JVM Memory Model and Garbage Collection
1. JVM Memory Model
Overview
The JVM (Java Virtual Machine) Memory Model defines how threads interact through memory and what behaviors are allowed in multi-threaded programs.
Memory Areas
- Heap Memory
- Stack Memory
- Method Area
- Program Counter Register
- Native Method Stack
Heap Memory
Heap memory is used for dynamic memory allocation and is shared among all threads. Objects and their instance variables are stored here.
Stack Memory
Stack memory is thread-specific, used to store local variables and method call information.
2. Garbage Collection
What is Garbage Collection?
Garbage Collection (GC) is the process of automatically identifying and reclaiming memory that is no longer in use by the program.
Types of Garbage Collection
- Mark and Sweep
- Generational Garbage Collection
- Reference Counting
How Garbage Collection Works
GC typically works in phases:
Mark phase: Identify which objects are reachable.
Sweep phase: Reclaim memory used by unreachable objects.Example: Enabling Garbage Collection Logging
-Xlog:gc*:file=gc.log:time3. Best Practices
Memory Management Tips
- Minimize object creation.
- Use object pools for frequently used objects.
- Leverage weak references where applicable.
- Monitor memory usage regularly.
- Optimize data structures for memory efficiency.
4. FAQ
What is the difference between heap and stack memory?
Heap memory is for dynamic allocations and shared across threads, while stack memory is used for method execution and is thread-specific.
How can I force garbage collection?
You can suggest garbage collection using System.gc(), but it's not guaranteed.
What are the performance impacts of garbage collection?
GC can introduce latency, especially in large applications. It's important to tune it based on your application's behavior and memory usage.