Public bug reported:
MirSurfaceItem::dropPendingBuffers contains a potentially
infinite/indefinite loop:
void MirSurfaceItem::dropPendingBuffers()
{
QMutexLocker locker(&m_mutex);
const void* const userId = (void*)123; // TODO: Multimonitor
support
while (m_surface->buffers_ready_for_compositor(userId) > 0) {
// The line below looks like an innocent, effect-less, getter. But as
this
// method returns a unique_pointer, not holding its reference causes the
// buffer to be destroyed/released straight away.
m_surface->compositor_snapshot(userId)->buffer();
qCDebug(QTMIR_SURFACES) << "MirSurfaceItem::dropPendingBuffers()"
<< "surface =" << this
<< "buffer dropped."
<< m_surface->buffers_ready_for_compositor(userId)
<< "left.";
}
}
The issue is the value of buffers_ready_for_compositor() could
theoretically grow just as quickly as you're consuming the buffers. So
that loop has no definite number of iterations before exiting.
The simple solution is to check buffers_ready_for_compositor() once,
save the result and use a for loop up to that limit. However even that's
an overkill. If you look at the purpose of dropPendingBuffers, it's a
misnomer and it should really be "dropPendingBuffer" as it only really
needs to consume a single frame to achieve its goal of unblocking the
client. No loop required.
** Affects: qtmir
Importance: Undecided
Status: New
** Affects: qtmir (Ubuntu)
Importance: Undecided
Status: New
** Description changed:
MirSurfaceItem::dropPendingBuffers contains a potentially
infinite/indefinite loop:
void MirSurfaceItem::dropPendingBuffers()
{
- QMutexLocker locker(&m_mutex);
+ QMutexLocker locker(&m_mutex);
- const void* const userId = (void*)123; // TODO: Multimonitor
+ const void* const userId = (void*)123; // TODO: Multimonitor
support
- while (m_surface->buffers_ready_for_compositor(userId) > 0) {
- // The line below looks like an innocent, effect-less, getter. But as
this
- // method returns a unique_pointer, not holding its reference causes
the
- // buffer to be destroyed/released straight away.
- m_surface->compositor_snapshot(userId)->buffer();
- qCDebug(QTMIR_SURFACES) << "MirSurfaceItem::dropPendingBuffers()"
- << "surface =" << this
- << "buffer dropped."
- << m_surface->buffers_ready_for_compositor(userId)
- << "left.";
- }
+ while (m_surface->buffers_ready_for_compositor(userId) > 0) {
+ // The line below looks like an innocent, effect-less, getter. But as
this
+ // method returns a unique_pointer, not holding its reference causes
the
+ // buffer to be destroyed/released straight away.
+ m_surface->compositor_snapshot(userId)->buffer();
+ qCDebug(QTMIR_SURFACES) << "MirSurfaceItem::dropPendingBuffers()"
+ << "surface =" << this
+ << "buffer dropped."
+ << m_surface->buffers_ready_for_compositor(userId)
+ << "left.";
+ }
}
The issue is the value of buffers_ready_for_compositor() could
theoretically grow just as quickly as you're consuming the buffers. So
that loop has no definite number of iterations before exiting.
The simple solution is to check buffers_ready_for_compositor() once,
- save the result and use a for loop up to that limit. However event
- that's an overkill. If you look at the purpose of dropPendingBuffers,
- it's a misnomer and it should really be "dropPendingBuffer" as it only
- really needs to consume a single frame to achieve its goal; no loop
- required.
+ save the result and use a for loop up to that limit. However even that's
+ an overkill. If you look at the purpose of dropPendingBuffers, it's a
+ misnomer and it should really be "dropPendingBuffer" as it only really
+ needs to consume a single frame to achieve its goal; no loop required.
** Also affects: qtmir (Ubuntu)
Importance: Undecided
Status: New
** Description changed:
MirSurfaceItem::dropPendingBuffers contains a potentially
infinite/indefinite loop:
void MirSurfaceItem::dropPendingBuffers()
{
QMutexLocker locker(&m_mutex);
const void* const userId = (void*)123; // TODO: Multimonitor
support
while (m_surface->buffers_ready_for_compositor(userId) > 0) {
// The line below looks like an innocent, effect-less, getter. But as
this
// method returns a unique_pointer, not holding its reference causes
the
// buffer to be destroyed/released straight away.
m_surface->compositor_snapshot(userId)->buffer();
qCDebug(QTMIR_SURFACES) << "MirSurfaceItem::dropPendingBuffers()"
<< "surface =" << this
<< "buffer dropped."
<< m_surface->buffers_ready_for_compositor(userId)
<< "left.";
}
}
The issue is the value of buffers_ready_for_compositor() could
theoretically grow just as quickly as you're consuming the buffers. So
that loop has no definite number of iterations before exiting.
The simple solution is to check buffers_ready_for_compositor() once,
save the result and use a for loop up to that limit. However even that's
an overkill. If you look at the purpose of dropPendingBuffers, it's a
misnomer and it should really be "dropPendingBuffer" as it only really
- needs to consume a single frame to achieve its goal; no loop required.
+ needs to consume a single frame to achieve its goal of unblocking the
+ client. No loop required.
--
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https://bugs.launchpad.net/bugs/1477430
Title:
MirSurfaceItem::dropPendingBuffers contains a potentially infinite
loop
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https://bugs.launchpad.net/qtmir/+bug/1477430/+subscriptions
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