转载请以链接形式标明出处: 本文出自:103style的博客
本文操作以 Android Studio 3.5 版本为例
本文为参考官方示例 hello-jniCallback 动手写的 Demo.
JNI
获取并调用静态内部类 JniHandler 的 静态方法getBuildVersion()
和 公开方法getRuntimeMemorySize()
获取 当前的系统版本 以及 当前可用内存。JNI
线程 实现 开始和停止每秒打印距离开始计时的秒数。编写测试代码 JniCallbackDemo.
public class JniCallbackDemo {
private static final String TAG = "JniCallbackDemo";
static {
System.loadLibrary("jni_callback");
}
private int timeCount;
public native void startTiming();
public native void stopTiming();
private void printTime() {
Log.e(TAG, "timeCount = " + timeCount);
timeCount++;
}
public static class JniHandler {
public static String getBuildVersion() {
return Build.VERSION.RELEASE;
}
public long getRuntimeMemorySize() {
return Runtime.getRuntime().freeMemory();
}
private void updateStatus(String msg) {
if (msg.toLowerCase().contains("error")) {
Log.e("JniHandler", "Native Err: " + msg);
} else {
Log.i("JniHandler", "Native Msg: " + msg);
}
}
}
}
创建 jni_callback.cpp.
添加以下代码到CMakeLists.txt
.
add_library(
jni_callback
SHARED
jni_callback.cpp)
target_link_libraries(
jni_callback
${log-lib})
获取当前的系统版本和可用内存。
JNI_OnLoad
方法中去实现(在应用层调用.so库首先会执行 JNI_OnLoad 方法
)。jniCallback
保存获取的 类 和 实例。void queryRuntimeInfo(JNIEnv *env) {
//获取getBuildVersion的方法id
jmethodID staticMethodId = env->GetStaticMethodID(jniCallback.jniHandlerClz, "getBuildVersion",
"()Ljava/lang/String;");
if (!staticMethodId) {
LOGE("Failed to retrieve getBuildVersion() methodID");
return;
}
//执行静态方法获取getBuildVersion的方法id
jstring releaseVersion = static_cast<jstring>(env->CallStaticObjectMethod(
jniCallback.jniHandlerClz, staticMethodId));
//获取字符串的地址
const char *version = env->GetStringUTFChars(releaseVersion, nullptr);
if (!version) {
LOGE("Unable to get version string");
return;
}
LOGD("releaseVersion = %s", version);
//释放字符串的内存
env->ReleaseStringUTFChars(releaseVersion, version);
//删除引用
env->DeleteLocalRef(releaseVersion);
//获取非静态方法 getRuntimeMemorySize 的id
jmethodID methodId = env->GetMethodID(jniCallback.jniHandlerClz, "getRuntimeMemorySize", "()J");
if (!methodId) {
LOGE("Failed to retrieve getRuntimeMemorySize() methodID");
return;
}
//调用 getRuntimeMemorySize
jlong freeMemorySize = env->CallLongMethod(jniCallback.jniHandlerObj, methodId);
//打印可用内存
LOGD("Runtime free memory size: %"
PRId64, freeMemorySize);
}
JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *vm, void *reserved) {
LOGD("JNI_OnLoad");
JNIEnv *env;
//给jniCallback初始化地址
memset(&jniCallback, 0, sizeof(jniCallback));
jniCallback.javaVM = vm;
if (vm->GetEnv(reinterpret_cast<void **>(&env), JNI_VERSION_1_6) != JNI_OK) {
return JNI_ERR;
}
//获取JniCallbackDemo.JniHandler 类
jclass clz = env->FindClass("com/lxk/ndkdemo/JniCallbackDemo$JniHandler");
//赋值到结构体
jniCallback.jniHandlerClz = static_cast<jclass>(env->NewGlobalRef(clz));
if (!clz) {
LOGE("FindClass JniCallbackDemo$JniHandler error");
return JNI_ERR;
}
//获取构造函数
jmethodID initMethodId = env->GetMethodID(jniCallback.jniHandlerClz, "<init>", "()V");
//构建类
jobject instance = env->NewObject(jniCallback.jniHandlerClz, initMethodId);
if (!instance) {
LOGE("NewObject jniHandler error")
return JNI_ERR;
}
//赋值到结构体
jniCallback.jniHandlerObj = env->NewGlobalRef(instance);
//调用 JniHandler 的相关方法
queryRuntimeInfo(env);
jniCallback.done = 0;
jniCallback.jniCallbackDemoObj = nullptr;
return JNI_VERSION_1_6;
}
创建线程执实现开始计时的逻辑:
pthread_create
创建线程的时候,第一个参数:线程id的指针;第二个参数:线程属性的指针;第一个参数:在线程中运行的函数;第四个参数:运行函数的参数extern "C"
JNIEXPORT void JNICALL
Java_com_lxk_ndkdemo_JniCallbackDemo_startTiming(JNIEnv *env, jobject instance) {
LOGD("jni startTiming");
//线程ID
pthread_t threadInfo;
//线程属性
pthread_attr_t threadAttr;
//初始化线程属性
pthread_attr_init(&threadAttr);
//设置脱离状态的属性
pthread_attr_setdetachstate(&threadAttr, PTHREAD_CREATE_DETACHED);
//互斥锁
pthread_mutex_t lock;
//初始化互斥锁
pthread_mutex_init(&lock, nullptr);
//获取当前类
jclass clz = env->GetObjectClass(instance);
//保存类和 实例 到 结构体中
jniCallback.jniCallbackDemoClz = static_cast<jclass>(env->NewGlobalRef(clz));
jniCallback.jniCallbackDemoObj = env->NewGlobalRef(instance);
// StartTiming :在线程中运行的函数 jniCallback 运行函数的参数
int result = pthread_create(&threadInfo, &threadAttr, StartTiming, &jniCallback);
assert(result == 0);
//删除线程属性
pthread_attr_destroy(&threadAttr);
}
线程的执行函数:
/**
* 调用 类 instance 的 void方法 methodId
*/
void sendJavaMsg(JNIEnv *env, jobject instance, jmethodID methodId, const char *msg) {
LOGD("jni sendJavaMsg");
//获取字符串
jstring javaMsg = env->NewStringUTF(msg);
//调用对应方法
env->CallVoidMethod(instance, methodId, javaMsg);
//删除本地引用
env->DeleteLocalRef(javaMsg);
}
void *StartTiming(void *context) {
//获取参数
JniCallback *JniCallback = static_cast<jni_callback *>(context);
JavaVM *javaVm = JniCallback->javaVM;
JNIEnv *env;
jint res = javaVm->GetEnv((void **) (&env), JNI_VERSION_1_6);
LOGD("javaVm->GetEnv() res = %d", res);
if (res != JNI_OK) {
//链接到虚拟机
res = javaVm->AttachCurrentThread(&env, nullptr);
if (JNI_OK != res) {
LOGE("Failed to AttachCurrentThread, ErrorCode = %d", res);
return nullptr;
}
} else {
LOGE("javaVm GetEnv JNI_OK");
}
//获取 JniHandler 的 updateStatus 函数
jmethodID statusId = env->GetMethodID(JniCallback->jniHandlerClz, "updateStatus",
"(Ljava/lang/String;)V");
sendJavaMsg(env, JniCallback->jniHandlerObj, statusId, "TimeThread status: initializing...");
//获取 JniCallbackDemo 的 printTime 函数
jmethodID timerId = env->GetMethodID(JniCallback->jniCallbackDemoClz, "printTime", "()V");
//声明时间变量
struct timeval beginTime, curTime, usedTime, leftTime;
const struct timeval kOneSecond = {
(__kernel_time_t) 1,
(__kernel_suseconds_t) 0
};
sendJavaMsg(env, JniCallback->jniHandlerObj, statusId,
"TimeThread status: prepare startTiming ...");
while (true) {
//获取当前的时间 赋值给 beginTime
gettimeofday(&beginTime, nullptr);
//占有互斥锁
pthread_mutex_lock(&JniCallback->lock);
//获取当前的状态
int done = JniCallback->done;
if (JniCallback->done) {
JniCallback->done = 0;
}
//释放互斥锁
pthread_mutex_unlock(&JniCallback->lock);
if (done) {
LOGD("JniCallback done");
break;
}
//调用 printTime 函数
env->CallVoidMethod(JniCallback->jniCallbackDemoObj, timerId);
//获取当前的时间 赋值给 curTime
gettimeofday(&curTime, nullptr);
//计算函数运行消耗的时间
//usedTime = curTime - beginTime
timersub(&curTime, &beginTime, &usedTime);
//计算需要等待的时间
//leftTime = kOneSecond - usedTime
timersub(&kOneSecond, &usedTime, &leftTime);
//构建等待的时间
struct timespec sleepTime;
sleepTime.tv_sec = leftTime.tv_sec;
sleepTime.tv_nsec = leftTime.tv_usec * 1000;
if (sleepTime.tv_sec <= 1) {
//睡眠对应纳秒的时间
nanosleep(&sleepTime, nullptr);
} else {
sendJavaMsg(env, JniCallback->jniHandlerObj, statusId,
"TimeThread error: processing too long!");
}
}
sendJavaMsg(env, JniCallback->jniHandlerObj, statusId,
"TimeThread status: ticking stopped");
//释放线程
javaVm->DetachCurrentThread();
return context;
}
停止计时的逻辑:
extern "C"
JNIEXPORT void JNICALL
Java_com_lxk_ndkdemo_JniCallbackDemo_stopTiming(JNIEnv *env, jobject instance) {
LOGD("jni stopTiming");
//占用互斥锁
pthread_mutex_lock(&jniCallback.lock);
//修改线程运行的条件
jniCallback.done = 1;
//释放互斥锁
pthread_mutex_unlock(&jniCallback.lock);
//初始化等待时间
struct timespec sleepTime;
memset(&sleepTime, 0, sizeof(sleepTime));
sleepTime.tv_nsec = 100000000;
while (jniCallback.done) {
nanosleep(&sleepTime, nullptr);
}
//删除引用
env->DeleteGlobalRef(jniCallback.jniCallbackDemoClz);
env->DeleteGlobalRef(jniCallback.jniCallbackDemoObj);
jniCallback.jniCallbackDemoObj = nullptr;
jniCallback.jniCallbackDemoClz = nullptr;
//删除互斥锁
pthread_mutex_destroy(&jniCallback.lock);
}
private void testJniCallback() {
jniCallbackRun(true);
}
private void jniCallbackRun(boolean run) {
if (jniCallbackDemo == null) {
jniCallbackDemo = new JniCallbackDemo();
}
if (run) {
Toast.makeText(this, "开始计时,请查看控制台日志输出", Toast.LENGTH_SHORT).show();
jniCallbackDemo.startTiming();
} else {
jniCallbackDemo.stopTiming();
}
}
点击按钮jni callback test,在控制台即会输出以下信息。
08-22 17:00:34.726 18711-18711/com.lxk.ndkdemo D/JNI: [jni_callback.cpp][63]: JNI_OnLoad
08-22 17:00:34.726 18711-18711/com.lxk.ndkdemo D/JNI: [jni_callback.cpp][42]: releaseVersion = 6.0.1
08-22 17:00:34.726 18711-18711/com.lxk.ndkdemo D/JNI: [jni_callback.cpp][59]: Runtime free memory size: 2439224
08-22 17:00:34.726 18711-18711/com.lxk.ndkdemo D/JNI: [jni_callback.cpp][207]: jni startTiming
08-22 17:00:34.726 18711-18758/com.lxk.ndkdemo D/JNI: [jni_callback.cpp][120]: javaVm->GetEnv() res = -2
08-22 17:00:34.726 18711-18758/com.lxk.ndkdemo D/JNI: [jni_callback.cpp][104]: jni sendJavaMsg
08-22 17:00:34.736 18711-18758/com.lxk.ndkdemo I/JniHandler: Native Msg: TimeThread status: initializing...
08-22 17:00:34.736 18711-18758/com.lxk.ndkdemo D/JNI: [jni_callback.cpp][104]: jni sendJavaMsg
08-22 17:00:34.736 18711-18758/com.lxk.ndkdemo I/JniHandler: Native Msg: TimeThread status: prepare startTiming ...
08-22 17:00:34.736 18711-18758/com.lxk.ndkdemo E/JniCallbackDemo: timeCount = 0
08-22 17:00:35.736 18711-18758/com.lxk.ndkdemo E/JniCallbackDemo: timeCount = 1
08-22 17:00:36.736 18711-18758/com.lxk.ndkdemo E/JniCallbackDemo: timeCount = 2
08-22 17:00:37.736 18711-18758/com.lxk.ndkdemo E/JniCallbackDemo: timeCount = 3
08-22 17:00:38.736 18711-18758/com.lxk.ndkdemo E/JniCallbackDemo: timeCount = 4
08-22 17:00:39.736 18711-18758/com.lxk.ndkdemo E/JniCallbackDemo: timeCount = 5
08-22 17:00:40.736 18711-18758/com.lxk.ndkdemo E/JniCallbackDemo: timeCount = 6
08-22 17:00:41.736 18711-18758/com.lxk.ndkdemo E/JniCallbackDemo: timeCount = 7
...
以上