[v5,4/4] maintenance: use Windows scheduled tasks

Commit Message

Derrick Stolee Nov. 24, 2020, 4:16 a.m. UTC

From: Derrick Stolee <[e-mail]>

Git's background maintenance uses cron by default, but this is not
available on Windows. Instead, integrate with Task Scheduler.

Tasks can be scheduled using the 'schtasks' command. There are several
command-line options that can allow for some advanced scheduling, but
unfortunately these seem to all require authenticating using a password.

Instead, use the "/xml" option to pass an XML file that contains the
configuration for the necessary schedule. These XML files are based on
some that I exported after constructing a schedule in the Task Scheduler
GUI. These options only run background maintenance when the user is
logged in, and more fields are populated with the current username and
SID at run-time by 'schtasks'.

Since the GIT_TEST_MAINT_SCHEDULER environment variable allows us to
specify 'schtasks' as the scheduler, we can test the Windows-specific
logic on other platforms. Thus, add a check that the XML file written
by Git is valid when xmllint exists on the system.

Since we use a temporary file for the XML files sent to 'schtasks', we
must copy the file to a predictable filename. Use the number of lines in
the 'args' file to provide a filename for xmllint. Instead of an exact
match on the 'args' file, we 'grep' for the arguments other than the
filename.

There is a deficiency in the current design. Windows has two kinds of
applications: GUI applications that start by "winmain()" and console
applications that start by "main()". Console applications are attached
to a new Console window if they are not already associated with a GUI
application. This means that every hour the scheudled task launches a
command window for the scheduled tasks. Not only is this visually
obtrusive, but it also takes focus from whatever else the user is
doing!

A simple fix would be to insert a GUI application that acts as a shim
between the scheduled task and Git. This is currently possible in Git
for Windows by setting the <Command> tag equal to

  C:\Program Files\Git\git-bash.exe

with options "--hide --no-needs-console --command=cmd\git.exe"
followed by the arguments currently used. Since git-bash.exe is not
included in Windows builds of core Git, I chose to leave out this
feature. My plan is to submit a small patch to Git for Windows that
converts the use of git.exe with this use of git-bash.exe in the
short term. In the long term, we can consider creating this GUI
shim application within core Git, perhaps in contrib/.

Co-authored-by: Eric Sunshine <[e-mail]>
Signed-off-by: Eric Sunshine <[e-mail]>
Signed-off-by: Derrick Stolee <[e-mail]>
---
 Documentation/git-maintenance.txt |  22 ++++
 builtin/gc.c                      | 160 ++++++++++++++++++++++++++++++
 t/t7900-maintenance.sh            |  44 ++++++++
 3 files changed, 226 insertions(+)

Comments

Eric Sunshine Nov. 27, 2020, 9:08 a.m. UTC | #1

On Mon, Nov 23, 2020 at 11:16 PM Derrick Stolee via GitGitGadget
<[e-mail]> wrote:
> Git's background maintenance uses cron by default, but this is not
> available on Windows. Instead, integrate with Task Scheduler.
> [...]
> Signed-off-by: Derrick Stolee <[e-mail]>
> ---
> diff --git a/builtin/gc.c b/builtin/gc.c
> @@ -1671,6 +1671,162 @@ static int launchctl_update_schedule(int run_maintenance, int fd, const char *cm
> +static int schtasks_schedule_task(const char *exec_path, enum schedule_priority schedule, const char *cmd)
> +{
> +       const char *frequency = get_frequency(schedule);
> +
> +       tfile = xmks_tempfile("schedule_XXXXXX");
> +       if (!tfile || !fdopen_tempfile(tfile, "w"))
> +               die(_("failed to create temp xml file"));

Several comments:

The "x" prefix on xmks_tempfile() means that it will die() if it can't
open the tempfile, so the `!tfile` condition is pointless, thus it
could be written:

    if (!fdopen_tempfile(tfile, "w"))

The mks_tempfile_t*() functions with a trailing "t" will place the
temporary file in TMPDIR, whereas xmks_tempfile() used here places it
in the worktree directory, which is not as desirable. Ideally, this
would be using xmks_tempfile_t(), however, that function doesn't exist
yet in tempfile.h, so the best you can do (without the extra work of
also adding the missing function) is to use mks_tempfile_t(). That
doesn't die(), so `!tfile` would still be needed in the conditional.

In earlier versions, you incorporated `frequency` into the temporary
filename which was nice because it made the test easier to understand.
It's not hard to do so here, as well, nor to extract a useful filename
in the test (as I'll show below). For instance:

    struct strbuf tpath = STRBUF_INIT;
    strbuf_addf(&tpath, "schedule-%s-XXXXXX", frequency);
    tfile = mks_tempfile_t(tpath.buf);
    strbuf_release(&tpath);
    if (!tfile || !fdopen(tempfile(tfile, "w"))
        die(...);

> +       strvec_pushl(&child.args, "/create", "/tn", name, "/f", "/xml", tfile->filename.buf, NULL);

Alternately, use the getter:

    strvec_pushl(..., get_tempfile_path(&tfile), ...);

> diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
> @@ -453,6 +453,50 @@ test_expect_success !MINGW 'start and stop macOS maintenance' '
> +test_expect_success 'start and stop Windows maintenance' '
> +       write_script print-args <<-\EOF &&
> +       echo $* >>args
> +       while test $# -gt 0
> +       do
> +               case "$1" in
> +               /xml) shift; xmlfile=$1; break ;;
> +               *) shift ;;
> +               esac
> +       done
> +       lines=$(wc -l args | awk "{print \$1;}")

You're using `awk` to pluck out the line count and ignore the
filename, but the same can be accomplished by feeding the file as
stdin to `wc` rather than naming it as an argument, thus this is
equivalent:

    lines=$(wc -l <args)

However, this idea of constructing stable names for the files by
assigning them numerically incrementing values is unnecessary and
makes the test harder to understand.

> +       test -z "$xmlfile" || cp "$xmlfile" "schedule-$lines.xml"

If you take the suggestion earlier in this review of naming the file
"schedule-${frequency}-XXXXXX.xml", then you can strip it down to just
"schedule-${frequency}.xml" using the expression `${xmlfile%-*}.xml`.
There is no need for `$lines`. Thus, copying the file would become:

    test -z "$xmlfile" || cp "$xmlfile" "${xmlfile%-*}.xml"

> +       for i in 1 2 3
> +       do

Which means that you can use the more easily understood `hourly daily
weekly` enumeration here rather than `1 2 3`.

Having said all this, I'm not sure it's worth a re-roll. These sort of
tweaks can be done atop the current series if someone wants to tackle
it.

Patch

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index 5f8f63f098..6970f2b898 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -313,6 +313,28 @@  To create more advanced customizations to your background tasks, see
 launchctl.plist(5) for more information.
 
 
+BACKGROUND MAINTENANCE ON WINDOWS SYSTEMS
+-----------------------------------------
+
+Windows does not support `cron` and instead has its own system for
+scheduling background tasks. The `git maintenance start` command uses
+the `schtasks` command to submit tasks to this system. You can inspect
+all background tasks using the Task Scheduler application. The tasks
+added by Git have names of the form `Git Maintenance (<frequency>)`.
+The Task Scheduler GUI has ways to inspect these tasks, but you can also
+export the tasks to XML files and view the details there.
+
+Note that since Git is a console application, these background tasks
+create a console window visible to the current user. This can be changed
+manually by selecting the "Run whether user is logged in or not" option
+in Task Scheduler. This change requires a password input, which is why
+`git maintenance start` does not select it by default.
+
+If you want to customize the background tasks, please rename the tasks
+so future calls to `git maintenance (start|stop)` do not overwrite your
+custom tasks.
+
+
 GIT
 ---
 Part of the linkgit:git[1] suite
diff --git a/builtin/gc.c b/builtin/gc.c
index 782769f243..43224e0dec 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -1671,6 +1671,162 @@  static int launchctl_update_schedule(int run_maintenance, int fd, const char *cm
 		return launchctl_remove_plists(cmd);
 }
 
+static char *schtasks_task_name(const char *frequency)
+{
+	struct strbuf label = STRBUF_INIT;
+	strbuf_addf(&label, "Git Maintenance (%s)", frequency);
+	return strbuf_detach(&label, NULL);
+}
+
+static int schtasks_remove_task(enum schedule_priority schedule, const char *cmd)
+{
+	int result;
+	struct strvec args = STRVEC_INIT;
+	const char *frequency = get_frequency(schedule);
+	char *name = schtasks_task_name(frequency);
+
+	strvec_split(&args, cmd);
+	strvec_pushl(&args, "/delete", "/tn", name, "/f", NULL);
+
+	result = run_command_v_opt(args.v, 0);
+
+	strvec_clear(&args);
+	free(name);
+	return result;
+}
+
+static int schtasks_remove_tasks(const char *cmd)
+{
+	return schtasks_remove_task(SCHEDULE_HOURLY, cmd) ||
+		schtasks_remove_task(SCHEDULE_DAILY, cmd) ||
+		schtasks_remove_task(SCHEDULE_WEEKLY, cmd);
+}
+
+static int schtasks_schedule_task(const char *exec_path, enum schedule_priority schedule, const char *cmd)
+{
+	int result;
+	struct child_process child = CHILD_PROCESS_INIT;
+	const char *xml;
+	struct tempfile *tfile;
+	const char *frequency = get_frequency(schedule);
+	char *name = schtasks_task_name(frequency);
+
+	tfile = xmks_tempfile("schedule_XXXXXX");
+	if (!tfile || !fdopen_tempfile(tfile, "w"))
+		die(_("failed to create temp xml file"));
+
+	xml = "<?xml version=\"1.0\" encoding=\"US-ASCII\"?>\n"
+	      "<Task version=\"1.4\" xmlns=\"http://schemas.microsoft.com/windows/2004/02/mit/task\">\n"
+	      "<Triggers>\n"
+	      "<CalendarTrigger>\n";
+	fputs(xml, tfile->fp);
+
+	switch (schedule) {
+	case SCHEDULE_HOURLY:
+		fprintf(tfile->fp,
+			"<StartBoundary>2020-01-01T01:00:00</StartBoundary>\n"
+			"<Enabled>true</Enabled>\n"
+			"<ScheduleByDay>\n"
+			"<DaysInterval>1</DaysInterval>\n"
+			"</ScheduleByDay>\n"
+			"<Repetition>\n"
+			"<Interval>PT1H</Interval>\n"
+			"<Duration>PT23H</Duration>\n"
+			"<StopAtDurationEnd>false</StopAtDurationEnd>\n"
+			"</Repetition>\n");
+		break;
+
+	case SCHEDULE_DAILY:
+		fprintf(tfile->fp,
+			"<StartBoundary>2020-01-01T00:00:00</StartBoundary>\n"
+			"<Enabled>true</Enabled>\n"
+			"<ScheduleByWeek>\n"
+			"<DaysOfWeek>\n"
+			"<Monday />\n"
+			"<Tuesday />\n"
+			"<Wednesday />\n"
+			"<Thursday />\n"
+			"<Friday />\n"
+			"<Saturday />\n"
+			"</DaysOfWeek>\n"
+			"<WeeksInterval>1</WeeksInterval>\n"
+			"</ScheduleByWeek>\n");
+		break;
+
+	case SCHEDULE_WEEKLY:
+		fprintf(tfile->fp,
+			"<StartBoundary>2020-01-01T00:00:00</StartBoundary>\n"
+			"<Enabled>true</Enabled>\n"
+			"<ScheduleByWeek>\n"
+			"<DaysOfWeek>\n"
+			"<Sunday />\n"
+			"</DaysOfWeek>\n"
+			"<WeeksInterval>1</WeeksInterval>\n"
+			"</ScheduleByWeek>\n");
+		break;
+
+	default:
+		break;
+	}
+
+	xml = "</CalendarTrigger>\n"
+	      "</Triggers>\n"
+	      "<Principals>\n"
+	      "<Principal id=\"Author\">\n"
+	      "<LogonType>InteractiveToken</LogonType>\n"
+	      "<RunLevel>LeastPrivilege</RunLevel>\n"
+	      "</Principal>\n"
+	      "</Principals>\n"
+	      "<Settings>\n"
+	      "<MultipleInstancesPolicy>IgnoreNew</MultipleInstancesPolicy>\n"
+	      "<Enabled>true</Enabled>\n"
+	      "<Hidden>true</Hidden>\n"
+	      "<UseUnifiedSchedulingEngine>true</UseUnifiedSchedulingEngine>\n"
+	      "<WakeToRun>false</WakeToRun>\n"
+	      "<ExecutionTimeLimit>PT72H</ExecutionTimeLimit>\n"
+	      "<Priority>7</Priority>\n"
+	      "</Settings>\n"
+	      "<Actions Context=\"Author\">\n"
+	      "<Exec>\n"
+	      "<Command>\"%s\\git.exe\"</Command>\n"
+	      "<Arguments>--exec-path=\"%s\" for-each-repo --config=maintenance.repo maintenance run --schedule=%s</Arguments>\n"
+	      "</Exec>\n"
+	      "</Actions>\n"
+	      "</Task>\n";
+	fprintf(tfile->fp, xml, exec_path, exec_path, frequency);
+	strvec_split(&child.args, cmd);
+	strvec_pushl(&child.args, "/create", "/tn", name, "/f", "/xml", tfile->filename.buf, NULL);
+	close_tempfile_gently(tfile);
+
+	child.no_stdout = 1;
+	child.no_stderr = 1;
+
+	if (start_command(&child))
+		die(_("failed to start schtasks"));
+	result = finish_command(&child);
+
+	delete_tempfile(&tfile);
+	free(name);
+	return result;
+}
+
+static int schtasks_schedule_tasks(const char *cmd)
+{
+	const char *exec_path = git_exec_path();
+
+	return schtasks_schedule_task(exec_path, SCHEDULE_HOURLY, cmd) ||
+		schtasks_schedule_task(exec_path, SCHEDULE_DAILY, cmd) ||
+		schtasks_schedule_task(exec_path, SCHEDULE_WEEKLY, cmd);
+}
+
+static int schtasks_update_schedule(int run_maintenance, int fd, const char *cmd)
+{
+	if (run_maintenance)
+		return schtasks_schedule_tasks(cmd);
+	else
+		return schtasks_remove_tasks(cmd);
+}
+
 #define BEGIN_LINE "# BEGIN GIT MAINTENANCE SCHEDULE"
 #define END_LINE "# END GIT MAINTENANCE SCHEDULE"
 
@@ -1761,6 +1917,8 @@  static int crontab_update_schedule(int run_maintenance, int fd, const char *cmd)
 
 #if defined(__APPLE__)
 static const char platform_scheduler[] = "launchctl";
+#elif defined(GIT_WINDOWS_NATIVE)
+static const char platform_scheduler[] = "schtasks";
 #else
 static const char platform_scheduler[] = "crontab";
 #endif
@@ -1789,6 +1947,8 @@  static int update_background_schedule(int enable)
 
 	if (!strcmp(scheduler, "launchctl"))
 		result = launchctl_update_schedule(enable, lk.tempfile->fd, cmd);
+	else if (!strcmp(scheduler, "schtasks"))
+		result = schtasks_update_schedule(enable, lk.tempfile->fd, cmd);
 	else if (!strcmp(scheduler, "crontab"))
 		result = crontab_update_schedule(enable, lk.tempfile->fd, cmd);
 	else
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 6d37312901..0246e4ce30 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -453,6 +453,50 @@  test_expect_success !MINGW 'start and stop macOS maintenance' '
 	test_line_count = 0 actual
 '
 
+test_expect_success 'start and stop Windows maintenance' '
+	write_script print-args <<-\EOF &&
+	echo $* >>args
+	while test $# -gt 0
+	do
+		case "$1" in
+		/xml) shift; xmlfile=$1; break ;;
+		*) shift ;;
+		esac
+	done
+	lines=$(wc -l args | awk "{print \$1;}")
+	test -z "$xmlfile" || cp "$xmlfile" "schedule-$lines.xml"
+	EOF
+
+	rm -f args &&
+	GIT_TEST_MAINT_SCHEDULER="schtasks:./print-args" git maintenance start &&
+
+	# start registers the repo
+	git config --get --global maintenance.repo "$(pwd)" &&
+
+	for frequency in hourly daily weekly
+	do
+		grep "/create /tn Git Maintenance ($frequency) /f /xml" args \
+			|| return 1
+	done &&
+
+	for i in 1 2 3
+	do
+		test_xmllint "schedule-$i.xml" &&
+		grep "encoding=.US-ASCII." "schedule-$i.xml" || return 1
+	done &&
+
+	rm -f args &&
+	GIT_TEST_MAINT_SCHEDULER="schtasks:./print-args" git maintenance stop &&
+
+	# stop does not unregister the repo
+	git config --get --global maintenance.repo "$(pwd)" &&
+
+	rm expect &&
+	printf "/delete /tn Git Maintenance (%s) /f\n" \
+		hourly daily weekly >expect &&
+	test_cmp expect args
+'
+
 test_expect_success 'register preserves existing strategy' '
 	git config maintenance.strategy none &&
 	git maintenance register &&