Code size analysis#

pw_async2: Cooperative async tasks for embedded

Core async2 implementation#

The following table shows the code size cost of adding pw_async2 to a system. These size reports assume a baseline system with an RTOS which already uses a handful of core Pigweed components including HAL abstractions and pw_allocator.

The first row captures the core of pw_async2: the dispatcher, tasks, and wakers, using the pw_async2_basic dispatcher backend. This is the minimum size cost a system must pay to adopt pw_async2. The following row demonstrates the cost of adding another task to this system. Of course, the majority of the cost of the task exists within its implementation — this simply shows that there is minimal internal overhead.

The following two rows in the table deal with the pair of OnceSender and OnceReceiver types, which allow for returning a delayed result from an async function, similar to a Future type in other languages. This type is templated on its stored value, causing specialization overhead for each type sent through the sender/receiver pair. The first OnceSender row showcases the base cost of using a OnceSender and OnceReceiver; the second row adds another template specialization on top of this to demonstrate the incremental cost.

Label

Segment

Delta

Full cost of including pw_async2

+2,492

+168

Base incremental cost of adding a task to an existing async system

+48

Size of OnceSender / OnceReceiver

+952

Cost of additional OnceSender / OnceReceiver template specialization

+776