CODEWITHSUNDEEP
phpheap-memorystack-memorydynamic-languages
gorgi93
gorgi93

Reputation: 2535

Stack and heap in PHP?

I am learning about operating systems and the thing that I do not understand exactly are heaps and stacks. I know the benefits and how each works, but in the case of dynamic languages I can not figure out how is the stack allocated.

In static typed languages all primitive data types are stored on the stack since they are small and will be deallocated more or less in the same order they were allocated, however in languages like PHP this is not known until the run time. So how is the stack size and variable allocation possible?

If I understand correctly stack size is determined on compile time by analysing number of primitive data types and some offset. How is the process done in PHP or other dynamic languages?

If this question is kick in the dark, please give me some guides how to learn about this

Upvotes: 8

Views: 9954

Answers (2)

The Mask
The Mask

Reputation: 17427

In the case of a dynamic programming language, the intepreter takes care of that. An interpret act is roughly like a computer. Let's assume a C-like interpreted programming language running on 32-bit machine:

c = 10;

Basically the following happens to every expression, in a minimal interpret:

  • the interpret implicitly deduce c variable type to as an integer;
  • c identifier is put on symbol table
  • right side of expression is evaluated and the result is associated to c identifier.

And when you write an expression like this:

a = c * 2

A look up in the symbol table is performed, looking for the c identifier and if found, this entry from the symbol table hold reference e.g, where our 10 value was stored in the memory. This 10 value is loaded and then "replaced" in the expression.

Upvotes: 0

Koala Yeung
Koala Yeung

Reputation: 7843

  1. If I understand it correctly, all PHP data types are zval. And zval is basing on a few "Z" data type (defined in C). There are limit number of "real" data type. I believe they are stored in the stack.

    So although users can create new data type, but they are not "real" data type but different zval values. And the number and definition of "real" data type are stable. Thus the size and content of stack won't change in run time.

  2. The size of memory is limited. PHP have to actively do reference counting and garbage collection. For more detail, please read this slide about PHP memory management.

Upvotes: 2

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