pollcat_list[i].events));

		fprintf(fp, "%-8s  %s\n", pollcat_bits(pollcat_list[i].revents), link);
	}
#endif
}