Our signal handler calls write() on a pipe or an eventfd in order to
deliver the notification. It's unlikely, but this could fail, setting
errno. We even check the case that it fails with EINTR.
If it does set errno, then it has potentially blown away the value or
errno that the preempted code cared about (ie: if the signal arrived
shortly after a system call but before errno was checked).
Wrap the handler with code to save errno.
https://bugzilla.gnome.org/show_bug.cgi?id=741791
This WIP patch moves the Windows Directory Monitoring code to the new
GLocalFileMonitor mechanism, and adds file monitoring in the process.
Progress from previous patch:
-File renames are now properly supported, but G_FILE_MONITOR_EVENT_MOVED_IN
and G_FILE_MONITOR_EVENT_MOVED_OUT needs to be investigated, as
ReadDirectoryChangesW() seems to send FILE_ACTION_REMOVED when a file is
moved out of a directory.
-Events are handled for both the long and short (8.3) variants of the
filenames, and files monitored will report changes when it is changed
via its short or long filenames.
Things to be done:
-Perhaps find out about attribute changes in files in a monitored
directory; if a file is monitored, attribute changes are correctly
handled.
-Investigate on G_FILE_MONITOR_EVENT_MOVED_OUT,
G_FILE_MONITOR_EVENT_MOVED_IN, G_FILE_MONITOR_EVENT_PRE_UNMOUNT,
G_FILE_MONITOR_EVENT_UNMOUNTED.
-Investigate on the "boredom" algoritm, and see how we can do it on
Windows.
https://bugzilla.gnome.org/show_bug.cgi?id=730116
Completely rewrite the FAM file monitor. Major changes:
- now runs in the worker thread
- dispatches events in a threadsafe way via GFileMonitorSource
- uses unix fd source instead of a GIOChannel
- is now simple enough to fit into one short file
This is the bare minimal effort. This seems not to crash immediately,
but it definitely needs some better testing.
The backend is not in good shape. It could use some serious work.
Use the "interesting" value from g_file_monitor_source_handle_event() to
decide if we're currently being flooded by a stream of boring events.
The main case here is when one or more files is being written to and the
change events are all being rate-limited in the GFileMonitor frontends.
In that case, we become "bored" with the event stream and add a backoff
timeout. In the case that it is exactly one large file being written
(which is the common case) then leaving the event in the queue also lets
the kernel perform merging on it, so when we wake up, we will only see
the one event. Even in the case that the kernel is unable to perform
merging, the context switch overhead will be vastly reduced.
In testing, this cuts down on the number of wake ups during a large file
copy, by a couple orders of magnitude (ie: less than 1% of the number of
wake ups).
Return an "interesting" boolean from the event handler function on
GFileMonitorSource.
An event was "interesting" if it will result in a signal actually being
dispatched to the user. It is "uninteresting" if it only hit an
already-dirty rate limiter.
We will use this information to do some backing off in the backends when
faced with a flood of uninteresting events.
We generally assume that an IN_CREATE event is the start of a series of
events in which another process is doing this:
fd = creat (...) -> IN_CREATE
write (fd, ..) -> IN_MODIFY
write (fd, ..) -> IN_MODIFY
close (fd) -> IN_CLOSE_WRITE
and as such, we use the CHANGES_DONE_HINT event after CREATED in order
to show when this sequence of events has completed (ie: when we receive
IN_CLOSE_WRITE when the user closes the file).
Renaming a file into place is handled by IN_MOVED_FROM so we don't have
to worry about that.
There are many other cases, however, where a new file 'appears' in a
directory in its completed form already, and the kernel reports
IN_CREATE. Examples include mkdir, mknod, and the creation of
hardlinks. In these cases, there is no corresponding IN_CLOSE_WRITE
event and the CHANGES_DONE_HINT will have to be emitted by an arbitrary
timeout.
Try to detect some of these cases and report CHANGES_DONE_HINT
immediately.
This is not perfect. There are some cases that will not be reliably
detected. An example is if the user makes a hardlink and then
immediately deletes the original (before we can stat the new file).
Another example is if the user creates a file with O_TMPFILE. In both
of these cases, CHANGES_DONE_HINT will still eventually be delivered via
the timeout.
Remove all event merging and dispatch logic from GFileMonitor. The only
implementation of GFileMonitor outside of glib is in gvfs and it already
does these things properly.
Get rid of GLocalDirectoryMonitor. We will use a single class,
GLocalFileMonitor, for both directory and file monitoring. This will
prevent every single backend from having to create two objects
separately (eg: ginotifydirectorymonitor.c and ginotifyfilemonitor.c).
Introduce GFileMonitorSource as a thread-safe cross-context dispatch
mechanism. Put it in GLocalFileMonitor. All backends will be expected
to dispatch via the source and not touch the GFileMonitor object at all
from the worker thread.
Remove all construct properties from GLocalFileMonitor and remove the
"context" construct property from GFileMonitor. All backends must now
get the information about what file to monitor from the ->start() call
which is mandatory to implement.
Remove the implementation of rate limiting in GFileMonitor and add an
implementation in GLocalFileMonitor. gvfs never did anything with this
anyway, but if it wanted to, it would have to implement it for itself.
This was done in order to get the rate_limit field into the
GFileMonitorSource so that it could be safely accessed from the worker
thread.
Expose g_local_file_is_remote() internally for NFS detection.
With the "is_remote" functionality exposed, we can now move all
functions for creating local file monitors to a proper location in
glocalfilemonitor.c
Port the inotify backend to adjust to the changes above. None of the
other backends are ported yet. Those will come in future commits.
Remove the hardwired 1 second event queue logic from inotify-kernel and
replace it with something vastly less complicated.
Events are now reported as soon as is possible instead of after a
delay.
We still must delay IN_MOVED_FROM events in order to look for the
matching IN_MOVED_TO events, and since we want to report events in order
this means that events behind those events can also be delayed. We
limit ourselves, however:
- no more than 100 events can be delayed at a time
- no event can be delayed by more than 10ms
https://bugzilla.gnome.org/show_bug.cgi?id=627285
Add a new internal constructor for GLocalFile (which itself is private).
This new constructor allows creating a GLocalFile from a dirname and a
basename, assuming that the dirname is already in canonical form and the
basename is a regular basename.
This will be used for creating GLocalFile instances from the file
monitoring code (for signal emissions).
For all of the effort spent ensuring that this algorithm would be
correctly threadsafe, I messed up the order of operations within a
single thread when porting to the new approach.
Fix that up.
Also: fix some overzealous asserting in the testcases. Since shutdown
is now lazy, we can never surely say !is_running at any particular point
in time.
Fix a few typical problems, and also stop wrapping the inline definition
of g_steal_pointer in parens, since it is not necessary and it confuses
gtk-doc.
It was added after G_END_DECLS, outside the #ifdef G_PLATFORM_WIN32,
and inside a #ifndef __GTK_DOC_IGNORE__ block. So it was missing from
the doc.
https://bugzilla.gnome.org/show_bug.cgi?id=743661
This can be used to query whether the task has completed, in the sense
that it has had a result set on it, and has already – or will soon –
invoke its callback function.
Notifications for this property are emitted immediately after the task’s
main callback, in the same main context as that callback. This allows
for multiple bits of code to listen for completion of the GTask, which
opens the door for blocking on cancellation of the GTask and improved
handling of ‘pending’ behaviour.
https://bugzilla.gnome.org/show_bug.cgi?id=743636
