C++ Design for Concurrency

Scheduler (Abstraction 1)

Sender (Abstraction 2)

• Describe work
• Responsible for scheduling work on execution resources (threads, GPUs, …)
• Sends work to be done in place
• Monad (send a value)

Receiver (Abstraction 3)

• Where work terminates
• Value channel
• Error channel
• Stopped channel

Basis of control

• Sequence
• Decision
• Recursion

To prevent bugs

• Elimininate explicit synchronization
• Eliminate OS-level deadlock
• Eliminate data races

The Cost

• Use the framework for all synchronization
• Avoid shared mutable state
• Change your design approach

Framework problems

• There can be data race
• There can be deadlock
• Dropping messages

Design guidelines

• Focus - Each microservice should be focused on one task
• Independence - Microservices should not overlap in their functionality
• Value Types - For the messages
• Avoid blocking - Replace blocking calls with separate microservices
• State Machines - Each microservice can be modelled as a single-thread state machine

References

• Using the C++ Sender/Receiver Framework: Implement Control Flow for Async Processing - Steve Downey
• Designing for C++ Concurrency Using Message Passing - Anthony Williams - ACCU 2023