Publisher and subscriber disagree on ownership kind

Rule 26 · applies to publisher and subscriber matching · Back to all rules

Won't connect. Ownership kind must match exactly, either both SHARED or both EXCLUSIVE.

If you set a Writer Ownership kind together with a Reader Ownership kind that differs from it

Won't connect

Settings involved: Ownership and Ownership
What QoS Guard checks: [Writer.OWNST ≠ Reader.OWNST]

Example

An EXCLUSIVE writer and a SHARED reader on the same topic are incompatible.

How to fix it

Set the same Ownership kind on both the writer and the reader.

Why this rule is flagged

What the DDS specification says

OMG DDS §	QoS policy	Standard statement
§2.2.3.9	OWNERSHIP	The value of the OWNERSHIP kind offered must exactly match the one requested or else they are considered incompatible.

What the engine source code shows

Both engines reject endpoint matching when writer and reader ownership kinds differ.

Fast DDS implementation evidence

// EDP::valid_matching: offered and requested ownership kinds must match.
if (wdata->m_qos.m_ownership.kind != rdata->m_qos.m_ownership.kind)
{
    incompatible_qos.set(fastdds::dds::OWNERSHIP_QOS_POLICY_ID);
}

Cyclone DDS implementation evidence

// q_qosmatch.c: ownership kind mismatch prevents endpoint matching.
if ((mask & QP_OWNERSHIP) &&
        rd_qos->ownership.kind != wr_qos->ownership.kind)
{
    *reason = DDS_OWNERSHIP_QOS_POLICY_ID;
    return false;
}

Item	Value
Dataset	Download CSV
Fixed QoS setting	None
Tested variable	`writer_ownership`, `reader_ownership`
Tested values	`writer_ownership ∈ {SHARED, EXCLUSIVE}`, `reader_ownership ∈ {SHARED, EXCLUSIVE}`
Valid / boundary cases	`writer_ownership = reader_ownership`, including `SHARED ↔ SHARED` and `EXCLUSIVE ↔ EXCLUSIVE`
Violating cases	`writer_ownership != reader_ownership`, including `SHARED ↔ EXCLUSIVE` and `EXCLUSIVE ↔ SHARED`
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)	`writer_ownership`, `reader_ownership ∈ {SHARED, EXCLUSIVE}`	`SHARED ↔ SHARED` matched; `EXCLUSIVE ↔ SHARED` match rejected; `EXCLUSIVE ↔ EXCLUSIVE` and `SHARED ↔ EXCLUSIVE` were rejected at creation time
Fast DDS 2.14.6 (Jazzy)	`writer_ownership`, `reader_ownership ∈ {SHARED, EXCLUSIVE}`	Matched when ownership kinds were identical; match rejected when they differed
Cyclone DDS 0.10.5	`writer_ownership`, `reader_ownership ∈ {SHARED, EXCLUSIVE}`	Matched when ownership kinds were identical; match rejected when they differed

What you'll see when you run it

QoS Guard reports this mismatch as a structural conflict:

[STRUCTURAL] [sensor_pub] Writer.OWNST <-> Reader.OWNST (Writer≠Reader)

At runtime the two endpoints never connect. Ownership is compatible under the Requested-Offered (RxO) rule only when both sides choose the same kind. Here the reader requests EXCLUSIVE while the writer offers SHARED, so the kinds differ and discovery refuses the match. No connection forms and no samples flow, with no error printed.