X-Git-Url: https://git.xandkar.net/?p=khatus.git;a=blobdiff_plain;f=x5%2Fkhatus.c;h=4dd42da54409bc9d19eb712982c535ec1ac85ccd;hp=6ecb1e7c5ef4c6f9e0b6497fbc206d4220327a25;hb=16e0239d76a7de132b20a564cc2c14ff2358ecf2;hpb=fb8745ba18e5b96680cd612d6a0be78cfcd7eaf3

diff --git a/x5/khatus.c b/x5/khatus.c
index 6ecb1e7..4dd42da 100644
--- a/x5/khatus.c
+++ b/x5/khatus.c
@@ -8,16 +8,20 @@
 #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 "khatus_lib_log.h"
+#include "khatus_lib_time.h"
 
+#define usage(...) { \
+	print_usage(); \
+	fprintf(stderr, "Error:\n    " __VA_ARGS__); \
+	exit(EXIT_FAILURE); \
+}
 #define ERRMSG "ERROR"
 
 static const char errmsg[] = ERRMSG;
@@ -31,50 +35,57 @@ struct Fifo {
 	char   *name;
 	int     fd;
 	int     width;
-	int     last_read;
-	int     ttl;
-	int     pos;  /* Position on the output buffer. */
+	struct timespec last_read;
+	struct timespec ttl;
+	int     pos_init;  /* Initial position on the output buffer. */
+	int     pos_curr;  /* Current position on the output buffer. */
+	int     pos_final; /* Final   position on the output buffer. */
 	Fifo   *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,
+};
+
+enum read_status {
+	END_OF_FILE,
+	END_OF_MESSAGE,
+	RETRY,
+	FAILURE
 };
 
 void
 fifo_print_one(Fifo *f)
 {
-	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
+	info("Fifo "
+	    "{"
+	    " name = %s,"
+	    " fd = %d,"
+	    " width = %d,"
+	    " last_read = {tv_sec = %ld, tv_nsec = %ld}"
+	    " ttl = {tv_sec = %ld, tv_nsec = %ld},"
+	    " pos_init = %d,"
+	    " pos_curr = %d,"
+	    " pos_final = %d,"
+	    " next = %p,"
+	    " }\n",
+	    f->name,
+	    f->fd,
+	    f->width,
+	    f->last_read.tv_sec,
+	    f->last_read.tv_nsec,
+	    f->ttl.tv_sec,
+	    f->ttl.tv_nsec,
+	    f->pos_init,
+	    f->pos_curr,
+	    f->pos_final,
+	    f->next
 	);
 }
 
@@ -87,23 +98,23 @@ fifo_print_all(Fifo *head)
 }
 
 void
-config_print(Config *c)
+config_print(Config *cfg)
 {
-	debug(
-		"Config "
-		"{"
-			" interval = %d,"
-			" separator = %s,"
-			" fifo_count = %d,"
-			" total_width = %d,"
-			" fifos = ..."
-		" }\n",
-		c->interval,
-		c->separator,
-		c->fifo_count,
-		c->total_width
+	info(
+	    "Config "
+	    "{"
+	    " interval = %f,"
+	    " separator = %s,"
+	    " fifo_count = %d,"
+	    " total_width = %d,"
+	    " fifos = ..."
+	    " }\n",
+	    cfg->interval,
+	    cfg->separator,
+	    cfg->fifo_count,
+	    cfg->total_width
 	);
-	fifo_print_all(c->fifos);
+	fifo_print_all(cfg->fifos);
 }
 
 int
@@ -115,83 +126,126 @@ is_pos_num(char *s)
 	return 1;
 }
 
+int
+is_decimal(char *s)
+{
+	char c;
+	int seen = 0;
+
+	while ((c = *(s++)) != '\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"
+	    "  SEPARATOR  = string\n"
+	    "  INTERVAL   = float  (* (positive) number of seconds *)\n"
+	    "  LOG_LEVEL  = int  (* %d through %d *)\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
+		);
+	_khatus_lib_log_level = log_level;
+	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':
-			/* 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->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->output_to_x_root_window = 1;
+		opts_parse_any(cfg, argc, argv, ++i);
+		break;
+	case 'l':
+		/* TODO: Generic set_int */
+		parse_opts_opt_l(cfg, argc, argv, ++i);
+		break;
+	default :
+		usage("Option \"%s\" is invalid\n", argv[i]);
 	}
 }
 
@@ -199,24 +253,33 @@ void
 parse_opts_spec(Config *cfg, int argc, char *argv[], int i)
 {
 	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++];
 
+	struct timespec last_read;
+
 	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);
+	last_read.tv_sec  = 0;
+	last_read.tv_nsec = 0;
 	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->ttl       = timespec_of_float(atof(t));
+		f->last_read = last_read;
+		f->pos_init  = cfg->total_width;
+		f->pos_curr  = f->pos_init;
+		f->pos_final = f->pos_init + f->width - 1;
 		f->next      = cfg->fifos;
 
 		cfg->fifos        = f;
@@ -233,11 +296,11 @@ 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);
 		}
 	}
 }
@@ -257,15 +320,28 @@ opts_parse(Config *cfg, int argc, char *argv[])
 	}
 }
 
+void
+fifo_expire(Fifo *f, struct timespec t, char *buf)
+{
+	struct timespec td;
+
+	timespecsub(&t, &(f->last_read), &td);
+	if (timespeccmp(&td, &(f->ttl), >=)) {
+		/* TODO: Maybe configurable expiry character. */
+		memset(buf + f->pos_init, '_', f->pos_final - f->pos_init);
+		warn("Data source expired: \"%s\"\n", f->name);
+	}
+}
+
 void
 fifo_read_error(Fifo *f, char *buf)
 {
 	char *b;
 	int i;
 
-	b = buf + f->pos;
+	b = buf + f->pos_init;
 	/* Copy as much of the error message as possible.
-	 * EXCLUDING the reminating \0. */
+	 * EXCLUDING the terminating \0. */
 	for (i = 0; i < errlen && i < f->width; i++)
 		b[i] = errmsg[i];
 	/* Any remaining slots: */
@@ -273,45 +349,72 @@ fifo_read_error(Fifo *f, char *buf)
 		b[i] = '_';
 }
 
-void
-fifo_read_one(Fifo *f, char *buf)
+enum read_status
+fifo_read_one(Fifo *f, struct timespec t, char *buf)
 {
-	ssize_t current;
-	ssize_t total;
-	char *b;
-	char c;
+	char c;  /* Character read. */
+	int  r;  /* Remaining unused slots in buffer range. */
 
-	current = 0;
-	total = 0;
-	c = '\0';
-	b = buf + f->pos;
-	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));
-		fifo_read_error(f, buf);
-	} else
-		while (total++ < f->width)
-			*b++ = ' ';
-	/* TODO Record timestamp read */
-	close(f->fd);
-	f->fd = -1;
+	for (;;) {
+		switch (read(f->fd, &c, 1)) {
+		case -1:
+			error("Failed to read: \"%s\". errno: %d, msg: %s\n",
+			    f->name, errno, strerror(errno));
+			switch (errno) {
+			case EINTR:
+			case EAGAIN:
+				return RETRY;
+			default:
+				return FAILURE;
+			}
+		case  0:
+			debug("%s: End of FILE\n", f->name);
+			f->pos_curr = f->pos_init;
+			return END_OF_FILE;
+		case  1:
+			/* TODO: Consider making msg term char a CLI option */
+			if (c == '\n' || c == '\0') {
+				r = f->pos_final - f->pos_curr;
+				if (r > 0)
+					memset(buf + f->pos_curr, ' ', r);
+				f->pos_curr = f->pos_init;
+				f->last_read = t;
+				return END_OF_MESSAGE;
+			} else {
+				if (f->pos_curr <= f->pos_final)
+					buf[f->pos_curr++] = c;
+				/* Drop beyond available range. */
+				/*
+				 * TODO Define max after which we stop reading.
+				 *      To ensure that a rogue large message
+				 *      doesn't trap us here.
+				 */
+			}
+			break;
+		default:
+			assert(0);
+		}
+	}
 }
 
 void
-fifo_read_all(Config *cfg, char *buf)
+fifo_read_all(Config *cfg, struct timespec *ti, char *buf)
 {
 	fd_set fds;
 	int maxfd = -1;
-	int ready;
+	int ready = 0;
 	struct stat st;
+	struct timespec t;
 
 	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));
+			error(
+			    "Cannot stat \"%s\". Error: %s\n",
+			    f->name,
+			    strerror(errno)
+			);
 			fifo_read_error(f, buf);
 			continue;
 		}
@@ -320,59 +423,125 @@ fifo_read_all(Config *cfg, char *buf)
 			fifo_read_error(f, buf);
 			continue;
 		}
-		debug("opening: %s\n", f->name);
-		if (f->fd < 0)
+		if (f->fd < 0) {
+			debug("%s: closed. opening. fd: %d\n", f->name, f->fd);
 			f->fd = open(f->name, O_RDONLY | O_NONBLOCK);
+		} else {
+			debug("%s: already openned. fd: %d\n", f->name, f->fd);
+		}
 		if (f->fd == -1) {
-			/* TODO: Consider backing off retries for failed fifos. */
+			/* TODO Consider backing off retries for failed fifos */
 			error("Failed to open \"%s\"\n", f->name);
 			fifo_read_error(f, buf);
 			continue;
 		}
+		debug("%s: open. fd: %d\n", f->name, f->fd);
 		if (f->fd > maxfd)
 			maxfd = f->fd;
 		FD_SET(f->fd, &fds);
 	}
 	debug("selecting...\n");
-	ready = select(maxfd + 1, &fds, NULL, NULL, NULL);
+	ready = pselect(maxfd + 1, &fds, NULL, NULL, ti, 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);
-			fifo_read_one(f, buf);
+	clock_gettime(CLOCK_MONOTONIC, &t);
+	if (ready == -1) {
+		switch (errno) {
+		case EINTR:
+			error("pselect temp failure: %d, errno: %d, msg: %s\n",
+			    ready, errno, strerror(errno));
+			/* TODO: Reconsider what to do here. */
+			return;
+		default:
+			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 (Fifo *f = cfg->fifos; f; f = f->next) {
+			if (FD_ISSET(f->fd, &fds)) {
+				debug("reading: %s\n", f->name);
+				switch (fifo_read_one(f, t, 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.
+				 */
+				case END_OF_MESSAGE:
+				case END_OF_FILE:
+				case FAILURE:
+					close(f->fd);
+					f->fd = -1;
+					ready--;
+					break;
+				case RETRY:
+					break;
+				default:
+					assert(0);
+				}
+			} else {
+				fifo_expire(f, t, buf);
+			}
+		}
+	} while (ready);
+	assert(ready == 0);
 }
 
 int
 main(int argc, char *argv[])
 {
+	Config cfg = {
+		.interval    = 1.0,
+		.separator   = "|",
+		.fifos       = NULL,
+		.fifo_count  = 0,
+		.total_width = 0,
+		.output_to_x_root_window = 0,
+	};
+
 	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;
+	Display *d = NULL;
 	struct stat st;
+	struct timespec
+		t0,  /* time stamp. before reading fifos */
+		t1,  /* time stamp. after  reading fifos */
+		ti,  /* time interval desired    (t1 - t0) */
+		td,  /* time interval measured   (t1 - t0) */
+		tc;  /* time interval correction (ti - td) when td < ti */
 
 	argv0 = argv[0];
 
-	opts_parse(cfg, argc, argv);
+	opts_parse(&cfg, argc, argv);
 	debug("argv0 = %s\n", argv0);
-	config_print(cfg);
-	if (cfg->fifos == NULL)
+	config_print(&cfg);
+
+	ti = timespec_of_float(cfg.interval);
+
+	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) {
+	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));
+			error(
+			    "Cannot stat \"%s\". Error: %s\n",
+			    f->name,
+			    strerror(errno)
+			);
 			errors++;
 			continue;
 		}
@@ -383,14 +552,16 @@ main(int argc, char *argv[])
 		}
 	}
 	if (errors)
-		fatal("Encountered errors with the given file paths. See log.\n");
+		fatal("Encountered errors with given file paths. See log.\n");
 
-	width  = cfg->total_width;
-	seplen = strlen(cfg->separator);
+	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;
+	for (Fifo *f = cfg.fifos; f; f = f->next) {
+		f->pos_init  += prefix;
+		f->pos_final += prefix;
+		f->pos_curr = f->pos_init;
 		prefix += seplen;
 		nfifos++;
 	}
@@ -401,32 +572,48 @@ main(int argc, char *argv[])
 	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 */
+	for (Fifo *f = cfg.fifos; f; f = f->next) {
+		if (f->pos_init) {  /* Skip the first, left-most */
 			/* Copying only seplen ensures we omit the '\0' byte. */
-			strncpy(buf + (f->pos - seplen), cfg->separator, seplen);
+			strncpy(
+			    buf + (f->pos_init - 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 */
+	if (cfg.output_to_x_root_window && !(d = XOpenDisplay(NULL)))
+		fatal("XOpenDisplay failed with: %p\n", d);
 	/* 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 fifo_read_all based on diff of last time of
-		 *       fifo_read_all and desired time of next TTL check.
-		 * */
-		fifo_read_all(cfg, buf);
-		if (cfg->output_to_x_root_window) {
-			if (XStoreName(display, DefaultRootWindow(display), buf) < 0)
+		clock_gettime(CLOCK_MONOTONIC, &t0); // FIXME: check errors
+		fifo_read_all(&cfg, &ti, buf);
+		if (cfg.output_to_x_root_window) {
+			if (XStoreName(d, DefaultRootWindow(d), buf) < 0)
 				fatal("XStoreName failed.\n");
-			XFlush(display);
+			XFlush(d);
 		} else {
 			puts(buf);
 			fflush(stdout);
 		}
+		clock_gettime(CLOCK_MONOTONIC, &t1); // FIXME: check errors
+		timespecsub(&t1, &t0, &td);
+		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);
+			debug("snooze YES\n");
+			snooze(&tc);
+		} else {
+			debug("snooze NO\n");
+		}
 	}
 
 	return EXIT_SUCCESS;