alt Hacker NewsEducate me: how to create a program in Goose which reads a JSON structure, prints it out and finishes. How is memory for JSON allocated on stack? It can be from 1K to 1M - depending on the file...
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https://github.com/aardappel/goose/blob/master/samples/18_js...
Goose can store entire trees (of variable sized things) inside an array.
> How is memory for JSON allocated on stack?
Check the features section (https://aardappel.github.io/goose/#features), which starts off with how memory works.
I don't see why this is problematic. Stack is just memory, you can allocate it by incrementing a pointer. Any amount you want, really.
Apache modules worked like this (still do, presumably). Each request has a stack; allocations bump the stack pointer; when a request is finished, the stack pointer is reset. Incredibly efficient as long as you don't need to keep memory longer than a single request.
Looks like in Goose, each scope acts like an apache "request".
I'm not familiar with Goose, but based on some research and my understanding of how memory works:
At compile time, Goose will analyze your program and determine a number of stacks, N, for it. N is the maximum number of "growable" items you can have in existence at any given point in time. Using virtual memory tricks, each stack can grow up to 2GB, but it uses a contiguous address space and only uses as much physical memory as it actually needs.
For the program you're describing, I think you would end up with two stacks: one to parse the input and a second to print it. When you parse the input, Goose reads characters from the string one at a time and puts them onto the stack. Once it has hit the end of value, it will update the stack so it now represents the decoded JSON value (strings will just leave the characters in place, numbers will pop off the characters and push the number onto the stack). Goose repeats this until it has parsed the whole JSON, and now the whole JSON is on the stack.
Then, when you print the JSON, Goose uses the second stack to build a string. Like the parsing approach, it iterates through each element of the JSON and pushes its string representation onto the stack. Once it's done, it resets the stack pointers to free the memory.
This is really nice because allocating memory is just adding to the pointer, and freeing it is subtracting from the pointer.
In contrast, Rust automatically inserts malloc() and free() calls throughout your code, which are much more expensive than pointer arithmetic. On top of that, freeing a vector of heap-allocated objects is O(n), whereas if done right in Goose, it would be O(1)