Instrumenting Android crashes with the Glean SDK

One of the things that might be useful to collect data on in an Android application is crashes. This guide will walk through a basic strategy for instrumenting an Android application with crash telemetry using a custom ping.

Note: This is a very simple example of instrumenting crashes using the Glean SDK. There will be challenges to using this approach in a production application that should be considered. For instance, when an app crashes it can be in an unknown state and may not be able to do things like upload data to a server. The recommended way of instrumenting crashes with Android Components is called lib-crash, which takes into consideration things like multiple processes and persistence.

Before You Start

There are a few things that need to be installed in order to proceed, mainly Android Studio. If you include the Android SDK, Android Studio can take a little while to download and get installed. This walk-through assumes some knowledge of Android application development. Knowing where to go to create a new project and how to add dependencies to a Gradle file will be helpful in following this guide.

Setup Build Configuration

Please follow the instruction in the "Adding Glean to your project" chapter in order to set up Glean in an Android project.

Add A Custom Metric

Since crashes will be instrumented with some custom metrics, the next step will be to add a metrics.yaml file to define the metrics used to record the crash information and a pings.yaml file to define a custom ping which will give some control over the scheduling of the uploading. See "Adding new metrics" for more information about adding metrics.

What metric type should be used to represent the crash data? While this could be implemented several ways, an event is an excellent choice, simply because events capture information in a nice concise way and they have a built-in way of passing additional information using the extras field. If it is necessary to pass along the cause of the exception or a few lines of description, events let us do that easily (with some limitations).

Now that a metric type has been chosen to represent the metric, the next step is creating the metrics.yaml. Inside of the root application folder of the Android Studio project create a new file named metrics.yaml. After adding the schema definition and event metric definition, the metrics.yaml should look like this:

# Required to indicate this is a `metrics.yaml` file
$schema: moz://

    type: event
    description: |
      Event to record crashes caused by unhandled exceptions
      - crash
        description: The cause of the crash
        description: The exception message

As a brief explanation, this creates a metric called exception within a metric category called crash. There is a text description and the required notification_emails, bugs, data_reviews, and expires fields. The send_in_pings field is important to note here that it has a value of - crash. This means that the crash event metric will be sent via a custom ping named crash (which hasn't been created yet). Finally, note the extra_keys field which has two keys defined, cause and message. This allows for sending additional information along with the event to be associated with these keys.

Note: For Mozilla applications, a mandatory data review is required in order to collect information with the Glean SDK.

Add A Custom Ping

Define the custom ping that will help control the upload scheduling by creating a pings.yaml file in the same directory as the metrics.yaml file. For more information about adding custom pings, see the section on custom pings.
The name of the ping will be crash, so the pings.yaml file should look like this:

# Required to indicate this is a `pings.yaml` file
$schema: moz://

  description: >
    A ping to transport crash data
  include_client_id: true

Before the newly defined metric or ping can be used, the application must first be built. This will cause the glean_parser to execute and generate the API files that represent the metric and ping that were newly defined.

Note: If changes to the YAML files aren't showing up in the project, try running the clean task on the project before building any time one of the Glean YAML files has been modified.

It is recommended that Glean be initialized as early in the application startup as possible, which is why it's good to use a custom Application, like the Glean Sample App GleanApplication.kt.

Initializing Glean in the Application.onCreate() is ideal for this purpose. Start by adding the import statement to allow the usage of the custom ping that was created, adding the following to the top of the file:

import org.mozilla.gleancrashexample.GleanMetrics.Pings

Next, register the custom ping by calling Glean.registerPings(Pings) in the onCreate() function, preferably before calling Glean.initialize(). The completed function should look something like this:

override fun onCreate() {

  // Register the application's custom pings.

  // Initialize the Glean library

This completes the registration of the custom ping with the Glean Kotlin SDK so that it knows about it and can manage the storage and other important details of it like sending it when send() is called.

Instrument The App To Record The Event

In order to make the custom Application class handle uncaught exceptions, extend the class definition by adding Thread.UncaughtExceptionHandler as an inherited class like this:

class MainActivity : AppCompatActivity(), Thread.UncaughtExceptionHandler {

As part of implementing the Thread.UncaughtExceptionHandler interface, the custom Application needs to implement the override of the uncaughtException() function. An example of this override that records data and sends the ping could look something like this:

override fun uncaughtException(thread: Thread, exception: Throwable) {
            Crash.exceptionKeys.cause to exception.cause!!.toString(),
            Crash.exceptionKeys.message to exception.message!!

This records data to the Crash.exception metric from the metrics.yaml. The category of the metric is crash and the name is exception so it is accessed it by calling record() on the Crash.exception object. The extra information for the cause and the message is set as well. Finally, calling Pings.crash.submit() forces the crash ping to be scheduled to be sent.

The final step is to register the custom Application as the default uncaught exception handler by adding the following to the onCreate() function after Glean.initialize(this):


Next Steps

This information didn't really get recorded by anything, as it would be rejected by the telemetry pipeline unless the application was already known. In order to collect telemetry from a new application, there is additional work that is necessary that is beyond the scope of this example. In order for data to be collected from your project, metadata must be added to the probe_scraper. The instructions for accomplishing this can be found in the probe_scraper documentation.