X-Git-Url: https://git.xandkar.net/?p=khatus.git;a=blobdiff_plain;f=x5%2Fkhatus.c;h=5407acde0b145131f038515d773e0a8d17bf2526;hp=b21336d8d4720acecb798a9536707620f4966dfe;hb=HEAD;hpb=e6c523cd4c30a1be6ac358ab6da910aaf9b6b70e

diff --git a/x5/khatus.c b/x5/khatus.c
index b21336d..5407acd 100644
--- a/x5/khatus.c
+++ b/x5/khatus.c
@@ -5,219 +5,641 @@
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 #include <unistd.h>
 
 #include <X11/Xlib.h>
 
-#define debug(args...) {fprintf(stderr, "[debug] " args);}
-#define info( args...) {fprintf(stderr, "[info] "  args);}
-#define error(args...) {fprintf(stderr, "[error] " args);}
-#define fatal(args...) {fprintf(stderr, "[fatal] " args); exit(EXIT_FAILURE);}
-#define usage(args...) {print_usage(); fatal("[usage] " args);}
+#include "bsdtimespec.h"
+#include "khlib_log.h"
+#include "khlib_time.h"
 
+#define usage(...) { \
+	print_usage(); \
+	fprintf(stderr, "Error:\n    " __VA_ARGS__); \
+	exit(EXIT_FAILURE); \
+}
 #define ERRMSG "ERROR"
 
+
 static const char errmsg[] = ERRMSG;
 static const int  errlen   = sizeof(ERRMSG) - 1;
 
-char *argv0;
-
-/* TODO: Convert fifo list to fifo array. */
-typedef struct Fifo Fifo;
-struct Fifo {
-	char   *name;
-	int     fd;
-	int     width;
-	int     last_read;
-	int     ttl;
-	int     pos;  /* Position on the output buffer. */
-	Fifo   *next;
+char *argv0 = NULL;
+int running = 1;
+
+/* TODO: Convert slot list to slot array. */
+typedef struct Slot Slot;
+struct Slot {
+	char            *in_fifo;
+	int              in_fd;
+	struct timespec  in_last_read;
+	struct timespec  out_ttl;
+	int              out_width;
+	int              out_pos_lo;   /* Lowest  position on the output buffer. */
+	int              out_pos_cur;  /* Current position on the output buffer. */
+	int              out_pos_hi;   /* Highest position on the output buffer. */
+	Slot            *next;
 };
 
 typedef struct Config Config;
 struct Config {
-	int    interval;
+	double interval;
 	char * separator;
-	Fifo * fifos;
-	int    fifo_count;
-	int    total_width;
-	int    output_to_x_root_window;
-} defaults = {
-	.interval    = 1,
-	.separator   = "|",
-	.fifos       = NULL,
-	.fifo_count  = 0,
-	.total_width = 0,
-	.output_to_x_root_window = 0,
+	char   expiry_character;
+	Slot * slots;
+	int    slot_count;
+	int    buf_width;
+	int    to_x_root;
+};
+
+enum read_status {
+	END_OF_FILE,
+	END_OF_MESSAGE,
+	RETRY,
+	FAILURE
 };
 
+char *
+buf_create(Config *cfg)
+{
+	int seplen;
+	char *buf;
+	Slot *s;
+
+	buf = calloc(1, cfg->buf_width + 1);
+	if (buf == NULL)
+		khlib_fatal(
+		    "[memory] Failed to allocate buffer of %d bytes",
+		    cfg->buf_width
+		);
+	memset(buf, ' ', cfg->buf_width);
+	buf[cfg->buf_width] = '\0';
+	seplen = strlen(cfg->separator);
+	/* Set the separators */
+	for (s = cfg->slots; s; s = s->next) {
+		/* Skip the first, left-most */
+		if (s->out_pos_lo) {
+			/* Copying only seplen ensures we omit the '\0' byte. */
+			strncpy(
+			    buf + (s->out_pos_lo - seplen),
+			    cfg->separator,
+			    seplen
+			);
+		}
+	}
+	return buf;
+}
+
+Slot *
+slots_rev(Slot *old)
+{
+	Slot *tmp = NULL;
+	Slot *new = NULL;
+
+	while (old) {
+		tmp       = old->next;
+		old->next = new;
+		new       = old;
+		old       = tmp;
+	}
+	return new;
+}
+
 void
-fifo_print_one(Fifo *f)
+slot_log(Slot *s)
 {
-	debug(
-		"Fifo "
-		"{"
-			" name = %s,"
-			" fd = %d,"
-			" width = %d,"
-			" last_read = %d,"
-			" ttl = %d,"
-			" pos = %d,"
-			" next = %p,"
-		" }\n",
-		f->name,
-		f->fd,
-		f->width,
-		f->last_read,
-		f->ttl,
-		f->pos,
-		f->next
+	khlib_info("Slot "
+	    "{"
+	    " in_fifo = %s,"
+	    " in_fd = %d,"
+	    " out_width = %d,"
+	    " in_last_read = {tv_sec = %ld, tv_nsec = %ld}"
+	    " out_ttl = {tv_sec = %ld, tv_nsec = %ld},"
+	    " out_pos_lo = %d,"
+	    " out_pos_cur = %d,"
+	    " out_pos_hi = %d,"
+	    " next = %p,"
+	    " }\n",
+	    s->in_fifo,
+	    s->in_fd,
+	    s->out_width,
+	    s->in_last_read.tv_sec,
+	    s->in_last_read.tv_nsec,
+	    s->out_ttl.tv_sec,
+	    s->out_ttl.tv_nsec,
+	    s->out_pos_lo,
+	    s->out_pos_cur,
+	    s->out_pos_hi,
+	    s->next
 	);
 }
 
 void
-fifo_print_all(Fifo *head)
+slots_log(Slot *head)
+{
+	Slot *s = head;
+
+	for (; s; s = s->next) {
+		slot_log(s);
+	}
+}
+
+void
+slots_assert_fifos_exist(Slot *s)
+{
+	struct stat st;
+	int errors = 0;
+
+	for (; s; s = s->next) {
+		if (lstat(s->in_fifo, &st) < 0) {
+			khlib_error(
+			    "Cannot stat \"%s\". Error: %s\n",
+			    s->in_fifo,
+			    strerror(errno)
+			);
+			errors++;
+			continue;
+		}
+		if (!(st.st_mode & S_IFIFO)) {
+			khlib_error("\"%s\" is not a FIFO\n", s->in_fifo);
+			errors++;
+			continue;
+		}
+	}
+	if (errors)
+		khlib_fatal(
+		    "Encountered errors with given file paths. See log.\n"
+		);
+}
+
+void
+slot_close(Slot *s)
+{
+	close(s->in_fd);
+	s->in_fd        = -1;
+	s->out_pos_cur  = s->out_pos_lo;
+}
+
+void
+slots_close(Slot *s)
+{
+	for (; s; s = s->next)
+		if (s->in_fd > -1)
+			slot_close(s);
+}
+
+
+void
+slot_expire(Slot *s, struct timespec t, char expiry_character, char *buf)
+{
+	struct timespec td;
+
+	timespecsub(&t, &(s->in_last_read), &td);
+	if (timespeccmp(&td, &(s->out_ttl), >=)) {
+		memset(
+		    buf + s->out_pos_lo,
+		    expiry_character,
+		    s->out_width
+		);
+		khlib_warn("Slot expired: \"%s\"\n", s->in_fifo);
+	}
+}
+
+void
+slot_set_error(Slot *s, char *buf)
+{
+	char *b;
+	int i;
+
+	s->in_fd = -1;
+	b = buf + s->out_pos_lo;
+	/* Copy as much of the error message as possible.
+	 * EXCLUDING the terminating \0. */
+	for (i = 0; i < errlen && i < s->out_width; i++)
+		b[i] = errmsg[i];
+	/* Any remaining positions: */
+	memset(b + i, '_', s->out_width - i);
+}
+
+enum read_status
+slot_read(Slot *s, char *buf)
 {
-	for (Fifo *f = head; f; f = f->next) {
-		fifo_print_one(f);
+	char c;  /* Character read. */
+	int  r;  /* Remaining unused positions in buffer range. */
+
+	for (;;) {
+		switch (read(s->in_fd, &c, 1)) {
+		case -1:
+			khlib_error(
+			    "Failed to read: \"%s\". errno: %d, msg: %s\n",
+			    s->in_fifo,
+			    errno,
+			    strerror(errno)
+			);
+			switch (errno) {
+			case EINTR:
+			case EAGAIN:
+				return RETRY;
+			default:
+				return FAILURE;
+			}
+		case  0:
+			khlib_debug("%s: End of FILE\n", s->in_fifo);
+			s->out_pos_cur = s->out_pos_lo;
+			return END_OF_FILE;
+		case  1:
+			/* TODO: Consider making msg term char a CLI option */
+			if (c == '\n' || c == '\0') {
+				r = (s->out_pos_hi - s->out_pos_cur) + 1;
+				if (r > 0)
+					memset(buf + s->out_pos_cur, ' ', r);
+				return END_OF_MESSAGE;
+			} else {
+				if (s->out_pos_cur <= s->out_pos_hi)
+					buf[s->out_pos_cur++] = c;
+				else
+					/*
+					 * Force EOM beyond available range.
+					 * To ensure that a rogue large message
+					 * doesn't trap us here needlessly
+					 * long.
+					 */
+					return END_OF_MESSAGE;
+			}
+			break;
+		default:
+			assert(0);
+		}
 	}
 }
 
 void
-config_print(Config *c)
+slots_read(Config *cfg, struct timespec *ti, char *buf)
 {
-	debug(
-		"Config "
-		"{"
-			" interval = %d,"
-			" separator = %s,"
-			" fifo_count = %d,"
-			" total_width = %d,"
-			" fifos = ..."
-		" }\n",
-		c->interval,
-		c->separator,
-		c->fifo_count,
-		c->total_width
+	fd_set fds;
+	int maxfd = -1;
+	int ready = 0;
+	struct stat st;
+	struct timespec t;
+	Slot *s;
+
+	FD_ZERO(&fds);
+	for (s = cfg->slots; s; s = s->next) {
+		/* TODO: Create the FIFO if it doesn't already exist. */
+		if (lstat(s->in_fifo, &st) < 0) {
+			khlib_error(
+			    "Cannot stat \"%s\". Error: %s\n",
+			    s->in_fifo,
+			    strerror(errno)
+			);
+			slot_set_error(s, buf);
+			continue;
+		}
+		if (!(st.st_mode & S_IFIFO)) {
+			khlib_error("\"%s\" is not a FIFO\n", s->in_fifo);
+			slot_set_error(s, buf);
+			continue;
+		}
+		if (s->in_fd < 0) {
+			khlib_debug(
+			    "%s: closed. opening. in_fd: %d\n",
+			    s->in_fifo,
+			    s->in_fd
+			);
+			s->in_fd = open(s->in_fifo, O_RDONLY | O_NONBLOCK);
+		} else {
+			khlib_debug(
+			    "%s: already openned. in_fd: %d\n",
+			    s->in_fifo,
+			    s->in_fd
+			);
+		}
+		if (s->in_fd == -1) {
+			/* TODO Consider backing off retries for failed slots */
+			khlib_error("Failed to open \"%s\"\n", s->in_fifo);
+			slot_set_error(s, buf);
+			continue;
+		}
+		khlib_debug("%s: open. in_fd: %d\n", s->in_fifo, s->in_fd);
+		if (s->in_fd > maxfd)
+			maxfd = s->in_fd;
+		FD_SET(s->in_fd, &fds);
+	}
+	khlib_debug("selecting...\n");
+	ready = pselect(maxfd + 1, &fds, NULL, NULL, ti, NULL);
+	khlib_debug("ready: %d\n", ready);
+	clock_gettime(CLOCK_MONOTONIC, &t);
+	if (ready == -1) {
+		switch (errno) {
+		case EINTR:
+			khlib_error(
+			    "pselect interrupted: %d, errno: %d, msg: %s\n",
+			    ready,
+			    errno,
+			    strerror(errno)
+			);
+			/* TODO: Reconsider what to do here. */
+			return;
+		default:
+			khlib_fatal(
+			    "pselect failed: %d, errno: %d, msg: %s\n",
+			    ready,
+			    errno,
+			    strerror(errno)
+			);
+		}
+	}
+	/* At-least-once ensures that expiries are still checked on timeouts. */
+	do {
+		for (s = cfg->slots; s; s = s->next) {
+			if (s->in_fd < 0)
+				continue;
+			if (FD_ISSET(s->in_fd, &fds)) {
+				khlib_debug("reading: %s\n", s->in_fifo);
+				switch (slot_read(s, buf)) {
+				/*
+				 * ### MESSAGE LOSS ###
+				 * is introduced by closing at EOM in addition
+				 * to EOF, since there may be unread messages
+				 * remaining in the pipe. However,
+				 *
+				 * ### INTER-MESSAGE PUSHBACK ###
+				 * is also gained, since pipes block at the
+				 * "open" call.
+				 *
+				 * This is an acceptable trade-off because we
+				 * are a stateless reporter of a _most-recent_
+				 * status, not a stateful accumulator.
+				 *
+				 * ### LOSSLESS ALTERNATIVES ###
+				 * - Read each pipe until EOF before reading
+				 *   another.
+				 *   PROBLEM: a fast writer can trap us in the
+				 *   read loop.
+				 *
+				 * - Read each pipe until EOM, but close only
+				 *   at EOF.
+				 *   PROBLEM: a fast writer can fill the pipe
+				 *   faster than we can read it and we end-up
+				 *   displaying stale data.
+				 *
+				 */
+				case END_OF_MESSAGE:
+				case END_OF_FILE:
+				case FAILURE:
+					slot_close(s);
+					s->in_last_read = t;
+					ready--;
+					break;
+				case RETRY:
+					break;
+				default:
+					assert(0);
+				}
+			} else {
+				slot_expire(s, t, cfg->expiry_character, buf);
+			}
+		}
+	} while (ready);
+	assert(ready == 0);
+}
+
+void
+config_log(Config *cfg)
+{
+	khlib_info(
+	    "Config "
+	    "{"
+	    " interval = %f,"
+	    " separator = %s,"
+	    " slot_count = %d,"
+	    " buf_width = %d,"
+	    " slots = ..."
+	    " }\n",
+	    cfg->interval,
+	    cfg->separator,
+	    cfg->slot_count,
+	    cfg->buf_width
 	);
-	fifo_print_all(c->fifos);
+	slots_log(cfg->slots);
+}
+
+void
+config_stretch_for_separators(Config *cfg)
+{
+	int seplen = strlen(cfg->separator);
+	int prefix = 0;
+	int nslots = 0;
+	Slot *s    = cfg->slots;
+
+	while (s) {
+		s->out_pos_lo  += prefix;
+		s->out_pos_hi  += prefix;
+		s->out_pos_cur  = s->out_pos_lo;
+		prefix         += seplen;
+		nslots++;
+		s = s->next;
+	}
+	cfg->buf_width += (seplen * (nslots - 1));
 }
 
 int
-is_pos_num(char *s)
+is_pos_num(char *str)
 {
-	while (*s != '\0')
-		if (!isdigit(*(s++)))
+	while (*str != '\0')
+		if (!isdigit(*(str++)))
 			return 0;
 	return 1;
 }
 
+int
+is_decimal(char *str)
+{
+	char c;
+	int seen = 0;
+
+	while ((c = *(str++)) != '\0')
+		if (!isdigit(c)) {
+			if (c == '.' && !seen++)
+				continue;
+			else
+				return 0;
+		}
+	return 1;
+}
+
 void
 print_usage()
 {
 	assert(argv0);
 	fprintf(
-		stderr,
-		"\n"
-		"Usage: %s [OPTION ...] SPEC [SPEC ...]\n"
-		"\n"
-		"  SPEC       = FILE_PATH DATA_WIDTH DATA_TTL\n"
-		"  FILE_PATH  = string\n"
-		"  DATA_WIDTH = int  (* (positive) number of characters *)\n"
-		"  DATA_TTL   = int  (* (positive) number of seconds *)\n"
-		"  OPTION     = -i INTERVAL\n"
-		"             | -s SEPARATOR\n"
-		"  SEPARATOR  = string\n"
-		"  INTERVAL   = int  (* (positive) number of seconds *)\n"
-		"\n",
-		argv0
+	    stderr,
+	    "\n"
+	    "Usage: %s [OPTION ...] SPEC [SPEC ...]\n"
+	    "\n"
+	    "  SPEC       = FILE_PATH DATA_WIDTH DATA_TTL\n"
+	    "  FILE_PATH  = string\n"
+	    "  DATA_WIDTH = int  (* (positive) number of characters *)\n"
+	    "  DATA_TTL   = float  (* (positive) number of seconds *)\n"
+	    "  OPTION     = -i INTERVAL\n"
+	    "             | -s SEPARATOR\n"
+	    "             | -x (* Output to X root window *)\n"
+	    "             | -l LOG_LEVEL\n"
+	    "             | -e EXPIRY_CHARACTER\n"
+	    "  SEPARATOR  = string\n"
+	    "  INTERVAL   = float  (* (positive) number of seconds *)\n"
+	    "  LOG_LEVEL  = int  (* %d through %d *)\n"
+	    "  EXPIRY_CHARACTER = string  "
+	    "(* Character with which to fill the slot upon expiration. *)\n"
+	    "\n",
+	    argv0,
+	    Nothing,
+	    Debug
 	);
 	fprintf(
-		stderr,
-		"Example: %s -i 1 /dev/shm/khatus/khatus_sensor_x 4 10\n"
-		"\n",
-		argv0
+	    stderr,
+	    "Example: %s -i 1 /dev/shm/khatus/khatus_sensor_x 4 10\n"
+	    "\n",
+	    argv0
 	);
 }
 
-void opts_parse_any(Config *, int, char *[], int);  /* For mutually-recursive calls. */
+/* For mutually-recursive calls. */
+void opts_parse_any(Config *, int, char *[], int);
 
 void
 parse_opts_opt_i(Config *cfg, int argc, char *argv[], int i)
 {
-	if (i < argc) {
-		char *param = argv[i++];
+	char *param;
 
-		if (is_pos_num(param)) {
-			cfg->interval = atoi(param);
-			opts_parse_any(cfg, argc, argv, i);
-		} else {
-			usage("Option -i parameter is invalid: \"%s\"\n", param);
-		}
-	} else {
+	if (i >= argc)
 		usage("Option -i parameter is missing.\n");
-	}
+	param = argv[i++];
+	if (!is_decimal(param))
+		usage("Option -i parameter is invalid: \"%s\"\n", param);
+	cfg->interval = atof(param);
+	opts_parse_any(cfg, argc, argv, i);
 }
 
 void
 parse_opts_opt_s(Config *cfg, int argc, char *argv[], int i)
 {
-	if (i < argc) {
-		cfg->separator = calloc((strlen(argv[i]) + 1), sizeof(char));
-		strcpy(cfg->separator, argv[i]);
-		opts_parse_any(cfg, argc, argv, ++i);
-	} else {
+	if (i >= argc)
 		usage("Option -s parameter is missing.\n");
-	}
+	cfg->separator = calloc((strlen(argv[i]) + 1), sizeof(char));
+	strcpy(cfg->separator, argv[i]);
+	opts_parse_any(cfg, argc, argv, ++i);
+}
+
+void
+parse_opts_opt_l(Config *cfg, int argc, char *argv[], int i)
+{
+	char *param;
+	int log_level;
+
+	if (i >= argc)
+		usage("Option -l parameter is missing.\n");
+	param = argv[i++];
+	if (!is_pos_num(param))
+		usage("Option -l parameter is invalid: \"%s\"\n", param);
+	log_level = atoi(param);
+	if (log_level > Debug)
+		usage(
+		    "Option -l value (%d) exceeds maximum (%d)\n",
+		    log_level,
+		    Debug
+		);
+	_khlib_log_level = log_level;
+	opts_parse_any(cfg, argc, argv, i);
+}
+
+void
+parse_opts_opt_e(Config *cfg, int argc, char *argv[], int i)
+{
+	if (i >= argc)
+		usage("Option -e parameter is missing.\n");
+	cfg->expiry_character = argv[i++][0];
+	opts_parse_any(cfg, argc, argv, i);
 }
 
 void
 parse_opts_opt(Config *cfg, int argc, char *argv[], int i)
 {
 	switch (argv[i][1]) {
-		case 'i': parse_opts_opt_i(cfg, argc, argv, ++i); break;  /* TODO: Generic set_int */
-		case 's': parse_opts_opt_s(cfg, argc, argv, ++i); break;  /* TODO: Generic set_str */
-		case 'x': {
-			cfg->output_to_x_root_window = 1;
-			opts_parse_any(cfg, argc, argv, ++i);
-			break;
-		}
-		default : usage("Option \"%s\" is invalid\n", argv[i]);
+	case 'i':
+		/* TODO: Generic set_int */
+		parse_opts_opt_i(cfg, argc, argv, ++i);
+		break;
+	case 's':
+		/* TODO: Generic set_str */
+		parse_opts_opt_s(cfg, argc, argv, ++i);
+		break;
+	case 'x':
+		cfg->to_x_root = 1;
+		opts_parse_any(cfg, argc, argv, ++i);
+		break;
+	case 'l':
+		/* TODO: Generic set_int */
+		parse_opts_opt_l(cfg, argc, argv, ++i);
+		break;
+	case 'e':
+		/* TODO: Generic set_str */
+		parse_opts_opt_e(cfg, argc, argv, ++i);
+		break;
+	default :
+		usage("Option \"%s\" is invalid\n", argv[i]);
 	}
 }
 
 void
 parse_opts_spec(Config *cfg, int argc, char *argv[], int i)
 {
+	char *n;
+	char *w;
+	char *t;
+	struct timespec in_last_read;
+	Slot *s;
+
 	if ((i + 3) > argc)
-		usage("[spec] Parameter(s) missing for fifo \"%s\".\n", argv[i]);
+		usage(
+		    "[spec] Parameter(s) missing for fifo \"%s\".\n",
+		    argv[i]
+		);
 
-	char *n = argv[i++];
-	char *w = argv[i++];
-	char *t = argv[i++];
+	n = argv[i++];
+	w = argv[i++];
+	t = argv[i++];
 
 	if (!is_pos_num(w))
 		usage("[spec] Invalid width: \"%s\", for fifo \"%s\"\n", w, n);
-	if (!is_pos_num(t))
+	if (!is_decimal(t))
 		usage("[spec] Invalid TTL: \"%s\", for fifo \"%s\"\n", t, n);
-	Fifo *f = calloc(1, sizeof(struct Fifo));
-	if (f) {
-		f->name      = n;
-		f->fd        = -1;
-		f->width     = atoi(w);
-		f->ttl       = atoi(t);
-		f->last_read = 0;
-		f->pos       = cfg->total_width;
-		f->next      = cfg->fifos;
-
-		cfg->fifos        = f;
-		cfg->total_width += f->width;
-		cfg->fifo_count++;
+
+	in_last_read.tv_sec  = 0;
+	in_last_read.tv_nsec = 0;
+	s = calloc(1, sizeof(struct Slot));
+
+	if (s) {
+		s->in_fifo      = n;
+		s->in_fd        = -1;
+		s->out_width    = atoi(w);
+		s->out_ttl      = khlib_timespec_of_float(atof(t));
+		s->in_last_read = in_last_read;
+		s->out_pos_lo   = cfg->buf_width;
+		s->out_pos_cur  = s->out_pos_lo;
+		s->out_pos_hi   = s->out_pos_lo + s->out_width - 1;
+		s->next		= cfg->slots;
+
+		cfg->slots        = s;
+		cfg->buf_width += s->out_width;
+		cfg->slot_count++;
 	} else {
-		fatal("[memory] Allocation failure.");
+		khlib_fatal("[memory] Allocation failure.");
 	}
 	opts_parse_any(cfg, argc, argv, i);
 }
@@ -227,8 +649,11 @@ opts_parse_any(Config *cfg, int argc, char *argv[], int i)
 {
 	if (i < argc) {
 		switch (argv[i][0]) {
-			case '-': parse_opts_opt(cfg, argc, argv, i); break;
-			default : parse_opts_spec(cfg, argc, argv, i);
+		case '-':
+			parse_opts_opt(cfg, argc, argv, i);
+			break;
+		default :
+			parse_opts_spec(cfg, argc, argv, i);
 		}
 	}
 }
@@ -237,188 +662,89 @@ void
 opts_parse(Config *cfg, int argc, char *argv[])
 {
 	opts_parse_any(cfg, argc, argv, 1);
-
-	Fifo *last = cfg->fifos;
-	cfg->fifos = NULL;
-	for (Fifo *f = last; f; ) {
-		Fifo *next = f->next;
-		f->next = cfg->fifos;
-		cfg->fifos = f;
-		f = next;
-	}
-}
-
-void
-read_error(Fifo *f, char *buf)
-{
-	char *b;
-	int i;
-
-	b = buf + f->pos;
-	/* Copy as much of the error message as possible.
-	 * EXCLUDING the reminating \0. */
-	for (i = 0; i < errlen && i < f->width; i++)
-		b[i] = errmsg[i];
-	/* Any remaining slots: */
-	for (; i < f->width; i++)
-		b[i] = '_';
+	cfg->slots = slots_rev(cfg->slots);
+	config_log(cfg);
+	if (cfg->slots == NULL)
+		usage("No slot specs were given!\n");
 }
 
 void
-read_one(Fifo *f, char *buf)
+loop(Config *cfg, char *buf, Display *d)
 {
-	ssize_t current;
-	ssize_t total;
-	char *b;
-	char c;
-
-	current = 0;
-	total = 0;
-	c = '\0';
-	b = buf + f->pos;
-	/* TODO: Could optimize here and only blank-out the remaining slots. */
-	memset(b, ' ', f->width);
-	while ((current = read(f->fd, &c, 1)) && c != '\n' && c != '\0' && total++ < f->width)
-		*b++ = c;
-	if (current == -1) {
-		error("Failed to read: \"%s\". Error: %s\n", f->name, strerror(errno));
-		read_error(f, buf);
+	struct timespec
+		t0,  /* time stamp. before reading slots */
+		t1,  /* time stamp. after  reading slots */
+		ti,  /* time interval desired    (t1 - t0) */
+		td,  /* time interval measured   (t1 - t0) */
+		tc;  /* time interval correction (ti - td) when td < ti */
+
+	ti = khlib_timespec_of_float(cfg->interval);
+	while (running) {
+		clock_gettime(CLOCK_MONOTONIC, &t0); // FIXME: check errors
+		slots_read(cfg, &ti, buf);
+		if (cfg->to_x_root) {
+			if (XStoreName(d, DefaultRootWindow(d), buf) < 0)
+				khlib_fatal("XStoreName failed.\n");
+			XFlush(d);
+		} else {
+			puts(buf);
+			fflush(stdout);
+		}
+		clock_gettime(CLOCK_MONOTONIC, &t1); // FIXME: check errors
+		timespecsub(&t1, &t0, &td);
+		khlib_debug(
+		    "td {tv_sec = %ld, tv_nsec = %ld}\n",
+		    td.tv_sec,
+		    td.tv_nsec
+		);
+		if (timespeccmp(&td, &ti, <)) {
+			/*
+			 * Pushback on data producers by refusing to read the
+			 * pipe more frequently than the interval.
+			 */
+			timespecsub(&ti, &td, &tc);
+			khlib_sleep(&tc);
+		}
 	}
-	/* TODO Record timestamp read */
-	close(f->fd);
-	f->fd = -1;
 }
 
 void
-read_all(Config *cfg, char *buf)
+terminate(int s)
 {
-	fd_set fds;
-	int maxfd = -1;
-	int ready;
-	struct stat st;
-
-	FD_ZERO(&fds);
-	/* TODO: Check TTL */
-	for (Fifo *f = cfg->fifos; f; f = f->next) {
-		/* TODO: Create the FIFO if it doesn't already exist. */
-		if (lstat(f->name, &st) < 0) {
-			error("Cannot stat \"%s\". Error: %s\n", f->name, strerror(errno));
-			read_error(f, buf);
-			continue;
-		}
-		if (!(st.st_mode & S_IFIFO)) {
-			error("\"%s\" is not a FIFO\n", f->name);
-			read_error(f, buf);
-			continue;
-		}
-		debug("opening: %s\n", f->name);
-		if (f->fd < 0)
-			f->fd = open(f->name, O_RDONLY | O_NONBLOCK);
-		if (f->fd == -1) {
-			/* TODO: Consider backing off retries for failed fifos. */
-			error("Failed to open \"%s\"\n", f->name);
-			read_error(f, buf);
-			continue;
-		}
-		if (f->fd > maxfd)
-			maxfd = f->fd;
-		FD_SET(f->fd, &fds);
-	}
-	debug("selecting...\n");
-	ready = select(maxfd + 1, &fds, NULL, NULL, NULL);
-	debug("ready: %d\n", ready);
-	assert(ready != 0);
-	if (ready < 0)
-		fatal("%s", strerror(errno));
-	for (Fifo *f = cfg->fifos; f; f = f->next) {
-		if (FD_ISSET(f->fd, &fds)) {
-			debug("reading: %s\n", f->name);
-			read_one(f, buf);
-		}
-	}
+	khlib_debug("terminating due to signal %d\n", s);
+	running = 0;
 }
 
 int
 main(int argc, char *argv[])
 {
-	int width  = 0;
-	int nfifos = 0;
-	int seplen = 0;
-	int prefix = 0;
-	int errors = 0;
-	char *buf;
-	Config cfg0 = defaults;
-	Config *cfg = &cfg0;
-	Display *display = NULL;
-	struct stat st;
-
 	argv0 = argv[0];
 
-	opts_parse(cfg, argc, argv);
-	debug("argv0 = %s\n", argv0);
-	config_print(cfg);
-	if (cfg->fifos == NULL)
-		usage("No fifo specs were given!\n");
-
-	/* 1st pass to check file existence and type */
-	for (Fifo *f = cfg->fifos; f; f = f->next) {
-		if (lstat(f->name, &st) < 0) {
-			error("Cannot stat \"%s\". Error: %s\n", f->name, strerror(errno));
-			errors++;
-			continue;
-		}
-		if (!(st.st_mode & S_IFIFO)) {
-			error("\"%s\" is not a FIFO\n", f->name);
-			errors++;
-			continue;
-		}
-	}
-	if (errors)
-		fatal("Encountered errors with the given file paths. See log.\n");
-
-	width  = cfg->total_width;
-	seplen = strlen(cfg->separator);
-
-	/* 2nd pass to make space for separators */
-	for (Fifo *f = cfg->fifos; f; f = f->next) {
-		f->pos += prefix;
-		prefix += seplen;
-		nfifos++;
-	}
-	width += (seplen * (nfifos - 1));
-	buf = calloc(1, width + 1);
-	if (buf == NULL)
-		fatal("[memory] Failed to allocate buffer of %d bytes", width);
-	memset(buf, ' ', width);
-	buf[width] = '\0';
-	/* 3rd pass to set the separators */
-	for (Fifo *f = cfg->fifos; f; f = f->next) {
-		if (f->pos) {  /* Skip the first, left-most */
-			/* Copying only seplen ensures we omit the '\0' byte. */
-			strncpy(buf + (f->pos - seplen), cfg->separator, seplen);
-		}
-	}
-
-	if (cfg->output_to_x_root_window && !(display = XOpenDisplay(NULL)))
-		fatal("XOpenDisplay failed with: %p\n", display);
-	/* TODO: nanosleep and nano time diff */
-	/* TODO: Handle signals */
-	for (;;) {
-		/* TODO: Check TTL and maybe blank-out */
-		/* TODO: How to trigger TTL check? On select? Alarm signal? */
-		/* TODO: Set timeout on read_all based on diff of last time of
-		 *       read_all and desired time of next TTL check.
-		 * */
-		read_all(cfg, buf);
-		if (cfg->output_to_x_root_window) {
-			if (XStoreName(display, DefaultRootWindow(display), buf) < 0)
-				fatal("XStoreName failed.\n");
-			XFlush(display);
-		} else {
-			puts(buf);
-			fflush(stdout);
-		}
-	}
-
+	Config cfg = {
+		.interval    = 1.0,
+		.separator   = "|",
+		.expiry_character = '_',
+		.slots       = NULL,
+		.slot_count  = 0,
+		.buf_width   = 0,
+		.to_x_root   = 0,
+	};
+	char *buf;
+	Display *d = NULL;
+	struct sigaction sa;
+
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_handler = terminate;
+	sigaction(SIGTERM, &sa, NULL);
+	sigaction(SIGINT , &sa, NULL);
+
+	opts_parse(&cfg, argc, argv);
+	slots_assert_fifos_exist(cfg.slots);
+	config_stretch_for_separators(&cfg);
+	buf = buf_create(&cfg);
+	if (cfg.to_x_root && !(d = XOpenDisplay(NULL)))
+		khlib_fatal("XOpenDisplay failed with: %p\n", d);
+	loop(&cfg, buf, d);
+	slots_close(cfg.slots);
 	return EXIT_SUCCESS;
 }