Node, Javascript - Garbage Collection

This post is a summary for The modern Javascript Tutorial.

Reachability

The main concept of memory managament in JavaScript is Reachability.
Reachable values are those that are accessible or usable somehow. They are guaranteed to be stored in memory.

• Root
  • Local variables and parameters of the current function
  • Variables and parameters for other functions on the current chain of nested calls.
  • Global variables

Internal Algorithm

• mark-and-seep
  • The garbage collector takes roots and “marks” (remembers) them.
  • Then it visits and “marks” all references from them.
  • Then it visits marked objects and marks their references. All visited objects are remembered, so as not to visit the same object twice in the future.
  • …And so on until every reachable (from the roots) references are visited.
  • All objects except marked ones are removed.
• Optimizations
  • Generational Collection: Split obejcts to “new ones” and “old ones”. Clean up new ones aggressively
  • Incremental Collection: Do not try to mark whole objects. Split the garbage collection into pieces
  • Idle-time Collection: Garbage collector runs only while the CPU is idle