top: lessen overhead when field is not being displayed

This program employs fixed size stacks which currently
total 85 result structures. When a field was not being
shown, those unused result structures were initialized
as 'PIDS_extra' items. As a result, that library would
then reset the results to zero with every interaction.

For any of those result structs holding values created
by top this was appropriate. But for most, it was not.

So this patch will reduce that use of PIDS_extra while
vastly increasing use of the less expensive PIDS_noop.

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

1 files changed, 12 insertions, 9 deletions

diff --git a/src/top/top.c b/src/top/top.c
index abe6e66..757b8d3 100644
--- a/src/top/top.c
+++ b/src/top/top.c
@@ -1993,24 +1993,25 @@ static struct {
    {     7,     -1,  A_right,  PIDS_UTILIZATION_C  },  // real     EU_CUC
    {    10,     -1,  A_right,  PIDS_NS_CGROUP      },  // ul_int   EU_NS7
    {    10,     -1,  A_right,  PIDS_NS_TIME        }   // ul_int   EU_NS8
-#define eu_LAST  EU_NS8
+#define eu_LAST        EU_NS8
 // xtra Fieldstab 'pseudo pflag' entries for the newlib interface . . . . . . .
 #define eu_CMDLINE     eu_LAST +1
 #define eu_TICS_ALL_C  eu_LAST +2
 #define eu_ID_FUID     eu_LAST +3
-#define eu_TREE_HID    eu_LAST +4
-#define eu_TREE_LVL    eu_LAST +5
-#define eu_TREE_ADD    eu_LAST +6
-#define eu_CMDLINE_V   eu_LAST +7
-#define eu_ENVIRON_V   eu_LAST +8
+#define eu_CMDLINE_V   eu_LAST +4
+#define eu_ENVIRON_V   eu_LAST +5
+#define eu_TREE_HID    eu_LAST +6
+#define eu_TREE_LVL    eu_LAST +7
+#define eu_TREE_ADD    eu_LAST +8
+#define eu_RESET       eu_TREE_HID       // demarcation for reset to zero (PIDS_extra)
    , {  -1, -1, -1,  PIDS_CMDLINE     }  // str      ( if Show_CMDLIN, eu_CMDLINE    )
    , {  -1, -1, -1,  PIDS_TICS_ALL_C  }  // ull_int  ( if Show_CTIMES, eu_TICS_ALL_C )
    , {  -1, -1, -1,  PIDS_ID_FUID     }  // u_int    ( if a usrseltyp, eu_ID_FUID    )
+   , {  -1, -1, -1,  PIDS_CMDLINE_V   }  // strv     ( if Ctrlk,       eu_CMDLINE_V  )
+   , {  -1, -1, -1,  PIDS_ENVIRON_V   }  // strv     ( if CtrlN,       eu_ENVIRON_V  )
    , {  -1, -1, -1,  PIDS_extra       }  // s_ch     ( if Show_FOREST, eu_TREE_HID   )
    , {  -1, -1, -1,  PIDS_extra       }  // s_int    ( if Show_FOREST, eu_TREE_LVL   )
    , {  -1, -1, -1,  PIDS_extra       }  // s_int    ( if Show_FOREST, eu_TREE_ADD   )
-   , {  -1, -1, -1,  PIDS_CMDLINE_V   }  // strv     ( if Ctrlk,       eu_CMDLINE_V  )
-   , {  -1, -1, -1,  PIDS_ENVIRON_V   }  // strv     ( if CtrlN,       eu_ENVIRON_V  )
  #undef A_left
  #undef A_right
 };
@@ -2165,7 +2166,9 @@ static void build_headers (void) {
    int i;
 
    // ensure fields not visible incur no significant library costs
-   for (i = 0; i < MAXTBL(Fieldstab); i++)
+   for (i = 0; i < eu_RESET; i++)
+      Pids_itms[i] = PIDS_noop;
+   for ( ; i < MAXTBL(Fieldstab); i++)
       Pids_itms[i] = PIDS_extra;
 
    ckITEM(EU_PID);      // these 2 fields may not display,