How does PHP garbage collection and memory internals work?

PHP manages memory using reference counting combined with cyclic garbage collection.

PHP internally uses zvals to represent variables. Each zval maintains a reference counter tracking how many variables reference the same memory.

When reference counts drop to zero, memory becomes eligible for cleanup.

However, circular references create problems:

Reference counts never reach zero.

To solve this, PHP includes a cyclic garbage collector that periodically scans for circular references.…