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Flow: Actor-based language for C++, used by FoundationDB
- pmarreck 10mo agohow does this compare to the inbox and supervisor model of erlang/elixir?
- yetihehe 10mo agoIt doesn't. It's "promise" based, not "communicating sequential processes". Erlang has more preemptive scheduling, a "thread" can be preempted at any time, here you can only be synchronized when you wait for result. It is called "actor-based", because only functions tagged as "actor" can call waiting functions. This is more node.js-like communication than erlang.
- jacquesm 10mo agoBy they looks of it they changed the word 'async' to 'actor' because they thought it was cool not because it actually uses the actor pattern. Which to me seems to be namespace pollution.
- junon 10mo agoUnfounded guess, they probably didn't want to bump into the new C++ keywords for async/await.
- voidmain 10mo agoIf I were designing it today rather than in... 2008?, I would use the terms 'async' and 'await' because they are a lingua franca now. And for a modern audience that already knows what promises are it probably makes sense to start the explanation with that part. But the thing as a whole was intended to build lightweight asynchronously communicating sequential processes with private state that can be run locally or in a distributed way transparently, restarted on failure, etc. I don't think the choice of terms was obviously a crime at the time.
- thesz 10mo agoThey build channels on top of these "promises" and "futures" and this made them square into communicating sequential processes category. Also, you can look at promise-future pair as a single-element channel, again, it's CSP. BTW, Erlang does not implement CSP fully. Its' interprocess communication is TCP based in general case and because of this is faulty.
- yetihehe 10mo agoIt is not TCP based. In Erlang processes have mailboxes. But they don't have promises, you send a message and wait for response with timeout or do something else. And TCP is only used between nodes (vm instances). But you can use any communication channel (UDP, unix sockets, tls, serial port, some other process doing funny things). > Its' interprocess communication is TCP based in general case and because of this is faulty. What? It's faulty because of TCP? No, in Erlang it is assumed that communication can be faulty for a lot of reasons, so you have to program to deal with that and the standard library gives you tools to deal with this.
- thesz 10mo agoThere is no such thing as "Communicating Sequential Processes with faulty channels and processes." I tried to find something like that, fruitlessly. This means that Erlang does not implement CSP, it implements something else. Again, general case of communication between Erlang processes includes communication between processes on different machines.
- pmarreck 10mo ago> BTW, Erlang does not implement CSP fully. Specific evidence? > Its' interprocess communication is TCP based in general case No, it is not. Only between machines is that true. > and because of this is faulty. LOL, no. Why are you rolling with "speaking a whole lot of BS based on ignorance" today? On the other hand, I now understand that one impediment to Elixir adoption is apparently "people repeating a lot of bullshit misinformation about it"
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- hawk_ 10mo agoOk a related note, how does it compare to SeaStar?
- websiteapi 10mo agoI'm always hearing about FoundationDB but not much about who uses it. I know Deno and obviously Apple is using it. Who else? I'd love to hear some stories about it.
- nish__ 10mo agoApple uses it for iMessage I believe.
- adobrawy 10mo agoSnowflake uses it as primary database for their metadata. https://www.snowflake.com/en/blog/how-foundationdb-powers-snowflake-metadata-forward/ https://www.snowflake.com/en/blog/how-foundationdb-powers-sn...
- dpedu 10mo agoMy company (Matterport, YC Winter '12) uses it to store metadata about 3d models. I really don't have that much to say about it because it's not my primary area of focus, and besides that, has been extremely reliable and hands-off, administration-wise. I particularly love that you can change redundancy modes on the fly, for example those listed here[1], and FDB will automatically re-arrange data to your liking, all without downtime. It handles offline/missing or replacing nodes quite well, and I credit my coworker's great efforts to make it work on top of Kubernetes for making our lives so much easier. 1: https://apple.github.io/foundationdb/configuration.html#choosing-a-redundancy-mode https://apple.github.io/foundationdb/configuration.html#choo...
- quettabit 10mo agoAt s2.dev (a serverless datastore for real-time streaming data), we started with DynamoDB for our metadata store, but our access patterns kept running into per-partition throughput limits. We switched to FoundationDB, and it’s been great so far.
- CharlesW 10mo agoSnowflake uses it: https://www.snowflake.com/en/blog/how-foundationdb-powers-snowflake-metadata-forward/ https://www.snowflake.com/en/blog/how-foundationdb-powers-sn... Tigris uses it: https://www.tigrisdata.com/blog/building-a-database-using-foundationdb/ https://www.tigrisdata.com/blog/building-a-database-using-fo... A good collection of papers, blog posts, talks, etc.: https://github.com/FoundationDB/awesome-foundationdb https://github.com/FoundationDB/awesome-foundationdb
- thisisauserid 10mo agoHow did they come up with such an original and unique name? Apple does it again.
- Hayvok 10mo agoFoundationDB was originally a startup, purchased by Apple in 2015.
- ttul 10mo agoType-safe message-passing is such a wonderful programming paradigm - and not just for distributed applications. I remember using QNX back in the 1990s. One of its fabulous features was a C message passing library allowing you to send arbitrary binary structs from one process to another. In the context of realtime software development, you often find yourself having one process that watches for events from a certain device, modify the information somehow, and then pass it on to another process that ends up doing something else. The message-passing idiom was far superior to what was available in Linux at the time (pipes and whatnot) because you were able to work with C structs. It was not strictly type safe (as is the case with FoundationDB’s library), but for the 1990s it was pretty great.
- mrbnprck 10mo agoI remnber that ASN.1 does sth similar. You'd give a ASN.1 notation to a language generator (aka producing C) and not have to worry about parsing the actual structure anymore!
- IshKebab 10mo agoLiterally every schema-based serialisation format does this. ASN.1 is a pretty terrible option. The best system for this I've ever used was Thrift, which properly abstracts data formats, transports and so on. https://thrift.apache.org/docs/Languages.html https://thrift.apache.org/docs/Languages.html Unfortunately Thrift is a dead (AKA "Apache") project and it doesn't seem like anyone since has tried to do this. It probably didn't help that there are so many gaps in that support matrix. I think "Google have made a thing! Let's blindly use it!" also helped contribute to its downfall, despite Thrift being better than Protobuf (it even supports required fields!). Actually I just took a look at the Thrift repo and there are a surprising number of commits from a couple of people consistently, so maybe it's not quite as dead as I thought. You never hear about people picking it for new projects though.
- computably 10mo agoFB maintains a distinct version of Thrift from the one they gave to Apache. fbthrift is far from dead as it's actively used across FB. However in typical FB fashion it's not supported for external use, making it open source in name (license) only. As an interesting historical note, Thrift was inspired by Protobuf.
- boris 10mo agoThe strangest thing about Flow is that its compiler is implemented in C#. So if you decide to use it in your C++ codebase, you now have a C#/.Net dependency, at least at build time.
- jermaustin1 10mo agoI wonder why that decision was made. I know why I, a C# developer, would make that decision, but why Apple?
- jeffbee 10mo agoThis entire codebase was acquired by apple in a state of substantial completion and since then relatively little has changed.
- atn34 10mo agoThe original developers (before Apple bought the company) used Visual Studio on Windows
- rdtsc 10mo agoSomeone knew C# and was good at parsers, would be my guess. It could have just as easily been Scala or something else.
- boxfire 10mo agoIt’s also funny because it’s a small, incomplete, incompatible subset of c++… seems like a perfect LLVM / clang rewriter case too, it would be easy to convert and be pure c++. Hell even a clang plugin to put the compile time into one process wouldn’t be awful. But i wonder looking at the rewrites if there’s not a terribly janky way to not need a compiler, if at some runtime cost of contextual control flow info.
- whizzter 10mo agoNot even that, this should more or less be directly translateable to C++ 20 coroutines.
- culebron21 10mo agoAt first glance, it looks like Rust's channels with a polymorphic type -- when you receive from a channel, you do match and write branches for each variant of the type. But I wonder if this can be a better abstraction than async. (And whether I can build something like this in existing Rust.)
- SoKamil 10mo agoFoundationDB is awesome testing wise as they have deterministic simulation testing [1] that can simulate distributed and operating system failures. > We wanted FoundationDB to survive failures of machines, networks, disks, clocks, racks, data centers, file systems, etc., so we created a simulation framework closely tied to Flow. By replacing physical interfaces with shims, replacing the main epoll-based run loop with a time-based simulation, and running multiple logical processes as concurrent Flow Actors, Simulation is able to conduct a deterministic simulation of an entire FoundationDB cluster within a single-thread! Even better, we are able to execute this simulation in a deterministic way, enabling us to reproduce problems and add instrumentation ex post facto. This incredible capability enabled us to build FoundationDB exclusively in simulation for the first 18 months and ensure exceptional fault tolerance long before it sent its first real network packet. For a database with as strong a contract as the FoundationDB, testing is crucial, and over the years we have run the equivalent of a trillion CPU-hours of simulated stress testing. [1]https://pierrezemb.fr/posts/notes-about-foundationdb/#simulation-driven-development https://pierrezemb.fr/posts/notes-about-foundationdb/#simula...
- gioazzi 10mo agoAnd they went on to build Antithesis to deliver the same capabilities to other systems, pretty cool stuff! [1]: https://antithesis.com/company/backstory/ https://antithesis.com/company/backstory/
- menaerus 10mo agoPretty cool. For it to scale they are building their own deterministic hypervisor too [0], but also a new distributed database to support their workloads more efficiently [1]. [0] https://antithesis.com/blog/deterministic_hypervisor https://antithesis.com/blog/deterministic_hypervisor [1] https://antithesis.com/blog/2025/testing_pangolin https://antithesis.com/blog/2025/testing_pangolin
- deleted 10mo ago[deleted]
- srinikhilr 10mo agoiirc there was a ticket/doc about FoundationDB deprecating usage of this and moving to C++ coroutines.
- maxmcd 10mo agoMaybe this? https://forums.foundationdb.org/t/swift-or-c-20-coroutine-which-is-the-future-of-fdb/4592/2 https://forums.foundationdb.org/t/swift-or-c-20-coroutine-wh...