Native Code and Memory Management in Android: Why Copying Memory is Necessary?

In Android, there is a process that occurs when an application needs to use native code that is written in C or C++. This process involves copying memory from Java’s memory heap to the native memory heap.

This article will provide an in-depth explanation of why this process is necessary and how it works in Android.

Why is copying memory necessary?

When an Android application needs to use native code, it is often because the code needs to interact with the operating system or hardware in a way that is not possible with Java alone. Native code is written in languages like C or C++ and compiled into machine code that can be executed directly by the operating system.

However, Java and native code have different memory management systems. Java uses a garbage collector to manage memory, while native code uses manual memory management. This means that native code needs to allocate and deallocate memory manually, while Java automatically manages memory for the application.

When an application needs to use native code, it is necessary to copy any data that is needed from Java’s memory heap to the native memory heap. This is because the native code cannot access Java’s memory directly. Copying the data to the native memory heap allows the native code to access the data it needs, and to manage the memory for that data manually.

How does the process of copying memory work?

The process of copying memory from Java’s memory heap to the native memory heap involves several steps. Here is an overview of how the process works:

Allocate memory in the native heap

The first step is to allocate memory in the native heap for the data that needs to be copied from Java’s memory heap. This is done using functions like malloc() or calloc().

Get a pointer to the data in Java’s memory heap

The next step is to get a pointer to the data in Java’s memory heap that needs to be copied. This is done using functions like GetObjectClass() or GetFieldID().

Copy the data to the native heap

Once a pointer to the data has been obtained, it can be copied to the memory that was allocated in the native heap. This is done using functions like memcpy() or memmove().

Use the data in the native code

Once the data has been copied to the native heap, it can be used by the native code. The native code can read and write to the memory directly, and it is responsible for managing the memory for that data.

Deallocate the memory in the native heap

When the native code is done using the data, it is responsible for deallocating the memory that was allocated in the native heap. This is done using functions like free().