Rust as a language for high performance GC implementation

Abstract

High performance garbage collectors build upon performancecritical low-level code, typically exhibit multiple levels of concurrency, and are prone to subtle bugs. Implementing, debugging and maintaining such collectors can therefore be extremely challenging. The choice of implementation language is a crucial consideration when building a collector. Typically, the drive for performance and the need for efficient support of low-level memory operations leads to the use of low-level languages like C or C++, which offer little by way of safety and software engineering benefits. This risks undermining the robustness and flexibility of the collector design.Rust's ownership model, lifetime specification, and reference borrowing deliver safety guarantees through a powerful static checker with little runtime overhead. These features make Rust a compelling candidate for a collector implementation language, but they come with restrictions that threaten expressiveness and efficiency.We describe our experience implementing an Immix garbage collector in Rust and C. We discuss the benefits of Rust, the obstacles encountered, and how we overcame them. We show that our Immix implementation has almost identical performance on micro benchmarks, compared to its implementation in C, and outperforms the popular BDW collector on the gcbench micro benchmark. We find that Rust's safety features do not create significant barriers to implementing a high performance collector. Though memory managers are usually considered low-level, our high performance implementation relies on very little unsafe code, with the vast majority of the implementation benefiting from Rust's safety. We see our experience as a compelling proof-of-concept of Rust as an implementation language for high performance garbage collection. } 132 } 133 134 // functions are inlined so we omit 135 // parameters/arguments 136 #[inline(always)] 137 #[cfg(feature = "parallel-gc")] 138 pub fn steal_trace_object(...) { 139 let addr = obj.to_address();

Floorplan: spatial layout in memory management systems

“…• Boilerplate reduction and memory safety results from integrating a Floorplan specification with the Rust implementation of immix [13].…”

“…Often such generic pointers are distinguishable based on their value. Suspicious pointer values are manually detected based on intrinsic properties, such [13].…”

“…Figure 5 shows the Floorplan specification for the Rust implementation [13] of the immix garbage collection algorithm. The heap is represented as a Region 1 parametrized by three formal arguments: the number of blocks, lines, and number of words wrds in the region.…”

“…In this [13] version of immix, objects do not have a header word. Instead each cell's corresponding RefBits 24 in the refs 17 array tracks which words 13 of memory in the Space 2 correspond to the start of an object, OBJ_-START 26 .…”

“…Grammars are a natural choice because they match the configuration of most modern memory managers, which comprise layers of code that carve up memory into smaller and smaller pieces. Every [1], [2], [5], [6], [8], [11], [12], [13], [15], [16], memory manager we've studied exhibits this allocation scheme.…”