Phony
![GoDoc](https://godoc.org/github.com/Arceliar/phony?status.svg)
Phony is a Pony-inspired proof-of-concept implementation of shared-memory actor-model concurrency in the Go programming language. Actor
s automatically manage goroutines and use asynchronous causal messaging (with backpressure) for communcation. This makes it easy to write programs that are free from deadlocks, goroutine leaks, and many of the for
loops over select
statements that show up in boilerplate code. The down side is that the code needs to be written in an asynchronous style, which is not idiomatic to Go, so it can take some getting used to.
Benchmarks
goos: linux
goarch: amd64
pkg: github.com/Arceliar/phony
cpu: Intel(R) Core(TM) i5-10300H CPU @ 2.50GHz
BenchmarkLoopActor-8 38022962 29.83 ns/op 0 B/op 0 allocs/op
BenchmarkLoopChannel-8 29876192 38.50 ns/op 0 B/op 0 allocs/op
BenchmarkSendActor-8 14235270 82.94 ns/op 0 B/op 0 allocs/op
BenchmarkSendChannel-8 8372472 143.9 ns/op 0 B/op 0 allocs/op
BenchmarkRequestResponseActor-8 10360731 116.6 ns/op 0 B/op 0 allocs/op
BenchmarkRequestResponseChannel-8 4226506 285.8 ns/op 0 B/op 0 allocs/op
BenchmarkBlock-8 2662929 450.9 ns/op 32 B/op 2 allocs/op
PASS
ok github.com/Arceliar/phony 9.463s
These are microbenchmarks, but they seem to indicate that Actor
messaging and goroutine+channel operations have comparable cost. I suspect that the difference is negligible in most applications.
Implementation Details
The code base is short, under 100 source lines of code as of writing, so reading the code is probably the best way to see what it does, but that doesn't necessarily explain why certain design decisions were made. To elaborate on a few things:
-
Phony only depends on packages from the standard library:
runtime
for some scheduler manipulation (Gosched()
).sync
for sync.Pool
, to minimize allocations.sync/atomic
to implement the Inbox
's message queues.
-
Attempts were make to make embedding and composition work:
Actor
is an interface
satisfied by the Inbox
struct
.- The zero value of an
Inbox
is a fully initialized and ready-to-use Actor
- This means any
struct
that anonymously embeds an Inbox
is an Actor
struct
s that don't want to export the Actor
interface can embed it as a field instead.
-
Inbox
was implemented with scalability in mind:
- The
Inbox
is basically an atomically updated single-consumer multiple-producer linked list. - Pushing a message is wait-free -- no locks, spinlocks, or
CompareAndSwap
loops. - Popping messages is wait-free in the normal case, with a busy loop (
LoadPointer
) if popping the last message lost a race with a push. - When backpressure is required, it's implemented by sending two extra messages (one to the receiver of the original message, and one to the sender).
-
The implementation aims to be as lightweight as reasonably possible:
- On
x86_64
, an empty Inbox
is 24 bytes, and messages overhead is 16 bytes, or half that on x86
. - An
Actor
with an empty Inbox
has no goroutine. - This means that idle
Actor
s can be collected as garbage when they're no longer reachable, just like any other struct
.