top: immunize against window manager flood of SIGWINCH

Whew, it was nip-and-tuck there for awhile but finally
we solved the SIGWINCH overload problem one finds with
most X window managers. Now if a window manager should
try to inundate ol' top with repeated SIGWINCH signals
they won't even be received so can't impact us at all.

And we achieve this miracle having never even issued a
sigprocmask, so all the top code executes with signals
totally unblocked. Intuition suggests it probably rubs
even more salt in the wound, but au contraire mon ami!

The key to our success was simply trading the 'select'
call for its cousin 'pselect'. Not only does that call
provide nanosecond granularity (vs. the former's usec)
but it takes a sigset_t parm which can then atomically
block the troublesome SIGWINCH guy until user input or
optional timeout. Net result? No more signal overload!

Now, if only we could just coax all terminal emulators
into one identical standard buffering scheme plus find
some way to emulate the most recent SIGWINCH, it would
be perfect. We would then obviate the user requirement
of typing yet 1 more key before seeing proper results.

(everything is perfectly justified plus right margins)
(are completely filled, but of course it must be luck)

Reference(s):
http://www.freelists.org/post/procps/unwanted-topinspect-window-enclosure-with-the-terminal-size-change
http://www.freelists.org/post/procps/Sourceforge-project,7

Signed-off-by: Jim Warner <james.warner@comcast.net>

diff --git a/top/top.c b/top/top.c
index 74ac7699565951a2061b0d4c0c12356bc7a242a6..ea3d9e0c410f4dd8974f472621f90174aebf191a 100644 (file)
--- a/top/top.c
+++ b/top/top.c
@@ -20,6 +20,7 @@
 
 #include <sys/ioctl.h>
 #include <sys/resource.h>
+#include <sys/select.h>
 #include <sys/time.h>
 #include <sys/types.h>
 
@@ -70,6 +71,9 @@ static int Ttychanged = 0;
         /* Program name used in error messages and local 'rc' file name */
 static char *Myname;
 
+        /* Our constant sigset, so we need initialize it but once */
+static sigset_t Sigwinch_set;
+
         /* The 'local' config file support */
 static char  Rc_name [OURPATHSZ];
 static RCF_t Rc = DEF_RCFILE;
@@ -164,7 +168,6 @@ static WIN_t *Curwin;
            [ or are used in response to async signals received ! ] */
 static volatile int Frames_resize;     // time to rebuild all column headers
 static          int Frames_libflags;   // PROC_FILLxxx flags
-
 static int          Frame_maxtask;     // last known number of active tasks
                                        // ie. current 'size' of proc table
 static float        Frame_etscale;     // so we can '*' vs. '/' WHEN 'pcpu'
@@ -874,16 +877,16 @@ static void *alloc_r (void *ptr, size_t num) {
          * unsolicited keyboard input that's susceptible to SIGWINCH
          * interrupts (or any other signal).  He also supports timout
          * in the absence of user keystrokes or some signal interrupt. */
-static inline int ioa (struct timeval *tv) {
+static inline int ioa (struct timespec *ts) {
    fd_set fs;
    int rc;
 
    FD_ZERO(&fs);
    FD_SET(STDIN_FILENO, &fs);
 
-   // hold here until we've got keyboard input, a signal interrupt
-   // or (optionally) we timeout with microsecond granularity
-   rc = select(STDIN_FILENO + 1, &fs, NULL, NULL, tv);
+   // hold here until we've got keyboard input, any signal except SIGWINCH
+   // or (optionally) we timeout with nanosecond granularity
+   rc = pselect(STDIN_FILENO + 1, &fs, NULL, NULL, ts, &Sigwinch_set);
 
    if (rc < 0) rc = 0;
    return rc;
@@ -1913,6 +1916,7 @@ signify_that:
       display_fields(i, (p != NULL));
       fflush(stdout);
 
+      if (Frames_resize) goto signify_that;
       key = iokey(0);
       if (key < 1) goto signify_that;
 
@@ -2772,6 +2776,7 @@ signify_that:
          lest repeated <Enter> keys produce immediate re-selection in caller */
       tcflush(STDIN_FILENO, TCIFLUSH);
 
+      if (Frames_resize) goto signify_that;
       key = iokey(0);
       if (key < 1) goto signify_that;
 
@@ -2876,6 +2881,7 @@ signify_that:
          , pid, p->cmd, p->euser, sels));
       INSP_MKSL(0, " ");
 
+      if (Frames_resize) goto signify_that;
       if (key == INT_MAX) key = iokey(0);
       if (key < 1) goto signify_that;
 
@@ -3584,6 +3590,7 @@ signify_that:
       putp(Cap_clr_eos);
       fflush(stdout);
 
+      if (Frames_resize) goto signify_that;
       key = iokey(0);
       if (key < 1) goto signify_that;
 
@@ -3713,7 +3720,9 @@ static void wins_stage_1 (void) {
 
         /*
          * This guy just completes the field group windows after the
-         * rcfiles have been read and command line arguments parsed */
+         * rcfiles have been read and command line arguments parsed.
+         * And since he's the cabose of startup, he'll also tidy up
+         * a few final things... */
 static void wins_stage_2 (void) {
    int i;
 
@@ -3729,6 +3738,10 @@ static void wins_stage_2 (void) {
    }
    // fill in missing Fieldstab members and build each window's columnhdr
    zap_fieldstab();
+
+   // lastly, initialize a signal set used to throttle one troublesome signal
+   sigemptyset(&Sigwinch_set);
+   sigaddset(&Sigwinch_set, SIGWINCH);
 } // end: wins_stage_2
 \f
 /*######  Interactive Input support (do_key helpers)  ####################*/
@@ -3856,6 +3869,7 @@ signify_that:
    putp(Cap_clr_eos);
    fflush(stdout);
 
+   if (Frames_resize) goto signify_that;
    key = iokey(0);
    if (key < 1) goto signify_that;
 
@@ -3871,8 +3885,8 @@ signify_that:
                , Winstk[2].rc.winname, Winstk[3].rc.winname));
             putp(Cap_clr_eos);
             fflush(stdout);
-            key = iokey(0);
-            if (key < 1) adj_geometry();
+            if (Frames_resize || (key = iokey(0)) < 1)
+               adj_geometry();
             else w = win_select(key);
          } while (key != kbd_ENTER && key != kbd_ESC);
          break;
@@ -5067,20 +5081,20 @@ int main (int dont_care_argc, char **argv) {
                                         //                 +-------------+
 
    for (;;) {
-      struct timeval tv;
+      struct timespec ts;
 
       frame_make();
 
       if (0 < Loops) --Loops;
       if (!Loops) bye_bye(NULL);
 
-      tv.tv_sec = Rc.delay_time;
-      tv.tv_usec = (Rc.delay_time - (int)Rc.delay_time) * 1000000;
+      ts.tv_sec = Rc.delay_time;
+      ts.tv_nsec = (Rc.delay_time - (int)Rc.delay_time) * 1000000000;
 
       if (Batch)
-         select(0, NULL, NULL, NULL, &tv);
+         pselect(0, NULL, NULL, NULL, &ts, NULL);
       else {
-         if (ioa(&tv))
+         if (ioa(&ts))
             do_key(iokey(0));
       }
          /* note:  the above ioa() routine exists to consolidate all logic

diff --git a/top/top.h b/top/top.h
index 7151594aae946fbaf92ce3605feaf0b58b7e2d6c..f2dcaf105161366d5a12434bb6a6d33a77f350de 100644 (file)
--- a/top/top.h
+++ b/top/top.h
@@ -630,7 +630,7 @@ typedef struct WIN_t {
 /*------  Low Level Memory/Keyboard/File I/O support  --------------------*/
 //atic void         *alloc_c (size_t num);
 //atic void         *alloc_r (void *ptr, size_t num);
-//atic inline int    ioa (struct timeval *tv);
+//atic inline int    ioa (struct timespec *ts);
 //atic int           ioch (int ech, char *buf, unsigned cnt);
 //atic int           iokey (int init);
 //atic char         *ioline (const char *prompt);