Escape analysis

Category: Safety in languages · Status: stub · Lessons: chapter 01, Threads

One line: The compiler deciding whether a local's address can outlive its frame, and moving the local to the heap when it can — which is how a language with a garbage collector lets a thread capture a local safely.

Also called: escapes to heap, moved to heap.

How it connects

flowchart LR
  n_dangling_pointer["Dangling pointer"]
  n_escape_analysis["Escape analysis"]
  n_escape_analysis -->|prevents| n_dangling_pointer
  classDef center stroke-width:3px
  class n_escape_analysis center
  classDef outside stroke-dasharray: 4 3
  class n_dangling_pointer outside

• Helps prevent: Dangling pointer
• See also: Object lifetime

In each language

Rust	None is needed for safety: a reference that would outlive its referent is a compile error instead, so the placement is the programmer's choice
Go	go build -gcflags=-m ↗ reports each decision, including moved to heap; the FAQ ↗ states the rule
Java	HotSpot may allocate a non-escaping object on the stack or split it into fields; JEP 8221340 ↗ tracks the analysis

Where to read more

• In this library: Can a thread borrow a local variable?
• Reference: Wikipedia: Escape analysis ↗