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Auto-dispose on unregister races exclusive-ownership failover

Rule 16 · applies to the publisher · Back to all rules

Breaks a guarantee. When the owner unregisters, auto-dispose can dispose the instance before ownership fails over, so the backup writer's data is treated as disposed.

If you set Ownership = EXCLUSIVE together with Writer autodispose_unregistered_instances = true
Breaks a guarantee

Example

The primary writer exits and auto-disposes the instance. The reader marks it disposed instead of switching to the still-live backup writer.

How to fix it

Disable autodispose_unregistered_instances on exclusive-ownership topics that use redundant writers.

Why this rule is flagged

What the DDS specification says

The DDS specification does not settle this case on its own, so the rule rests on the engine's implementation and direct measurement.

What the engine source code shows

Under exclusive ownership, the current owner state is cleared when the owning writer is unregistered. The autodispose/unregister path therefore interacts with ownership failover: once the current owner is cleared, another writer can become the owner.

Fast DDS implementation evidence

// writer_unregister(): owner clear and re-selection
if (writer_guid == current_owner.first)
{
    current_owner.second = 0;
    current_owner.first  = fastrtps::rtps::c_Guid_Unknown;

    if (ALIVE_INSTANCE_STATE == instance_state)
    {
        update_owner();
    }
}

Source: DataReaderInstance.hpp writer unregister / ownership update path.

Cyclone DDS implementation evidence

// unregister path: unregister the writer from the reader history cache
if (delta < 0 && rd->rhc)
{
    struct ddsi_writer_info wrinfo;
    ddsi_make_writer_info(&wrinfo, &pwr->e, pwr->c.xqos, DDSI_STATUSINFO_UNREGISTER);
    ddsi_rhc_unregister_wr(rd->rhc, &wrinfo);
}

// unregister releases the live-owner marker
if (inst->wr_iid_islive && wrinfo->iid == inst->wr_iid)
{
    inst->wr_iid_islive = 0;
    inst->strength = 0;
}

Source: ddsi_endpoint.c unregister path and dds_rhc_default.c ownership-state release path.

In both implementations, unregistering the current writer clears the ownership state under exclusive ownership. With autodispose_unregistered_instances = true, this writer-lifecycle path can therefore trigger ownership failover behavior.

What the measurements show

Item Value
Dataset Download CSV
Fixed QoS setting None
Tested variable OWNST.kind, WDLIFE.autodispose_unregistered_instances
Tested values OWNST ∈ {SHARED, EXCLUSIVE}, WDLIFE.autodispose ∈ {true, false}
Rule-relevant case OWNST = EXCLUSIVE, WDLIFE.autodispose = true
Tested engines / versions Fast DDS 2.6.11 (Humble), Fast DDS 2.14.6 (Jazzy), Cyclone DDS 0.10.5
Network setting RTT = 1 ms, loss = 0%, PP = 50 ms, message size = 1024 B
Engine Tested setting Observed behavior
Fast DDS 2.6.11 (Humble) OWNST ∈ {SHARED, EXCLUSIVE}, WDLIFE.autodispose ∈ {true, false} Profile accepted, matched, and delivered; ownership failover observed
Fast DDS 2.14.6 (Jazzy) OWNST ∈ {SHARED, EXCLUSIVE}, WDLIFE.autodispose ∈ {true, false} Profile accepted, matched, and delivered; ownership failover observed with average latency around 385 ms
Cyclone DDS 0.10.5 OWNST ∈ {SHARED, EXCLUSIVE}, WDLIFE.autodispose ∈ {true, false} Profile accepted, matched, and delivered; ownership failover observed with average latency around 37 ms