[PATCH 4/5] index-pack: Use the new worker pool

[PATCH 4/5] index-pack: Use the new worker pool

[Stefan Beller]

By treating each object as its own task the workflow is easier to follow
as the function used in the worker threads doesn't need any control logic
any more.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/index-pack.c | 71 +++++++++++++++++++++++-----------------------------
 1 file changed, 32 insertions(+), 39 deletions(-)

diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 3f10840..826bd22 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -11,6 +11,7 @@
 #include "exec_cmd.h"
 #include "streaming.h"
 #include "thread-utils.h"
+#include "run-command.h"
 
 static const char index_pack_usage[] =
 "git index-pack [-v] [-o <index-file>] [--keep | --keep=<msg>] [--verify] [--strict] (<pack-file> | --stdin [--fix-thin] [<pack-file>])";
@@ -95,7 +96,6 @@ static const char *curr_pack;
 #ifndef NO_PTHREADS
 
 static struct thread_local *thread_data;
-static int nr_dispatched;
 static int threads_active;
 
 static pthread_mutex_t read_mutex;
@@ -106,10 +106,6 @@ static pthread_mutex_t counter_mutex;
 #define counter_lock()		lock_mutex(&counter_mutex)
 #define counter_unlock()	unlock_mutex(&counter_mutex)
 
-static pthread_mutex_t work_mutex;
-#define work_lock()		lock_mutex(&work_mutex)
-#define work_unlock()		unlock_mutex(&work_mutex)
-
 static pthread_mutex_t deepest_delta_mutex;
 #define deepest_delta_lock()	lock_mutex(&deepest_delta_mutex)
 #define deepest_delta_unlock()	unlock_mutex(&deepest_delta_mutex)
@@ -140,7 +136,6 @@ static void init_thread(void)
 	int i;
 	init_recursive_mutex(&read_mutex);
 	pthread_mutex_init(&counter_mutex, NULL);
-	pthread_mutex_init(&work_mutex, NULL);
 	pthread_mutex_init(&type_cas_mutex, NULL);
 	if (show_stat)
 		pthread_mutex_init(&deepest_delta_mutex, NULL);
@@ -163,7 +158,6 @@ static void cleanup_thread(void)
 	threads_active = 0;
 	pthread_mutex_destroy(&read_mutex);
 	pthread_mutex_destroy(&counter_mutex);
-	pthread_mutex_destroy(&work_mutex);
 	pthread_mutex_destroy(&type_cas_mutex);
 	if (show_stat)
 		pthread_mutex_destroy(&deepest_delta_mutex);
@@ -181,9 +175,6 @@ static void cleanup_thread(void)
 #define counter_lock()
 #define counter_unlock()
 
-#define work_lock()
-#define work_unlock()
-
 #define deepest_delta_lock()
 #define deepest_delta_unlock()
 
@@ -1075,28 +1066,29 @@ static void resolve_base(struct object_entry *obj)
 }
 
 #ifndef NO_PTHREADS
-static void *threaded_second_pass(void *data)
+static int threaded_second_pass(struct task_queue *tq, void *data)
 {
-	set_thread_data(data);
-	for (;;) {
-		int i;
-		counter_lock();
-		display_progress(progress, nr_resolved_deltas);
-		counter_unlock();
-		work_lock();
-		while (nr_dispatched < nr_objects &&
-		       is_delta_type(objects[nr_dispatched].type))
-			nr_dispatched++;
-		if (nr_dispatched >= nr_objects) {
-			work_unlock();
-			break;
-		}
-		i = nr_dispatched++;
-		work_unlock();
+	if (!get_thread_data()) {
+		struct thread_local *t = xmalloc(sizeof(*t));
+		t->pack_fd = open(curr_pack, O_RDONLY);
+		if (t->pack_fd == -1)
+			die_errno(_("unable to open %s"), curr_pack);
 
-		resolve_base(&objects[i]);
+		set_thread_data(t);
 	}
-	return NULL;
+
+	resolve_base(data);
+
+	counter_lock();
+	display_progress(progress, nr_resolved_deltas);
+	counter_unlock();
+	return 0;
+}
+
+void cleanup_threaded_second_pass(struct task_queue *aq)
+{
+	struct thread_local *t = get_thread_data();
+	free(t);
 }
 #endif
 
@@ -1195,18 +1187,19 @@ static void resolve_deltas(void)
 					  nr_ref_deltas + nr_ofs_deltas);
 
 #ifndef NO_PTHREADS
-	nr_dispatched = 0;
 	if (nr_threads > 1 || getenv("GIT_FORCE_THREADS")) {
+		struct task_queue *tq;
+
 		init_thread();
-		for (i = 0; i < nr_threads; i++) {
-			int ret = pthread_create(&thread_data[i].thread, NULL,
-						 threaded_second_pass, thread_data + i);
-			if (ret)
-				die(_("unable to create thread: %s"),
-				    strerror(ret));
-		}
-		for (i = 0; i < nr_threads; i++)
-			pthread_join(thread_data[i].thread, NULL);
+		tq = create_task_queue(nr_threads);
+
+		for (i = 0; i < nr_objects; i++)
+			if (!is_delta_type(objects[i].type))
+				add_task(tq, threaded_second_pass, &objects[i]);
+
+		if (finish_task_queue(tq, cleanup_threaded_second_pass))
+			die("Not all threads have finished");
+
 		cleanup_thread();
 		return;
 	}
-- 
2.5.0.400.gff86faf

Re: [PATCH 4/5] index-pack: Use the new worker pool

[Jeff King]

On Tue, Aug 25, 2015 at 10:28:25AM -0700, Stefan Beller wrote:

> By treating each object as its own task the workflow is easier to follow
> as the function used in the worker threads doesn't need any control logic
> any more.

Have you tried running t/perf/p5302 on this?

I seem to get a pretty consistent 2%-ish slowdown, both against git.git
and linux.git. That's not a lot, but I'm wondering if there is some
low-hanging fruit in the locking, or in the pattern of work being
dispatched. Or it may just be noise, but it seems fairly consistent.

-Peff

Re: [PATCH 4/5] index-pack: Use the new worker pool

[Stefan Beller]

On Tue, Aug 25, 2015 at 12:03 PM, Jeff King <peff@peff.net> wrote:
> On Tue, Aug 25, 2015 at 10:28:25AM -0700, Stefan Beller wrote:
>
>> By treating each object as its own task the workflow is easier to follow
>> as the function used in the worker threads doesn't need any control logic
>> any more.
>
> Have you tried running t/perf/p5302 on this?
>
> I seem to get a pretty consistent 2%-ish slowdown, both against git.git
> and linux.git. That's not a lot, but I'm wondering if there is some
> low-hanging fruit in the locking, or in the pattern of work being
> dispatched. Or it may just be noise, but it seems fairly consistent.

I did not run any perf tests, just the standard tests.

Maybe the progress display can be moved out to another thread,
such that it doesn't block the threads doing actual work.
Also the progress display can be done a bit more sloppy,
we are allowed to drop old events, if we have newer information.
[Though this reasoning is not looking at the threading pool code,
because ..um.. my code is perfect]

>
> -Peff

Re: [PATCH 4/5] index-pack: Use the new worker pool

[Junio C Hamano]

Jeff King <peff@peff.net> writes:

> On Tue, Aug 25, 2015 at 10:28:25AM -0700, Stefan Beller wrote:
>
>> By treating each object as its own task the workflow is easier to follow
>> as the function used in the worker threads doesn't need any control logic
>> any more.
>
> Have you tried running t/perf/p5302 on this?
>
> I seem to get a pretty consistent 2%-ish slowdown, both against git.git
> and linux.git. That's not a lot, but I'm wondering if there is some
> low-hanging fruit in the locking, or in the pattern of work being
> dispatched. Or it may just be noise, but it seems fairly consistent.

The pattern of work dispatch hopefully is the same, no?  add_task()
does the "append at the end" thing and next_task() picks from the
front of the queue.  The original is "we have globally N things,
so far M things have been handled, and we want a new one, so we pick
the M+1th one and do it".

The amount of memory that is used to represent a single task may be
much larger than the original, with overhead coming from job_list
structure and the doubly-linked list.  We may not be able to spin up
30 threads and throw a million tasks at them using this, because of
the overhead.  It would be more suited to handle a pattern in which
an overlord actively creates new tasks while worker threads chew
them, using the add_task/dispatch as the medium for communication
between them.

Re: [PATCH 4/5] index-pack: Use the new worker pool

[Stefan Beller]

On Tue, Aug 25, 2015 at 1:41 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Jeff King <peff@peff.net> writes:
>
>> On Tue, Aug 25, 2015 at 10:28:25AM -0700, Stefan Beller wrote:
>>
>>> By treating each object as its own task the workflow is easier to follow
>>> as the function used in the worker threads doesn't need any control logic
>>> any more.
>>
>> Have you tried running t/perf/p5302 on this?
>>
>> I seem to get a pretty consistent 2%-ish slowdown, both against git.git
>> and linux.git. That's not a lot, but I'm wondering if there is some
>> low-hanging fruit in the locking, or in the pattern of work being
>> dispatched. Or it may just be noise, but it seems fairly consistent.
>
> The pattern of work dispatch hopefully is the same, no?  add_task()
> does the "append at the end" thing and next_task() picks from the
> front of the queue.  The original is "we have globally N things,
> so far M things have been handled, and we want a new one, so we pick
> the M+1th one and do it".
>
> The amount of memory that is used to represent a single task may be
> much larger than the original, with overhead coming from job_list
> structure and the doubly-linked list.  We may not be able to spin up
> 30 threads and throw a million tasks at them using this, because of
> the overhead.

I thought about making the add_task block after a certain size of job_list
such that there is always just enough tasks available to process.
Then we would not need to used a huge amount of memory for having
a long line of waiting tasks; the shorter the line is the less we can tolerate
burst behavior in the threads.

> It would be more suited to handle a pattern in which
> an overlord actively creates new tasks while worker threads chew
> them, using the add_task/dispatch as the medium for communication
> between them.

Not sure I follow there.

Original implementation:
We have M threads sitting around the table, all of them trying to obtain food
from the one bowl on the table and then eating it.
Once the bowl is all eaten, we can stop.

New pattern:
One cook puts all the food items on the sushi-go-round-belt with a fancy plate
and the threads grab them one by one still using locks (but they are internal to
the belt).

Are you saying we're content with just a bowl and everyone helps themselves
for getting food?

Re: [PATCH 4/5] index-pack: Use the new worker pool

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> Not sure I follow there.
>
> Original implementation:
> We have M threads sitting around the table, all of them trying to obtain food
> from the one bowl on the table and then eating it.
> Once the bowl is all eaten, we can stop.
>
> New pattern:
> One cook puts all the food items on the sushi-go-round-belt with a fancy plate
> and the threads grab them one by one still using locks (but they are internal to
> the belt).
>
> Are you saying we're content with just a bowl and everyone helps themselves
> for getting food?

No.  I am questioning how big overhead is for having the
go-round-belt that must hold all dishes to be eaten, which did not
exist in the original arrangement.

Re: [PATCH 4/5] index-pack: Use the new worker pool

[Stefan Beller]

On Tue, Aug 25, 2015 at 2:12 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Stefan Beller <sbeller@google.com> writes:
>
>> Not sure I follow there.
>>
>> Original implementation:
>> We have M threads sitting around the table, all of them trying to obtain food
>> from the one bowl on the table and then eating it.
>> Once the bowl is all eaten, we can stop.
>>
>> New pattern:
>> One cook puts all the food items on the sushi-go-round-belt with a fancy plate
>> and the threads grab them one by one still using locks (but they are internal to
>> the belt).
>>
>> Are you saying we're content with just a bowl and everyone helps themselves
>> for getting food?
>
> No.  I am questioning how big overhead is for having the
> go-round-belt that must hold all dishes to be eaten, which did not
> exist in the original arrangement.
>
>

Then please don't pick up this patch. This and patch 5 are there to convince
Jeff this is a good API, worth being introduced and not over engineered, just
solving a problem we're interested in with a minimal amount of code to side
track from the actual goal we want to pursue.

Re: [PATCH 4/5] index-pack: Use the new worker pool

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> Then please don't pick up this patch. This and patch 5 are there to convince
> Jeff this is a good API, worth being introduced and not over engineered, just
> solving a problem we're interested in with a minimal amount of code to side
> track from the actual goal we want to pursue.

Don't worry.  I did not have intention to queue index-pack and
pack-objects rewrite unless the use of the new API makes them
demonstratably better.

The criteria for "worth being introduced" would include "not
excessively heavyweight", I would think.  And it was good that we
have these two patches to judge if the earlier one (2-3/5) is a good
thing to add in a concrete way.  Perhaps the 2% slowdown might be
showing the performance characteristics of your worker pool model,
and Peff's suggestion to at least see (if not solve) where the
overhead is coming from was a very reasonable one, I would think.

[RFC PATCH 0/5] Progressing with `git submodule foreach_parallel`

[Stefan Beller]

This series applies on top of 10d0bef9981c8045b8c9aac1ca7b8761896bed0c in
the branch origin/sb/submodule-helper

The first patch is a resend of module_clone, which now contains all
memory leak fixes. 

The second patch adding the new task queue is rewritten to not
use semaphores any more, but only mutexes and condition variables
as that's what we use at other places in the code base. So it is
better to align to these places, it makes the threading pool also
easier to understand internally.
Originally there were 2 semaphores to control the queue length
(0 < queue length < number of threads), such that we don't overallocate
memory, but rather slow down the thread adding new tasks to the queue.
This has been removed and the queue may grow infinitely large.

The third patch adding `git submodule foreach_parallel` learned a
totally different behavior how to interact with the output channels
(way better for human consumption as you have early feedback and
feedback all the time, ok-ish for machine consumption, but far from
perfect).

The fourth patch rewriting index-pack was made smaller and doesn't 
rewrite the workflow any more, but only plugs in the new threading
API instead of constructing the pthreads themselves.
I started benchmarking that patch, but I seem to get only bogus results,
so I cannot tell if it still makes it 2 % slower as Jeff claimed.

The fifth patch refactors pack-objects to be *way* more understandable IMHO!
It also switches to the new threading pool, but the refactor may be
suitable also if we decide to not use the threading API there.
The reason for it being more readable is the movement of the rebalancing
into the threads themselves, which then turns out to require a lot less
of locking and communication variables.

Any feedback is welcome!
Thanks,
Stefan

Stefan Beller (5):
  submodule: implement `module_clone` as a builtin helper
  thread-utils: add a threaded task queue
  submodule: helper to run foreach in parallel
  index-pack: Use the new worker pool
  pack-objects: Use new worker pool

 builtin/index-pack.c        |  23 ++--
 builtin/pack-objects.c      | 175 ++++++++----------------
 builtin/submodule--helper.c | 318 +++++++++++++++++++++++++++++++++++++++++++-
 git-submodule.sh            |  91 ++-----------
 run-command.c               |  29 ++--
 thread-utils.c              | 227 +++++++++++++++++++++++++++++++
 thread-utils.h              |  35 +++++
 7 files changed, 677 insertions(+), 221 deletions(-)

-- 
2.5.0.264.g784836d

[PATCH 1/5] submodule: implement `module_clone` as a builtin helper

[Stefan Beller]

`module_clone` is part of the update command, which I want to convert
to C next.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin/submodule--helper.c | 160 +++++++++++++++++++++++++++++++++++++++++++-
 git-submodule.sh            |  80 +---------------------
 2 files changed, 162 insertions(+), 78 deletions(-)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 4b32a3c..f11fb9c 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -8,6 +8,7 @@
 #include "submodule.h"
 #include "submodule-config.h"
 #include "string-list.h"
+#include "run-command.h"
 
 static const struct cache_entry **ce_entries;
 static int ce_alloc, ce_used;
@@ -124,6 +125,160 @@ static int module_name(int argc, const char **argv, const char *prefix)
 	return 0;
 }
 
+static int clone_submodule(const char *path, const char *gitdir, const char *url,
+			   const char *depth, const char *reference, int quiet)
+{
+	struct child_process cp;
+	child_process_init(&cp);
+
+	argv_array_push(&cp.args, "clone");
+	argv_array_push(&cp.args, "--no-checkout");
+	if (quiet)
+		argv_array_push(&cp.args, "--quiet");
+	if (depth && strcmp(depth, "")) {
+		argv_array_push(&cp.args, "--depth");
+		argv_array_push(&cp.args, depth);
+	}
+	if (reference && strcmp(reference, "")) {
+		argv_array_push(&cp.args, "--reference");
+		argv_array_push(&cp.args, reference);
+	}
+	if (gitdir) {
+		argv_array_push(&cp.args, "--separate-git-dir");
+		argv_array_push(&cp.args, gitdir);
+	}
+	argv_array_push(&cp.args, url);
+	argv_array_push(&cp.args, path);
+
+	cp.git_cmd = 1;
+	cp.env = local_repo_env;
+
+	cp.no_stdin = 1;
+	cp.no_stdout = 1;
+	cp.no_stderr = 1;
+
+	return run_command(&cp);
+}
+
+/*
+ * Clone a submodule
+ *
+ * $1 = submodule path
+ * $2 = submodule name
+ * $3 = URL to clone
+ * $4 = reference repository to reuse (empty for independent)
+ * $5 = depth argument for shallow clones (empty for deep)
+ *
+ * Prior to calling, cmd_update checks that a possibly existing
+ * path is not a git repository.
+ * Likewise, cmd_add checks that path does not exist at all,
+ * since it is the location of a new submodule.
+ */
+static int module_clone(int argc, const char **argv, const char *prefix)
+{
+	const char *path = NULL, *name = NULL, *url = NULL, *reference = NULL, *depth = NULL;
+	int quiet = 0;
+	FILE *submodule_dot_git;
+	const char *sm_gitdir, *p;
+	struct strbuf rel_path = STRBUF_INIT;
+	struct strbuf sb = STRBUF_INIT;
+
+	struct option module_update_options[] = {
+		OPT_STRING(0, "prefix", &alternative_path,
+			   N_("path"),
+			   N_("alternative anchor for relative paths")),
+		OPT_STRING(0, "path", &path,
+			   N_("path"),
+			   N_("where the new submodule will be cloned to")),
+		OPT_STRING(0, "name", &name,
+			   N_("string"),
+			   N_("name of the new submodule")),
+		OPT_STRING(0, "url", &url,
+			   N_("string"),
+			   N_("url where to clone the submodule from")),
+		OPT_STRING(0, "reference", &reference,
+			   N_("string"),
+			   N_("reference repository")),
+		OPT_STRING(0, "depth", &depth,
+			   N_("string"),
+			   N_("depth for shallow clones")),
+		OPT_END()
+	};
+
+	static const char * const git_submodule_helper_usage[] = {
+		N_("git submodule--helper update [--prefix=<path>] [--quiet] [--remote] [-N|--no-fetch]"
+		   "[-f|--force] [--rebase|--merge] [--reference <repository>]"
+		   "[--depth <depth>] [--recursive] [--] [<path>...]"),
+		NULL
+	};
+
+	argc = parse_options(argc, argv, prefix, module_update_options,
+			     git_submodule_helper_usage, 0);
+
+	if (getenv("GIT_QUIET"))
+		quiet = 1;
+
+	strbuf_addf(&sb, "%s/modules/%s", get_git_dir(), name);
+	sm_gitdir = strbuf_detach(&sb, NULL);
+
+	if (!file_exists(sm_gitdir)) {
+		safe_create_leading_directories_const(sm_gitdir);
+		if (clone_submodule(path, sm_gitdir, url, depth, reference, quiet))
+			die(N_("Clone of '%s' into submodule path '%s' failed"),
+			    url, path);
+	} else {
+		safe_create_leading_directories_const(path);
+		unlink(sm_gitdir);
+	}
+
+	/* Write a .git file in the submodule to redirect to the superproject. */
+	if (alternative_path && !strcmp(alternative_path, "")) {
+		p = relative_path(path, alternative_path, &sb);
+		strbuf_reset(&sb);
+	} else
+		p = path;
+
+	if (safe_create_leading_directories_const(p) < 0)
+		die("Could not create directory '%s'", p);
+
+	strbuf_addf(&sb, "%s/.git", p);
+
+	if (safe_create_leading_directories_const(sb.buf) < 0)
+		die(_("could not create leading directories of '%s'"), sb.buf);
+	submodule_dot_git = fopen(sb.buf, "w");
+	if (!submodule_dot_git)
+		die ("Cannot open file '%s': %s", sb.buf, strerror(errno));
+
+	fprintf(submodule_dot_git, "gitdir: %s\n",
+		relative_path(sm_gitdir, path, &rel_path));
+	if (fclose(submodule_dot_git))
+		die("Could not close file %s", sb.buf);
+	strbuf_reset(&sb);
+
+	/* Redirect the worktree of the submodule in the superprojects config */
+	if (!is_absolute_path(sm_gitdir)) {
+		char *s = (char*)sm_gitdir;
+		if (strbuf_getcwd(&sb))
+			die_errno("unable to get current working directory");
+		strbuf_addf(&sb, "/%s", sm_gitdir);
+		sm_gitdir = strbuf_detach(&sb, NULL);
+		free(s);
+	}
+
+	if (strbuf_getcwd(&sb))
+		die_errno("unable to get current working directory");
+	strbuf_addf(&sb, "/%s", path);
+
+	p = git_pathdup_submodule(path, "config");
+	if (!p)
+		die("Could not get submodule directory for '%s'", path);
+	git_config_set_in_file(p, "core.worktree",
+			       relative_path(sb.buf, sm_gitdir, &rel_path));
+	strbuf_release(&sb);
+	free((char*)sm_gitdir);
+	return 0;
+}
+
 int cmd_submodule__helper(int argc, const char **argv, const char *prefix)
 {
 	if (argc < 2)
@@ -135,6 +290,9 @@ int cmd_submodule__helper(int argc, const char **argv, const char *prefix)
 	if (!strcmp(argv[1], "module_name"))
 		return module_name(argc - 2, argv + 2, prefix);
 
+	if (!strcmp(argv[1], "module_clone"))
+		return module_clone(argc - 1, argv + 1, prefix);
+
 usage:
-	usage("git submodule--helper [module_list module_name]\n");
+	usage("git submodule--helper [module_list module_name module_clone]\n");
 }
diff --git a/git-submodule.sh b/git-submodule.sh
index e6ff38d..fb5155e 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -178,80 +178,6 @@ get_submodule_config () {
 	printf '%s' "${value:-$default}"
 }
 
-#
-# Clone a submodule
-#
-# $1 = submodule path
-# $2 = submodule name
-# $3 = URL to clone
-# $4 = reference repository to reuse (empty for independent)
-# $5 = depth argument for shallow clones (empty for deep)
-#
-# Prior to calling, cmd_update checks that a possibly existing
-# path is not a git repository.
-# Likewise, cmd_add checks that path does not exist at all,
-# since it is the location of a new submodule.
-#
-module_clone()
-{
-	sm_path=$1
-	name=$2
-	url=$3
-	reference="$4"
-	depth="$5"
-	quiet=
-	if test -n "$GIT_QUIET"
-	then
-		quiet=-q
-	fi
-
-	gitdir=
-	gitdir_base=
-	base_name=$(dirname "$name")
-
-	gitdir=$(git rev-parse --git-dir)
-	gitdir_base="$gitdir/modules/$base_name"
-	gitdir="$gitdir/modules/$name"
-
-	if test -d "$gitdir"
-	then
-		mkdir -p "$sm_path"
-		rm -f "$gitdir/index"
-	else
-		mkdir -p "$gitdir_base"
-		(
-			clear_local_git_env
-			git clone $quiet ${depth:+"$depth"} -n ${reference:+"$reference"} \
-				--separate-git-dir "$gitdir" "$url" "$sm_path"
-		) ||
-		die "$(eval_gettext "Clone of '\$url' into submodule path '\$sm_path' failed")"
-	fi
-
-	# We already are at the root of the work tree but cd_to_toplevel will
-	# resolve any symlinks that might be present in $PWD
-	a=$(cd_to_toplevel && cd "$gitdir" && pwd)/
-	b=$(cd_to_toplevel && cd "$sm_path" && pwd)/
-	# Remove all common leading directories after a sanity check
-	if test "${a#$b}" != "$a" || test "${b#$a}" != "$b"; then
-		die "$(eval_gettext "Gitdir '\$a' is part of the submodule path '\$b' or vice versa")"
-	fi
-	while test "${a%%/*}" = "${b%%/*}"
-	do
-		a=${a#*/}
-		b=${b#*/}
-	done
-	# Now chop off the trailing '/'s that were added in the beginning
-	a=${a%/}
-	b=${b%/}
-
-	# Turn each leading "*/" component into "../"
-	rel=$(printf '%s\n' "$b" | sed -e 's|[^/][^/]*|..|g')
-	printf '%s\n' "gitdir: $rel/$a" >"$sm_path/.git"
-
-	rel=$(printf '%s\n' "$a" | sed -e 's|[^/][^/]*|..|g')
-	(clear_local_git_env; cd "$sm_path" && GIT_WORK_TREE=. git config core.worktree "$rel/$b")
-}
-
 isnumber()
 {
 	n=$(($1 + 0)) 2>/dev/null && test "$n" = "$1"
@@ -301,7 +227,7 @@ cmd_add()
 			shift
 			;;
 		--depth=*)
-			depth=$1
+			depth="$1"
 			;;
 		--)
 			shift
@@ -412,7 +338,7 @@ Use -f if you really want to add it." >&2
 				echo "$(eval_gettext "Reactivating local git directory for submodule '\$sm_name'.")"
 			fi
 		fi
-		module_clone "$sm_path" "$sm_name" "$realrepo" "$reference" "$depth" || exit
+		git submodule--helper module_clone --prefix "$wt_prefix" --path "$sm_path" --name "$sm_name" --url "$realrepo" "$reference" "$depth" || exit
 		(
 			clear_local_git_env
 			cd "$sm_path" &&
@@ -774,7 +700,7 @@ Maybe you want to use 'update --init'?")"
 
 		if ! test -d "$sm_path"/.git && ! test -f "$sm_path"/.git
 		then
-			module_clone "$sm_path" "$name" "$url" "$reference" "$depth" || exit
+			git submodule--helper module_clone --prefix "$prefix" --path "$sm_path" --name "$name" --url "$url" "$reference" "$depth" || exit
 			cloned_modules="$cloned_modules;$name"
 			subsha1=
 		else
-- 
2.5.0.264.g784836d

[PATCH 2/5] thread-utils: add a threaded task queue

[Stefan Beller]

This adds functionality to do work in a parallel threaded
fashion while the boiler plate code for setting up threads
and tearing them down as well as queuing up tasks is hidden
behind the new API.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 run-command.c  |  29 +++++---
 thread-utils.c | 227 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 thread-utils.h |  35 +++++++++
 3 files changed, 279 insertions(+), 12 deletions(-)

diff --git a/run-command.c b/run-command.c
index 28e1d55..cb15cd9 100644
--- a/run-command.c
+++ b/run-command.c
@@ -668,6 +668,22 @@ int git_atexit(void (*handler)(void))
 
 #endif
 
+void setup_main_thread(void)
+{
+	if (!main_thread_set) {
+		/*
+		 * We assume that the first time that start_async is called
+		 * it is from the main thread.
+		 */
+		main_thread_set = 1;
+		main_thread = pthread_self();
+		pthread_key_create(&async_key, NULL);
+		pthread_key_create(&async_die_counter, NULL);
+		set_die_routine(die_async);
+		set_die_is_recursing_routine(async_die_is_recursing);
+	}
+}
+
 int start_async(struct async *async)
 {
 	int need_in, need_out;
@@ -740,18 +756,7 @@ int start_async(struct async *async)
 	else if (async->out)
 		close(async->out);
 #else
-	if (!main_thread_set) {
-		/*
-		 * We assume that the first time that start_async is called
-		 * it is from the main thread.
-		 */
-		main_thread_set = 1;
-		main_thread = pthread_self();
-		pthread_key_create(&async_key, NULL);
-		pthread_key_create(&async_die_counter, NULL);
-		set_die_routine(die_async);
-		set_die_is_recursing_routine(async_die_is_recursing);
-	}
+	setup_main_thread();
 
 	if (proc_in >= 0)
 		set_cloexec(proc_in);
diff --git a/thread-utils.c b/thread-utils.c
index a2135e0..b45ab92 100644
--- a/thread-utils.c
+++ b/thread-utils.c
@@ -1,5 +1,7 @@
 #include "cache.h"
 #include "thread-utils.h"
+#include "run-command.h"
+#include "git-compat-util.h"
 
 #if defined(hpux) || defined(__hpux) || defined(_hpux)
 #  include <sys/pstat.h>
@@ -75,3 +77,228 @@ int init_recursive_mutex(pthread_mutex_t *m)
 	}
 	return ret;
 }
+
+#ifndef NO_PTHREADS
+struct job_list {
+	int (*fct)(struct task_queue *tq, void *task);
+	void *task;
+	struct job_list *next;
+};
+
+static pthread_t main_thread;
+static int main_thread_set;
+static pthread_key_t async_key;
+static pthread_key_t async_die_counter;
+
+static NORETURN void die_async(const char *err, va_list params)
+{
+	vreportf("fatal: ", err, params);
+
+	if (!pthread_equal(main_thread, pthread_self()))
+		pthread_exit((void *)128);
+
+	exit(128);
+}
+
+static int async_die_is_recursing(void)
+{
+	void *ret = pthread_getspecific(async_die_counter);
+	pthread_setspecific(async_die_counter, (void *)1);
+	return ret != NULL;
+}
+
+/* FIXME: deduplicate this code with run-command.c */
+static void setup_main_thread(void)
+{
+	if (!main_thread_set) {
+		main_thread_set = 1;
+		main_thread = pthread_self();
+		pthread_key_create(&async_key, NULL);
+		pthread_key_create(&async_die_counter, NULL);
+		set_die_routine(die_async);
+		set_die_is_recursing_routine(async_die_is_recursing);
+	}
+}
+
+struct task_queue {
+	pthread_mutex_t mutex;
+	pthread_cond_t cond_non_empty;
+
+	int queued_tasks;
+	struct job_list *first;
+	struct job_list *last;
+
+	pthread_t *threads;
+	unsigned max_threads;
+	unsigned max_tasks;
+
+	void (*finish_function)(struct task_queue *tq);
+	int early_return;
+};
+
+static void next_task(struct task_queue *tq,
+		      int (**fct)(struct task_queue *tq, void *task),
+		      void **task,
+		      int *early_return)
+{
+	struct job_list *job = NULL;
+
+	pthread_mutex_lock(&tq->mutex);
+	while (tq->queued_tasks == 0)
+		pthread_cond_wait(&tq->cond_non_empty, &tq->mutex);
+
+	tq->early_return |= *early_return;
+
+	if (!tq->early_return) {
+		job = tq->first;
+		tq->first = job->next;
+		if (!tq->first)
+			tq->last = NULL;
+		tq->queued_tasks--;
+	}
+
+	pthread_mutex_unlock(&tq->mutex);
+
+	if (job) {
+		*fct = job->fct;
+		*task = job->task;
+	} else {
+		*fct = NULL;
+		*task = NULL;
+	}
+
+	free(job);
+}
+
+static void *dispatcher(void *args)
+{
+	void *task;
+	int (*fct)(struct task_queue *tq, void *task);
+	int early_return = 0;
+	struct task_queue *tq = args;
+
+	next_task(tq, &fct, &task, &early_return);
+	while (fct && !early_return) {
+		early_return = fct(tq, task);
+		next_task(tq, &fct, &task, &early_return);
+	}
+
+	if (tq->finish_function)
+		tq->finish_function(tq);
+
+	pthread_exit(0);
+}
+
+struct task_queue *create_task_queue(unsigned max_threads)
+{
+	struct task_queue *tq = xmalloc(sizeof(*tq));
+
+	int i, ret;
+	if (!max_threads)
+		tq->max_threads = online_cpus();
+	else
+		tq->max_threads = max_threads;
+
+	pthread_mutex_init(&tq->mutex, NULL);
+	pthread_cond_init(&tq->cond_non_empty, NULL);
+
+	tq->threads = xmalloc(tq->max_threads * sizeof(pthread_t));
+
+	tq->queued_tasks = 0;
+	tq->first = NULL;
+	tq->last = NULL;
+
+	setup_main_thread();
+
+	for (i = 0; i < tq->max_threads; i++) {
+		ret = pthread_create(&tq->threads[i], 0, &dispatcher, tq);
+		if (ret)
+			die("unable to create thread: %s", strerror(ret));
+	}
+
+	tq->early_return = 0;
+
+	return tq;
+}
+
+void add_task(struct task_queue *tq,
+	      int (*fct)(struct task_queue *tq, void *task),
+	      void *task)
+{
+	struct job_list *job_list;
+
+	job_list = xmalloc(sizeof(*job_list));
+	job_list->task = task;
+	job_list->fct = fct;
+	job_list->next = NULL;
+
+	pthread_mutex_lock(&tq->mutex);
+
+	if (!tq->last) {
+		tq->last = job_list;
+		tq->first = tq->last;
+	} else {
+		tq->last->next = job_list;
+		tq->last = tq->last->next;
+	}
+	tq->queued_tasks++;
+
+	pthread_mutex_unlock(&tq->mutex);
+	pthread_cond_signal(&tq->cond_non_empty);
+}
+
+int finish_task_queue(struct task_queue *tq, void (*fct)(struct task_queue *tq))
+{
+	int ret;
+	int i;
+
+	tq->finish_function = fct;
+
+	for (i = 0; i < tq->max_threads; i++)
+		add_task(tq, NULL, NULL);
+
+	for (i = 0; i < tq->max_threads; i++)
+		pthread_join(tq->threads[i], 0);
+
+	pthread_mutex_destroy(&tq->mutex);
+	pthread_cond_destroy(&tq->cond_non_empty);
+
+	if (tq->first)
+		die("BUG: internal error with queuing jobs for threads");
+
+	free(tq->threads);
+	ret = tq->early_return;
+
+	free(tq);
+	return ret;
+}
+#else /* NO_PTHREADS */
+
+struct task_queue {
+	int early_return;
+};
+
+struct task_queue *create_task_queue(unsigned max_threads)
+{
+	struct task_queue *tq = xmalloc(sizeof(*tq));
+
+	tq->early_return = 0;
+}
+
+void add_task(struct task_queue *tq,
+	      int (*fct)(struct task_queue *tq, void *task),
+	      void *task)
+{
+	if (tq->early_return)
+		return;
+
+	tq->early_return |= fct(tq, task);
+}
+
+int finish_task_queue(struct task_queue *tq, void (*fct)(struct task_queue *tq))
+{
+	int ret = tq->early_return;
+	free(tq);
+	return ret;
+}
+#endif
diff --git a/thread-utils.h b/thread-utils.h
index d9a769d..f41cfb1 100644
--- a/thread-utils.h
+++ b/thread-utils.h
@@ -12,4 +12,39 @@ extern int init_recursive_mutex(pthread_mutex_t*);
 #define online_cpus() 1
 
 #endif
+
+/*
+ * Creates a struct `task_queue`, which holds a list of tasks. Up to
+ * `max_threads` threads are active to process the enqueued tasks
+ * processing the tasks in a first in first out order.
+ *
+ * If `max_threads` is zero the number of cores available will be used.
+ *
+ * Currently this only works in environments with pthreads, in other
+ * environments, the task will be processed sequentially in `add_task`.
+ */
+struct task_queue *create_task_queue(unsigned max_threads);
+
+/*
+ * The function and data are put into the task queue.
+ *
+ * The function `fct` must not be NULL, as that's used internally
+ * in `finish_task_queue` to signal shutdown. If the return code
+ * of `fct` is unequal to 0, the tasks will stop eventually,
+ * the current parallel tasks will be flushed out.
+ */
+void add_task(struct task_queue *tq,
+	      int (*fct)(struct task_queue *tq, void *task),
+	      void *task);
+
+/*
+ * Waits for all tasks to be done and frees the object. The return code
+ * is zero if all enqueued tasks were processed.
+ *
+ * The function `fct` is called once in each thread after the last task
+ * for that thread was processed. If no thread local cleanup needs to be
+ * performed, pass NULL.
+ */
+int finish_task_queue(struct task_queue *tq, void (*fct)(struct task_queue *tq));
+
 #endif /* THREAD_COMPAT_H */
-- 
2.5.0.264.g784836d

[PATCH 3/5] submodule: helper to run foreach in parallel

[Stefan Beller]

Similar to `git submodule foreach` the new command
`git submodule foreach_parallel` will run a command
on each submodule.

The commands are run in parallel up to the number of
cores by default, or you can specify '-j 4' tun just
run with 4 threads for example.

One major difference to `git submodule foreach` is the
handling of input and output to the commands. Because
of the parallel nature of the execution it is not trivial
how to schedule the std{in,out,err} channel for submodule
the command is run in. So in this patch there is no
support for stdin.

The goal of the output for std{out, err} is to look like
the single threaded version as much as possible, so
stdout and stderr from one submodule operation are
buffered together in one single channel and output
together when the output is allowed.

To do that, we'll have a mutex for the output, which
each thread will try to acquire and directly pipe their
output to the standard output if they are lucky to
get the mutex.

If they do not have the mutex each thread will buffer
their output.

Example:
Let's assume we have 5 submodules A,B,C,D,E and the
operation on each submodule takes a different amount
of time (say `git fetch`), then the output of
`git submodule foreach` might look like this:

 time -->
 output: |---A---|   |-B-|   |----C-----------|   |-D-|   |-E-|

When we schedule these threads into two threads, a schedule
and sample output over time may look like this:

thread 1: |---A---|   |-D-|   |-E-|
thread 2: |-B-|   |----C-----------|

output:   |---A---| B |----C-------| E D

So A will be perceived as it would run normally in
the single threaded version of foreach. As B has finished
by the time the mutex becomes available, the whole buffer
will just be dumped into the standard output. This will be
perceived by the user as just a 'very fast' operation of B.
Once that is done, C takes the mutex, and flushes the piled
up buffer to standard output. In case the subcommand is a
git command, we have a progress display, which will just
look like the first half of C happend really quickly.

Notice how E and D are put out in a different order than the
original as the new parallel foreach doesn't care about the
order.

So this way of output is really good for human consumption
and not for machine consumption as you always see the progress,
but it is not easy to tell which output comes from which
command as there is no indication other than displaying
"Entering <submodule path>" for each beginning section of
output.

Maybe we want to integrate the unthreaded foreach eventually
into the new code base in C and have special cases for that,
such as accepting stdin again.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/submodule--helper.c | 160 +++++++++++++++++++++++++++++++++++++++++++-
 git-submodule.sh            |  11 ++-
 2 files changed, 168 insertions(+), 3 deletions(-)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index f11fb9c..2c06f28 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -8,8 +8,11 @@
 #include "submodule.h"
 #include "submodule-config.h"
 #include "string-list.h"
+#include "thread-utils.h"
 #include "run-command.h"
-
+#ifndef NO_PTHREADS
+#include <semaphore.h>
+#endif
 static const struct cache_entry **ce_entries;
 static int ce_alloc, ce_used;
 static const char *alternative_path;
@@ -279,6 +282,155 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 	return 0;
 }
 
+struct submodule_args {
+	const char *name;
+	const char *path;
+	const char *sha1;
+	const char *toplevel;
+	const char *prefix;
+	const char **cmd;
+	pthread_mutex_t *mutex;
+};
+
+int run_cmd_submodule(struct task_queue *aq, void *task)
+{
+	int i, lock_acquired = 0;
+	struct submodule_args *args = task;
+	struct strbuf out = STRBUF_INIT;
+	struct strbuf sb = STRBUF_INIT;
+	struct child_process *cp = xmalloc(sizeof(*cp));
+	char buf[1024];
+
+	strbuf_addf(&out, N_("Entering %s\n"), relative_path(args->path, args->prefix, &sb));
+
+	child_process_init(cp);
+	argv_array_pushv(&cp->args, args->cmd);
+
+	argv_array_pushf(&cp->env_array, "name=%s", args->name);
+	argv_array_pushf(&cp->env_array, "path=%s", args->path);
+	argv_array_pushf(&cp->env_array, "sha1=%s", args->sha1);
+	argv_array_pushf(&cp->env_array, "toplevel=%s", args->toplevel);
+
+	for (i = 0; local_repo_env[i]; i++)
+		argv_array_push(&cp->env_array, local_repo_env[i]);
+
+	cp->no_stdin = 1;
+	cp->out = 0;
+	cp->err = -1;
+	cp->dir = args->path;
+	cp->stdout_to_stderr = 1;
+	cp->use_shell = 1;
+
+	if (start_command(cp)) {
+		die("Could not start command");
+		for (i = 0; cp->args.argv; i++)
+			fprintf(stderr, "%s\n", cp->args.argv[i]);
+	}
+
+	while (1) {
+		ssize_t len = xread(cp->err, buf, sizeof(buf));
+		if (len < 0)
+			die("Read from child failed");
+		else if (len == 0)
+			break;
+		else {
+			strbuf_add(&out, buf, len);
+		}
+		if (!pthread_mutex_trylock(args->mutex))
+			lock_acquired = 1;
+		if (lock_acquired) {
+			fputs(out.buf, stderr);
+			strbuf_reset(&out);
+		}
+	}
+	if (finish_command(cp))
+		die("command died with error");
+
+	if (!lock_acquired)
+		pthread_mutex_lock(args->mutex);
+
+	fputs(out.buf, stderr);
+	pthread_mutex_unlock(args->mutex);
+
+	return 0;
+}
+
+int module_foreach_parallel(int argc, const char **argv, const char *prefix)
+{
+	int i, recursive = 0, number_threads = 0, quiet = 0;
+	static struct pathspec pathspec;
+	struct strbuf sb = STRBUF_INIT;
+	struct task_queue *aq;
+	char **cmd;
+	const char **nullargv = {NULL};
+	pthread_mutex_t mutex;
+
+	struct option module_update_options[] = {
+		OPT_STRING(0, "prefix", &alternative_path,
+			   N_("path"),
+			   N_("alternative anchor for relative paths")),
+		OPT_STRING(0, "cmd", &cmd,
+			   N_("string"),
+			   N_("command to run")),
+		OPT_BOOL('r', "--recursive", &recursive,
+			 N_("Recurse into nexted submodules")),
+		OPT_INTEGER('j', "jobs", &number_threads,
+			    N_("Recurse into nexted submodules")),
+		OPT__QUIET(&quiet, N_("Suppress output")),
+		OPT_END()
+	};
+
+	static const char * const git_submodule_helper_usage[] = {
+		N_("git submodule--helper foreach [--prefix=<path>] [<path>...]"),
+		NULL
+	};
+
+	argc = parse_options(argc, argv, prefix, module_update_options,
+			     git_submodule_helper_usage, 0);
+
+	if (module_list_compute(0, nullargv, NULL, &pathspec) < 0)
+		return 1;
+
+	gitmodules_config();
+
+	pthread_mutex_init(&mutex, NULL);
+	aq = create_task_queue(number_threads);
+
+	for (i = 0; i < ce_used; i++) {
+		const struct submodule *sub;
+		const struct cache_entry *ce = ce_entries[i];
+		struct submodule_args *args = malloc(sizeof(*args));
+
+		if (ce_stage(ce))
+			args->sha1 = xstrdup(sha1_to_hex(null_sha1));
+		else
+			args->sha1 = xstrdup(sha1_to_hex(ce->sha1));
+
+		strbuf_reset(&sb);
+		strbuf_addf(&sb, "%s/.git", ce->name);
+		if (!file_exists(sb.buf)) {
+			free(args);
+			continue;
+		}
+
+		args->path = ce->name;
+		sub = submodule_from_path(null_sha1, args->path);
+		if (!sub)
+			die("No submodule mapping found in .gitmodules for path '%s'", args->path);
+
+		args->name = sub->name;
+		args->toplevel = xgetcwd();
+		args->cmd = argv;
+		args->mutex = &mutex;
+		args->prefix = alternative_path;
+		add_task(aq, run_cmd_submodule, args);
+	}
+
+	finish_task_queue(aq, NULL);
+	pthread_mutex_destroy(&mutex);
+	return 0;
+}
+
 int cmd_submodule__helper(int argc, const char **argv, const char *prefix)
 {
 	if (argc < 2)
@@ -293,6 +445,10 @@ int cmd_submodule__helper(int argc, const char **argv, const char *prefix)
 	if (!strcmp(argv[1], "module_clone"))
 		return module_clone(argc - 1, argv + 1, prefix);
 
+	if (!strcmp(argv[1], "foreach_parallel"))
+		return module_foreach_parallel(argc - 1, argv + 1, prefix);
+
 usage:
-	usage("git submodule--helper [module_list module_name module_clone]\n");
+	fprintf(stderr, "%s", argv[1]);
+	usage("git submodule--helper [module_list module_name module_clone foreach_parallel]\n");
 }
diff --git a/git-submodule.sh b/git-submodule.sh
index fb5155e..f06488a 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -431,6 +431,15 @@ cmd_foreach()
 }
 
 #
+# Execute an arbitrary command sequence in each checked out
+# submodule in parallel.
+#
+cmd_foreach_parallel()
+{
+	git submodule--helper foreach_parallel --prefix "$wt_prefix" $@
+}
+
+#
 # Register submodules in .git/config
 #
 # $@ = requested paths (default to all)
@@ -1225,7 +1234,7 @@ cmd_sync()
 while test $# != 0 && test -z "$command"
 do
 	case "$1" in
-	add | foreach | init | deinit | update | status | summary | sync)
+	add | foreach | foreach_parallel | init | deinit | update | status | summary | sync)
 		command=$1
 		;;
 	-q|--quiet)
-- 
2.5.0.264.g784836d

[PATCH 4/5] index-pack: Use the new worker pool

[Stefan Beller]

This demonstrates how the new threading API may be used.
There is no change in the workflow, just using the new
threading API instead of keeping track of the pthreads
ourselves.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/index-pack.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 3f10840..187b281 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -1075,7 +1075,7 @@ static void resolve_base(struct object_entry *obj)
 }
 
 #ifndef NO_PTHREADS
-static void *threaded_second_pass(void *data)
+static int threaded_second_pass(struct task_queue *tq, void *data)
 {
 	set_thread_data(data);
 	for (;;) {
@@ -1096,7 +1096,7 @@ static void *threaded_second_pass(void *data)
 
 		resolve_base(&objects[i]);
 	}
-	return NULL;
+	return 0;
 }
 #endif
 
@@ -1195,18 +1195,19 @@ static void resolve_deltas(void)
 					  nr_ref_deltas + nr_ofs_deltas);
 
 #ifndef NO_PTHREADS
-	nr_dispatched = 0;
+
 	if (nr_threads > 1 || getenv("GIT_FORCE_THREADS")) {
+		struct task_queue *tq;
+		nr_dispatched = 0;
 		init_thread();
-		for (i = 0; i < nr_threads; i++) {
-			int ret = pthread_create(&thread_data[i].thread, NULL,
-						 threaded_second_pass, thread_data + i);
-			if (ret)
-				die(_("unable to create thread: %s"),
-				    strerror(ret));
-		}
+
+		tq = create_task_queue(nr_threads);
 		for (i = 0; i < nr_threads; i++)
-			pthread_join(thread_data[i].thread, NULL);
+			add_task(tq, threaded_second_pass, thread_data + i);
+
+		if (finish_task_queue(tq, NULL))
+			die("Not all threads have finished");
+
 		cleanup_thread();
 		return;
 	}
-- 
2.5.0.264.g784836d

[PATCH 5/5] pack-objects: Use new worker pool

[Stefan Beller]

Before we had <n> threads doing the delta finding work, and the main thread
was load balancing the threads, i.e. moving work from a thread with a large
amount left to an idle thread whenever such a situation arose.

This moves the load balancing to the threads themselves. As soon as one
thread is done working it will look at its peer threads and will pickup
half the work load from the thread with the largest pending load.

By having the load balancing as part of the threads, the locking and
communication model becomes easier, such that we don't need so many
mutexes any more.

It also demonstrates the usage of the new threading pool being easily
applied in different situations.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/pack-objects.c | 175 ++++++++++++++++---------------------------------
 1 file changed, 57 insertions(+), 118 deletions(-)

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 62cc16d..f46d2df 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -17,6 +17,7 @@
 #include "pack-objects.h"
 #include "progress.h"
 #include "refs.h"
+#include "run-command.h"
 #include "streaming.h"
 #include "thread-utils.h"
 #include "pack-bitmap.h"
@@ -1887,26 +1888,12 @@ static void try_to_free_from_threads(size_t size)
 
 static try_to_free_t old_try_to_free_routine;
 
-/*
- * The main thread waits on the condition that (at least) one of the workers
- * has stopped working (which is indicated in the .working member of
- * struct thread_params).
- * When a work thread has completed its work, it sets .working to 0 and
- * signals the main thread and waits on the condition that .data_ready
- * becomes 1.
- */
-
 struct thread_params {
-	pthread_t thread;
 	struct object_entry **list;
 	unsigned list_size;
 	unsigned remaining;
 	int window;
 	int depth;
-	int working;
-	int data_ready;
-	pthread_mutex_t mutex;
-	pthread_cond_t cond;
 	unsigned *processed;
 };
 
@@ -1933,7 +1920,52 @@ static void cleanup_threaded_search(void)
 	pthread_mutex_destroy(&progress_mutex);
 }
 
-static void *threaded_find_deltas(void *arg)
+static struct thread_params *p;
+
+static void threaded_split_largest_workload(struct thread_params *target)
+{
+	int i;
+
+	struct object_entry **list;
+	struct thread_params *victim = NULL;
+	unsigned sub_size = 0;
+
+	/* Find a victim */
+	progress_lock();
+	for (i = 0; i < delta_search_threads; i++)
+		if (p[i].remaining > 2*window &&
+		    (!victim || victim->remaining < p[i].remaining))
+			victim = &p[i];
+
+	if (victim) {
+		sub_size = victim->remaining / 2;
+		list = victim->list + victim->list_size - sub_size;
+		while (sub_size && list[0]->hash &&
+		       list[0]->hash == list[-1]->hash) {
+			list++;
+			sub_size--;
+		}
+		if (!sub_size) {
+			/*
+			 * It is possible for some "paths" to have
+			 * so many objects that no hash boundary
+			 * might be found.  Let's just steal the
+			 * exact half in that case.
+			 */
+			sub_size = victim->remaining / 2;
+			list -= sub_size;
+		}
+		victim->list_size -= sub_size;
+		victim->remaining -= sub_size;
+
+		target->list = list;
+		target->list_size = sub_size;
+		target->remaining = sub_size;
+	}
+	progress_unlock();
+}
+
+static int threaded_find_deltas(struct task_queue *tq, void *arg)
 {
 	struct thread_params *me = arg;
 
@@ -1941,34 +1973,17 @@ static void *threaded_find_deltas(void *arg)
 		find_deltas(me->list, &me->remaining,
 			    me->window, me->depth, me->processed);
 
-		progress_lock();
-		me->working = 0;
-		pthread_cond_signal(&progress_cond);
-		progress_unlock();
-
-		/*
-		 * We must not set ->data_ready before we wait on the
-		 * condition because the main thread may have set it to 1
-		 * before we get here. In order to be sure that new
-		 * work is available if we see 1 in ->data_ready, it
-		 * was initialized to 0 before this thread was spawned
-		 * and we reset it to 0 right away.
-		 */
-		pthread_mutex_lock(&me->mutex);
-		while (!me->data_ready)
-			pthread_cond_wait(&me->cond, &me->mutex);
-		me->data_ready = 0;
-		pthread_mutex_unlock(&me->mutex);
+		threaded_split_largest_workload(me);
 	}
-	/* leave ->working 1 so that this doesn't get more work assigned */
-	return NULL;
+
+	return 0;
 }
 
 static void ll_find_deltas(struct object_entry **list, unsigned list_size,
 			   int window, int depth, unsigned *processed)
 {
-	struct thread_params *p;
-	int i, ret, active_threads = 0;
+	struct task_queue *tq;
+	int i;
 
 	init_threaded_search();
 
@@ -1980,8 +1995,11 @@ static void ll_find_deltas(struct object_entry **list, unsigned list_size,
 	if (progress > pack_to_stdout)
 		fprintf(stderr, "Delta compression using up to %d threads.\n",
 				delta_search_threads);
+
 	p = xcalloc(delta_search_threads, sizeof(*p));
 
+	tq = create_task_queue(delta_search_threads);
+
 	/* Partition the work amongst work threads. */
 	for (i = 0; i < delta_search_threads; i++) {
 		unsigned sub_size = list_size / (delta_search_threads - i);
@@ -1993,8 +2011,6 @@ static void ll_find_deltas(struct object_entry **list, unsigned list_size,
 		p[i].window = window;
 		p[i].depth = depth;
 		p[i].processed = processed;
-		p[i].working = 1;
-		p[i].data_ready = 0;
 
 		/* try to split chunks on "path" boundaries */
 		while (sub_size && sub_size < list_size &&
@@ -2008,87 +2024,10 @@ static void ll_find_deltas(struct object_entry **list, unsigned list_size,
 
 		list += sub_size;
 		list_size -= sub_size;
+		add_task(tq, threaded_find_deltas, &p[i]);
 	}
 
-	/* Start work threads. */
-	for (i = 0; i < delta_search_threads; i++) {
-		if (!p[i].list_size)
-			continue;
-		pthread_mutex_init(&p[i].mutex, NULL);
-		pthread_cond_init(&p[i].cond, NULL);
-		ret = pthread_create(&p[i].thread, NULL,
-				     threaded_find_deltas, &p[i]);
-		if (ret)
-			die("unable to create thread: %s", strerror(ret));
-		active_threads++;
-	}
-
-	/*
-	 * Now let's wait for work completion.  Each time a thread is done
-	 * with its work, we steal half of the remaining work from the
-	 * thread with the largest number of unprocessed objects and give
-	 * it to that newly idle thread.  This ensure good load balancing
-	 * until the remaining object list segments are simply too short
-	 * to be worth splitting anymore.
-	 */
-	while (active_threads) {
-		struct thread_params *target = NULL;
-		struct thread_params *victim = NULL;
-		unsigned sub_size = 0;
-
-		progress_lock();
-		for (;;) {
-			for (i = 0; !target && i < delta_search_threads; i++)
-				if (!p[i].working)
-					target = &p[i];
-			if (target)
-				break;
-			pthread_cond_wait(&progress_cond, &progress_mutex);
-		}
-
-		for (i = 0; i < delta_search_threads; i++)
-			if (p[i].remaining > 2*window &&
-			    (!victim || victim->remaining < p[i].remaining))
-				victim = &p[i];
-		if (victim) {
-			sub_size = victim->remaining / 2;
-			list = victim->list + victim->list_size - sub_size;
-			while (sub_size && list[0]->hash &&
-			       list[0]->hash == list[-1]->hash) {
-				list++;
-				sub_size--;
-			}
-			if (!sub_size) {
-				/*
-				 * It is possible for some "paths" to have
-				 * so many objects that no hash boundary
-				 * might be found.  Let's just steal the
-				 * exact half in that case.
-				 */
-				sub_size = victim->remaining / 2;
-				list -= sub_size;
-			}
-			target->list = list;
-			victim->list_size -= sub_size;
-			victim->remaining -= sub_size;
-		}
-		target->list_size = sub_size;
-		target->remaining = sub_size;
-		target->working = 1;
-		progress_unlock();
-
-		pthread_mutex_lock(&target->mutex);
-		target->data_ready = 1;
-		pthread_cond_signal(&target->cond);
-		pthread_mutex_unlock(&target->mutex);
-
-		if (!sub_size) {
-			pthread_join(target->thread, NULL);
-			pthread_cond_destroy(&target->cond);
-			pthread_mutex_destroy(&target->mutex);
-			active_threads--;
-		}
-	}
+	finish_task_queue(tq, NULL);
 	cleanup_threaded_search();
 	free(p);
 }
-- 
2.5.0.264.g784836d

Re: [PATCH 1/5] submodule: implement `module_clone` as a builtin helper

[Johannes Schindelin]

Hi Stefan,

thank you so much for doing this. `git submodule` is really, really slow on Windows...

On 2015-08-27 02:52, Stefan Beller wrote:

> diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
> index 4b32a3c..f11fb9c 100644
> --- a/builtin/submodule--helper.c
> +++ b/builtin/submodule--helper.c
> [...]
> +
> +/*
> + * Clone a submodule
> + *
> + * $1 = submodule path
> + * $2 = submodule name
> + * $3 = URL to clone
> + * $4 = reference repository to reuse (empty for independent)
> + * $5 = depth argument for shallow clones (empty for deep)

I think this description is now safely obsolete and can be deleted: you introduced explicit options like --depth to avoid the "magic" of positional parameters.

> +static int module_clone(int argc, const char **argv, const char *prefix)
> +{
> +	const char *path = NULL, *name = NULL, *url = NULL, *reference =
> NULL, *depth = NULL;

This line is a little long ;-)

> @@ -135,6 +290,9 @@ int cmd_submodule__helper(int argc, const char
> **argv, const char *prefix)
>  	if (!strcmp(argv[1], "module_name"))
>  		return module_name(argc - 2, argv + 2, prefix);
>  
> +	if (!strcmp(argv[1], "module_clone"))
> +		return module_clone(argc - 1, argv + 1, prefix);
> +
>  usage:
> -	usage("git submodule--helper [module_list module_name]\n");
> +	usage("git submodule--helper [module_list module_name module_clone]\n");

Was the convention not to use ( ... | ... | ... )?

Thanks,
Dscho

Re: [PATCH 2/5] thread-utils: add a threaded task queue

[Johannes Schindelin]

Hi Stefan,

On 2015-08-27 02:52, Stefan Beller wrote:

> diff --git a/run-command.c b/run-command.c
> index 28e1d55..cb15cd9 100644
> --- a/run-command.c
> +++ b/run-command.c
> @@ -668,6 +668,22 @@ int git_atexit(void (*handler)(void))
>  
>  #endif
>  
> +void setup_main_thread(void)
> [...]
>
> diff --git a/thread-utils.c b/thread-utils.c
> index a2135e0..b45ab92 100644
> --- a/thread-utils.c
> +++ b/thread-utils.c
> [...]
> +/* FIXME: deduplicate this code with run-command.c */
> +static void setup_main_thread(void)

Do you remember off-hand why the code could not be moved to thread-utils.c wholesale? Just curious.

> +#else /* NO_PTHREADS */
> +
> +struct task_queue {
> +	int early_return;
> +};
> +
> +struct task_queue *create_task_queue(unsigned max_threads)
> +{
> +	struct task_queue *tq = xmalloc(sizeof(*tq));
> +
> +	tq->early_return = 0;
> +}
> +
> +void add_task(struct task_queue *tq,
> +	      int (*fct)(struct task_queue *tq, void *task),

Might make sense to typedef this... Maybe task_t?

> +	      void *task)
> +{
> +	if (tq->early_return)
> +		return;

Ah, so "early_return" actually means "interrupted" or "canceled"?

I guess I will have to set aside some time to wrap my head around the way tasks are handled here, in particular how the two `early_return` variables (`dispatcher()`'s local variable and the field in the `task_queue`) interact.

Thanks!
Dscho

Re: [PATCH 2/5] thread-utils: add a threaded task queue

[Stefan Beller]

On Thu, Aug 27, 2015 at 5:59 AM, Johannes Schindelin
<johannes.schindelin@gmx.de> wrote:
> Hi Stefan,
>
> On 2015-08-27 02:52, Stefan Beller wrote:
>
>> diff --git a/run-command.c b/run-command.c
>> index 28e1d55..cb15cd9 100644
>> --- a/run-command.c
>> +++ b/run-command.c
>> @@ -668,6 +668,22 @@ int git_atexit(void (*handler)(void))
>>
>>  #endif
>>
>> +void setup_main_thread(void)
>> [...]
>>
>> diff --git a/thread-utils.c b/thread-utils.c
>> index a2135e0..b45ab92 100644
>> --- a/thread-utils.c
>> +++ b/thread-utils.c
>> [...]
>> +/* FIXME: deduplicate this code with run-command.c */
>> +static void setup_main_thread(void)
>
> Do you remember off-hand why the code could not be moved to thread-utils.c wholesale? Just curious.

The code in run-command has a few things regarding the struct async
handling in there,
which we don't  need/want. I just realized there is some duplicate
code, but I couldn't cut
it clearly out.

>
>> +#else /* NO_PTHREADS */
>> +
>> +struct task_queue {
>> +     int early_return;
>> +};
>> +
>> +struct task_queue *create_task_queue(unsigned max_threads)
>> +{
>> +     struct task_queue *tq = xmalloc(sizeof(*tq));
>> +
>> +     tq->early_return = 0;
>> +}
>> +
>> +void add_task(struct task_queue *tq,
>> +           int (*fct)(struct task_queue *tq, void *task),
>
> Might make sense to typedef this... Maybe task_t?
>
>> +           void *task)
>> +{
>> +     if (tq->early_return)
>> +             return;
>
> Ah, so "early_return" actually means "interrupted" or "canceled"?

The early_return is meant to return early in case of an error in some thread.
In the threaded version, the `dispatcher` is executed in each thread.
It gets its
new tasks via `next_task`, which takes the early_return value from the thread,
ORs it into the early_return of the task queue (which all threads have
access to).
So by the ORing into the task queues early_return the signal to abort
early is propagated to a place all threads have access to. And in case
that value is
set, the `next_task` will return NULL as an indication to cleanup and
pthread_exit.

>
> I guess I will have to set aside some time to wrap my head around the way tasks are handled here, in particular how the two `early_return` variables (`dispatcher()`'s local variable and the field in the `task_queue`) interact.
>
> Thanks!
> Dscho

Re: [PATCH 1/5] submodule: implement `module_clone` as a builtin helper

[Stefan Beller]

On Thu, Aug 27, 2015 at 5:36 AM, Johannes Schindelin
<johannes.schindelin@gmx.de> wrote:
> Hi Stefan,
>
> thank you so much for doing this. `git submodule` is really, really slow on Windows...
>
> On 2015-08-27 02:52, Stefan Beller wrote:
>
>> diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
>> index 4b32a3c..f11fb9c 100644
>> --- a/builtin/submodule--helper.c
>> +++ b/builtin/submodule--helper.c
>> [...]
>> +
>> +/*
>> + * Clone a submodule
>> + *
>> + * $1 = submodule path
>> + * $2 = submodule name
>> + * $3 = URL to clone
>> + * $4 = reference repository to reuse (empty for independent)
>> + * $5 = depth argument for shallow clones (empty for deep)
>
> I think this description is now safely obsolete and can be deleted: you introduced explicit options like --depth to avoid the "magic" of positional parameters.

ok I'll remove that in a reroll.

>
>> +static int module_clone(int argc, const char **argv, const char *prefix)
>> +{
>> +     const char *path = NULL, *name = NULL, *url = NULL, *reference =
>> NULL, *depth = NULL;
>
> This line is a little long ;-)

fixed in reroll.

>
>> @@ -135,6 +290,9 @@ int cmd_submodule__helper(int argc, const char
>> **argv, const char *prefix)
>>       if (!strcmp(argv[1], "module_name"))
>>               return module_name(argc - 2, argv + 2, prefix);
>>
>> +     if (!strcmp(argv[1], "module_clone"))
>> +             return module_clone(argc - 1, argv + 1, prefix);
>> +
>>  usage:
>> -     usage("git submodule--helper [module_list module_name]\n");
>> +     usage("git submodule--helper [module_list module_name module_clone]\n");
>
> Was the convention not to use ( ... | ... | ... )?

git tag puts it as
    usage: git tag [-a | -s | -u <key-id>]

I looked at other --helper (git-difftool--helper which has no help to
be invoced on the command line
and git-bisect--helper which doesn't have the problem as the help is clear).

So I'll go with [brackets | separated | by | pipes | inside ] then,
just as git-tag.

>
> Thanks,
> Dscho

Re: [PATCH 2/5] thread-utils: add a threaded task queue

[Junio C Hamano]

Johannes Schindelin <johannes.schindelin@gmx.de> writes:

>> +void add_task(struct task_queue *tq,
>> +	      int (*fct)(struct task_queue *tq, void *task),
>
> Might make sense to typedef this... Maybe task_t?

Let's not introduce user defined type that ends with _t that is seen
globally.

>> +	      void *task)
>> +{
>> +	if (tq->early_return)
>> +		return;
>
> Ah, so "early_return" actually means "interrupted" or "canceled"?
>
> I guess I will have to set aside some time to wrap my head around the
> way tasks are handled here, in particular how the two `early_return`
> variables (`dispatcher()`'s local variable and the field in the
> task_queue`) interact.

We had a very similar conversation in $gmane/276324 as the
early-return and get_task interaction was not quite intuitive.

I thought Stefan said something about this part of the logic being
unreadable and needs rework.  Perhaps that will come in the next
reroll, or something?

I tend to agree with you that interrupted or cancelled would be a
good name for this thing; at least it would help understanding what
is going on than "early-return".

Thanks.