Only do an update every 100 commits when drawing the graph.

On a large repository with > 60,000 commits, each call to the Tk
update primitive (which gives Tk a chance to respond to events and
redraw the screen) was taking up to 0.2 seconds.  Because the logic
was to call update after drawing a commit if 0.1 seconds had passed
since the last update call, we were calling it for every commit,
which was slowing us down enormously.  Now we also require that we
have drawn 100 commits since the last update (as well as it being
at least 0.1 seconds since the last update).  Drawing 100 commits
takes around 0.1 - 0.2 seconds (even in this large repo) on my G5.

gitk

@@ -18,7 +18,7 @@ proc gitdir {} {
 
 proc getcommits {rargs} {
     global commits commfd phase canv mainfont env
-    global startmsecs nextupdate
+    global startmsecs nextupdate ncmupdate
     global ctext maincursor textcursor leftover
 
     # check that we can find a .git directory somewhere...
@@ -31,6 +31,7 @@ proc getcommits {rargs} {
     set phase getcommits
     set startmsecs [clock clicks -milliseconds]
     set nextupdate [expr $startmsecs + 100]
+    set ncmupdate 0
     if [catch {
 	set parse_args [concat --default HEAD $rargs]
 	set parsed_args [split [eval exec git-rev-parse $parse_args] "\n"]
@@ -49,7 +50,7 @@ proc getcommits {rargs} {
     }
     set leftover {}
     fconfigure $commfd -blocking 0 -translation lf
-    fileevent $commfd readable "getcommitlines $commfd"
+    fileevent $commfd readable [list getcommitlines $commfd]
     $canv delete all
     $canv create text 3 3 -anchor nw -text "Reading commits..." \
 	-font $mainfont -tags textitems
@@ -61,6 +62,7 @@ proc getcommitlines {commfd}  {
     global commits parents cdate children nchildren
     global commitlisted phase commitinfo nextupdate
     global stopped redisplaying leftover
+    global numcommits ncmupdate
 
     set stuff [read $commfd]
     if {$stuff == {}} {
@@ -108,8 +110,10 @@ to allow selection of commits to be displayed.)}
 	set commitlisted($id) 1
 	parsecommit $id $cmit 1
 	drawcommit $id
-	if {[clock clicks -milliseconds] >= $nextupdate} {
+	if {[clock clicks -milliseconds] >= $nextupdate
+	    && $numcommits >= $ncmupdate + 100} {
 	    doupdate
+	    set ncmupdate $numcommits
 	}
 	while {$redisplaying} {
 	    set redisplaying 0
@@ -119,8 +123,10 @@ to allow selection of commits to be displayed.)}
 		foreach id $commits {
 		    drawcommit $id
 		    if {$stopped} break
-		    if {[clock clicks -milliseconds] >= $nextupdate} {
+		    if {[clock clicks -milliseconds] >= $nextupdate
+			&& $numcommits >= $ncmupdate + 100} {
 			doupdate
+			set ncmupdate $numcommits
 		    }
 		}
 	    }
@@ -134,7 +140,7 @@ proc doupdate {} {
     incr nextupdate 100
     fileevent $commfd readable {}
     update
-    fileevent $commfd readable "getcommitlines $commfd"
+    fileevent $commfd readable [list getcommitlines $commfd]
 }
 
 proc readcommit {id} {
@@ -1090,7 +1096,7 @@ proc decidenext {{noread 0}} {
 
 proc drawcommit {id} {
     global phase todo nchildren datemode nextupdate
-    global startcommits
+    global startcommits numcommits ncmupdate
 
     if {$phase != "incrdraw"} {
 	set phase incrdraw
@@ -1119,8 +1125,10 @@ proc drawcommit {id} {
 	    if {![info exists commitlisted($id)]} {
 		break
 	    }
-	    if {[clock clicks -milliseconds] >= $nextupdate} {
+	    if {[clock clicks -milliseconds] >= $nextupdate
+		&& $numcommits >= $ncmupdate} {
 		doupdate
+		set ncmupdate $numcommits
 		if {$stopped} break
 	    }
 	}
@@ -1158,11 +1166,12 @@ proc settextcursor {c} {
 }
 
 proc drawgraph {} {
-    global nextupdate startmsecs startcommits todo
+    global nextupdate startmsecs startcommits todo ncmupdate
 
     if {$startcommits == {}} return
     set startmsecs [clock clicks -milliseconds]
     set nextupdate [expr $startmsecs + 100]
+    set ncmupdate 0
     initgraph
     set todo [lindex $startcommits 0]
     drawrest 0 1
@@ -1171,7 +1180,7 @@ proc drawgraph {} {
 proc drawrest {level startix} {
     global phase stopped redisplaying selectedline
     global datemode currentparents todo
-    global numcommits
+    global numcommits ncmupdate
     global nextupdate startmsecs startcommits idline
 
     if {$level >= 0} {
@@ -1200,9 +1209,11 @@ proc drawrest {level startix} {
 		if {$level < 0} break
 		drawslants $level
 	    }
-	    if {[clock clicks -milliseconds] >= $nextupdate} {
+	    if {[clock clicks -milliseconds] >= $nextupdate
+	        && $numcommits >= $ncmupdate + 100} {
 		update
 		incr nextupdate 100
+		set ncmupdate $numcommits
 	    }
 	}
     }