Pushback on data producers

[khatus.git] / x5 / khatus.c

diff --git a/x5/khatus.c b/x5/khatus.c
index 6ecb1e7..cc28cba 100644 (file)
--- a/x5/khatus.c
+++ b/x5/khatus.c
@@ -8,10 +8,13 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 #include <unistd.h>
 
 #include <X11/Xlib.h>
 
+#include "bsdtimespec.h"
+
 #define debug(args...) {fprintf(stderr, "[debug] " args);}
 #define info( args...) {fprintf(stderr, "[info] "  args);}
 #define error(args...) {fprintf(stderr, "[error] " args);}
@@ -307,7 +310,6 @@ fifo_read_all(Config *cfg, char *buf)
        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) {
@@ -347,6 +349,29 @@ fifo_read_all(Config *cfg, char *buf)
        }
 }
 
+void
+snooze(struct timespec *t)
+{
+       struct timespec remainder;
+       int result;
+
+       result = nanosleep(t, &remainder);
+
+       if (result < 0) {
+               if (errno == EINTR) {
+                       info(
+                               "nanosleep interrupted. Remainder: "
+                               "{ tv_sec = %ld, tv_nsec = %ld }",
+                               remainder.tv_sec, remainder.tv_nsec);
+                       /* No big deal if we occasionally sleep less,
+                        * so not attempting to correct after an interruption.
+                        */
+               } else {
+                       fatal("nanosleep: %s\n", strerror(errno));
+               }
+       }
+}
+
 int
 main(int argc, char *argv[])
 {
@@ -360,12 +385,23 @@ main(int argc, char *argv[])
        Config *cfg = &cfg0;
        Display *display = 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);
        debug("argv0 = %s\n", argv0);
        config_print(cfg);
+
+       /* TODO: Support interval < 1. i.e. implement timespec_of_float */
+       ti.tv_sec  = cfg->interval;
+       ti.tv_nsec = 0;
+
        if (cfg->fifos == NULL)
                usage("No fifo specs were given!\n");
 
@@ -410,14 +446,15 @@ main(int argc, char *argv[])
 
        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 */
+               clock_gettime(CLOCK_MONOTONIC, &t0); // FIXME: check errors
+               /* TODO: Cache expiration. i.e. use the TTL */
                /* 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.
-                * */
+                */
+               /* TODO: How long to wait on IO? Max TTL? */
                fifo_read_all(cfg, buf);
                if (cfg->output_to_x_root_window) {
                        if (XStoreName(display, DefaultRootWindow(display), buf) < 0)
@@ -427,6 +464,18 @@ main(int argc, char *argv[])
                        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;