TracingController

Kotlin |Java

abstract class TracingController

kotlin.Any
↳	androidx.webkit.TracingController

Manages tracing of WebViews. In particular provides functionality for the app to enable/disable tracing of parts of code and to collect tracing data. This is useful for profiling performance issues, debugging and memory usage analysis in production and real life scenarios.

The resulting trace data is sent back as a byte sequence in json format. This file can be loaded in "chrome://tracing" for further analysis.

Example usage:

TracingController tracingController = TracingController.getInstance();
  tracingController.start(new TracingConfig.Builder()
                   .addCategories(CATEGORIES_WEB_DEVELOPER).build());
  ...
  tracingController.stop(new FileOutputStream("trace.json"),
                         Executors.newSingleThreadExecutor());
  

Summary

Public methods
open static TracingController	getInstance() Returns the default TracingController instance.
abstract Boolean	isTracing() Returns whether the WebView framework is tracing.
abstract Unit	start(@NonNull tracingConfig: TracingConfig) Starts tracing all webviews.
abstract Boolean	stop(@Nullable outputStream: OutputStream?, @NonNull executor: Executor) Stops tracing and flushes tracing data to the specified outputStream.

Public methods

getInstance

@NonNull open static fun getInstance(): TracingController

Returns the default TracingController instance. At present there is only one TracingController instance for all WebView instances.

This method should only be called if WebViewFeature#isFeatureSupported(String) returns true for WebViewFeature#TRACING_CONTROLLER_BASIC_USAGE.

isTracing

abstract fun isTracing(): Boolean

Returns whether the WebView framework is tracing.

Return
Boolean: True if tracing is enabled.

start

abstract fun start(@NonNull tracingConfig: TracingConfig): Unit

Starts tracing all webviews. Depending on the trace mode in traceConfig specifies how the trace events are recorded.

For tracing modes android.webkit.TracingConfig#RECORD_UNTIL_FULL and android.webkit.TracingConfig#RECORD_CONTINUOUSLY the events are recorded using an internal buffer and flushed to the outputStream when stop(OutputStream, Executor) is called.

This method should only be called if WebViewFeature#isFeatureSupported(String) returns true for WebViewFeature#TRACING_CONTROLLER_BASIC_USAGE.

Parameters
tracingConfig	TracingConfig: Configuration options to use for tracing.

Exceptions
IllegalStateException	If the system is already tracing.
IllegalArgumentException	If the configuration is invalid (e.g. invalid category pattern or invalid tracing mode).

stop

abstract fun stop(@Nullable outputStream: OutputStream?, @NonNull executor: Executor): Boolean

Stops tracing and flushes tracing data to the specified outputStream. The data is sent to the specified output stream in json format typically in chunks by invoking OutputStream#write(byte[]). On completion the OutputStream#close() method is called.

This method should only be called if WebViewFeature#isFeatureSupported(String) returns true for WebViewFeature#TRACING_CONTROLLER_BASIC_USAGE.

Parameters
outputStream	OutputStream?: The output stream the tracing data will be sent to. If null the tracing data will be discarded.
executor	OutputStream?: The Executor on which the outputStream OutputStream#write(byte[]) and OutputStream#close() methods will be invoked. Callback and listener events are dispatched through this Executor, providing an easy way to control which thread is used. To dispatch events through the main thread of your application, you can use Context#getMainExecutor(). To dispatch events through a shared thread pool, you can use AsyncTask#THREAD_POOL_EXECUTOR.

Return
Boolean: false if the WebView framework was not tracing at the time of the call, true otherwise.