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reserve: Fix leaking NameLost signals after release+acquire

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The use of the pseudo-blocking D-Bus calls leads to the problem that
NameLost signals are received after the reply to ReleaseName().

The problem with this is that a later acquisition of the same audio
device can potentially receive the NameLost signal corresponding to
the previous instance, due to the fact that the signal hasn't been
popped from the D-Bus message queue.

The simplest approach to solve this problem is to poll the actual name
owner from the D-Bus daemon, in order to make sure that we did really
lose the name.

The proposal uses a blocking call to GetNameOwner to avoid incosistent
states in the internal APIs: it would otherwise be possible to have a
"busy" device before the reservation has been lost, in the unlikely
case if some other process acquires the name before we got the
confirmation that the NameLost was actually true.
This commit is contained in:
Mikel Astiz 2013-01-30 09:30:31 +01:00 • committed by Tanu Kaskinen
parent 88a7b31ca7
commit 1db09d3013
1 changed files with 17 additions and 0 deletions
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17
src/modules/reserve.c
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@ -293,6 +293,7 @@ static DBusHandlerResult filter_handler(
rd_device *d;
DBusError error;
char *name_owner = NULL;
dbus_error_init(&error);
@ -310,6 +311,21 @@ static DBusHandlerResult filter_handler(
goto invalid;
if (strcmp(name, d->service_name) == 0 && d->owning) {
/* Verify the actual owner of the name to avoid leaked NameLost
* signals from previous reservations. The D-Bus daemon will send
* all messages asynchronously in the correct order, but we could
* potentially process them too late due to the pseudo-blocking
* call mechanism used during both acquisition and release. This
* can happen if we release the device and immediately after
* reacquire it before NameLost is processed. */
if (!d->gave_up) {
const char *un;
if ((un = dbus_bus_get_unique_name(c)) && rd_dbus_get_name_owner(c, d->service_name, &name_owner, &error) == 0)
if (strcmp(name_owner, un) == 0)
goto invalid; /* Name still owned by us */
}
d->owning = 0;
if (!d->gave_up) {
@ -326,6 +342,7 @@ static DBusHandlerResult filter_handler(
}
invalid:
free(name_owner);
dbus_error_free(&error);
return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;