Android组件保活，service保活

     首先介绍一下android的进程. Android 进程分为两种 :其一，java层的进程，也就是在虚拟机里运行的进程，他们的父进程是zygote进程，我们平时调用的AM里面的类似getrunningprocess()方法，返回的就是这类进程信息，这类进程很容易被杀死。其二，native层的原生进程 也就是linux c的进程，这类进程比较安全，其中父进程是init进程的更加安全，很难杀死，在linux里叫守护进程，像surfaceflinger(控制界面呈现)进程，一旦启动会在底层一直运行。

    那么 我们的目的就是要写一个守护进程 实时监视自己app java层进程的情况 如果被杀死 就立即创建。

   首先是最重要的守护程序代码 linuxC的 带注释

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
/**
*守护进程的名字"/proc/pid/status"文件的第一行 linux内核把所有进程信息的节点映射在了"/proc"下
*注意不同android版本 status里进程名字格式可能不一样
*楼主的4.0.3是下面这行 具体的自己到/proc里看一下
**/
char *procdeam = "Name: com.gy.textndk";
//判断进程是否还在运行
int ifprocrun(char *rootpath)
{
DIR *dir;
struct dirent *ptr; //遍历文件夹需要dirent结构体
int bufsize = strlen(procdeam);

if((dir = opendir(rootpath)) == NULL)
{
perror("dir opened failed\n");
exit(1);
}

//遍历"/proc"下所有文件夹
while((ptr = readdir(dir)) != NULL)
{
if(ptr->d_type == 4)
{
char path[128];
memset(path,'\0',sizeof(path));
strcpy(path,rootpath);
strcat(path,"/");
strcat(path,ptr->d_name);
strcat(path,"/status");
//判断是否存在"status" 文件
if(access(path,F_OK) != -1) 
{
int fd = open(path,O_RDONLY);
char tmp_buf[bufsize];
read(fd,tmp_buf,bufsize);
close(fd);
printf(tmp_buf,"\n");
//判断进程名是否相等
if(strcmp(tmp_buf,procdeam) == 0)
{ 
printf("-----------------proc is running------------------\n");
return 1;
}
}
}
}
return 0;
}
int main()
{ 
int i;
int fd;
//1.创建子进程，结束父进程，子进程由init接管成为守护进程
pid_t pid = fork();
if(pid<0)
exit(1);
else if(pid>0)
exit(0);
//设置新的 session
setsid();
//2.关闭所有fd管道 
for(i=0;i<=48608;i++)
{
close(i);
}
//3.改变工作目录到跟文件夹
chdir("/");
//4.umask
umask(0);
//5.do sth
while(1)
{

if(ifprocrun("/proc") == 0)
{ 
//调用app_process 的命令 "com.gy.Autostart_Activity"这个实在manifest里注册的 intent-filter action
//自己定义 这样AMS才能根据action启动你app组件 类似注册表
system("am start -a com.gy.Autostart_Activity");
}
sleep(10); //10s判断一次 自己定
}
}

上面这个程序不能用arm-linux-gcc编译 因为不支持 android新版的 程序调用接口，用 ndk-build命令编译 源码放在名叫的jni目录下

接下来就是实现把编译好的linux c守护程序打包进apk并在安装时将其释放到data目录下，便于运行。

首先将编译好的linux c程序放进assets文件夹
下面就是java层释放assets资源文件并且运行的代码，涉及jni

package com.gy.textndk;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.app.Activity;
import android.content.Context;
import android.util.Log;
import android.widget.TextView;
import android.os.Bundle;

public class HelloJni extends Activity
{
/** Called when the activity is first created. */
private static String TAG = "gy";
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
/* Create a TextView and set its content.
* the text is retrieved by calling a native
* function.
*/
TextView tv = new TextView(this);
tv.setText( stringFromJNI() );
setContentView(tv);
StringBuilder sb = new StringBuilder();
sb.append(getAppPrivateDir(this)).append("/gyarmdeomproc");
copyAsset(HelloJni.this, "gyarmdeomproc", sb.toString());
startproc();
}
/* A native method that is implemented by the
* 'hello-jni' native library, which is packaged
* with this application.
*/
public native String stringFromJNI();
/* This is another native method declaration that is *not*
* implemented by 'hello-jni'. This is simply to show that
* you can declare as many native methods in your Java code
* as you want, their implementation is searched in the
* currently loaded native libraries only the first time
* you call them.
*
* Trying to call this function will result in a
* java.lang.UnsatisfiedLinkError exception !
*/
public native String unimplementedStringFromJNI();

public native int startproc();
/* this is used to load the 'hello-jni' library on application
* startup. The library has already been unpacked into
* /data/data/com.example.hellojni/lib/libhello-jni.so at
* installation time by the package manager.
*/
static {
System.loadLibrary("hello-jni");
}

//文件复制
public static boolean copyStream(InputStream in, OutputStream out) {
Log.d(TAG, "copyStream("+ in + " ," + out+ ")");
try {
byte[] buf = new byte[8192];
int len;
while ((len = in.read(buf)) > 0)
out.write(buf, 0, len); 
} catch (Exception e) {
e.printStackTrace();
return false;
}
return true;
}

//获得app私有文件夹路径
public static String getAppPrivateDir(Context ctx) {
File dataDir = ctx.getDir("data", Context.MODE_PRIVATE);
return dataDir.getAbsolutePath();
}

//拷贝assets资源文件到data私有文件夹下
public static boolean copyAsset(Context ctx, String assetFile,
String saveToFile) {
Log.d(TAG, "copyAssets(" + assetFile + " -> " + saveToFile);
File outputFile = new File(saveToFile);
if (outputFile.exists()) {
return true;
}
// init output stream(file)
OutputStream out;
try {
out = new FileOutputStream(outputFile);
} catch (FileNotFoundException e1) {
e1.printStackTrace();
return false;
}
boolean copyResult = false;
InputStream in = null;
try {
in = ctx.getAssets().open(assetFile);
copyResult = copyStream(in, out);
Log.d(TAG, "copy " + assetFile + " - " + copyResult);
} catch (IOException e1) {
e1.printStackTrace();
} finally {
// close input stream(file)
try {
if (in != null)
in.close();
} catch (IOException e) {
}
}
// close output stream (file)
try {
if (out != null)
out.close();
} catch (IOException e) {
e.printStackTrace();
}
// return copy result
// add file execute permission
File fs = new File(saveToFile);
try {
//这句很重要 赋予文件可执行权限 不然文件无法执行 
fs.setExecutable(true, true);
} catch (Exception e) {
e.printStackTrace();
}
Log.d(TAG, "copyAsset() return " + copyResult);
return copyResult;
}
}

最后 是jni的c代码 很简单 直接调用

/*
* deomproc.c
*
* Created on: 2015年2月9日
* Author: gy

#include 
#include 
#include 
JNIEXPORT jint JNICALL Java_com_gy_textndk_HelloJni_startproc()
{ 
system("/data/data/com.gy.textndk/app_data/gyarmdeomproc");
}