Heap and Stack

The stack and heap can be anywhere in physical or virtual memory.

The heap is memory set aside for dynamic allocation:

• Allocated when the application starts by the runtime.
• Managed by the Garbage Collector.
• Data stored on the heap is valid as long as it can be tracked back to a reference type variable on a stack.
  • When no more pointers point to the data, it becomes garbage.
• Heap memory is reclaimed when the application exits.

The stack is memory set aside as overhead space for a thread of execution:

• It is faster than heap memory because:
  • It is managed directly by the CPU
  • It uses a LIFO mechanism (most recently reserved block is the first to be freed), which means it is more likely to have the data in its L1 or L2 cache.
• It is a consecutive block of memory that is allocated when a thread is first created.
• Every function call in a thread shares the same stack.
• The stack pointer points to the last location where memory was allocated.
• When a function is invoked, a new stack frame is created for that function’s data.
• When a function exits, its return values are copied back to the calling function via the stack:
  • The stack pointer is then moved back to the beginning of the stack frame.
• When the thread exits, the stack is reclaimed (or reused by the next thread).