Taking a reference to the GFileMonitor when handling events may cause
object destruction from th worker thread that calls the function. This
condition happens if the surrounding code drops the otherwise last
reference ot the GFileMonitor. The series of events causes destruction
from an unrelated worker thread and also triggers g_file_monitor_cancel
to be called from g_file_monitor_source_handle_event.
For the inotify backend, this results in a deadlock as cancellation
needs to take a lock that protects data structures from being modified
while events are dispatched.
One alternative to this approach might be to add an RCU (release, copy,
update) approach to the lists contained in the wd_dir_hash and
wd_file_hash hash tables.
Fixes: #1941
An example stack trace of this happening is:
Thread 2 (Thread 0x7fea68b1d640 (LWP 260961) "gmain"):
#0 syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
#1 0x00007fea692215dc in g_mutex_lock_slowpath (mutex=mutex@entry=0x7fea6911e148 <g.inotify_lock_lock>) at ../glib/gthread-posix.c:1493
#2 0x00007fea69222062 in g_mutex_lock (mutex=mutex@entry=0x7fea6911e148 <g.inotify_lock_lock>) at ../glib/gthread-posix.c:1517
#3 0x00007fea6908025a in _ih_sub_cancel (sub=0x1492620) at ../gio/inotify/inotify-helper.c:131
#4 0x00007fea6907f9da in g_inotify_file_monitor_cancel (monitor=0x14a3550) at ../gio/inotify/ginotifyfilemonitor.c:75
#5 0x00007fea68fae959 in g_file_monitor_cancel (monitor=0x14a3550) at ../gio/gfilemonitor.c:241
#6 0x00007fea68fae9dc in g_file_monitor_dispose (object=0x14a3550) at ../gio/gfilemonitor.c:123
#7 0x00007fea69139341 in g_object_unref (_object=<optimized out>) at ../gobject/gobject.c:3636
#8 g_object_unref (_object=0x14a3550) at ../gobject/gobject.c:3553
#9 0x00007fea6907507a in g_file_monitor_source_handle_event (fms=0x14c3560, event_type=<optimized out>, child=0x7fea64001460 "spawned-1", rename_to=rename_to@entry=0x0, other=other@entry=0x0, event_time=<optimized out>) at ../gio/glocalfilemonitor.c:457
#10 0x00007fea6907fe0e in ih_event_callback (event=0x7fea64001420, sub=0x1492620, file_event=<optimized out>) at ../gio/inotify/inotify-helper.c:218
#11 0x00007fea6908075c in ip_event_dispatch (dir_list=dir_list@entry=0x14c14c0, file_list=0x0, event=event@entry=0x7fea64001420) at ../gio/inotify/inotify-path.c:493
#12 0x00007fea6908094e in ip_event_dispatch (event=0x7fea64001420, file_list=<optimized out>, dir_list=0x14c14c0) at ../gio/inotify/inotify-path.c:448
#13 ip_event_callback (event=0x7fea64001420) at ../gio/inotify/inotify-path.c:548
#14 ip_event_callback (event=0x7fea64001420) at ../gio/inotify/inotify-path.c:530
#15 0x00007fea69081391 in ik_source_dispatch (source=0x14a2bf0, func=0x7fea69080890 <ip_event_callback>, user_data=<optimized out>) at ../gio/inotify/inotify-kernel.c:327
#16 0x00007fea691d0824 in g_main_dispatch (context=0x14a2cc0) at ../glib/gmain.c:3417
#17 g_main_context_dispatch (context=0x14a2cc0) at ../glib/gmain.c:4135
#18 0x00007fea691d0b88 in g_main_context_iterate (context=context@entry=0x14a2cc0, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../glib/gmain.c:4211
#19 0x00007fea691d0c2f in g_main_context_iteration (context=0x14a2cc0, may_block=may_block@entry=1) at ../glib/gmain.c:4276
#20 0x00007fea691d0c81 in glib_worker_main (data=<optimized out>) at ../glib/gmain.c:6176
#21 0x00007fea691f9c2d in g_thread_proxy (data=0x1487cc0) at ../glib/gthread.c:827
#22 0x00007fea68d93b1a in start_thread (arg=<optimized out>) at pthread_create.c:443
#23 0x00007fea68e18650 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81
This introduces no functional changes but will make refactoring a bit
easier in the following commit.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
GArray supports a "zero_terminated" flag, but GPtrArray doesn't.
This is odd, because especially for a pointer array it makes sense
to have a %NULL sentinel. This would be for example useful to track
or construct a strv array with a GPtrArray.
As workaround for this missing feature you could use a GArray instead
(ugly) or to explicitly add the %NULL element. However the latter increases
the "len" of the array, which can be problematic if you want to still use
the GPtrArray for other purposes.
Add API for marking a GPtrArray as %NULL terminated. In that case, the
API will ensure that there is always a valid %NULL sentinel after the
array. Note that the API does not enforce that a %NULL terminated API
actually has any data allocated. That means, even with a %NULL terminated
array, pdata can still be %NULL (only if len is zero).
Add g_ptr_array_new_null_terminated() constructor. The null-terminated flag
cannot be cleared. Once the GPtrArray is flagged to be %NULL terminated, it
sticks. The purpose is that once a user checks whether a GPtrArray instance
is safe to be treated as a %NULL terminated array, the decision does
not need to be re-evaluated.
Also add a g_ptr_array_is_null_terminated(). That is useful because it
allows you to check whether a GPtrArray created by somebody else is safe
to use as a %NULL terminated array. Since there is no API to make an
array not %NULL terminated anymore, this is not error prone.
The new flag is tracked as a guint8 in GRealPtrArray. On common 64 bit
architectures this does not increase the size of the struct as it fits
in an existing hole. Note that this is not a bitfield because it's
probably more efficient to access the entire guint8. However, there is
still a 3 bytes hole (on common 32 and 64 architectures), so if we need
to add more flags in the future, we still have space for 24 bits,
despite the new flag not being a bitfield.
The biggest downside of the patch is the runtime overhead that most
operations now need to check whether %NULL termination is requested.
Includes some tweaks and additional tests by Philip Withnall.
https://gitlab.gnome.org/GNOME/glib/-/issues/353
Instead store a bit inside `GTimeoutSource` and `GIdleSource` to
indicate that they are one-shot sources, and that their callbacks have a
different type and should always be assumed to return `G_SOURCE_REMOVE`.
This should make one-shot idle and timeout sources a teeny weeny little
bit cheaper to set up.
From a suggestion here: https://gitlab.gnome.org/GNOME/glib/-/merge_requests/2684#note_1462917
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
This allows it to be reused and extended (internally) a little more.
This commit introduces no functional changes, but allows for more easy
additions in a following commit.
It introduces `GIdleSource` as a simple wrapper around `GSource`, which
will be extended in a following commit.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
This allows it to be reused and extended (internally) a little more.
This commit introduces no functional changes, but allows for more easy
additions in a following commit.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Many idle and timeout sources are installed as "one shot": called once
and immediately removed. While it's easy to write a simple callback that
returns G_SOURCE_REMOVE, it would also be useful to have some sort of
"visual" marker when reading the code; a way to immediately see that a
callback (which may be defined elsewhere in the code) is meant to be
invoked just once.
Includes additional unit tests by Philip Withnall.
Modified by Philip Withnall to omit the subdirectory and drop the
`refcount` suite as both seem like unnecessary over-categorisation.
Related to issue #1434
This avoids walking the construct params list
one extra time just to count when constructing
objects, for a small speedup of object construction
in the presence of construct params.
