Problem with Runtime.exec and Android

Question

I have an issue when I'm using Runtime.exec with my Android device and just can't figure out why it happens...

Here is an example of the tests I did :

public class MainActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Runtime runtime = Runtime.getRuntime();
        for(int i=0; i< 20; i++){
            Log.d("TESTEXEC", "EXEC N°"+i+" : BEGIN");
            try {
                Process process = runtime.exec("/system/bin/ps");
                process.getErrorStream().close();
                process.getOutputStream().close();
                process.getInputStream().close();
                process.waitFor();
            } catch (Throwable e) {
                e.printStackTrace();
            }
            Log.d("TESTEXEC", "EXEC N°"+i+" : END");
        }
    }
}

So, basically, when this snippet works, it prints this :

EXEC N°0 : BEGIN
EXEC N°0 : END
EXEC N°1 : BEGIN
EXEC N°1 : END
...
EXEC N°19 : BEGIN
EXEC N°19 : END

But instead of that, sometimes (it looks like it's a bit random), it just prints

EXEC N°0 : BEGIN

And everything locks... The whole things seems to crash into the runtime.exec("..."), and the process.getErrorStream.close() is never called. Another strange thing : The bug always occurs on the first exec.

Here is what I get with DDMS : DDMS

I also retrieved the /data/anr/traces.txt, but it's not really useful :

----- pid 11489 at 2011-05-16 15:15:10 -----
Cmd line: com.testexec

DALVIK THREADS:
"main" prio=5 tid=1 NATIVE
  | group="main" sCount=1 dsCount=0 s=N obj=0x4001d8d0 self=0xcca0
  | sysTid=11489 nice=0 sched=0/0 cgrp=unknown handle=-1345021856
  at java.lang.ProcessManager.exec(Native Method)
  at java.lang.ProcessManager.exec(ProcessManager.java:224)
  at java.lang.Runtime.exec(Runtime.java:196)
  at java.lang.Runtime.exec(Runtime.java:285)
  at java.lang.Runtime.exec(Runtime.java:218)
  at com.testexec.MainActivity.onCreate(MainActivity.java:17)
  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2629)
  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2681)
  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
  at android.os.Handler.dispatchMessage(Handler.java:99)
  at android.os.Looper.loop(Looper.java:123)
  at android.app.ActivityThread.main(ActivityThread.java:4641)
  at java.lang.reflect.Method.invokeNative(Native Method)
  at java.lang.reflect.Method.invoke(Method.java:521)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
  at dalvik.system.NativeStart.main(Native Method)

"java.lang.ProcessManager" daemon prio=5 tid=8 NATIVE
  | group="main" sCount=1 dsCount=0 s=N obj=0x460969f0 self=0x240f58
  | sysTid=11496 nice=0 sched=0/0 cgrp=unknown handle=2363544
  at java.lang.ProcessManager.watchChildren(Native Method)
  at java.lang.ProcessManager$1.run(ProcessManager.java:87)

"Binder Thread #2" prio=5 tid=7 NATIVE
  | group="main" sCount=1 dsCount=0 s=N obj=0x460895a0 self=0x1248e0
  | sysTid=11495 nice=0 sched=0/0 cgrp=unknown handle=1236304
  at dalvik.system.NativeStart.run(Native Method)

"Binder Thread #1" prio=5 tid=6 NATIVE
  | group="main" sCount=1 dsCount=0 s=N obj=0x46086cf8 self=0x143480
  | sysTid=11494 nice=0 sched=0/0 cgrp=unknown handle=1324096
  at dalvik.system.NativeStart.run(Native Method)

"Compiler" daemon prio=5 tid=5 VMWAIT
  | group="system" sCount=1 dsCount=0 s=N obj=0x46084558 self=0x144560
  | sysTid=11493 nice=0 sched=0/0 cgrp=unknown handle=1153256
  at dalvik.system.NativeStart.run(Native Method)

"JDWP" daemon prio=5 tid=4 VMWAIT
  | group="system" sCount=1 dsCount=0 s=N obj=0x460842a0 self=0x12dc10
  | sysTid=11492 nice=0 sched=0/0 cgrp=unknown handle=1152968
  at dalvik.system.NativeStart.run(Native Method)

"Signal Catcher" daemon prio=5 tid=3 RUNNABLE
  | group="system" sCount=0 dsCount=0 s=N obj=0x460841e8 self=0x124d00
  | sysTid=11491 nice=0 sched=0/0 cgrp=unknown handle=1199296
  at dalvik.system.NativeStart.run(Native Method)

"HeapWorker" daemon prio=5 tid=2 VMWAIT
  | group="system" sCount=1 dsCount=0 s=N obj=0x441e2ee8 self=0x11fdd8
  | sysTid=11490 nice=0 sched=0/0 cgrp=unknown handle=1185776
  at dalvik.system.NativeStart.run(Native Method)

----- end 11489 -----

I'm kinda desesperate right now, so if anyone has an idea, I'd really appreciate it.

The solution is simple: don't use `Runtime.exec()`. There are no command-line programs that are part of the Android SDK. Any command-line program that you would want to use should be rewritten as an NDK library and called directly from your Java app via JNI. — CommonsWare, May 16 '11 at 13:34
So I should rewrite the whole ps command with the NDK instead of just using 5 lines with Runtime.exec ? :/ — Lyrkan, May 16 '11 at 13:47
You solve whatever problem that you are trying to solve using techniques that will work across whatever devices you are trying to deploy it to. If this is just for your phone, and you want to use `ps`, you are welcome to beat your head against a wall to get it to work. If you are trying to build an application for the Android Market or similar wide distribution, do not use `ps`, but rather implement your desired functionality in some other way, possibly using the NDK. — CommonsWare, May 16 '11 at 13:59
What is the functionality you need to achieve? 'ps' mostly reads and interprets information contained in the numbered pid directories under /proc — Chris Stratton, May 16 '11 at 15:02
I hadn't thought of reading directly /proc/xxx/status. I just need to retrieve PIDs and names of current processes. — Lyrkan, May 16 '11 at 15:20

score 5 · Accepted Answer · answered Feb 14 '12 at 07:27

5

That's most likely the bug fixed in this Github commit. In essence, it deadlocks directly after fork() but before doing the actual exec() because somebody tried to malloc.

answered Feb 14 '12 at 07:27

dascandy

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Problem with Runtime.exec and Android

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