flutter_flutter/mojo/devtools/common

Devtools

Unopinionated tools for running, debugging and testing Mojo apps.

Install

git clone https://github.com/domokit/devtools.git

Contents

Devtools offers the following tools:

• mojo_run - shell runner
• mojo_test - apptest runner
• mojo_debug - debugger supporting interactive tracing and debugging of a running mojo shell

Additionally, remote_adb_setup script helps to configure adb on a remote machine to communicate with a device attached to a local machine, forwarding the ports used by mojo_run.

Runner

mojo_run allows you to run a Mojo shell either on the host, or on an attached Android device.

mojo_run APP_URL  # Run on the host.
mojo_run APP_URL --android  # Run on Android device.
mojo_run "APP_URL APP_ARGUMENTS"  # Run an app with startup arguments

Unless running within a Mojo checkout, we need to indicate the path to the shell binary:

mojo_run --shell-path path/to/shell/binary APP_URL

Some applications are running embedded inside a window manager. To start such an app, you have to first start the window manager app, then have it embed the app you are interested in. It is done as follows using the default window manager:

mojo_run "mojo:window_manager APP_URL"

By default, mojo_run uses mojo:kiosk_wm as the default window manager. It can be changed using the --window-manager flag.

Sky apps

To run a Sky app, you need to build sky_viewer.mojo in a Sky checkout, and indicate the path to the binary using the --map-url parameter:

mojo_run --map-url mojo:sky_viewer=/path/to/sky/viewer "mojo:window_manager APP_URL"

If the app does not declare a shebang indicating that it needs to be run in sky_viewer, pass --sky to map sky_viewer as a default content handler for dart apps:

mojo_run --map-url mojo:sky_viewer=/path/to/sky/viewer "mojo:window_manager APP_URL" --sky

Note that Sky apps will need the --use-osmesa flag to run over chromoting:

Debugger

mojo_debug allows you to interactively inspect a running shell, collect performance traces and attach a gdb debugger.

Tracing

To collect performance traces and retrieve the result:

mojo_debug tracing start
mojo_debug tracing stop [result.json]

The trace file can be then loaded using the trace viewer in Chrome available at about://tracing.

GDB

It is possible to inspect a Mojo Shell process using GDB. The mojo_debug script can be used to launch GDB and attach it to a running shell process (android only):

mojo_debug gdb attach

Once started, GDB will first stop the Mojo Shell execution, then load symbols from loaded Mojo applications. Please note that this initial step can take some time (up to several minutes in the worst case).

After each execution pause, GDB will update the set of loaded symbols based on the selected thread only. If you need symbols for all threads, use the update-symbols GDB command:

(gdb) update-symbols

If you only want to update symbols for the current selected thread (for example, after changing threads), use the current option:

(gdb) update-symbols current

If you want to debug the startup of your application, you can pass --wait-for-debugger to mojo_run to have the Mojo Shell stop and wait to be attached by gdb before continuing.

Android crash stacks

When Mojo shell crashes on Android ("Unfortunately, Mojo shell has stopped.") due to a crash in native code, mojo_debug can be used to find and symbolize the stack trace present in the device log:

mojo_debug device stack

Development

The library is canonically developed in the mojo repository, https://github.com/domokit/devtools is a mirror allowing to consume it separately.