When Meta’s fashionable apps, together with Instagram and Fb Messenger, utilised a decade-old C codebase for his or her messaging library, it led to issues with reminiscence administration and a subpar developer expertise. 

The corporate finally switched to Rust, one of the fashionable languages in the present day. 

In an episode of Meta Tech Podcast, three of the corporate’s engineers – Eliane W, Buping W, and Pascal Hartig shared their expertise with utilizing C, discussing the challenges confronted, the migration course of, and their success with Rust. 

The Issues With C

The corporate selected C for its velocity, compact binaries, and seamless integration on iOS by way of Core Basis and Android by way of JNI. Furthermore, it helped keep away from the additional overhead and complexity of C++ runtimes.

However because the codebase grew and extra engineers contributed, C’s limitations turned more and more painful bottlenecks. It introduced a number of reminiscence administration points, leading to a poor consumer expertise that led to crashes. 

Probably the most extreme points weren’t simply inconveniences; they have been labeled as Website Occasions, Meta’s time period for manufacturing incidents, demanding weeks of intensive debugging from a number of engineers. Guide reminiscence administration led to crashes that have been “extraordinarily arduous to debug”, usually stemming from use-after-free bugs or double-free errors that solely surfaced underneath particular situations.

“It took possibly half of the folks engaged on this complete massive undertaking to actually spend weeks to debug that,” Buping, who has been at Meta for 11 years, identified. 

C’s absence of recent abstractions led to a growth course of that hindered productiveness. Engineers needed to comply with error-prone patterns, declaring and initialising probably a whole bunch of variables firstly of features, then manually monitoring and liberating each, usually over a thousand strains later.

This sample pressured engineers to scroll by way of huge features simply to match allocations with deallocations, making code opinions a nightmare and bugs inevitable. 

“Now we have this horrible observe the place you allocate all of the variables in the beginning of a do-while loop, after which, 1,000 strains later, once you’re performed utilizing them, you launch all of them,” Elaine defined. 

Moreover, Meta’s open engineering tradition, the place anybody can modify any codebase, amplified the weak point of C. 

With out trendy language options like interfaces or robust sort programs, engineers couldn’t create clear abstractions that prevented code air pollution.

New contributors would add logging, error dealing with, or function flags instantly into current features, creating more and more unmaintainable code.

Meta’s transition to Rust systematically tackled these points whereas upholding the efficiency and portability wants of their cellular infrastructure. 

How Rust Eradicated These Challenges

Rust’s possession system prevents complete kinds of reminiscence bugs at compile time. The borrow checker avoids use-after-free, double-free, and information races earlier than code reaches manufacturing, eliminating bugs that prompted Meta’s most severe incidents.

“I believe one of many greatest issues about Rust is the compile-time reminiscence security enforcement. C++ doesn’t have that. Since quite a lot of the problems that we face within the day-to-day are associated to reminiscence administration, it doesn’t make sense that we wouldn’t select a language that combats that the majority successfully,” Elaine added. 

Furthermore, Rust’s tooling ecosystem offers the mandatory scaffolding for large-team growth by way of an built-in suite of developer instruments that work seamlessly collectively. 

For example, Rust analyser offers real-time sort hints, error suggestions, and autocompletion options. “Autocompletion has been nice, particularly with the AI-based model. You simply don’t have to write down quite a lot of code manually these days,” Buping mentioned. 

As well as, rustfmt mechanically codecs code on save, eliminating model debates that always plague massive engineering groups. 

Moreover, Rust additionally helped the corporate not solely remedy reminiscence security issues but in addition set up cleaner, extra maintainable coding requirements throughout its workforce. 

“C++ has quite a lot of bloat which you can probably add to, which could be very simple to abuse. All people has completely different experiences with C++ and has most popular methods of doing issues. It turns into more durable to make issues standardised,” Elaine mentioned, indicating why Meta selected Rust over different languages like C++.

“So I believe Rust being comparatively newer, we’re all form of on an excellent taking part in discipline, and we are able to all form of work collectively to resolve what the usual ought to be, which makes it loads simpler to handle that form of bloat,” she added. 

Furthermore, when Meta initially began that undertaking, there have been a number of variations of the errors. Groups needed to deal with a Home windows-specific concern, an Android emulator downside, an Apple Silicon concern, or perhaps a Linux downside. Nonetheless, with Rust, the corporate might apply all the brand new code to all the identical platforms the place their current C code runs.

“I believe we’ve come to some extent the place we’ve just about overcome all these kinks, and we are able to get to some extent the place you possibly can simply land the Rust code in all places our code is linked, which is just about additionally in all places,” Buping defined. 

The debugging expertise was additionally remarkably sturdy, working seamlessly throughout C and Rust boundaries, the place breakpoints, stack traces, and variable inspection all functioned reliably.

“Principally, can you place a debugger and may you place a breakpoint and have the debugger pause when the breakpoint will get hit? Are you able to see the stack hint? Are you able to see the values of the variables? All of these helps are there, which is superb for us,” Buping added. 

For groups managing legacy C/C++ codebases, Meta’s migration demonstrated that trendy programs languages can ship each improved developer expertise and manufacturing reliability. Whereas Meta’s incremental migration continues to be ongoing, the early outcomes have been promising for the corporate.