diff mbox series

[v5,2/3] git-gui: update status bar to track operations

Message ID aa05a78d285dd9c5f4897b03467f1d43d7a5ad83.1574627876.git.gitgitgadget@gmail.com (mailing list archive)
State New, archived
Headers show
Series git-gui: revert untracked files by deleting them | expand

Commit Message

John Passaro via GitGitGadget Nov. 24, 2019, 8:37 p.m. UTC
From: Jonathan Gilbert <JonathanG@iQmetrix.com>

Update the status bar to track updates as individual "operations" that
can overlap. Update all call sites to interact with the new status bar
mechanism. Update initialization to explicitly clear status text,
since otherwise it may persist across future operations.

Signed-off-by: Jonathan Gilbert <JonathanG@iQmetrix.com>
---
 git-gui.sh          |   7 +-
 lib/blame.tcl       |  22 +++--
 lib/checkout_op.tcl |  15 +--
 lib/index.tcl       |  31 +++---
 lib/merge.tcl       |  14 ++-
 lib/status_bar.tcl  | 228 +++++++++++++++++++++++++++++++++++++++-----
 6 files changed, 260 insertions(+), 57 deletions(-)

Comments

Pratyush Yadav Nov. 27, 2019, 9:55 p.m. UTC | #1
Hi Jonathan,

Thanks for the re-roll.

On 24/11/19 08:37PM, Jonathan Gilbert via GitGitGadget wrote:
> From: Jonathan Gilbert <JonathanG@iQmetrix.com>
> 
> Update the status bar to track updates as individual "operations" that
> can overlap. Update all call sites to interact with the new status bar
> mechanism. Update initialization to explicitly clear status text,
> since otherwise it may persist across future operations.
> 
> Signed-off-by: Jonathan Gilbert <JonathanG@iQmetrix.com>
> ---
>  git-gui.sh          |   7 +-
>  lib/blame.tcl       |  22 +++--
>  lib/checkout_op.tcl |  15 +--
>  lib/index.tcl       |  31 +++---
>  lib/merge.tcl       |  14 ++-
>  lib/status_bar.tcl  | 228 +++++++++++++++++++++++++++++++++++++++-----
>  6 files changed, 260 insertions(+), 57 deletions(-)
> 
> diff --git a/git-gui.sh b/git-gui.sh
> index 0d21f5688b..db02e399e7 100755
> --- a/git-gui.sh
> +++ b/git-gui.sh
> @@ -1797,10 +1797,10 @@ proc ui_status {msg} {
>  	}
>  }
>  
> -proc ui_ready {{test {}}} {
> +proc ui_ready {} {

This is not quite correct. There is one user of 'ui_ready' that uses 
'test'. It is in git-gui.sh:2211. It is used when starting gitk. This 
change breaks that call. 10 seconds after opening gitk via the 
"Visualise master's history" option, I get the following error:

  wrong # args: should be "ui_ready"
      while executing
  "ui_ready $starting_gitk_msg"
      ("after" script)
 
The code that calls it (git-gui.sh:2211) looks like:

  ui_status $::starting_gitk_msg
  after 10000 {
  	ui_ready $starting_gitk_msg
  }

I am not quite sure why this is done though. It was introduced in 
e210e67 (git-gui: Corrected keyboard bindings on Windows, improved state 
management., 2006-11-06) [0], but the commit message doesn't really 
explain why (probably because it is a small part of a larger change, 
though it doesn't really fit in with the topic of the change). I can't 
find a mailing list thread about the commit so I don't think we'll ever 
know for sure.

From looking at it, my guess is that it was added because gitk took a 
long time to start up (maybe it still does, but for me its almost 
instant). And so, this message was shown for 10 seconds, and then 
cleared because by then it probably would have started. But to avoid 
over-writing some other message, 'test' was used to make sure only the 
message intended to be cleared is cleared.

I'm not sure if this heuristic/hack is really needed, and that we need 
to keep the "Starting gitk..." message around for 10 seconds. The way I 
see it, it doesn't add too much value unless gitk takes a long time to 
start up on other platforms or repos. In that case an indication of 
"we're working on starting gitk" would be nice. Otherwise, I don't mind 
seeing this go. And even then, I think it is gitk's responsibility to 
give some sort of indication to the user that it is booting up, and not 
ours.

So, I vote for just getting rid of this hack.

>  	global main_status
>  	if {[info exists main_status]} {
> -		$main_status show [mc "Ready."] $test
> +		$main_status show [mc "Ready."]
>  	}
>  }
>  
> @@ -4159,6 +4159,9 @@ if {$picked && [is_config_true gui.autoexplore]} {
>  	do_explore
>  }
>  
> +# Clear "Initializing..." status
> +after 500 {$main_status show ""}
> +
>  # Local variables:
>  # mode: tcl
>  # indent-tabs-mode: t
> diff --git a/lib/blame.tcl b/lib/blame.tcl
> index a1aeb8b96e..888f98bab2 100644
> --- a/lib/blame.tcl
> +++ b/lib/blame.tcl
> @@ -24,6 +24,7 @@ field w_cviewer  ; # pane showing commit message
>  field finder     ; # find mini-dialog frame
>  field gotoline   ; # line goto mini-dialog frame
>  field status     ; # status mega-widget instance
> +field status_operation ; # status operation

Nitpick: The comment doesn't give any information the field name doesn't 
already give. Either remove it or replace it with something more 
descriptive.

>  field old_height ; # last known height of $w.file_pane
>  
>  
> @@ -274,6 +275,7 @@ constructor new {i_commit i_path i_jump} {
>  	pack $w_cviewer -expand 1 -fill both
>  
>  	set status [::status_bar::new $w.status]
> +	set status_operation {}
>  
>  	menu $w.ctxm -tearoff 0
>  	$w.ctxm add command \
> @@ -602,16 +604,21 @@ method _exec_blame {cur_w cur_d options cur_s} {
>  	} else {
>  		lappend options $commit
>  	}
> +
> +	# We may recurse in from another call to _exec_blame and already have
> +	# a status operation.

Thanks for being thorough enough to spot this :)

> +	if {$status_operation == {}} {
> +		set status_operation [$status start \
> +			$cur_s \
> +			[mc "lines annotated"]]

The call to this method from '_read_blame' specifies a different $cur_s. 
So shouldn't we be destroying $status_operation (after stopping it), and 
creating a new one?

> +	}
> +
>  	lappend options -- $path
>  	set fd [eval git_read --nice blame $options]
>  	fconfigure $fd -blocking 0 -translation lf -encoding utf-8
>  	fileevent $fd readable [cb _read_blame $fd $cur_w $cur_d]
>  	set current_fd $fd
>  	set blame_lines 0
> -
> -	$status start \
> -		$cur_s \
> -		[mc "lines annotated"]
>  }
>  
>  method _read_blame {fd cur_w cur_d} {

You did not update 'lib/choose_repository.tcl'. It still uses the old 
version of the status bar. Other than that, the rest of the patch looks 
good. Thanks.

[0]:
  Curiously, if I do 'git log -L 2208,+5:git-gui.sh' to find the origins 
  of the line, it leads me to the commit 25476c6. And looking at the 
  commit, it does indeed appear to be the origin of the line since the 
  line is in the post-image, and not the pre-image. But I accidentally 
  noticed the line in a parent of that commit. Looking further, it turns 
  out the line originated in e210e67. Probably a bug in some really old 
  versions of git. Interesting nonetheless.
Jonathan Gilbert Nov. 28, 2019, 7:34 a.m. UTC | #2
On Wed, Nov 27, 2019 at 3:59 PM Pratyush Yadav me-at-yadavpratyush.com
|GitHub Public/Example Allow| <172q77k4bxwj0zt@sneakemail.com> wrote:
> On 24/11/19 08:37PM, Jonathan Gilbert via GitGitGadget wrote:
> > -proc ui_ready {{test {}}} {
> > +proc ui_ready {} {
>
> This is not quite correct. There is one user of 'ui_ready' that uses
> 'test'. It is in git-gui.sh:2211. It is used when starting gitk. This
> change breaks that call. 10 seconds after opening gitk via the
> "Visualise master's history" option, I get the following error:
>
>   wrong # args: should be "ui_ready"
>       while executing
>   "ui_ready $starting_gitk_msg"
>       ("after" script)
[..]
> I'm not sure if this heuristic/hack is really needed, and that we need
> to keep the "Starting gitk..." message around for 10 seconds.
[..]
> So, I vote for just getting rid of this hack.

Oh geeze, I can't believe I missed this. This looks like it ought to
be relatively straightforward to port to the new operations, though,
which is a more isolated approach (keeping this change's fingers where
they belong), and then the operation provides segregation that means
it can just be ended after X seconds without caring what anything else
might be doing with the status bar. We can independently figure out if
we want to restructure that part. Given that computers are faster now
and that the status bar could end up doing something else in the
meantime (well let's be realistic, probably not, but who knows :-) ),
I'd vote for reducing the time the message is shown from 10 seconds
to, I dunno, 3 or 4 seconds.

One other thing I note is that both `do_gitk` and `do_git_gui` use
`$starting_gitk_msg`, which means that when `do_git_gui` is invoked to
launch a Git Gui child process for a submodule, it will be setting the
status bar text to say that it is launching Gitk.

Speaking of things that are out of scope for this PR, I did notice
this in the code:

> # -- Always start git gui through whatever we were loaded with.  This
> #    lets us bypass using shell process on Windows systems.
> #
> set exe [list [_which git]]

As far as I can tell, there's virtually no connection between the
comment and what the code is actually doing. I haven't yet figured out
what exactly it is or where it comes from, but on my Windows systems,
`git-gui` is actually an EXE file `git-gui.exe`, and I _think_ what it
is doing is running `wish.exe`, which I'm guessing has something to do
with hosting a Tcl interpreter with Win32 support for Tk GUI.

I'm not sure whether the code is doing the right thing here or not,
but I'm pretty sure what it's _not_ doing is figuring out how the
current `git-gui` process was started/is being hosted. :-P

> >  field finder     ; # find mini-dialog frame
> >  field gotoline   ; # line goto mini-dialog frame
> >  field status     ; # status mega-widget instance
> > +field status_operation ; # status operation
>
> Nitpick: The comment doesn't give any information the field name doesn't
> already give. Either remove it or replace it with something more
> descriptive.

Hmm, okay. I didn't want something that felt wildly imbalanced with
respect to the other lines, but you're right that this particular line
is literally just repeating the variable name. :-P

> > +     if {$status_operation == {}} {
> > +             set status_operation [$status start \
> > +                     $cur_s \
> > +                     [mc "lines annotated"]]
>
> The call to this method from '_read_blame' specifies a different $cur_s.
> So shouldn't we be destroying $status_operation (after stopping it), and
> creating a new one?

We can change the text by calling `$status_operation show`.

> >  method _read_blame {fd cur_w cur_d} {
>
> You did not update 'lib/choose_repository.tcl'. It still uses the old
> version of the status bar. Other than that, the rest of the patch looks
> good. Thanks.

Ugh, I can't believe I overlooked this. I was aware of the file using
the status bar, because it's the one place that uses the `two_line`
constructor, but then I forgot to actually make it create and use the
(single concurrent) operation that a `two_line`-er is allowed.

The code in there seems to overload the purpose of the `o_cons`
variable, so that sometimes it is pointing at a status bar and
sometimes it is pointing at whatever `console::embed` returns. I will
change this.

This code also depends heavily on `update` to keep the UI active,
which as I understand it is problematic because it could potentially
result in re-entrance since the user can interact with the UI in the
middle of the operation. I will not make any attempt to change this,
though. :-)

> [0]:
>   Curiously, if I do 'git log -L 2208,+5:git-gui.sh' to find the origins
>   of the line, it leads me to the commit 25476c6. And looking at the
>   commit, it does indeed appear to be the origin of the line since the
>   line is in the post-image, and not the pre-image. But I accidentally
>   noticed the line in a parent of that commit. Looking further, it turns
>   out the line originated in e210e67. Probably a bug in some really old
>   versions of git. Interesting nonetheless.

In e210e67, I see this:

set starting_gitk_msg {Please wait... Starting gitk...}
proc do_gitk {} {
        global tcl_platform ui_status_value starting_gitk_msg

        set ui_status_value $starting_gitk_msg
        after 5000 {
                if {$ui_status_value == $starting_gitk_msg} {
                        set ui_status_value {Ready.}
                }
        }
        ...

In 043f7011, all string comparisons were changed from ==/!= to eq/ne.
The commit message explains that when you use == and !=, Tcl will
attempt to convert either side to numeric if one of the two sides
looks like a numeric. Guess I should review my commit for this error
:-P

-                if {$ui_status_value == $starting_gitk_msg} {
+                if {$ui_status_value eq $starting_gitk_msg} {

In 699d5601 "Refactor our ui_status_value update technique", this became:

set starting_gitk_msg [mc "Starting gitk... please wait..."]
...
        global ... starting_gitk_msg
...
        ui_status $starting_gitk_msg
        after 10000 {
                ui_ready $starting_gitk_msg
        }

Finally it became this in 02efd48f, apparently an unrelated
refactoring removed the global variable declaration:

set starting_gitk_msg [mc "Starting gitk... please wait..."]
...
        ui_status $::starting_gitk_msg
        after 10000 {
                ui_ready $starting_gitk_msg
        }

I gathered this information using Git Gui's blame function, which I
guess is a good demonstration that my latest blame.tcl revision
corrects the problems in the earlier submission :-D

Next revision coming soon.

Jonathan Gilbert
diff mbox series

Patch

diff --git a/git-gui.sh b/git-gui.sh
index 0d21f5688b..db02e399e7 100755
--- a/git-gui.sh
+++ b/git-gui.sh
@@ -1797,10 +1797,10 @@  proc ui_status {msg} {
 	}
 }
 
-proc ui_ready {{test {}}} {
+proc ui_ready {} {
 	global main_status
 	if {[info exists main_status]} {
-		$main_status show [mc "Ready."] $test
+		$main_status show [mc "Ready."]
 	}
 }
 
@@ -4159,6 +4159,9 @@  if {$picked && [is_config_true gui.autoexplore]} {
 	do_explore
 }
 
+# Clear "Initializing..." status
+after 500 {$main_status show ""}
+
 # Local variables:
 # mode: tcl
 # indent-tabs-mode: t
diff --git a/lib/blame.tcl b/lib/blame.tcl
index a1aeb8b96e..888f98bab2 100644
--- a/lib/blame.tcl
+++ b/lib/blame.tcl
@@ -24,6 +24,7 @@  field w_cviewer  ; # pane showing commit message
 field finder     ; # find mini-dialog frame
 field gotoline   ; # line goto mini-dialog frame
 field status     ; # status mega-widget instance
+field status_operation ; # status operation
 field old_height ; # last known height of $w.file_pane
 
 
@@ -274,6 +275,7 @@  constructor new {i_commit i_path i_jump} {
 	pack $w_cviewer -expand 1 -fill both
 
 	set status [::status_bar::new $w.status]
+	set status_operation {}
 
 	menu $w.ctxm -tearoff 0
 	$w.ctxm add command \
@@ -602,16 +604,21 @@  method _exec_blame {cur_w cur_d options cur_s} {
 	} else {
 		lappend options $commit
 	}
+
+	# We may recurse in from another call to _exec_blame and already have
+	# a status operation.
+	if {$status_operation == {}} {
+		set status_operation [$status start \
+			$cur_s \
+			[mc "lines annotated"]]
+	}
+
 	lappend options -- $path
 	set fd [eval git_read --nice blame $options]
 	fconfigure $fd -blocking 0 -translation lf -encoding utf-8
 	fileevent $fd readable [cb _read_blame $fd $cur_w $cur_d]
 	set current_fd $fd
 	set blame_lines 0
-
-	$status start \
-		$cur_s \
-		[mc "lines annotated"]
 }
 
 method _read_blame {fd cur_w cur_d} {
@@ -806,10 +813,11 @@  method _read_blame {fd cur_w cur_d} {
 				[mc "Loading original location annotations..."]
 		} else {
 			set current_fd {}
-			$status stop [mc "Annotation complete."]
+			$status_operation stop [mc "Annotation complete."]
+			set status_operation {}
 		}
 	} else {
-		$status update $blame_lines $total_lines
+		$status_operation update $blame_lines $total_lines
 	}
 } ifdeleted { catch {close $fd} }
 
@@ -1124,7 +1132,7 @@  method _blameparent {} {
 			set diffcmd [list diff-tree --unified=0 $cparent $cmit -- $new_path]
 		}
 		if {[catch {set fd [eval git_read $diffcmd]} err]} {
-			$status stop [mc "Unable to display parent"]
+			$status_operation stop [mc "Unable to display parent"]
 			error_popup [strcat [mc "Error loading diff:"] "\n\n$err"]
 			return
 		}
diff --git a/lib/checkout_op.tcl b/lib/checkout_op.tcl
index a5228297db..21ea768d80 100644
--- a/lib/checkout_op.tcl
+++ b/lib/checkout_op.tcl
@@ -341,9 +341,9 @@  method _readtree {} {
 	global HEAD
 
 	set readtree_d {}
-	$::main_status start \
+	set status_bar_operation [$::main_status start \
 		[mc "Updating working directory to '%s'..." [_name $this]] \
-		[mc "files checked out"]
+		[mc "files checked out"]]
 
 	set fd [git_read --stderr read-tree \
 		-m \
@@ -354,26 +354,27 @@  method _readtree {} {
 		$new_hash \
 		]
 	fconfigure $fd -blocking 0 -translation binary
-	fileevent $fd readable [cb _readtree_wait $fd]
+	fileevent $fd readable [cb _readtree_wait $fd $status_bar_operation]
 }
 
-method _readtree_wait {fd} {
+method _readtree_wait {fd status_bar_operation} {
 	global current_branch
 
 	set buf [read $fd]
-	$::main_status update_meter $buf
+	$status_bar_operation update_meter $buf
 	append readtree_d $buf
 
 	fconfigure $fd -blocking 1
 	if {![eof $fd]} {
 		fconfigure $fd -blocking 0
+		$status_bar_operation stop
 		return
 	}
 
 	if {[catch {close $fd}]} {
 		set err $readtree_d
 		regsub {^fatal: } $err {} err
-		$::main_status stop [mc "Aborted checkout of '%s' (file level merging is required)." [_name $this]]
+		$status_bar_operation stop [mc "Aborted checkout of '%s' (file level merging is required)." [_name $this]]
 		warn_popup [strcat [mc "File level merge required."] "
 
 $err
@@ -384,7 +385,7 @@  $err
 		return
 	}
 
-	$::main_status stop
+	$status_bar_operation stop
 	_after_readtree $this
 }
 
diff --git a/lib/index.tcl b/lib/index.tcl
index 28d4d2a54e..62f4773ef4 100644
--- a/lib/index.tcl
+++ b/lib/index.tcl
@@ -45,13 +45,13 @@  proc _close_updateindex {fd after} {
 		wm deiconify $w
 		tkwait window $w
 
-		$::main_status stop
+		$::main_status stop_all
 		unlock_index
 		rescan $after 0
 		return
 	}
 
-	$::main_status stop
+	$::main_status stop_all
 	unlock_index
 	uplevel #0 $after
 }
@@ -67,7 +67,7 @@  proc update_indexinfo {msg path_list after} {
 	set batch [expr {int($total_cnt * .01) + 1}]
 	if {$batch > 25} {set batch 25}
 
-	$::main_status start $msg [mc "files"]
+	set status_bar_operation [$::main_status start $msg [mc "files"]]
 	set fd [git_write update-index -z --index-info]
 	fconfigure $fd \
 		-blocking 0 \
@@ -81,15 +81,18 @@  proc update_indexinfo {msg path_list after} {
 		$path_list \
 		$total_cnt \
 		$batch \
+		$status_bar_operation \
 		$after \
 		]
 }
 
-proc write_update_indexinfo {fd path_list total_cnt batch after} {
+proc write_update_indexinfo {fd path_list total_cnt batch status_bar_operation \
+	after} {
 	global update_index_cp
 	global file_states current_diff_path
 
 	if {$update_index_cp >= $total_cnt} {
+		$status_bar_operation stop
 		_close_updateindex $fd $after
 		return
 	}
@@ -119,7 +122,7 @@  proc write_update_indexinfo {fd path_list total_cnt batch after} {
 		display_file $path $new
 	}
 
-	$::main_status update $update_index_cp $total_cnt
+	$status_bar_operation update $update_index_cp $total_cnt
 }
 
 proc update_index {msg path_list after} {
@@ -133,7 +136,7 @@  proc update_index {msg path_list after} {
 	set batch [expr {int($total_cnt * .01) + 1}]
 	if {$batch > 25} {set batch 25}
 
-	$::main_status start $msg [mc "files"]
+	set status_bar_operation [$::main_status start $msg [mc "files"]]
 	set fd [git_write update-index --add --remove -z --stdin]
 	fconfigure $fd \
 		-blocking 0 \
@@ -147,15 +150,18 @@  proc update_index {msg path_list after} {
 		$path_list \
 		$total_cnt \
 		$batch \
+		$status_bar_operation \
 		$after \
 		]
 }
 
-proc write_update_index {fd path_list total_cnt batch after} {
+proc write_update_index {fd path_list total_cnt batch status_bar_operation \
+	after} {
 	global update_index_cp
 	global file_states current_diff_path
 
 	if {$update_index_cp >= $total_cnt} {
+		$status_bar_operation stop
 		_close_updateindex $fd $after
 		return
 	}
@@ -190,7 +196,7 @@  proc write_update_index {fd path_list total_cnt batch after} {
 		display_file $path $new
 	}
 
-	$::main_status update $update_index_cp $total_cnt
+	$status_bar_operation update $update_index_cp $total_cnt
 }
 
 proc checkout_index {msg path_list after} {
@@ -204,7 +210,7 @@  proc checkout_index {msg path_list after} {
 	set batch [expr {int($total_cnt * .01) + 1}]
 	if {$batch > 25} {set batch 25}
 
-	$::main_status start $msg [mc "files"]
+	set status_bar_operation [$::main_status start $msg [mc "files"]]
 	set fd [git_write checkout-index \
 		--index \
 		--quiet \
@@ -224,15 +230,18 @@  proc checkout_index {msg path_list after} {
 		$path_list \
 		$total_cnt \
 		$batch \
+		$status_bar_operation \
 		$after \
 		]
 }
 
-proc write_checkout_index {fd path_list total_cnt batch after} {
+proc write_checkout_index {fd path_list total_cnt batch status_bar_operation \
+	after} {
 	global update_index_cp
 	global file_states current_diff_path
 
 	if {$update_index_cp >= $total_cnt} {
+		$status_bar_operation stop
 		_close_updateindex $fd $after
 		return
 	}
@@ -253,7 +262,7 @@  proc write_checkout_index {fd path_list total_cnt batch after} {
 		}
 	}
 
-	$::main_status update $update_index_cp $total_cnt
+	$status_bar_operation update $update_index_cp $total_cnt
 }
 
 proc unstage_helper {txt paths} {
diff --git a/lib/merge.tcl b/lib/merge.tcl
index 9f253db5b3..8df8ffae55 100644
--- a/lib/merge.tcl
+++ b/lib/merge.tcl
@@ -241,23 +241,27 @@  Continue with resetting the current changes?"]
 	if {[ask_popup $op_question] eq {yes}} {
 		set fd [git_read --stderr read-tree --reset -u -v HEAD]
 		fconfigure $fd -blocking 0 -translation binary
-		fileevent $fd readable [namespace code [list _reset_wait $fd]]
-		$::main_status start [mc "Aborting"] [mc "files reset"]
+		set status_bar_operation [$::main_status \
+			start \
+			[mc "Aborting"] \
+			[mc "files reset"]
+		fileevent $fd readable [namespace code [list \
+			_reset_wait $fd $status_bar_operation]]
 	} else {
 		unlock_index
 	}
 }
 
-proc _reset_wait {fd} {
+proc _reset_wait {fd status_bar_operation} {
 	global ui_comm
 
-	$::main_status update_meter [read $fd]
+	$status_bar_operation update_meter [read $fd]
 
 	fconfigure $fd -blocking 1
 	if {[eof $fd]} {
 		set fail [catch {close $fd} err]
-		$::main_status stop
 		unlock_index
+		$status_bar_operation stop
 
 		$ui_comm delete 0.0 end
 		$ui_comm edit modified false
diff --git a/lib/status_bar.tcl b/lib/status_bar.tcl
index 02111a1742..c4bff98856 100644
--- a/lib/status_bar.tcl
+++ b/lib/status_bar.tcl
@@ -1,16 +1,42 @@ 
 # git-gui status bar mega-widget
 # Copyright (C) 2007 Shawn Pearce
 
+# The status_bar class manages the entire status bar. It is possible for
+# multiple overlapping asynchronous operations to want to display status
+# simultaneously. Each one receives a status_bar_operation when it calls the
+# start method, and the status bar combines all active operations into the
+# line of text it displays. Most of the time, there will be at most one
+# ongoing operation.
+#
+# Note that the entire status bar can be either in single-line or two-line
+# mode, depending on the constructor. Multiple active operations are only
+# supported for single-line status bars.
+
 class status_bar {
 
+field allow_multiple ; # configured at construction
+
 field w         ; # our own window path
 field w_l       ; # text widget we draw messages into
 field w_c       ; # canvas we draw a progress bar into
 field c_pack    ; # script to pack the canvas with
-field status  {}; # single line of text we show
-field prefix  {}; # text we format into status
-field units   {}; # unit of progress
-field meter   {}; # current core git progress meter (if active)
+
+field baseline_text   ; # text to show if there are no operations
+field status_bar_text ; # combined text for all operations
+
+field operations ; # list of current ongoing operations
+
+# The status bar can display a progress bar, updated when consumers call the
+# update method on their status_bar_operation. When there are multiple
+# operations, the status bar shows the combined status of all operations.
+#
+# When an overlapping operation completes, the progress bar is going to
+# abruptly have one fewer operation in the calculation, causing a discontinuity.
+# Therefore, whenever an operation completes, if it is not the last operation,
+# this counter is increased, and the progress bar is calculated as though there
+# were still another operation at 100%. When the last operation completes, this
+# is reset to 0.
+field completed_operation_count
 
 constructor new {path} {
 	global use_ttk NS
@@ -18,12 +44,19 @@  constructor new {path} {
 	set w_l $w.l
 	set w_c $w.c
 
+	# Standard single-line status bar: Permit overlapping operations
+	set allow_multiple 1
+
+	set baseline_text ""
+	set operations [list]
+	set completed_operation_count 0
+
 	${NS}::frame $w
 	if {!$use_ttk} {
 		$w configure -borderwidth 1 -relief sunken
 	}
 	${NS}::label $w_l \
-		-textvariable @status \
+		-textvariable @status_bar_text \
 		-anchor w \
 		-justify left
 	pack $w_l -side left
@@ -44,9 +77,15 @@  constructor two_line {path} {
 	set w_l $w.l
 	set w_c $w.c
 
+	# Two-line status bar: Only one ongoing operation permitted.
+	set allow_multiple 0
+
+	set baseline_text ""
+	set operations [list]
+
 	${NS}::frame $w
 	${NS}::label $w_l \
-		-textvariable @status \
+		-textvariable @status_bar_text \
 		-anchor w \
 		-justify left
 	pack $w_l -anchor w -fill x
@@ -56,7 +95,7 @@  constructor two_line {path} {
 	return $this
 }
 
-method start {msg uds} {
+method ensure_canvas {} {
 	if {[winfo exists $w_c]} {
 		$w_c coords bar 0 0 0 20
 	} else {
@@ -68,31 +107,170 @@  method start {msg uds} {
 		$w_c create rectangle 0 0 0 20 -tags bar -fill navy
 		eval $c_pack
 	}
+}
+
+method show {msg} {
+	$this ensure_canvas
+	set baseline_text $msg
+	$this refresh
+}
+
+method start {msg uds} {
+	set baseline_text ""
+
+	if {!$allow_multiple && [llength $operations]} {
+		return [lindex $operations 0]
+	}
+
+	$this ensure_canvas
+
+	set operation [status_bar_operation::new $this $msg $uds]
+
+	lappend operations $operation
+
+	$this refresh
+
+	return $operation
+}
+
+method refresh {} {
+	set new_text ""
+
+	set total [expr $completed_operation_count * 100]
+	set have $total
+
+	foreach operation $operations {
+		if {$new_text != ""} {
+			append new_text " / "
+		}
+
+		append new_text [$operation get_status]
+
+		set total [expr $total + 100]
+		set have [expr $have + [$operation get_progress]]
+	}
+
+	if {$new_text == ""} {
+		set new_text $baseline_text
+	}
+
+	set status_bar_text $new_text
+
+	if {[winfo exists $w_c]} {
+		set pixel_width 0
+		if {$have > 0} {
+			set pixel_width [expr {[winfo width $w_c] * $have / $total}]
+		}
+
+		$w_c coords bar 0 0 $pixel_width 20
+	}
+}
+
+method stop {operation stop_msg} {
+	set idx [lsearch $operations $operation]
+
+	if {$idx >= 0} {
+		set operations [lreplace $operations $idx $idx]
+		set completed_operation_count [expr \
+			$completed_operation_count + 1]
+
+		if {[llength $operations] == 0} {
+			set completed_operation_count 0
+
+			destroy $w_c
+			if {$stop_msg ne {}} {
+				set baseline_text $stop_msg
+			}
+		}
+
+		$this refresh
+	}
+}
+
+method stop_all {{stop_msg {}}} {
+	# This makes the operation's call to stop a no-op.
+	set operations_copy $operations
+	set operations [list]
+
+	foreach operation $operations_copy {
+		$operation stop
+	}
+
+	if {$stop_msg ne {}} {
+		set baseline_text $stop_msg
+	}
+
+	$this refresh
+}
+
+method _delete {current} {
+	if {$current eq $w} {
+		delete_this
+	}
+}
+
+}
+
+# The status_bar_operation class tracks a single consumer's ongoing status bar
+# activity, with the context that there are a few situations where multiple
+# overlapping asynchronous operations might want to display status information
+# simultaneously. Instances of status_bar_operation are created by calling
+# start on the status_bar, and when the caller is done with its stauts bar
+# operation, it calls stop on the operation.
+
+class status_bar_operation {
+
+field status_bar; # reference back to the status_bar that owns this object
+
+field is_active;
+
+field status   {}; # single line of text we show
+field progress {}; # current progress (0 to 100)
+field prefix   {}; # text we format into status
+field units    {}; # unit of progress
+field meter    {}; # current core git progress meter (if active)
+
+constructor new {owner msg uds} {
+	set status_bar $owner
 
 	set status $msg
+	set progress 0
 	set prefix $msg
 	set units  $uds
 	set meter  {}
+
+	set is_active 1
+
+	return $this
 }
 
+method get_is_active {} { return $is_active }
+method get_status {} { return $status }
+method get_progress {} { return $progress }
+
 method update {have total} {
-	set pdone 0
-	set cdone 0
+	if {!$is_active} { return }
+
+	set progress 0
+
 	if {$total > 0} {
-		set pdone [expr {100 * $have / $total}]
-		set cdone [expr {[winfo width $w_c] * $have / $total}]
+		set progress [expr {100 * $have / $total}]
 	}
 
 	set prec [string length [format %i $total]]
+
 	set status [mc "%s ... %*i of %*i %s (%3i%%)" \
 		$prefix \
 		$prec $have \
 		$prec $total \
-		$units $pdone]
-	$w_c coords bar 0 0 $cdone 20
+		$units $progress]
+
+	$status_bar refresh
 }
 
 method update_meter {buf} {
+	if {!$is_active} { return }
+
 	append meter $buf
 	set r [string last "\r" $meter]
 	if {$r == -1} {
@@ -109,23 +287,23 @@  method update_meter {buf} {
 	}
 }
 
-method stop {{msg {}}} {
-	destroy $w_c
-	if {$msg ne {}} {
-		set status $msg
+method stop {{stop_msg {}}} {
+	if {$is_active} {
+		set is_active 0
+		$status_bar stop $this $stop_msg
 	}
 }
 
-method show {msg {test {}}} {
-	if {$test eq {} || $status eq $test} {
-		set status $msg
-	}
+method show {msg} {
+	if {!$is_active} { return }
+
+	set status $msg
+	$status_bar refresh
 }
 
-method _delete {current} {
-	if {$current eq $w} {
-		delete_this
-	}
+method _delete {} {
+	stop
+	delete_this
 }
 
 }