Publish-Subscribe#
Publish-Subscribe Communication Model#
A popular unidirectional, multi-producer, multi-consumer messaging pattern that decouples the producer (publisher) from the consumer (subscriber). This enables each participant to have their own lifecycle and operate completely independently. Publishers send messages without knowing who will receive them, while subscribers express interest in receiving payloads from a service and are automatically connected to matching publishers.
The publish-subscribe messaging pattern excels at communicating large payloads to multiple participants. The zero-copy capability enables essentially constant latency regardless of payload size.
The pattern is not optimal for cases where data must be kept available to participants indefinitely (blackboard) or when two-way communication is required (request-response).
Mechanism#
Publish-Subscribe over Shared Memory#
The publish-subscribe messaging pattern is implemented using data structures in shared memory. The following structures are involved:
Payload Segment
A region in shared memory used to communicate payload data between participants
Publishers have a payload segment to share samples with subscribers
The organization of memory in the payload segment depends on the allocator used in the
iceoryx2deploymentThis flexibility allows different deployments (e.g. desktop applications vs. safety-critical applications) to utilize a different strategy appropriate to their use-case
Offset Channel
A channel for communicating the offsets of payloads within the payload segment
Each publisher-subscriber pair has their own offset channel
Further Reading#
See how the Event messaging pattern can be used to coordinate participants.
See how to set up a basic PublishSubscribe service.
See how to set up a PublishSubscribe service with dynamic memory allocations.