从非主线程读取/ proc / self / exe时，Android权限被拒绝

Question

I'm trying to get the canonical path of /proc/self/exe. When I do this on the Main Thread it works, when I do this on an different thread it crashes with an IOException: "Permission denied":

                   DBG  E  Thread: main
                        E  Path: /system/bin/app_process32
                        E  Thread: Thread-21656
            System.err  W  java.io.IOException: Permission denied
                        W      at java.io.File.canonicalizePath(Native Method)
                        W      at java.io.File.getCanonicalPath(File.java:414)
                        W      at java.io.File.getCanonicalFile(File.java:428)
                        W      at com.quanturium.testbugprocselfexe.MyActivity.getPathOfExecutable(MyActivity.java:36)
                        W      at com.quanturium.testbugprocselfexe.MyActivity.access$000(MyActivity.java:12)
                        W      at com.quanturium.testbugprocselfexe.MyActivity$1.run(MyActivity.java:26)
                        W      at java.lang.Thread.run(Thread.java:818)

Code:

@Override
protected void onCreate (Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    getPathOfExecutable(); // Works as expected

    new Thread(new Runnable() {
        @Override
        public void run ()
        {
            getPathOfExecutable(); // Trigger the IOException: Permission denied
        }
    }).start();
}

private void getPathOfExecutable()
{
    try
    {
        Log.e("DBG", "Thread: " + Thread.currentThread().getName());
        Log.e("DBG", "Path: " + new File("/proc/self/exe").getCanonicalFile().getPath());
    }
    catch (IOException e)
    {
        e.printStackTrace();
    }
}

This error only happens when debuggable is configured to false in the build.gradle file

Code to try it out: https://github.com/quanturium/TestBugProcSelfExe

Is this a bug or an intended behavior? What would be a workaround to get the path of the current executable?

Answer 1

Does the code block? If it doesn't, there should be no ramifications of running it in the main thread. You can, however, do that from another thread, with:

Context.runOnUiThread(new Runnable() {
    getPathOfExecutable();
});

This is the cleanest work around I can think of, short of editing the permissions of your file (that you can't get the path of without running your code on the main thread anyways) because you have r/w privileges on /proc/self/exe.

This is very weird, and I am still researching the permission differences in different threads on android.

If you can get it working in the main thread, my opinion would be to just do it in the main thread, and not worry much about optimization, as the performance is no different on different threads.

Answer 2

What would be a workaround to get the path of the current executable?

Since every Android app is forked from Zygote, which is the first Java vm process when the virtual machine created by /system/bin/app_process at system booting.

If you try to read the /proc/self/exe from your Android app, the actual executable will be /system/bin/app_process . Even if you read this outside of your app's main thread, the result is the same and it wouldn't have the permission error in theory.

The question you asked is a kind of weird problem, I have tested with the following code on Android 2.3.3 and worked fine.

new Thread() {

    /* (non-Javadoc)
     * @see java.lang.Thread#run()
     */
    @Override
    public void run() {
        // TODO Auto-generated method stub
        super.run();
        try {
            Log.d(TAG, new File("/proc/self/exe").getCanonicalFile().getPath());
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}.start();