Typically, garbage collection strategies would start from the pointers on the stack and traverses the heap to determine which objects are live. The unreachable objects can be garbage collected.
Stop the World
A stop the world GC pause occurs when a runtime suspends an application’s threads to reclaim memory. During this pause, your service is effectively frozen. This is important to consider in:
- Low latency systems
- Distributed systems
- Corrupted writes (lease-lock example)
Remember to keep this in mind when designing systems. You can fix the lease-lock issue by using a fencing token.
Diagramming
Draw the Stack and the Heap at the point of execution like normal program understanding questions.
Reference Counting Scenario
In this situation here, Person1 and Person2 each have one reference even though they are unreachable, therefore memory is leaked.
Clean Up Options
- Don’t lol
- TUI applications usually just reclaim memory when they terminate, but most interactive programs cannot do this.
- Programming languages like C++ let you manage your own memory. This is why you want to implement destructors
- Automatic
- The programmer can just rely on automatic garbage collection to reclaim space by objects that are no longer needed. Most modern programming languages implement this. Rust is interesting here.
Related
- Reference Counting
- Mark & Sweep
- Semi-Space Copying Collection
- Generational Collection
- Object Allocation with Free List
- Fast Object Allocation
- Memory Safety and Language Selection
- DieHard
Choosing a strategy is about Engineering Design and judgement.