静态缓存

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import android.os.Bundle;
import android.view.View;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

// TODO 02. 静态缓存
public class MainActivity2 extends AppCompatActivity {

    /*MainActivity2() {
        // 初始化静态缓存
        initStaticCache(); // 如果是在类里面， Person Student ，必须在类的构造函数初始化
    }*/

    static {
        System.loadLibrary("native-lib");
    }

    // 假设这里定义了一堆变量
    static String name1  ="T1";
    static String name2  ="T2";
    static String name3  ="T3";
    static String name4  ="T4";
    static String name5  ="T5";
    static String name6  ="T6";
    // ... 省略很多变量
    // ...

    public static native void localCache(String name); // 普通的局部缓存，弊端演示

    // 下面 静态缓存
    public static native void initStaticCache(); // 初始化静态缓存
    public static native void staticCache(String name);
    public static native void clearStaticCache(); // 清除化静态缓存

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    // 事件
    public void staticCacheAction(View view) {
        localCache("AAAA");
        localCache("AAAA");
        localCache("AAAA");
        localCache("AAAA");
        localCache("AAAA");
        localCache("AAAA");
        localCache("AAAA");
        // ...

        // =========================== 下面是静态缓存相关
        // 初始化静态缓存
        initStaticCache(); // 如果是在类里面， Person Student ，必须在类的构造函数初始化

        staticCache("BBB");
        staticCache("BBB");
        staticCache("BBB");
        staticCache("BBB");
        staticCache("BBB");
        staticCache("BBB");
        staticCache("BBB");
        // ....

    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        clearStaticCache(); // 清除化静态缓存
    }
}
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extern "C"
JNIEXPORT void JNICALL
Java_com_derry_as_1jni_1project_MainActivity2_localCache(JNIEnv *env, jclass clazz, jstring name) {

    // 非静态缓存

    jfieldID f_id = nullptr;

    if (f_id == nullptr) {
        f_id = env->GetStaticFieldID(clazz, "name1", "Ljava/lang/String;"); // 有点耗费性能
    } else  {
        LOGE("空的");
    }

    env->SetStaticObjectField(clazz, f_id, name); // 修改 AAA

    f_id = nullptr;
}




// 像OpenCV，WebRTC，等等 大量使用 静态缓存 ..

static jfieldID f_name1_id = nullptr;
static jfieldID f_name2_id = nullptr;
static jfieldID f_name3_id = nullptr;
static jfieldID f_name4_id = nullptr;
static jfieldID f_name5_id = nullptr;
static jfieldID f_name6_id = nullptr;

// 先缓存
extern "C"
JNIEXPORT void JNICALL
Java_com_derry_as_1jni_1project_MainActivity2_initStaticCache(JNIEnv *env, jclass clazz) {
    f_name1_id = env->GetStaticFieldID(clazz, "name1", "Ljava/lang/String;");
    f_name2_id = env->GetStaticFieldID(clazz, "name2", "Ljava/lang/String;");
    f_name3_id = env->GetStaticFieldID(clazz, "name3", "Ljava/lang/String;");
    f_name4_id = env->GetStaticFieldID(clazz, "name4", "Ljava/lang/String;");
    f_name5_id = env->GetStaticFieldID(clazz, "name5", "Ljava/lang/String;");
    f_name6_id = env->GetStaticFieldID(clazz, "name6", "Ljava/lang/String;");
}

// 使用
extern "C"
JNIEXPORT void JNICALL
Java_com_derry_as_1jni_1project_MainActivity2_staticCache(JNIEnv *env, jclass clazz, jstring name) {
    // 不会反复 GetStaticFieldID 提供性能
    env->SetStaticObjectField(clazz, f_name1_id, name);
    env->SetStaticObjectField(clazz, f_name2_id, name);
    env->SetStaticObjectField(clazz, f_name3_id, name);
    env->SetStaticObjectField(clazz, f_name4_id, name);
    env->SetStaticObjectField(clazz, f_name5_id, name);
    env->SetStaticObjectField(clazz, f_name6_id, name);
}

// 清除
extern "C"
JNIEXPORT void JNICALL
Java_com_derry_as_1jni_1project_MainActivity2_clearStaticCache(JNIEnv *env, jclass clazz) {
    f_name1_id = nullptr;
    f_name2_id = nullptr;
    f_name3_id = nullptr;
    f_name4_id = nullptr;
    f_name5_id = nullptr;
    f_name6_id = nullptr;
}