在机器人的dlopen比赛条件（）？ [英] Race condition in android dlopen()?

问题描述

我的Andr​​oid应用程序有一个简单的装载机NativeActivity的使用非常简单的 android_main（）只加载不同的共享对象，并将其控制：

My Android app has a simple "loader" NativeActivity with a very simple android_main() which only loads a different shared object and passes control to it:

typedef void (*Tandroid_main)( android_app*);
void android_main( android_app* state )
{
    void* glib = dlopen("libmain.so", RTLD_NOW);
    void* fmain = dlsym(glib, "android_main");
    Tandroid_main libmain = (Tandroid_main)fmain;
    libmain(state)
}

这工作得很好..大约一半的时间。因为的dlopen其他时候它崩溃（）失败，返回NULL，并将errno = 2（没有这样的文件）。
由于奇怪的不一致发生这种情况的我怀疑是一个时间问题，事实上，加入睡眠（1）在的dlopen（）从发生停止它。一些更强大的比睡眠（1）将只是想在一个循环：

This works well.. about half of the times. Other times it crashes since dlopen() fails and return NULL with errno=2 (No such file).
Due to the strange inconsistency of this occurrence I suspected a timing issue and indeed, adding a sleep(1) before dlopen() stopped it from happening. Something more robust than sleep(1) would be just trying it in a loop:

int count = 0;
void* glib = dlopen(soName, RTLD_NOW);
while(glib == NULL) {
    sched_yield();
    ++count;
    glib = dlopen(soName, RTLD_NOW);
}

我是从这个循环获得的计数通常是一些在10-70的范围内我的设备上。但是，这是一个hackish的丑陋的解决方案。

The count I'm getting from this loop is usually something in the range of 10-70 on my device. But this is a hackish ugly solution.

什么是真正回事？为什么我只能加载其它共享对象只是轻微的NativeActivity的启动后？有没有更好的办法找到的时候，当它是安全的加载？

What is really going on here? How come I can only load other shared objects only slightly after the NativeActivity starts? Is there a better way to find when when it's safe to load it?

应该指出的是，我也打电话的System.loadLibrary（主）从我的NativeActivity的的的onCreate（）

It should be noted that I am also calling System.loadLibrary("main") from my NativeActivity's onCreate()

推荐答案

不知道，但建议从静态初始化调用LoadLibrary（）：

Not sure, but it is recommended to call loadLibrary() from a static initializer:

public class MainActivity extends Activity {
    static {
        System.loadLibrary("main")
    }
    ...
}

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