WebAssembly (WASM) for High Performance Apps · درس

تمرير بنى البيانات المعقدة

تعلّم استراتيجيات نقل السلاسل والمصفوفات والكائنات المخصّصة بكفاءة بين WASM وJavaScript

تمرير بنى البيانات المعقدة درس مجاني في WebAssembly (WASM) for High Performance Apps على CoddyKit. هذا هو الدرس 1 من أصل 4. يمكنك قراءة الدرس كاملاً أدناه مجاناً — ثم تمرن عليه مباشرة في المتصفح باستخدام محرر أكواد مدمج ومدرس ذكاء اصطناعي متاح 24/7. هذا الدرس جزء من مسار التعلم في WebAssembly (WASM) for High Performance Apps، وتقدمك يتزامن عبر الويب وتطبيق CoddyKit. تتضمن دورة WebAssembly (WASM) for High Performance Apps 4 دروس في المجموع.

بعض أجزاء هذا الدرس لم تُترجم بعد وتظهر باللغة الإنجليزية.

Complex Data in WASM

When building high-performance applications with WebAssembly (WASM), you often need to exchange more than just simple numbers between your WASM module and JavaScript.

How do you pass a string?
What about an array of numbers?
Or even a custom object structure?

This lesson explores strategies for efficiently handling these complex data types.

WASM's Linear Memory

The key to passing complex data lies in understanding WASM's linear memory. This is a contiguous block of memory (like a large array of bytes) that is shared between your WASM module and the JavaScript environment.

WASM functions can only return numbers. So, instead of passing the entire data, we pass a pointer (a memory address, which is just a number!) to where the data resides in this shared memory.

Strings: Pointer & Length

Strings are sequences of characters. To pass a string from WASM to JavaScript, the WASM module will:

Write the string's bytes into its linear memory.
Return two pieces of information to JavaScript:
- The starting memory address (pointer) of the string.
- The length of the string (how many bytes it occupies).

JavaScript then uses these to read the bytes from the shared memory and decode them into a JavaScript string.

C String to JS Example

Here's a C function that returns a pointer to a string. When compiled with Emscripten, JavaScript can call this function and then read the string from the WASM memory.

EMSCRIPTEN_KEEPALIVE makes the function callable from JavaScript.

#include <emscripten/emscripten.h>
#include <string.h>

// A static string for demonstration
const char* myString = "Hello WASM!";

EMSCRIPTEN_KEEPALIVE
const char* getGreetingPtr() {
  return myString;
}

EMSCRIPTEN_KEEPALIVE
int getGreetingLength() {
  return strlen(myString);
}

int main() {
  // Required for a complete C program
  return 0;
}

Arrays: Contiguous Data

Numeric arrays (like int[] or float[]) are similar to strings. They are stored as a contiguous block of values in WASM's linear memory.

To pass an array, WASM returns:

A pointer to the first element of the array.
The number of elements in the array.

JavaScript then reads the raw bytes from the shared memory, knowing the type and size of each element (e.g., 4 bytes for an integer).

C Array to JS Example

This C code creates an array, populates it, and provides functions to get its pointer and length. JavaScript would then use Module.HEAP32 (for 32-bit integers) to access the elements.

#include <emscripten/emscripten.h>
#include <stdlib.h> // For malloc

int* dynamicArray = NULL;
int currentArrayLength = 0;

EMSCRIPTEN_KEEPALIVE
int* createAndGetArray(int size) {
  if (dynamicArray) {
    free(dynamicArray);
  }
  dynamicArray = (int*)malloc(size * sizeof(int));
  currentArrayLength = size;
  for (int i = 0; i < size; ++i) {
    dynamicArray[i] = i * 10 + 5;
  }
  return dynamicArray;
}

EMSCRIPTEN_KEEPALIVE
int getArrayLength() {
  return currentArrayLength;
}

int main() {
  // Required for a complete C program
  return 0;
}

Custom Objects (Structs)

Passing custom objects (like structs in C/C++) is more involved. These objects are collections of different data types (e.g., an integer, a float, and a string).

The strategy is to manually lay out the object's fields in WASM's linear memory. WASM then returns a pointer to the start of this memory block. JavaScript must then know the exact memory layout (offsets and types of each field) to correctly read the data.

C Struct to JS Example

This C example defines a Person struct and a function to create one. JavaScript would receive a pointer and then read values from specific offsets in the WASM memory buffer, knowing the struct's layout.

id (int) at offset 0
age (int) at offset 4
height (float) at offset 8

#include <emscripten/emscripten.h>
#include <stdlib.h> // For malloc
#include <string.h> // For strcpy

typedef struct {
  int id;
  int age;
  float height; // assuming 4 bytes after age
  char name[16]; // Fixed-size string buffer
} Person;

EMSCRIPTEN_KEEPALIVE
Person* createPerson(int id, int age, float height, const char* name) {
  Person* p = (Person*)malloc(sizeof(Person));
  p->id = id;
  p->age = age;
  p->height = height;
  strncpy(p->name, name, sizeof(p->name) - 1);
  p->name[sizeof(p->name) - 1] = '\0'; // Ensure null termination
  return p;
}

int main() {
  // Required for a complete C program
  return 0;
}

JS Allocates WASM Memory

What if JavaScript needs to pass complex data *into* WASM? For example, a large image array for WASM to process.

JavaScript can call WASM's exposed memory allocation functions (like Emscripten's _malloc) to reserve space within WASM's linear memory. Then, JavaScript writes the data into that allocated space and passes the pointer to a WASM function for processing.

Quick Check

You've learned how WASM handles complex data. Let's test your understanding!

Recap: Complex Data

Congratulations! You've learned the fundamental techniques for passing complex data between WebAssembly and JavaScript.

WASM and JavaScript communicate via a shared linear memory.
Complex data (strings, arrays, structs) are passed by their pointer (memory address) and often their length or size.
JavaScript then reads the raw bytes from the shared memory, interpreting them based on the known data structure.
For custom objects, understanding the exact memory layout is crucial.

These techniques allow for efficient, high-performance data exchange!

الأسئلة الشائعة

هل درس «تمرير بنى البيانات المعقدة» مجاني؟

نعم — نص درس «تمرير بنى البيانات المعقدة» كامل متاح مجاناً هنا على الويب. لتمرينه بشكل تفاعلي (محرر أكواد مدمج ومدرس ذكاء اصطناعي متاح 24/7) وفتح باقي دورة WebAssembly (WASM) for High Performance Apps، انتقل إلى CoddyKit PRO. تتضمن دورة WebAssembly (WASM) for High Performance Apps 4 دروس في المجموع.

ماذا ستتعلم في «تمرير بنى البيانات المعقدة»؟

تعلّم استراتيجيات نقل السلاسل والمصفوفات والكائنات المخصّصة بكفاءة بين WASM وJavaScript تتمرن على WebAssembly (WASM) for High Performance Apps مع أكواد عملية تشغلها مباشرة في المتصفح، ومدرس ذكاء اصطناعي متاح 24/7 يجيب على أسئلتك أثناء عملك.

هل أحتاج إلى خبرة سابقة لأبدأ WebAssembly (WASM) for High Performance Apps؟

لا تُشترط خبرة سابقة. WebAssembly (WASM) for High Performance Apps على CoddyKit منظم للمبتدئين حتى المتقدمين، لذا يمكنك البدء من هنا أو من البداية والتقدم بسرعتك الخاصة. هذا هو الدرس 1 من أصل 4.

كم من الوقت يستغرق درس «تمرير بنى البيانات المعقدة»؟

معظم دروس CoddyKit تستغرق حوالي 5–10 دقائق. كل منها موجز وتفاعلي، لذا تحرز تقدماً مستمراً وتستأنف من حيث توقفت عبر الويب والتطبيق.

هل يمكنني كتابة وتشغيل أكواد في درس WebAssembly (WASM) for High Performance Apps هذا؟

نعم. كل درس في WebAssembly (WASM) for High Performance Apps يتضمن محرر أكواد مدمج، لذا تكتب وتشغل أكواداً حقيقية مباشرة في متصفحك وتحصل على تعليقات فورية من الذكاء الاصطناعي — بدون إعداد محلي.

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