android jni交互之c层对象指针缓存

以soundtouch源码为例（https://www.surina.net/soundtouch/sourcecode.html）

java层：

public final class SoundTouch
{
    private native final static long newInstance();//初始化
    
    private native final void deleteInstance(long handle);//销毁

    private native final void setTempo(long handle, float tempo);//函数调用的时候传入handle，在c层转为相应指针

    long handle = 0;//保留c层创建的对象的指针地址
    
    
    public SoundTouch()
    {
        handle = newInstance();     
    }
    
    
    public void close()
    {
        deleteInstance(handle);
        handle = 0;
    }
}

c层：
soundtouch-jni.cpp

#include <jni.h>
#include <android/log.h>

#define LOGV(...)   __android_log_print((int)ANDROID_LOG_INFO, "SOUNDTOUCH", __VA_ARGS__)

extern "C" DLL_PUBLIC jlong Java_net_surina_soundtouch_SoundTouch_newInstance(JNIEnv *env, jobject thiz)
{
    return (jlong)(new SoundTouch());//分配对象内存，并把指针地址返回
}


extern "C" DLL_PUBLIC void Java_net_surina_soundtouch_SoundTouch_deleteInstance(JNIEnv *env, jobject thiz, jlong handle)
{
    SoundTouch *ptr = (SoundTouch*)handle;//将handle转为对象
    delete ptr;
}


extern "C" DLL_PUBLIC void Java_net_surina_soundtouch_SoundTouch_setTempo(JNIEnv *env, jobject thiz, jlong handle, jfloat tempo)
{
    SoundTouch *ptr = (SoundTouch*)handle;
    ptr->setTempo(tempo);
}