Also known as: garbage collection, GC

Garbage collection (GC) is a form of automatic memory management in which the language runtime reclaims memory the program can no longer reach, so the programmer never has to free it by hand.¹

The collector keeps objects reachable from the program's roots and reclaims the rest.

How it works

The runtime periodically determines which heap objects are still reachable by following references from a set of roots (stack variables, globals, registers). Anything with no path from the roots is garbage and its memory is reclaimed. Common strategies include mark-and-sweep (mark reachable objects, sweep the rest), generational collection (collect short-lived objects more often), and reference counting (track how many references point at each object).¹

Trade-offs

GC eliminates entire classes of bugs that plague manual memory code — use-after-free, double-free, and many memory leaks — and removes a great deal of boilerplate. The price is runtime overhead and occasional pauses (historically “stop-the-world” collections),¹ which is why latency-sensitive and systems languages such as C and C++ leave memory to the programmer, and why Rust achieves safety at compile time without a collector at all.

In practice

Most mainstream languages are garbage-collected, including Go, Java, Python, and C#. Their collectors have grown sophisticated enough that GC pauses are a non-issue for the vast majority of applications.

Sources

1. Garbage collection (computer science) — Wikipedia, on reachability-based reclamation, collection strategies, and the overhead/pause trade-offs. ↩ ↩² ↩³

See also

• Memory management
• Static binary
• Compiler
• Go
• Java
• C
• Type system

Learn it step by step

• Memory management across languages
• Performance vs productivity