diff mbox series

[15/23] fsmonitor-fs-listen-macos: implement FSEvent listener on MacOS

Message ID d469d3f02e335292f4debd55ff67184b2b91b04f.1617291666.git.gitgitgadget@gmail.com (mailing list archive)
State New
Headers show
Series Builtin FSMonitor Feature | expand

Commit Message

Jeff Hostetler April 1, 2021, 3:40 p.m. UTC
From: Jeff Hostetler <jeffhost@microsoft.com>

Implement file system event listener on MacOS using FSEvent,
CoreFoundation, and CoreServices.

Co-authored-by: Kevin Willford <Kevin.Willford@microsoft.com>
Co-authored-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
---
 compat/fsmonitor/fsmonitor-fs-listen-macos.c | 368 +++++++++++++++++++
 1 file changed, 368 insertions(+)

Comments

Derrick Stolee April 27, 2021, 6:35 p.m. UTC | #1
On 4/1/2021 11:40 AM, Jeff Hostetler via GitGitGadget wrote:
> From: Jeff Hostetler <jeffhost@microsoft.com>
> 
> Implement file system event listener on MacOS using FSEvent,
> CoreFoundation, and CoreServices.

Again, I'm not sure if we _should_ be including URLs to
documentation in our messages, but here are some I found helpful:

[1] https://developer.apple.com/library/archive/documentation/Darwin/Conceptual/FSEvents_ProgGuide/UsingtheFSEventsFramework/UsingtheFSEventsFramework.html
[2] https://developer.apple.com/documentation/corefoundation/1541796-cfrunloopstop
[3] https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/Multithreading/RunLoopManagement/RunLoopManagement.html

> Co-authored-by: Kevin Willford <Kevin.Willford@microsoft.com>
> Co-authored-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
> ---
>  compat/fsmonitor/fsmonitor-fs-listen-macos.c | 368 +++++++++++++++++++
>  1 file changed, 368 insertions(+)
> 
> diff --git a/compat/fsmonitor/fsmonitor-fs-listen-macos.c b/compat/fsmonitor/fsmonitor-fs-listen-macos.c
> index bec5130d9e1d..e055fb579cc4 100644
> --- a/compat/fsmonitor/fsmonitor-fs-listen-macos.c
> +++ b/compat/fsmonitor/fsmonitor-fs-listen-macos.c
> @@ -97,20 +97,388 @@ void FSEventStreamRelease(FSEventStreamRef stream);
>  #include "cache.h"
>  #include "fsmonitor.h"
>  #include "fsmonitor-fs-listen.h"
> +#include "fsmonitor--daemon.h"
> +
> +struct fsmonitor_daemon_backend_data
> +{
> +	CFStringRef cfsr_worktree_path;
> +	CFStringRef cfsr_gitdir_path;
> +
> +	CFArrayRef cfar_paths_to_watch;
> +	int nr_paths_watching;
> +
> +	FSEventStreamRef stream;
> +
> +	CFRunLoopRef rl;
> +
> +	enum shutdown_style {
> +		SHUTDOWN_EVENT = 0,
> +		FORCE_SHUTDOWN,
> +		FORCE_ERROR_STOP,
> +	} shutdown_style;
> +
> +	unsigned int stream_scheduled:1;
> +	unsigned int stream_started:1;
> +};
> +
> +static void log_flags_set(const char *path, const FSEventStreamEventFlags flag)
> +{
> +	struct strbuf msg = STRBUF_INIT;

Before going through these ifs and constructing a string, it
might be a good idea to check if the trace event will actually
be sent somewhere. If the logging method is switched to a
trace2 method, then up here we can do:

	if (!trace2_is_enabled())
		return;

> +	if (flag & kFSEventStreamEventFlagMustScanSubDirs)
> +		strbuf_addstr(&msg, "MustScanSubDirs|");
> +	if (flag & kFSEventStreamEventFlagUserDropped)
> +		strbuf_addstr(&msg, "UserDropped|");
> +	if (flag & kFSEventStreamEventFlagKernelDropped)
> +		strbuf_addstr(&msg, "KernelDropped|");
> +	if (flag & kFSEventStreamEventFlagEventIdsWrapped)
> +		strbuf_addstr(&msg, "EventIdsWrapped|");
> +	if (flag & kFSEventStreamEventFlagHistoryDone)
> +		strbuf_addstr(&msg, "HistoryDone|");
> +	if (flag & kFSEventStreamEventFlagRootChanged)
> +		strbuf_addstr(&msg, "RootChanged|");
> +	if (flag & kFSEventStreamEventFlagMount)
> +		strbuf_addstr(&msg, "Mount|");
> +	if (flag & kFSEventStreamEventFlagUnmount)
> +		strbuf_addstr(&msg, "Unmount|");
> +	if (flag & kFSEventStreamEventFlagItemChangeOwner)
> +		strbuf_addstr(&msg, "ItemChangeOwner|");
> +	if (flag & kFSEventStreamEventFlagItemCreated)
> +		strbuf_addstr(&msg, "ItemCreated|");
> +	if (flag & kFSEventStreamEventFlagItemFinderInfoMod)
> +		strbuf_addstr(&msg, "ItemFinderInfoMod|");
> +	if (flag & kFSEventStreamEventFlagItemInodeMetaMod)
> +		strbuf_addstr(&msg, "ItemInodeMetaMod|");
> +	if (flag & kFSEventStreamEventFlagItemIsDir)
> +		strbuf_addstr(&msg, "ItemIsDir|");
> +	if (flag & kFSEventStreamEventFlagItemIsFile)
> +		strbuf_addstr(&msg, "ItemIsFile|");
> +	if (flag & kFSEventStreamEventFlagItemIsHardlink)
> +		strbuf_addstr(&msg, "ItemIsHardlink|");
> +	if (flag & kFSEventStreamEventFlagItemIsLastHardlink)
> +		strbuf_addstr(&msg, "ItemIsLastHardlink|");
> +	if (flag & kFSEventStreamEventFlagItemIsSymlink)
> +		strbuf_addstr(&msg, "ItemIsSymlink|");
> +	if (flag & kFSEventStreamEventFlagItemModified)
> +		strbuf_addstr(&msg, "ItemModified|");
> +	if (flag & kFSEventStreamEventFlagItemRemoved)
> +		strbuf_addstr(&msg, "ItemRemoved|");
> +	if (flag & kFSEventStreamEventFlagItemRenamed)
> +		strbuf_addstr(&msg, "ItemRenamed|");
> +	if (flag & kFSEventStreamEventFlagItemXattrMod)
> +		strbuf_addstr(&msg, "ItemXattrMod|");
> +	if (flag & kFSEventStreamEventFlagOwnEvent)
> +		strbuf_addstr(&msg, "OwnEvent|");
> +	if (flag & kFSEventStreamEventFlagItemCloned)
> +		strbuf_addstr(&msg, "ItemCloned|");
> +
> +	trace_printf_key(&trace_fsmonitor, "fsevent: '%s', flags=%u %s",
> +			 path, flag, msg.buf);

Should this be a trace2 call?

> +
> +	strbuf_release(&msg);
> +}
> +
> +static int ef_is_root_delete(const FSEventStreamEventFlags ef)
> +{
> +	return (ef & kFSEventStreamEventFlagItemIsDir &&
> +		ef & kFSEventStreamEventFlagItemRemoved);
> +}
> +
> +static int ef_is_root_renamed(const FSEventStreamEventFlags ef)
> +{
> +	return (ef & kFSEventStreamEventFlagItemIsDir &&
> +		ef & kFSEventStreamEventFlagItemRenamed);
> +}

Will these be handled differently? Or is it enough to detect
ef_is_root_moved_or_deleted()?

> +static void fsevent_callback(ConstFSEventStreamRef streamRef,
> +			     void *ctx,
> +			     size_t num_of_events,
> +			     void *event_paths,
> +			     const FSEventStreamEventFlags event_flags[],
> +			     const FSEventStreamEventId event_ids[])
> +{
> +	struct fsmonitor_daemon_state *state = ctx;
> +	struct fsmonitor_daemon_backend_data *data = state->backend_data;
> +	char **paths = (char **)event_paths;
> +	struct fsmonitor_batch *batch = NULL;
> +	struct string_list cookie_list = STRING_LIST_INIT_DUP;
> +	const char *path_k;
> +	const char *slash;
> +	int k;
> +
> +	/*
> +	 * Build a list of all filesystem changes into a private/local
> +	 * list and without holding any locks.
> +	 */
> +	for (k = 0; k < num_of_events; k++) {
> +		/*
> +		 * On Mac, we receive an array of absolute paths.
> +		 */
> +		path_k = paths[k];
> +
> +		/*
> +		 * If you want to debug FSEvents, log them to GIT_TRACE_FSMONITOR.
> +		 * Please don't log them to Trace2.
> +		 *
> +		 * trace_printf_key(&trace_fsmonitor, "XXX '%s'", path_k);
> +		 */

Oh, I see. _Not_ trace2. What should we do to see if this is enabled
to avoid over-working in the case we are not using GIT_TRACE_FSMONITOR?

> +		/*
> +		 * If event[k] is marked as dropped, we assume that we have
> +		 * lost sync with the filesystem and should flush our cached
> +		 * data.  We need to:
> +		 *
> +		 * [1] Abort/wake any client threads waiting for a cookie and
> +		 *     flush the cached state data (the current token), and
> +		 *     create a new token.
> +		 *
> +		 * [2] Discard the batch that we were locally building (since
> +		 *     they are conceptually relative to the just flushed
> +		 *     token).
> +		 */
> +		if ((event_flags[k] & kFSEventStreamEventFlagKernelDropped) ||
> +		    (event_flags[k] & kFSEventStreamEventFlagUserDropped)) {

Perhaps create a macro EVENT_FLAG_DROPPED that is the union of these two? Then
a single "event_flags[k] & EVENT_FLAG_DROPPED" would suffice here. Helps cover
up how complicated the macOS API names are, too.

> +			/*
> +			 * see also kFSEventStreamEventFlagMustScanSubDirs
> +			 */
> +			trace2_data_string("fsmonitor", NULL,
> +					   "fsm-listen/kernel", "dropped");
> +
> +			fsmonitor_force_resync(state);
> +
> +			if (fsmonitor_batch__free(batch))
> +				BUG("batch should not have a next");

I mentioned before that BUG() seems overkill for these processes, but this
one fits. If this batch has a next, then we did something wrong, right? Do
we have an automated test that checks enough events to maybe cause a second
batch to be created?

> +			string_list_clear(&cookie_list, 0);
> +
> +			/*
> +			 * We assume that any events that we received
> +			 * in this callback after this dropped event
> +			 * may still be valid, so we continue rather
> +			 * than break.  (And just in case there is a
> +			 * delete of ".git" hiding in there.)
> +			 */
> +			continue;
> +		}
> +
> +		switch (fsmonitor_classify_path_absolute(state, path_k)) {
> +
> +		case IS_INSIDE_DOT_GIT_WITH_COOKIE_PREFIX:
> +		case IS_INSIDE_GITDIR_WITH_COOKIE_PREFIX:
> +			/* special case cookie files within .git or gitdir */
> +
> +			/* Use just the filename of the cookie file. */
> +			slash = find_last_dir_sep(path_k);
> +			string_list_append(&cookie_list,
> +					   slash ? slash + 1 : path_k);
> +			break;
> +
> +		case IS_INSIDE_DOT_GIT:
> +		case IS_INSIDE_GITDIR:
> +			/* ignore all other paths inside of .git or gitdir */
> +			break;
> +
> +		case IS_DOT_GIT:
> +		case IS_GITDIR:
> +			/*
> +			 * If .git directory is deleted or renamed away,
> +			 * we have to quit.
> +			 */
> +			if (ef_is_root_delete(event_flags[k])) {
> +				trace2_data_string("fsmonitor", NULL,
> +						   "fsm-listen/gitdir",
> +						   "removed");
> +				goto force_shutdown;
> +			}
> +			if (ef_is_root_renamed(event_flags[k])) {
> +				trace2_data_string("fsmonitor", NULL,
> +						   "fsm-listen/gitdir",
> +						   "renamed");
> +				goto force_shutdown;
> +			}

I see. The only difference is in how we trace the result. I'm not sure
this tracing message is worth the differentiation.

> +			break;
> +
> +		case IS_WORKDIR_PATH:
> +			/* try to queue normal pathnames */
> +
> +			if (trace_pass_fl(&trace_fsmonitor))
> +				log_flags_set(path_k, event_flags[k]);
> +
> +			/* fsevent could be marked as both a file and directory */

The _same_ event? Interesting. And I see that you need to log the name
differently in the case of a file or a directory.

> +			if (event_flags[k] & kFSEventStreamEventFlagItemIsFile) {
> +				const char *rel = path_k +
> +					state->path_worktree_watch.len + 1;
> +
> +				if (!batch)
> +					batch = fsmonitor_batch__new();
> +				fsmonitor_batch__add_path(batch, rel);
> +			}
> +
> +			if (event_flags[k] & kFSEventStreamEventFlagItemIsDir) {
> +				const char *rel = path_k +
> +					state->path_worktree_watch.len + 1;
> +				char *p = xstrfmt("%s/", rel);

In a critical path, xstrfmt() may be too slow for such a simple case.
Likely we should instead use a strbuf with:

	strbuf_addstr(&p, rel);
	strbuf_addch(&p, '/');

Bonus points if we can use the data to predict the size of the strbuf's
buffer.

> +
> +				if (!batch)
> +					batch = fsmonitor_batch__new();
> +				fsmonitor_batch__add_path(batch, p);
> +
> +				free(p);
> +			}
> +
> +			break;
> +
> +		case IS_OUTSIDE_CONE:
> +		default:
> +			trace_printf_key(&trace_fsmonitor,
> +					 "ignoring '%s'", path_k);
> +			break;
> +		}
> +	}
> +
> +	fsmonitor_publish(state, batch, &cookie_list);
> +	string_list_clear(&cookie_list, 0);
> +	return;
> +
> +force_shutdown:
> +	if (fsmonitor_batch__free(batch))
> +		BUG("batch should not have a next");
> +	string_list_clear(&cookie_list, 0);
> +
> +	data->shutdown_style = FORCE_SHUTDOWN;
> +	CFRunLoopStop(data->rl);
> +	return;
> +}
> +
> +/*
> + * TODO Investigate the proper value for the `latency` argument in the call
> + * TODO to `FSEventStreamCreate()`.  I'm not sure that this needs to be a
> + * TODO config setting or just something that we tune after some testing.
> + * TODO
> + * TODO With a latency of 0.1, I was seeing lots of dropped events during
> + * TODO the "touch 100000" files test within t/perf/p7519, but with a
> + * TODO latency of 0.001 I did not see any dropped events.  So the "correct"
> + * TODO value may be somewhere in between.
> + * TODO
> + * TODO https://developer.apple.com/documentation/coreservices/1443980-fseventstreamcreate
> + */

As Eric mentioned in another thread, this should say "NEEDSWORK" at
the top. This is a good candidate for follow-up after the basics of
the series is stable.

>  int fsmonitor_fs_listen__ctor(struct fsmonitor_daemon_state *state)
>  {
> +	FSEventStreamCreateFlags flags = kFSEventStreamCreateFlagNoDefer |
> +		kFSEventStreamCreateFlagWatchRoot |
> +		kFSEventStreamCreateFlagFileEvents;
> +	FSEventStreamContext ctx = {
> +		0,
> +		state,
> +		NULL,
> +		NULL,
> +		NULL
> +	};
> +	struct fsmonitor_daemon_backend_data *data;
> +	const void *dir_array[2];
> +
> +	data = xcalloc(1, sizeof(*data));

CALLOC_ARRAY()

> +	state->backend_data = data;
> +
> +	data->cfsr_worktree_path = CFStringCreateWithCString(
> +		NULL, state->path_worktree_watch.buf, kCFStringEncodingUTF8);
> +	dir_array[data->nr_paths_watching++] = data->cfsr_worktree_path;
> +
> +	if (state->nr_paths_watching > 1) {
> +		data->cfsr_gitdir_path = CFStringCreateWithCString(
> +			NULL, state->path_gitdir_watch.buf,
> +			kCFStringEncodingUTF8);
> +		dir_array[data->nr_paths_watching++] = data->cfsr_gitdir_path;
> +	}
> +
> +	data->cfar_paths_to_watch = CFArrayCreate(NULL, dir_array,
> +						  data->nr_paths_watching,
> +						  NULL);
> +	data->stream = FSEventStreamCreate(NULL, fsevent_callback, &ctx,
> +					   data->cfar_paths_to_watch,
> +					   kFSEventStreamEventIdSinceNow,
> +					   0.001, flags);
> +	if (data->stream == NULL)
> +		goto failed;
> +
> +	/*
> +	 * `data->rl` needs to be set inside the listener thread.
> +	 */
> +
> +	return 0;
> +
> +failed:
> +	error("Unable to create FSEventStream.");
> +
> +	FREE_AND_NULL(state->backend_data);
>  	return -1;
>  }
>  
>  void fsmonitor_fs_listen__dtor(struct fsmonitor_daemon_state *state)
>  {
> +	struct fsmonitor_daemon_backend_data *data;
> +
> +	if (!state || !state->backend_data)
> +		return;
> +
> +	data = state->backend_data;
> +
> +	if (data->stream) {
> +		if (data->stream_started)
> +			FSEventStreamStop(data->stream);
> +		if (data->stream_scheduled)
> +			FSEventStreamInvalidate(data->stream);
> +		FSEventStreamRelease(data->stream);
> +	}
> +
> +	FREE_AND_NULL(state->backend_data);
>  }
>  
>  void fsmonitor_fs_listen__stop_async(struct fsmonitor_daemon_state *state)
>  {
> +	struct fsmonitor_daemon_backend_data *data;
> +
> +	data = state->backend_data;
> +	data->shutdown_style = SHUTDOWN_EVENT;
> +
> +	CFRunLoopStop(data->rl);
>  }
>  
>  void fsmonitor_fs_listen__loop(struct fsmonitor_daemon_state *state)
>  {
> +	struct fsmonitor_daemon_backend_data *data;
> +
> +	data = state->backend_data;
> +
> +	data->rl = CFRunLoopGetCurrent();
> +
> +	FSEventStreamScheduleWithRunLoop(data->stream, data->rl, kCFRunLoopDefaultMode);
> +	data->stream_scheduled = 1;
> +
> +	if (!FSEventStreamStart(data->stream)) {
> +		error("Failed to start the FSEventStream");
> +		goto force_error_stop_without_loop;
> +	}
> +	data->stream_started = 1;
> +
> +	CFRunLoopRun();
> +
> +	switch (data->shutdown_style) {
> +	case FORCE_ERROR_STOP:
> +		state->error_code = -1;
> +		/* fall thru */
> +	case FORCE_SHUTDOWN:
> +		ipc_server_stop_async(state->ipc_server_data);
> +		/* fall thru */
> +	case SHUTDOWN_EVENT:
> +	default:
> +		break;
> +	}
> +	return;
> +
> +force_error_stop_without_loop:
> +	state->error_code = -1;
> +	ipc_server_stop_async(state->ipc_server_data);
> +	return;
>  }

Thanks,
-Stolee
Jeff Hostetler April 30, 2021, 8:05 p.m. UTC | #2
On 4/27/21 2:35 PM, Derrick Stolee wrote:
> On 4/1/2021 11:40 AM, Jeff Hostetler via GitGitGadget wrote:
>> From: Jeff Hostetler <jeffhost@microsoft.com>
>>
>> Implement file system event listener on MacOS using FSEvent,
>> CoreFoundation, and CoreServices.
> 
> Again, I'm not sure if we _should_ be including URLs to
> documentation in our messages, but here are some I found helpful:
> 
> [1] https://developer.apple.com/library/archive/documentation/Darwin/Conceptual/FSEvents_ProgGuide/UsingtheFSEventsFramework/UsingtheFSEventsFramework.html
> [2] https://developer.apple.com/documentation/corefoundation/1541796-cfrunloopstop
> [3] https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/Multithreading/RunLoopManagement/RunLoopManagement.html
> 

Sure.

>> Co-authored-by: Kevin Willford <Kevin.Willford@microsoft.com>
>> Co-authored-by: Johannes Schindelin <johannes.schindelin@gmx.de>
>> Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
>> ---
>>   compat/fsmonitor/fsmonitor-fs-listen-macos.c | 368 +++++++++++++++++++
>>   1 file changed, 368 insertions(+)
>>
>> diff --git a/compat/fsmonitor/fsmonitor-fs-listen-macos.c b/compat/fsmonitor/fsmonitor-fs-listen-macos.c
>> index bec5130d9e1d..e055fb579cc4 100644
>> --- a/compat/fsmonitor/fsmonitor-fs-listen-macos.c
>> +++ b/compat/fsmonitor/fsmonitor-fs-listen-macos.c
>> @@ -97,20 +97,388 @@ void FSEventStreamRelease(FSEventStreamRef stream);
>>   #include "cache.h"
>>   #include "fsmonitor.h"
>>   #include "fsmonitor-fs-listen.h"
>> +#include "fsmonitor--daemon.h"
>> +
>> +struct fsmonitor_daemon_backend_data
>> +{
>> +	CFStringRef cfsr_worktree_path;
>> +	CFStringRef cfsr_gitdir_path;
>> +
>> +	CFArrayRef cfar_paths_to_watch;
>> +	int nr_paths_watching;
>> +
>> +	FSEventStreamRef stream;
>> +
>> +	CFRunLoopRef rl;
>> +
>> +	enum shutdown_style {
>> +		SHUTDOWN_EVENT = 0,
>> +		FORCE_SHUTDOWN,
>> +		FORCE_ERROR_STOP,
>> +	} shutdown_style;
>> +
>> +	unsigned int stream_scheduled:1;
>> +	unsigned int stream_started:1;
>> +};
>> +
>> +static void log_flags_set(const char *path, const FSEventStreamEventFlags flag)
>> +{
>> +	struct strbuf msg = STRBUF_INIT;
> 
> Before going through these ifs and constructing a string, it
> might be a good idea to check if the trace event will actually
> be sent somewhere. If the logging method is switched to a
> trace2 method, then up here we can do:
> 
> 	if (!trace2_is_enabled())
> 		return;

No, we're routing these messages (very noisy and low value) to
the old-style GIT_TRACE_FSMONITOR key.  There's a whole set of
existing FSMonitor tracing that Ben and Kevin added that is
useful for interactive debugging.

> 
>> +	if (flag & kFSEventStreamEventFlagMustScanSubDirs)
>> +		strbuf_addstr(&msg, "MustScanSubDirs|");
>> +	if (flag & kFSEventStreamEventFlagUserDropped)
>> +		strbuf_addstr(&msg, "UserDropped|");
>> +	if (flag & kFSEventStreamEventFlagKernelDropped)
>> +		strbuf_addstr(&msg, "KernelDropped|");
>> +	if (flag & kFSEventStreamEventFlagEventIdsWrapped)
>> +		strbuf_addstr(&msg, "EventIdsWrapped|");
>> +	if (flag & kFSEventStreamEventFlagHistoryDone)
>> +		strbuf_addstr(&msg, "HistoryDone|");
>> +	if (flag & kFSEventStreamEventFlagRootChanged)
>> +		strbuf_addstr(&msg, "RootChanged|");
>> +	if (flag & kFSEventStreamEventFlagMount)
>> +		strbuf_addstr(&msg, "Mount|");
>> +	if (flag & kFSEventStreamEventFlagUnmount)
>> +		strbuf_addstr(&msg, "Unmount|");
>> +	if (flag & kFSEventStreamEventFlagItemChangeOwner)
>> +		strbuf_addstr(&msg, "ItemChangeOwner|");
>> +	if (flag & kFSEventStreamEventFlagItemCreated)
>> +		strbuf_addstr(&msg, "ItemCreated|");
>> +	if (flag & kFSEventStreamEventFlagItemFinderInfoMod)
>> +		strbuf_addstr(&msg, "ItemFinderInfoMod|");
>> +	if (flag & kFSEventStreamEventFlagItemInodeMetaMod)
>> +		strbuf_addstr(&msg, "ItemInodeMetaMod|");
>> +	if (flag & kFSEventStreamEventFlagItemIsDir)
>> +		strbuf_addstr(&msg, "ItemIsDir|");
>> +	if (flag & kFSEventStreamEventFlagItemIsFile)
>> +		strbuf_addstr(&msg, "ItemIsFile|");
>> +	if (flag & kFSEventStreamEventFlagItemIsHardlink)
>> +		strbuf_addstr(&msg, "ItemIsHardlink|");
>> +	if (flag & kFSEventStreamEventFlagItemIsLastHardlink)
>> +		strbuf_addstr(&msg, "ItemIsLastHardlink|");
>> +	if (flag & kFSEventStreamEventFlagItemIsSymlink)
>> +		strbuf_addstr(&msg, "ItemIsSymlink|");
>> +	if (flag & kFSEventStreamEventFlagItemModified)
>> +		strbuf_addstr(&msg, "ItemModified|");
>> +	if (flag & kFSEventStreamEventFlagItemRemoved)
>> +		strbuf_addstr(&msg, "ItemRemoved|");
>> +	if (flag & kFSEventStreamEventFlagItemRenamed)
>> +		strbuf_addstr(&msg, "ItemRenamed|");
>> +	if (flag & kFSEventStreamEventFlagItemXattrMod)
>> +		strbuf_addstr(&msg, "ItemXattrMod|");
>> +	if (flag & kFSEventStreamEventFlagOwnEvent)
>> +		strbuf_addstr(&msg, "OwnEvent|");
>> +	if (flag & kFSEventStreamEventFlagItemCloned)
>> +		strbuf_addstr(&msg, "ItemCloned|");
>> +
>> +	trace_printf_key(&trace_fsmonitor, "fsevent: '%s', flags=%u %s",
>> +			 path, flag, msg.buf);
> 
> Should this be a trace2 call?

No. I wanted to keep these messages on the old-style key.

> 
>> +
>> +	strbuf_release(&msg);
>> +}
>> +
>> +static int ef_is_root_delete(const FSEventStreamEventFlags ef)
>> +{
>> +	return (ef & kFSEventStreamEventFlagItemIsDir &&
>> +		ef & kFSEventStreamEventFlagItemRemoved);
>> +}
>> +
>> +static int ef_is_root_renamed(const FSEventStreamEventFlags ef)
>> +{
>> +	return (ef & kFSEventStreamEventFlagItemIsDir &&
>> +		ef & kFSEventStreamEventFlagItemRenamed);
>> +}
> 
> Will these be handled differently? Or is it enough to detect
> ef_is_root_moved_or_deleted()?

The whole set of Apple kernel APIs are very foreign territory
to me, so I kept it simple and distinct.  Also, it will let us
log different trace events.

> 
>> +static void fsevent_callback(ConstFSEventStreamRef streamRef,
>> +			     void *ctx,
>> +			     size_t num_of_events,
>> +			     void *event_paths,
>> +			     const FSEventStreamEventFlags event_flags[],
>> +			     const FSEventStreamEventId event_ids[])
>> +{
>> +	struct fsmonitor_daemon_state *state = ctx;
>> +	struct fsmonitor_daemon_backend_data *data = state->backend_data;
>> +	char **paths = (char **)event_paths;
>> +	struct fsmonitor_batch *batch = NULL;
>> +	struct string_list cookie_list = STRING_LIST_INIT_DUP;
>> +	const char *path_k;
>> +	const char *slash;
>> +	int k;
>> +
>> +	/*
>> +	 * Build a list of all filesystem changes into a private/local
>> +	 * list and without holding any locks.
>> +	 */
>> +	for (k = 0; k < num_of_events; k++) {
>> +		/*
>> +		 * On Mac, we receive an array of absolute paths.
>> +		 */
>> +		path_k = paths[k];
>> +
>> +		/*
>> +		 * If you want to debug FSEvents, log them to GIT_TRACE_FSMONITOR.
>> +		 * Please don't log them to Trace2.
>> +		 *
>> +		 * trace_printf_key(&trace_fsmonitor, "XXX '%s'", path_k);
>> +		 */
> 
> Oh, I see. _Not_ trace2. What should we do to see if this is enabled
> to avoid over-working in the case we are not using GIT_TRACE_FSMONITOR?

Right. I'll see if there's a nice way to avoid the log_flags_set() call.
And I should rename the "XXX" message.

> 
>> +		/*
>> +		 * If event[k] is marked as dropped, we assume that we have
>> +		 * lost sync with the filesystem and should flush our cached
>> +		 * data.  We need to:
>> +		 *
>> +		 * [1] Abort/wake any client threads waiting for a cookie and
>> +		 *     flush the cached state data (the current token), and
>> +		 *     create a new token.
>> +		 *
>> +		 * [2] Discard the batch that we were locally building (since
>> +		 *     they are conceptually relative to the just flushed
>> +		 *     token).
>> +		 */
>> +		if ((event_flags[k] & kFSEventStreamEventFlagKernelDropped) ||
>> +		    (event_flags[k] & kFSEventStreamEventFlagUserDropped)) {
> 
> Perhaps create a macro EVENT_FLAG_DROPPED that is the union of these two? Then
> a single "event_flags[k] & EVENT_FLAG_DROPPED" would suffice here. Helps cover
> up how complicated the macOS API names are, too.
> 
>> +			/*
>> +			 * see also kFSEventStreamEventFlagMustScanSubDirs
>> +			 */
>> +			trace2_data_string("fsmonitor", NULL,
>> +					   "fsm-listen/kernel", "dropped");
>> +
>> +			fsmonitor_force_resync(state);
>> +
>> +			if (fsmonitor_batch__free(batch))
>> +				BUG("batch should not have a next");
> 
> I mentioned before that BUG() seems overkill for these processes, but this
> one fits. If this batch has a next, then we did something wrong, right? Do
> we have an automated test that checks enough events to maybe cause a second
> batch to be created?

This is me being parnoid.  I hate to see a returned pointer go to waste.

The local variable `batch` has a flexarray of interned paths, it should
never have a next pointer until it has been "published".  Publishing the
batch links it into the list of batches (and we lose ownership of it).

The flexarray grows as needed, so we won't have a second batch locally.

> 
>> +			string_list_clear(&cookie_list, 0);
>> +
>> +			/*
>> +			 * We assume that any events that we received
>> +			 * in this callback after this dropped event
>> +			 * may still be valid, so we continue rather
>> +			 * than break.  (And just in case there is a
>> +			 * delete of ".git" hiding in there.)
>> +			 */
>> +			continue;
>> +		}
>> +
>> +		switch (fsmonitor_classify_path_absolute(state, path_k)) {
>> +
>> +		case IS_INSIDE_DOT_GIT_WITH_COOKIE_PREFIX:
>> +		case IS_INSIDE_GITDIR_WITH_COOKIE_PREFIX:
>> +			/* special case cookie files within .git or gitdir */
>> +
>> +			/* Use just the filename of the cookie file. */
>> +			slash = find_last_dir_sep(path_k);
>> +			string_list_append(&cookie_list,
>> +					   slash ? slash + 1 : path_k);
>> +			break;
>> +
>> +		case IS_INSIDE_DOT_GIT:
>> +		case IS_INSIDE_GITDIR:
>> +			/* ignore all other paths inside of .git or gitdir */
>> +			break;
>> +
>> +		case IS_DOT_GIT:
>> +		case IS_GITDIR:
>> +			/*
>> +			 * If .git directory is deleted or renamed away,
>> +			 * we have to quit.
>> +			 */
>> +			if (ef_is_root_delete(event_flags[k])) {
>> +				trace2_data_string("fsmonitor", NULL,
>> +						   "fsm-listen/gitdir",
>> +						   "removed");
>> +				goto force_shutdown;
>> +			}
>> +			if (ef_is_root_renamed(event_flags[k])) {
>> +				trace2_data_string("fsmonitor", NULL,
>> +						   "fsm-listen/gitdir",
>> +						   "renamed");
>> +				goto force_shutdown;
>> +			}
> 
> I see. The only difference is in how we trace the result. I'm not sure
> this tracing message is worth the differentiation.

I could get rid of it.  It was helpful during development to ensure
that I had covered all the bases.

> 
>> +			break;
>> +
>> +		case IS_WORKDIR_PATH:
>> +			/* try to queue normal pathnames */
>> +
>> +			if (trace_pass_fl(&trace_fsmonitor))
>> +				log_flags_set(path_k, event_flags[k]);
>> +
>> +			/* fsevent could be marked as both a file and directory */
> 
> The _same_ event? Interesting. And I see that you need to log the name
> differently in the case of a file or a directory.

Apple will consolidate messages, so if you delete a file and create a
directory with the same name quick enough, they will send a single event
with both bits set.  We receive a batch of events from the kernel with a
certain frequency, so we might get 2 events in separate bins, or 1 event
with both bits.

Yes, we queue up different paths.  Adding the trailing slash tells the
client to invalidate a range of cache-entries, for example.

> 
>> +			if (event_flags[k] & kFSEventStreamEventFlagItemIsFile) {
>> +				const char *rel = path_k +
>> +					state->path_worktree_watch.len + 1;
>> +
>> +				if (!batch)
>> +					batch = fsmonitor_batch__new();
>> +				fsmonitor_batch__add_path(batch, rel);
>> +			}
>> +
>> +			if (event_flags[k] & kFSEventStreamEventFlagItemIsDir) {
>> +				const char *rel = path_k +
>> +					state->path_worktree_watch.len + 1;
>> +				char *p = xstrfmt("%s/", rel);
> 
> In a critical path, xstrfmt() may be too slow for such a simple case.
> Likely we should instead use a strbuf with:
> 
> 	strbuf_addstr(&p, rel);
> 	strbuf_addch(&p, '/');
> 
> Bonus points if we can use the data to predict the size of the strbuf's
> buffer.

Good point!

> 
>> +
>> +				if (!batch)
>> +					batch = fsmonitor_batch__new();
>> +				fsmonitor_batch__add_path(batch, p);
>> +
>> +				free(p);
>> +			}
>> +
>> +			break;
>> +
>> +		case IS_OUTSIDE_CONE:
>> +		default:
>> +			trace_printf_key(&trace_fsmonitor,
>> +					 "ignoring '%s'", path_k);
>> +			break;
>> +		}
>> +	}
>> +
>> +	fsmonitor_publish(state, batch, &cookie_list);
>> +	string_list_clear(&cookie_list, 0);
>> +	return;
>> +
>> +force_shutdown:
>> +	if (fsmonitor_batch__free(batch))
>> +		BUG("batch should not have a next");
>> +	string_list_clear(&cookie_list, 0);
>> +
>> +	data->shutdown_style = FORCE_SHUTDOWN;
>> +	CFRunLoopStop(data->rl);
>> +	return;
>> +}
>> +
>> +/*
>> + * TODO Investigate the proper value for the `latency` argument in the call
>> + * TODO to `FSEventStreamCreate()`.  I'm not sure that this needs to be a
>> + * TODO config setting or just something that we tune after some testing.
>> + * TODO
>> + * TODO With a latency of 0.1, I was seeing lots of dropped events during
>> + * TODO the "touch 100000" files test within t/perf/p7519, but with a
>> + * TODO latency of 0.001 I did not see any dropped events.  So the "correct"
>> + * TODO value may be somewhere in between.
>> + * TODO
>> + * TODO https://developer.apple.com/documentation/coreservices/1443980-fseventstreamcreate
>> + */
> 
> As Eric mentioned in another thread, this should say "NEEDSWORK" at
> the top. This is a good candidate for follow-up after the basics of
> the series is stable.

Right.

> 
>>   int fsmonitor_fs_listen__ctor(struct fsmonitor_daemon_state *state)
>>   {
>> +	FSEventStreamCreateFlags flags = kFSEventStreamCreateFlagNoDefer |
>> +		kFSEventStreamCreateFlagWatchRoot |
>> +		kFSEventStreamCreateFlagFileEvents;
>> +	FSEventStreamContext ctx = {
>> +		0,
>> +		state,
>> +		NULL,
>> +		NULL,
>> +		NULL
>> +	};
>> +	struct fsmonitor_daemon_backend_data *data;
>> +	const void *dir_array[2];
>> +
>> +	data = xcalloc(1, sizeof(*data));
> 
> CALLOC_ARRAY()
> 
>> +	state->backend_data = data;
>> +
>> +	data->cfsr_worktree_path = CFStringCreateWithCString(
>> +		NULL, state->path_worktree_watch.buf, kCFStringEncodingUTF8);
>> +	dir_array[data->nr_paths_watching++] = data->cfsr_worktree_path;
>> +
>> +	if (state->nr_paths_watching > 1) {
>> +		data->cfsr_gitdir_path = CFStringCreateWithCString(
>> +			NULL, state->path_gitdir_watch.buf,
>> +			kCFStringEncodingUTF8);
>> +		dir_array[data->nr_paths_watching++] = data->cfsr_gitdir_path;
>> +	}
>> +
>> +	data->cfar_paths_to_watch = CFArrayCreate(NULL, dir_array,
>> +						  data->nr_paths_watching,
>> +						  NULL);
>> +	data->stream = FSEventStreamCreate(NULL, fsevent_callback, &ctx,
>> +					   data->cfar_paths_to_watch,
>> +					   kFSEventStreamEventIdSinceNow,
>> +					   0.001, flags);
>> +	if (data->stream == NULL)
>> +		goto failed;
>> +
>> +	/*
>> +	 * `data->rl` needs to be set inside the listener thread.
>> +	 */
>> +
>> +	return 0;
>> +
>> +failed:
>> +	error("Unable to create FSEventStream.");
>> +
>> +	FREE_AND_NULL(state->backend_data);
>>   	return -1;
>>   }
>>   
>>   void fsmonitor_fs_listen__dtor(struct fsmonitor_daemon_state *state)
>>   {
>> +	struct fsmonitor_daemon_backend_data *data;
>> +
>> +	if (!state || !state->backend_data)
>> +		return;
>> +
>> +	data = state->backend_data;
>> +
>> +	if (data->stream) {
>> +		if (data->stream_started)
>> +			FSEventStreamStop(data->stream);
>> +		if (data->stream_scheduled)
>> +			FSEventStreamInvalidate(data->stream);
>> +		FSEventStreamRelease(data->stream);
>> +	}
>> +
>> +	FREE_AND_NULL(state->backend_data);
>>   }
>>   
>>   void fsmonitor_fs_listen__stop_async(struct fsmonitor_daemon_state *state)
>>   {
>> +	struct fsmonitor_daemon_backend_data *data;
>> +
>> +	data = state->backend_data;
>> +	data->shutdown_style = SHUTDOWN_EVENT;
>> +
>> +	CFRunLoopStop(data->rl);
>>   }
>>   
>>   void fsmonitor_fs_listen__loop(struct fsmonitor_daemon_state *state)
>>   {
>> +	struct fsmonitor_daemon_backend_data *data;
>> +
>> +	data = state->backend_data;
>> +
>> +	data->rl = CFRunLoopGetCurrent();
>> +
>> +	FSEventStreamScheduleWithRunLoop(data->stream, data->rl, kCFRunLoopDefaultMode);
>> +	data->stream_scheduled = 1;
>> +
>> +	if (!FSEventStreamStart(data->stream)) {
>> +		error("Failed to start the FSEventStream");
>> +		goto force_error_stop_without_loop;
>> +	}
>> +	data->stream_started = 1;
>> +
>> +	CFRunLoopRun();
>> +
>> +	switch (data->shutdown_style) {
>> +	case FORCE_ERROR_STOP:
>> +		state->error_code = -1;
>> +		/* fall thru */
>> +	case FORCE_SHUTDOWN:
>> +		ipc_server_stop_async(state->ipc_server_data);
>> +		/* fall thru */
>> +	case SHUTDOWN_EVENT:
>> +	default:
>> +		break;
>> +	}
>> +	return;
>> +
>> +force_error_stop_without_loop:
>> +	state->error_code = -1;
>> +	ipc_server_stop_async(state->ipc_server_data);
>> +	return;
>>   }
> 
> Thanks,
> -Stolee
> 

Big thanks for looking at all of this!
Jeff
diff mbox series

Patch

diff --git a/compat/fsmonitor/fsmonitor-fs-listen-macos.c b/compat/fsmonitor/fsmonitor-fs-listen-macos.c
index bec5130d9e1d..e055fb579cc4 100644
--- a/compat/fsmonitor/fsmonitor-fs-listen-macos.c
+++ b/compat/fsmonitor/fsmonitor-fs-listen-macos.c
@@ -97,20 +97,388 @@  void FSEventStreamRelease(FSEventStreamRef stream);
 #include "cache.h"
 #include "fsmonitor.h"
 #include "fsmonitor-fs-listen.h"
+#include "fsmonitor--daemon.h"
+
+struct fsmonitor_daemon_backend_data
+{
+	CFStringRef cfsr_worktree_path;
+	CFStringRef cfsr_gitdir_path;
+
+	CFArrayRef cfar_paths_to_watch;
+	int nr_paths_watching;
+
+	FSEventStreamRef stream;
+
+	CFRunLoopRef rl;
+
+	enum shutdown_style {
+		SHUTDOWN_EVENT = 0,
+		FORCE_SHUTDOWN,
+		FORCE_ERROR_STOP,
+	} shutdown_style;
+
+	unsigned int stream_scheduled:1;
+	unsigned int stream_started:1;
+};
+
+static void log_flags_set(const char *path, const FSEventStreamEventFlags flag)
+{
+	struct strbuf msg = STRBUF_INIT;
+
+	if (flag & kFSEventStreamEventFlagMustScanSubDirs)
+		strbuf_addstr(&msg, "MustScanSubDirs|");
+	if (flag & kFSEventStreamEventFlagUserDropped)
+		strbuf_addstr(&msg, "UserDropped|");
+	if (flag & kFSEventStreamEventFlagKernelDropped)
+		strbuf_addstr(&msg, "KernelDropped|");
+	if (flag & kFSEventStreamEventFlagEventIdsWrapped)
+		strbuf_addstr(&msg, "EventIdsWrapped|");
+	if (flag & kFSEventStreamEventFlagHistoryDone)
+		strbuf_addstr(&msg, "HistoryDone|");
+	if (flag & kFSEventStreamEventFlagRootChanged)
+		strbuf_addstr(&msg, "RootChanged|");
+	if (flag & kFSEventStreamEventFlagMount)
+		strbuf_addstr(&msg, "Mount|");
+	if (flag & kFSEventStreamEventFlagUnmount)
+		strbuf_addstr(&msg, "Unmount|");
+	if (flag & kFSEventStreamEventFlagItemChangeOwner)
+		strbuf_addstr(&msg, "ItemChangeOwner|");
+	if (flag & kFSEventStreamEventFlagItemCreated)
+		strbuf_addstr(&msg, "ItemCreated|");
+	if (flag & kFSEventStreamEventFlagItemFinderInfoMod)
+		strbuf_addstr(&msg, "ItemFinderInfoMod|");
+	if (flag & kFSEventStreamEventFlagItemInodeMetaMod)
+		strbuf_addstr(&msg, "ItemInodeMetaMod|");
+	if (flag & kFSEventStreamEventFlagItemIsDir)
+		strbuf_addstr(&msg, "ItemIsDir|");
+	if (flag & kFSEventStreamEventFlagItemIsFile)
+		strbuf_addstr(&msg, "ItemIsFile|");
+	if (flag & kFSEventStreamEventFlagItemIsHardlink)
+		strbuf_addstr(&msg, "ItemIsHardlink|");
+	if (flag & kFSEventStreamEventFlagItemIsLastHardlink)
+		strbuf_addstr(&msg, "ItemIsLastHardlink|");
+	if (flag & kFSEventStreamEventFlagItemIsSymlink)
+		strbuf_addstr(&msg, "ItemIsSymlink|");
+	if (flag & kFSEventStreamEventFlagItemModified)
+		strbuf_addstr(&msg, "ItemModified|");
+	if (flag & kFSEventStreamEventFlagItemRemoved)
+		strbuf_addstr(&msg, "ItemRemoved|");
+	if (flag & kFSEventStreamEventFlagItemRenamed)
+		strbuf_addstr(&msg, "ItemRenamed|");
+	if (flag & kFSEventStreamEventFlagItemXattrMod)
+		strbuf_addstr(&msg, "ItemXattrMod|");
+	if (flag & kFSEventStreamEventFlagOwnEvent)
+		strbuf_addstr(&msg, "OwnEvent|");
+	if (flag & kFSEventStreamEventFlagItemCloned)
+		strbuf_addstr(&msg, "ItemCloned|");
+
+	trace_printf_key(&trace_fsmonitor, "fsevent: '%s', flags=%u %s",
+			 path, flag, msg.buf);
+
+	strbuf_release(&msg);
+}
+
+static int ef_is_root_delete(const FSEventStreamEventFlags ef)
+{
+	return (ef & kFSEventStreamEventFlagItemIsDir &&
+		ef & kFSEventStreamEventFlagItemRemoved);
+}
+
+static int ef_is_root_renamed(const FSEventStreamEventFlags ef)
+{
+	return (ef & kFSEventStreamEventFlagItemIsDir &&
+		ef & kFSEventStreamEventFlagItemRenamed);
+}
+
+static void fsevent_callback(ConstFSEventStreamRef streamRef,
+			     void *ctx,
+			     size_t num_of_events,
+			     void *event_paths,
+			     const FSEventStreamEventFlags event_flags[],
+			     const FSEventStreamEventId event_ids[])
+{
+	struct fsmonitor_daemon_state *state = ctx;
+	struct fsmonitor_daemon_backend_data *data = state->backend_data;
+	char **paths = (char **)event_paths;
+	struct fsmonitor_batch *batch = NULL;
+	struct string_list cookie_list = STRING_LIST_INIT_DUP;
+	const char *path_k;
+	const char *slash;
+	int k;
+
+	/*
+	 * Build a list of all filesystem changes into a private/local
+	 * list and without holding any locks.
+	 */
+	for (k = 0; k < num_of_events; k++) {
+		/*
+		 * On Mac, we receive an array of absolute paths.
+		 */
+		path_k = paths[k];
+
+		/*
+		 * If you want to debug FSEvents, log them to GIT_TRACE_FSMONITOR.
+		 * Please don't log them to Trace2.
+		 *
+		 * trace_printf_key(&trace_fsmonitor, "XXX '%s'", path_k);
+		 */
+
+		/*
+		 * If event[k] is marked as dropped, we assume that we have
+		 * lost sync with the filesystem and should flush our cached
+		 * data.  We need to:
+		 *
+		 * [1] Abort/wake any client threads waiting for a cookie and
+		 *     flush the cached state data (the current token), and
+		 *     create a new token.
+		 *
+		 * [2] Discard the batch that we were locally building (since
+		 *     they are conceptually relative to the just flushed
+		 *     token).
+		 */
+		if ((event_flags[k] & kFSEventStreamEventFlagKernelDropped) ||
+		    (event_flags[k] & kFSEventStreamEventFlagUserDropped)) {
+			/*
+			 * see also kFSEventStreamEventFlagMustScanSubDirs
+			 */
+			trace2_data_string("fsmonitor", NULL,
+					   "fsm-listen/kernel", "dropped");
+
+			fsmonitor_force_resync(state);
+
+			if (fsmonitor_batch__free(batch))
+				BUG("batch should not have a next");
+			string_list_clear(&cookie_list, 0);
+
+			/*
+			 * We assume that any events that we received
+			 * in this callback after this dropped event
+			 * may still be valid, so we continue rather
+			 * than break.  (And just in case there is a
+			 * delete of ".git" hiding in there.)
+			 */
+			continue;
+		}
+
+		switch (fsmonitor_classify_path_absolute(state, path_k)) {
+
+		case IS_INSIDE_DOT_GIT_WITH_COOKIE_PREFIX:
+		case IS_INSIDE_GITDIR_WITH_COOKIE_PREFIX:
+			/* special case cookie files within .git or gitdir */
+
+			/* Use just the filename of the cookie file. */
+			slash = find_last_dir_sep(path_k);
+			string_list_append(&cookie_list,
+					   slash ? slash + 1 : path_k);
+			break;
+
+		case IS_INSIDE_DOT_GIT:
+		case IS_INSIDE_GITDIR:
+			/* ignore all other paths inside of .git or gitdir */
+			break;
+
+		case IS_DOT_GIT:
+		case IS_GITDIR:
+			/*
+			 * If .git directory is deleted or renamed away,
+			 * we have to quit.
+			 */
+			if (ef_is_root_delete(event_flags[k])) {
+				trace2_data_string("fsmonitor", NULL,
+						   "fsm-listen/gitdir",
+						   "removed");
+				goto force_shutdown;
+			}
+			if (ef_is_root_renamed(event_flags[k])) {
+				trace2_data_string("fsmonitor", NULL,
+						   "fsm-listen/gitdir",
+						   "renamed");
+				goto force_shutdown;
+			}
+			break;
+
+		case IS_WORKDIR_PATH:
+			/* try to queue normal pathnames */
+
+			if (trace_pass_fl(&trace_fsmonitor))
+				log_flags_set(path_k, event_flags[k]);
+
+			/* fsevent could be marked as both a file and directory */
+
+			if (event_flags[k] & kFSEventStreamEventFlagItemIsFile) {
+				const char *rel = path_k +
+					state->path_worktree_watch.len + 1;
+
+				if (!batch)
+					batch = fsmonitor_batch__new();
+				fsmonitor_batch__add_path(batch, rel);
+			}
+
+			if (event_flags[k] & kFSEventStreamEventFlagItemIsDir) {
+				const char *rel = path_k +
+					state->path_worktree_watch.len + 1;
+				char *p = xstrfmt("%s/", rel);
+
+				if (!batch)
+					batch = fsmonitor_batch__new();
+				fsmonitor_batch__add_path(batch, p);
+
+				free(p);
+			}
+
+			break;
+
+		case IS_OUTSIDE_CONE:
+		default:
+			trace_printf_key(&trace_fsmonitor,
+					 "ignoring '%s'", path_k);
+			break;
+		}
+	}
+
+	fsmonitor_publish(state, batch, &cookie_list);
+	string_list_clear(&cookie_list, 0);
+	return;
+
+force_shutdown:
+	if (fsmonitor_batch__free(batch))
+		BUG("batch should not have a next");
+	string_list_clear(&cookie_list, 0);
+
+	data->shutdown_style = FORCE_SHUTDOWN;
+	CFRunLoopStop(data->rl);
+	return;
+}
+
+/*
+ * TODO Investigate the proper value for the `latency` argument in the call
+ * TODO to `FSEventStreamCreate()`.  I'm not sure that this needs to be a
+ * TODO config setting or just something that we tune after some testing.
+ * TODO
+ * TODO With a latency of 0.1, I was seeing lots of dropped events during
+ * TODO the "touch 100000" files test within t/perf/p7519, but with a
+ * TODO latency of 0.001 I did not see any dropped events.  So the "correct"
+ * TODO value may be somewhere in between.
+ * TODO
+ * TODO https://developer.apple.com/documentation/coreservices/1443980-fseventstreamcreate
+ */
 
 int fsmonitor_fs_listen__ctor(struct fsmonitor_daemon_state *state)
 {
+	FSEventStreamCreateFlags flags = kFSEventStreamCreateFlagNoDefer |
+		kFSEventStreamCreateFlagWatchRoot |
+		kFSEventStreamCreateFlagFileEvents;
+	FSEventStreamContext ctx = {
+		0,
+		state,
+		NULL,
+		NULL,
+		NULL
+	};
+	struct fsmonitor_daemon_backend_data *data;
+	const void *dir_array[2];
+
+	data = xcalloc(1, sizeof(*data));
+	state->backend_data = data;
+
+	data->cfsr_worktree_path = CFStringCreateWithCString(
+		NULL, state->path_worktree_watch.buf, kCFStringEncodingUTF8);
+	dir_array[data->nr_paths_watching++] = data->cfsr_worktree_path;
+
+	if (state->nr_paths_watching > 1) {
+		data->cfsr_gitdir_path = CFStringCreateWithCString(
+			NULL, state->path_gitdir_watch.buf,
+			kCFStringEncodingUTF8);
+		dir_array[data->nr_paths_watching++] = data->cfsr_gitdir_path;
+	}
+
+	data->cfar_paths_to_watch = CFArrayCreate(NULL, dir_array,
+						  data->nr_paths_watching,
+						  NULL);
+	data->stream = FSEventStreamCreate(NULL, fsevent_callback, &ctx,
+					   data->cfar_paths_to_watch,
+					   kFSEventStreamEventIdSinceNow,
+					   0.001, flags);
+	if (data->stream == NULL)
+		goto failed;
+
+	/*
+	 * `data->rl` needs to be set inside the listener thread.
+	 */
+
+	return 0;
+
+failed:
+	error("Unable to create FSEventStream.");
+
+	FREE_AND_NULL(state->backend_data);
 	return -1;
 }
 
 void fsmonitor_fs_listen__dtor(struct fsmonitor_daemon_state *state)
 {
+	struct fsmonitor_daemon_backend_data *data;
+
+	if (!state || !state->backend_data)
+		return;
+
+	data = state->backend_data;
+
+	if (data->stream) {
+		if (data->stream_started)
+			FSEventStreamStop(data->stream);
+		if (data->stream_scheduled)
+			FSEventStreamInvalidate(data->stream);
+		FSEventStreamRelease(data->stream);
+	}
+
+	FREE_AND_NULL(state->backend_data);
 }
 
 void fsmonitor_fs_listen__stop_async(struct fsmonitor_daemon_state *state)
 {
+	struct fsmonitor_daemon_backend_data *data;
+
+	data = state->backend_data;
+	data->shutdown_style = SHUTDOWN_EVENT;
+
+	CFRunLoopStop(data->rl);
 }
 
 void fsmonitor_fs_listen__loop(struct fsmonitor_daemon_state *state)
 {
+	struct fsmonitor_daemon_backend_data *data;
+
+	data = state->backend_data;
+
+	data->rl = CFRunLoopGetCurrent();
+
+	FSEventStreamScheduleWithRunLoop(data->stream, data->rl, kCFRunLoopDefaultMode);
+	data->stream_scheduled = 1;
+
+	if (!FSEventStreamStart(data->stream)) {
+		error("Failed to start the FSEventStream");
+		goto force_error_stop_without_loop;
+	}
+	data->stream_started = 1;
+
+	CFRunLoopRun();
+
+	switch (data->shutdown_style) {
+	case FORCE_ERROR_STOP:
+		state->error_code = -1;
+		/* fall thru */
+	case FORCE_SHUTDOWN:
+		ipc_server_stop_async(state->ipc_server_data);
+		/* fall thru */
+	case SHUTDOWN_EVENT:
+	default:
+		break;
+	}
+	return;
+
+force_error_stop_without_loop:
+	state->error_code = -1;
+	ipc_server_stop_async(state->ipc_server_data);
+	return;
 }