Android NDK计时器

Question

我在c中编写了一段代码来计算C代码的一部分所花费的时间,然后尝试将其报告回Java代码.但问题是定时器差分总是回零.这是原生C

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h> /* sleep() */
#include <time.h>
#include <jni.h>

jstring Java_com_nsf_ndkfoo_NDKFooActivity_invokeNativeFunction(JNIEnv* env, jobject javaThis) {

    time_t start, end;

    start = time(NULL);
    if(start == (time_t)-1) {
      return 1;
    }

    sleep(5);

    end = time(NULL);

    char buf[60] = { 0 };

    sprintf(buf,"according to difftime(), slept for %.8f seconds\n", (int)difftime(end, start));

    return (*env)->NewStringUTF(env, buf);
}

当我运行这个时,我总是得到"根据difftime(),睡了-0.00000000秒".有什么想法有什么不对吗？

-------------------------------- 最终代码解决方案 --------------- -----------------------------------------

这是我发现最终工作不确定为什么因为我不是C大师,但无论如何它在这里.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h> /* sleep() */
#include <sys/time.h>
#include <jni.h>

jstring Java_com_nsf_ndkfoo_NDKFooActivity_invokeNativeFunction(JNIEnv* env, jobject javaThis) {

    struct timeval start;
    struct timeval end;

    gettimeofday(&start, NULL);
    sleep(5);

    gettimeofday(&end, NULL);

    char buf[60] = { 0 };

    sprintf(buf,"according to difftime(), slept for %ld seconds\n",  ((end.tv_sec * 1000000 + end.tv_usec) - (start.tv_sec * 1000000 + start.tv_usec)));

    return (*env)->NewStringUTF(env, buf);
}

android的Java代码如下所示:

package com.nsf.ndkfoo;

import android.app.Activity;
import android.app.AlertDialog;
import android.os.Bundle;

public class NDKFooActivity extends Activity {
    // load the library - name matches jni/Android.mk
    static {
        System.loadLibrary("ndkfoo");
    }

    // declare the native code function - must match ndkfoo.c
    private native String invokeNativeFunction();

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        // this is where we call the native code
        String hello = invokeNativeFunction();

        new AlertDialog.Builder(this).setMessage(hello).show();
    }
}

Answer 1

尝试gettimeofday()用来衡量时间.我已经成功地将它与NDK一起使用,尽管在我的情况下它与之相关pthread_cond_timedwait().