WebAssembly (WASM) for High Performance Apps · Aula

Modelo e gerenciamento de memória do WASM

Compreenda o modelo de memória linear do WebAssembly e como a memória é alocada, acessada e gerenciada nos módulos WASM.

Aula 2 de 410 etapas

Modelo e gerenciamento de memória do WASM é uma aula grátis de WebAssembly (WASM) for High Performance Apps no CoddyKit. Esta é a aula 2 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de WebAssembly (WASM) for High Performance Apps, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de WebAssembly (WASM) for High Performance Apps inclui 4 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

WASM Linear Memory: The Basics

WebAssembly uses a linear memory model. Think of it as a single, large, contiguous array of bytes, similar to how traditional programs manage memory.

This memory is separate from JavaScript's memory.
It's accessed by WASM modules as a flat address space, starting from address 0.
All data (integers, floats, strings, arrays) lives within this single memory block.

The `WebAssembly.Memory` Object

In JavaScript, WASM memory is represented by the WebAssembly.Memory object. This object holds the actual memory buffer.

You can create it:

When instantiating a WASM module, it can declare and create its own memory.
You can also pass an existing WebAssembly.Memory instance from JavaScript to the module.

const memory = new WebAssembly.Memory({
  initial: 1, // Start with 1 page (64KB)
  maximum: 10 // Max allowed 10 pages
});

// This 'memory' object is then passed to the
// WASM module during instantiation.

Memory Pages: The Unit of Size

WASM memory is organized into fixed-size units called pages. Each page is exactly 64 KiB (65,536 bytes) in size.

The initial and maximum properties of WebAssembly.Memory are always defined in terms of pages.
A WASM module might start with just 1 page, growing its memory as needed for efficiency.
This page-based system allows for efficient memory management and protection.

JavaScript's View into Memory

JavaScript cannot directly access WASM's linear memory using raw pointers. Instead, it gets an ArrayBuffer view of the memory.

You then use TypedArrays (like Uint8Array, Int32Array, Float64Array) or a DataView to read and write specific data types at specific offsets within that ArrayBuffer.

const memoryBuffer = instance.exports.memory.buffer;
const uint8Array = new Uint8Array(memoryBuffer); // Byte-level view
const int32Array = new Int32Array(memoryBuffer); // 4-byte integer view

Allocating Memory in C/WASM

When you compile C/C++ to WASM, functions like malloc allocate memory from WASM's linear memory. This example shows a C function that allocates space for an integer array.

It returns a memory offset (an integer) rather than a direct pointer, which JavaScript then uses.

#include <stdlib.h>
#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#else
#define EMSCRIPTEN_KEEPALIVE
#endif

EMSCRIPTEN_KEEPALIVE
int* allocate_int_array(int size) {
  int* arr = (int*) malloc(size * sizeof(int));
  if (arr) {
    for (int i = 0; i < size; ++i) {
      arr[i] = i * 10; // Initialize with some data
    }
  }
  return arr; // Returns memory offset
}

int main() {
  // Main function is often a placeholder for WASM modules
  return 0;
}

Accessing C-Allocated Memory from JS

After WASM allocates memory (e.g., using allocate_int_array), JavaScript can access it using the returned offset and a TypedArray.

The offset tells JS exactly where in the underlying ArrayBuffer the allocated data begins, allowing precise read/write operations.

// Assuming 'instance' is your WASM module instance
const offset = instance.exports.allocate_int_array(5);
const memoryBuffer = instance.exports.memory.buffer;

// Create an Int32Array view starting at the offset
const intArray = new Int32Array(memoryBuffer, offset, 5);

console.log(intArray[0]); // Expected: 0
console.log(intArray[1]); // Expected: 10
// ... and so on

Deallocating Memory with `free`

Just like in C, it's crucial to deallocate memory you've allocated using malloc to prevent memory leaks. The free function in WASM works similarly, releasing the memory back to the WASM runtime.

This C function frees a previously allocated memory block using its offset.

#include <stdlib.h>
#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#else
#define EMSCRIPTEN_KEEPALIVE
#endif

EMSCRIPTEN_KEEPALIVE
void free_wasm_memory(int* ptr) {
  if (ptr) {
    free(ptr); // Release the memory block
  }
}

int main() {
  return 0;
}

Dynamically Growing Memory

WASM memory isn't fixed; it can grow! The memory.grow(numPages) method, exposed on the WebAssembly.Memory object, allows you to increase the memory size by a specified number of pages.

This method returns the previous number of pages.
If grow fails (e.g., exceeds the maximum), it returns -1.
Important: Existing TypedArray views become invalid after a grow operation; you must create new ones from the updated memory.buffer.

const currentPages = instance.exports.memory.grow(1); // Add 1 page
console.log(`Memory grew from ${currentPages} pages.`);

// After growing, always recreate TypedArray views!
const newMemoryBuffer = instance.exports.memory.buffer;
const newUint8Array = new Uint8Array(newMemoryBuffer);

Memory Management Check

Which of the following statements about WebAssembly's linear memory model are TRUE?

Responda na aula interativa

Recap: WASM Memory Management

We've explored WebAssembly's linear memory model, a foundational concept for high-performance applications.

WASM memory is a contiguous byte array, separate from JS memory.
It's managed by the WebAssembly.Memory object and organized into 64 KiB pages.
JavaScript interacts with this memory using ArrayBuffer and TypedArrays to read and write data.
C functions like malloc and free operate within this WASM memory space, with `malloc` returning an offset.
Memory can be dynamically increased using memory.grow(), but requires re-creating JS views.

Understanding these concepts is key to efficient data exchange and memory handling in WASM applications.

Grátis para começar

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Cursos: 12
Aulas: 48

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Perguntas Frequentes

A aula “Modelo e gerenciamento de memória do WASM” é grátis?

Sim — o texto completo de “Modelo e gerenciamento de memória do WASM” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de WebAssembly (WASM) for High Performance Apps, atualize para CoddyKit PRO. O curso de WebAssembly (WASM) for High Performance Apps inclui 4 aulas no total.

O que vou aprender em “Modelo e gerenciamento de memória do WASM”?

Compreenda o modelo de memória linear do WebAssembly e como a memória é alocada, acessada e gerenciada nos módulos WASM. Você pratica WebAssembly (WASM) for High Performance Apps com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

Preciso ter experiência prévia para começar WebAssembly (WASM) for High Performance Apps?

Nenhuma experiência prévia é necessária. WebAssembly (WASM) for High Performance Apps no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 2 de 4.

Quanto tempo leva a aula “Modelo e gerenciamento de memória do WASM”?

A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.

Posso escrever e executar código nesta aula de WebAssembly (WASM) for High Performance Apps?

Sim. Cada aula de WebAssembly (WASM) for High Performance Apps inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.

Todas as aulas deste curso

Passando estruturas de dados complexas
Modelo e gerenciamento de memória do WASM
Memória compartilhada e atômicos
Expandindo e gerenciando a memória linear

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