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Table of Contents

Custom Android system properties used by .NET for Android

Introduction

.NET for Android uses a number of custom Android system properties to communicate settings to application at the run time. Each property value can be no longer than 91 characters (as per Android OS limits) and can be set from the command line using the following syntax:

$ adb shell setprop property_name property_value

To unset any of the properties, the following syntax needs to be used:

$ adb shell setprop property_name "''"

Known properties

debug.mono.connect

Used mostly by the IDEs to set arguments for the remote debugger connection required to attach the debugger to application running on device. Arguments must be specified as a comma-separated list without any whitespace. Known arguments:

  • port=PORT Debugger port (a short integer)
  • timeout=VALUE Debugger session start timeout (in milliseconds)

debug.mono.debug

Indicates that Mono debug session needs to be initialized. Property value doesn't matter, only its presence is checked.

debug.mono.env

Specifies a list of environment properties to set. Property is only used in Debug builds of .NET for Android applications. Its value is a list of NAME=VALUE pairs separated with the pipe character (|), without any whitespace surrounding each of the pipe separators.

debug.mono.extra

Contains a whitespace separated list of additional command line arguments to pass to the Mono runtime initialization function.

debug.mono.gc

Enable GC logging if set to any non-empty value. Property is only used in Debug builds of .NET for Android applications.

debug.mono.gdb

Set additional parameters when starting a .NET for Android application under GDB. Each argument follows the NAME:VALUE format. Supported arguments:

  • wait:TIMESTAMP TIMESTAMP should be the output of date +%s in the android shell. If this property is set, wait for a native debugger to attach by spinning in a loop. If the current time is later than TIMESTAMP + 10s, the property is ignored.

debug.mono.log

Configure the .NET for Android runtime categories. By default only the default category is enabled, which logs a handful of messages during application startup and operation. This property enables all the messages logged below the info level for any of the categories. Value of the property is a comma-separated list of NAME[=VALUE] categories:

  • assembly Log all messages related to embedded assembly activities (lookup, typemaps, loading etc).
  • bundle Log all messages related to bundled app processing.
  • debugger-log-level=LEVEL Set the Mono soft debugger logging level.
  • debugger Log all messages related to setting up the Mono soft debugger.
  • default Enable messages that don't belong to any of the other, more specific, categories.
  • gc Log garbage collector messages.
  • gref- Enable global reference logging but without writing the logged messages to a file.
  • gref=FILE Enable global reference logging and write messages to the specified FILE
  • gref Enable global reference logging and log messages to the default grefs.txt file.
  • gref+ Enable global reference logging, writing messages to adb logcat. Note: this will spam adb logcat, possibly impacting app performance, and Android might not preserve all messages. This is provided as a "last ditch effort", and is not as reliable as the normal gref or gref= options which write to a file. Added in Xamarin.Android 12.2.
  • lref- Enable local reference logging but without writing the logged messages to a file.
  • lref=FILE Enable local reference logging and write messages to the specified FILE
  • lref Enable local reference logging and log messages to the default lrefs.txt file, unless gref or gref= are also present, in which case messages will be logged to the gref file.
  • lref+ Enable local reference logging, writing messages to adb logcat. Note: this will spam adb logcat, possibly impacting app performance, and Android might not preserve all messages. This is provided as a "last ditch effort", and is not as reliable as the normal lref or lref= options which write to a file. Added in Xamarin.Android 12.2.
  • mono_log_level=LEVEL Set Mono runtime log level. The default value is error to log only errors, unless gc or assembly log categories are enabled, in which case the default value for this property is info.
  • mono_log_mask=MASK Set Mono runtime log mask. Value of this argument is a list of categories separated with :, without any whitespace surrounding the separator. Full list of categories is available here
  • netlink Enable logging of low-level Linux netlink device used to enumerate network interfaces and their associated IP addresses.
  • network Enable logging for messages related to network activity.
  • timing=bare Enable logging of native code performance information, without logging method execution timing information to a file. Timed events are logged to logcat immediately, which affects the accuracy of measurements and introduces an element of unpredictability to measurements.
  • timing=fast-bare Similar to timing=bare above, but the timings aren't logged until the mono.android.app.DUMP_TIMING_DATA broadcast is sent to the application. This can be done with adb shell am broadcast -a mono.android.app.DUMP_TIMING_DATA [PACKAGE_NAME] command.
  • timing Enable logging of native code performance information, including method execution timing which is written to a file named methods.txt. timing=bare should be used in preference to this category.

Timing events format

In any of the timing modes, the logged messages have the following format:

<TAG>: [<S>/<E>] <MESSAGE>; elapsed s:ms::ns

Where:

All lower case and punctuation characters are verbatim in every message

<TAG> is always monodroid-timing

<S> denotes a "stage":

  • 0: events before control is handed over to the managed runtime (the "native init" stage)
  • 1: events after the above "native init" stage
  • 2: used only in the timing=fast-bare mode to mark the summary information.

<E> denotes an "event":

  • For the 0 and 1 stages it's one of
    • 0: assembly decompression
    • 1: assembly load
    • 2: assembly preload
    • 3: initialization and start of debugging
    • 4: timing subsystem initialization
    • 5: java-to-managed type lookup
    • 6: managed-to-java type lookup
    • 7: Mono runtime initialization
    • 8: native to managed transition (a call to Android.Runtime.JNIEnv.Initialize)
    • 9: time spent registering the runtime config blob on NET6+
    • 10: managed type registration
    • 11: total time spent initializing the native runtime
    • 12: unspecified event
  • For the 2 stage it's one of:
    • 1: mode marker message logged at the very beginning of the app
    • 2: performance results "heading"
    • 3: no events logged message
    • 4: accumulated results "heading"
    • 5: total time spent loading assemblies
    • 6: total time spent performing java-to-managed type lookups
    • 7: total time spent performing managed-to-java type lookups

The format is meant to make it easier for scripts/other software which look at the log to find timing events without having to rely on the actual wording of the event message.

Reading the timing information

timing and timing=bare modes write all the event messages to logcat immediately, so it is sufficient to either watch the logcat buffer in real time:

adb logcat

or dump the buffer it after the timing sequence is entirely recorded:

adb logcat -d > logcat.txt

The timing=fast-bare mode is slightly more involved in that in requires the broadcast to be sent before data is logged in logcat. The following sequence of commands can be placed in a script and used to obtain the information:

# Enable only timing log messages, to minimize impact on application
# performance
$ adb shell setprop debug.mono.log timing=fast-bare

# Build and install the application
$ dotnet build -t:Install -p:Configuration=Release

# Increase logcat buffer size so that we don't miss any messages
$ adb logcat -G 16M

# Clear logcat buffer
$ adb logcat -c

# Start the activity and wait for the startup process to finish. This
# is marked by Android by logging the `Displayed` message in logcat,
# formatted similarly to:
#
#  ActivityTaskManager: Displayed PACKAGE_NAME/ACTIVITY_NAME: +398ms
#
$ adb shell am start -n PACKAGE_NAME/ACTIVITY_NAME -S -W

# Tell the timing infrastructure to log all the gathered events to
# logcat:
$ adb shell am broadcast -a mono.android.app.DUMP_TIMING_DATA PACKAGE_NAME

# Dump logcat contents into a file
adb logcat -d > logcat.txt

Technically, the broadcast can be sent to all applications running on the device, but in event there are more .NET for Android applications which happen to have timing enabled, the output could be confusing so it's better to send the broadcast to a specific application/package only.

debug.mono.max_grefc

If set, override the number of maximum global references. The number defaults to 2000 if the application is running in an emulator and 51200 otherwise.

debug.mono.profile

In "legacy" Xamarin.Android applications (that is not NET6+ ones), value of this property specifies argument to the Mono logging profiler.

In NET6+ applications, the only accepted value is [aot:]PORTS where PORTS becomes value of the DOTNET_DiagnosticPorts environment variable used by the NET6+ profiling infrastructure to configure the client/server ports.

debug.mono.runtime_args

Additional arguments passed to the Mono's mono_jit_parse_options function.

debug.mono.soft_breakpoints

If set to 0, disable Mono debugger's soft breakpoints. By default breakpoints are enabled.

debug.mono.trace

Set Mono JIT trace options, passed to the Mono's mono_jit_set_trace_options function.

debug.mono.wref

Configures use of Java (value java) or JNI (value jni) weak references.