book: indirection for faster message passing

This commit is contained in:
Jorge Aparicio 2019-04-22 22:21:46 +02:00
parent 485601245b
commit ccd7f4586b
5 changed files with 128 additions and 3 deletions

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@ -89,3 +89,27 @@ after the function, not the interrupt / exception. Example below:
``` console
$ cargo run --example binds
{{#include ../../../../ci/expected/binds.run}}```
## Indirection for faster message passing
Message passing always involves copying the payload from the sender into a
static variable and then from the static variable into the receiver. Thus
sending a large buffer, like a `[u8; 128]`, as a message involves two expensive
`memcpy`s. To minimize the message passing overhead one can use indirection:
instead of sending the buffer by value, one can send an owning pointer into the
buffer.
One can use a global allocator to achieve indirection (`alloc::Box`,
`alloc::Rc`, etc.), which requires using the nightly channel as of Rust v1.34.0,
or one can use a statically allocated memory pool like [`heapless::Pool`].
[`heapless::Pool`]: https://docs.rs/heapless/0.4.3/heapless/pool/index.html
Here's an example where `heapless::Pool` is used to "box" buffers of 128 bytes.
``` rust
{{#include ../../../../examples/pool.rs}}
```
``` console
$ cargo run --example binds
{{#include ../../../../ci/expected/pool.run}}```