Tutorial: Investigating silent crash of Release build (e.g. Port death watcher fired)

Release build (shared IPA) crashes when shared with QA team or even being uploaded to Apple Store doesn’t give any reason in crash reports. Device console logs shows as much as:

Feb 12 09:32:12 iPhone assertiond[67] : [DemoApp:620] Port death watcher fired.

This can be reproduced with this minimal snippet – it will produce output while on wire with debugger but once started without it (or from IPA or Apple store) will be silent:

public class Main extends UIApplicationDelegateAdapter {
    @Override
    public boolean didFinishLaunching(UIApplication application, UIApplicationLaunchOptions launchOptions) {
        throw new RuntimeException("You will not see me!");
    }
}

With very high chance crash is Java code and it is not causes any log output/crash report because developer didn’t configured app so. What has to be done:

All java exception shall go to NSException

This can be easily enable with one line of code somewhere in UIApplicationDelegate implementation:

public class Main extends UIApplicationDelegateAdapter {
    @Override
    public boolean didFinishLaunching(UIApplication application, UIApplicationLaunchOptions launchOptions) {
        ...
        NSException.registerDefaultJavaUncaughtExceptionHandler();
        ...
    }
}

This small change give crash report in console to allow work with:

Feb 12 10:24:41 iPhone DemoApp(CoreFoundation)[690] <Notice>: *** Terminating app due to uncaught exception 'java.lang.RuntimeException', reason: 'java.lang.RuntimeException: You will not see me!
	at com.mycompany.myapp.Main.didFinishLaunching(Main.java:51)
	at com.mycompany.myapp.Main.$cb$application$didFinishLaunchingWithOptions$(Main.java)
	at org.robovm.apple.uikit.UIApplication.main(Native Method)
	at org.robovm.apple.uikit.UIApplication.main(UIApplication.java:428)
	at com.mycompany.myapp.Main.main(Main.java:64)

Why there is no uncaught Exception console output from JVM itself when running Release code

Even without NSException.registerDefaultJavaUncaughtExceptionHandler() there shall be console output about uncaught exception from JVM. First of all lets see how stdout and stderr find their way to Device console. In release run it got redirected by this code in UIApplication:

public static <P extends UIApplication, D extends NSObject & UIApplicationDelegate>
    void main(String[] args, Class<P> principalClass, Class<D> delegateClass) {
        ...
        if (System.getenv("ROBOVM_LAUNCH_MODE") == null) {
            if (!(System.err instanceof FoundationLogPrintStream)) {
                System.setErr(new FoundationLogPrintStream());
            }
            if (!(System.out instanceof FoundationLogPrintStream)) {
                System.setOut(new FoundationLogPrintStream());
            }
        }
        ...
}

So there is FoundationLogPrintStream which will redirects all outputs to NSLog but this is happening in following cases:

• explicit flush is called;
• as final part of printLn methods.

Still why there is no uncaught Exception console output from JVM even with FoundationLogPrintStream included

The reason for this is way how uncaught exception being printed by JVM. It is being done in ThreadGroup.uncaughtException(Thread t, Throwable e):

public void uncaughtException(Thread t, Throwable e) {
    if (parent != null) {
        parent.uncaughtException(t, e);
    } else if (Thread.getDefaultUncaughtExceptionHandler() != null) {
        // TODO The spec is unclear regarding this. What do we do?
        Thread.getDefaultUncaughtExceptionHandler().uncaughtException(t, e);
    } else if (!(e instanceof ThreadDeath)) {
        // No parent group, has to be 'system' Thread Group
        e.printStackTrace(System.err);
    }
}

Uncaught exception will end up with e.printStackTrace(System.err) which seems pretty ok considering that System.err == FoundationLogPrintStream, but lets see what is wrong with Throwable.printStackTrace. it all ends with lot of code that output information using err.append() calls.

Root case of problem is that FoundationLogPrintStream is not implementing append() method and all output is that goes after it will not get any flush(). This means all buffered data will not go to NSLog() as app will be terminated after uncaught exception.

quick fix

Using of NSException.registerDefaultJavaUncaughtExceptionHandler() would be enough as it does the flush() inside;

long term solution

PR267. Is to add flush after print of uncaught exception in ThreadGroup.uncaughtException(Thread t, Throwable e):

public void uncaughtException(Thread t, Throwable e) {
    ...
    } else if (!(e instanceof ThreadDeath)) {
        // No parent group, has to be 'system' Thread Group
        e.printStackTrace(System.err);
        System.err.flush();
    }
}

short term solution

It is possible to use own implementation of PrintStream which will catch new line symbol and do flush, like this:

public class Main extends UIApplicationDelegateAdapter {
    @Override
    public boolean didFinishLaunching(UIApplication application, UIApplicationLaunchOptions launchOptions) {
        ...
        // override robovm bug to allow console logging on release/run
        if (System.getenv("ROBOVM_LAUNCH_MODE") == null) {
            System.setErr(new FoundationLogPrintStream());
            System.setOut(new FoundationLogPrintStream());
        }
        ...
    }

    public class FoundationLogPrintOutputStream extends OutputStream {
    StringBuffer st = new StringBuffer();

    @Override
    public void write(int ch) throws IOException {
        if(ch != 10) {
            this.st.append((char)ch);
        } else {
            try {
                this.flush();
            } catch (IOException ignored) {
            }
        }
    }

    @Override
    public void flush() throws IOException {
        if(this.st.length() > 0) {
            Foundation.log("%@", new NSString(this.st.toString()));
            this.st.setLength(0);
        }
    }
}