Thread Safety

In a native application built with Cocos Creator, there are at least two threads: the GL Thread and Native UI Thread。

• GL Thread: Executes rendering-related code of the Cocos Engine and JavaScript code.
• UI Thread: Handles the creation, response, and update of the platform's native UI.

Therefore, we need to be aware of the following two issues:

1. When code in the UI thread needs to call code in the GL thread, we need to handle thread safety.
2. When code in the GL thread needs to call code in the UI thread, we need to handle thread safety.

Now let's take a look at how to handle thread safety in different situations.

Executing on the UI Thread

When we write Java methods on the Android platform that involve UI-related operations, and they are called in the GL thread, we need to use the app.runOnUiThread method to execute the code on the UI thread, ensuring thread safety.

Let's take an example of displaying an Alert dialog on Android.

public class AppActivity extends CocosActivity {
    
    private static AppActivity app = null;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        app = this;
    }
    
    public static void showAlertDialog(final String title,final String message) {
        app.runOnUiThread(new Runnable() {
            @Override
            public void run() {
                AlertDialog alertDialog = new AlertDialog.Builder(app).create();
                alertDialog.setTitle(title);
                alertDialog.setMessage(message);
                alertDialog.setIcon(R.drawable.icon);
                alertDialog.show();
            }
        });
    }
}

In this example, the showAlert method creates and displays an Alert dialog. By using app.runOnUiThread, we ensure that the code runs on the UI thread, preventing any thread safety issues.

Executing on the GL Thread

When code running on the UI thread needs to call code in the GL thread, we need to use CocosHelper.runOnGameThread to ensure thread safety.

Let's take an example of a button event response:

alertDialog.setButton("OK", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dialog, int which) {
        // Must run on GL Thread
        CocosHelper.runOnGameThread(new Runnable() {
            @Override
            public void run() {
                CocosJavascriptJavaBridge.evalString("cc.log(\"Javascript Java bridge!\")");
            }
        });
    }
});

Objective-C / C++

If you are writing Objective-C or C++ code and want to ensure thread safety, you can use the CC_CURRENT_ENGINE()->getScheduler()->performFunctionInCocosThread method to execute the code on the GL thread.

Here's an example:

CC_CURRENT_ENGINE()->getScheduler()->performFunctionInCocosThread([=](){
    //TO DO
});

Please note that the above code is in C++. If you want to call it from Objective-C code, you need to use the *.mm file extension for your Objective-C code file.