Mojo Embedder Development Kit (EDK)

This document is a subset of the Mojo documentation.


The Mojo EDK is a (binary-unstable) API which enables a process to initialize and use Mojo for IPC to other processes. Note that this library is only usable when statically linking the EDK into your application. Applications which want to use a shared external copy of the Mojo implementation should instead call MojoInitialize() to initialize Mojo and IPC. See the note about mojo_core here.

Using any of the API surface in //mojo/edk/embedder requires a direct dependency on the GN //mojo/edk target. Headers in mojo/edk/system are reserved for internal use by the EDK only.

NOTE: Unless you are introducing a new binary entry point into the system (e.g., a new executable with a new main() definition), you probably don‘t need to know anything about the EDK API. Most processes defined in the Chrome repo today already fully initialize the EDK so that Mojo’s other public APIs “just work” out of the box.

Basic Initialization

In order to use Mojo in an application statically linking the EDK, it's necessary to call mojo::edk::Init exactly once:

#include "mojo/edk/embedder/embedder.h"

int main(int argc, char** argv) {

  // Now you can create message pipes, write messages, etc

  return 0;

This enables local API calls to work, so message pipes etc can be created and used. In some cases (particuarly many unit testing scenarios) this is sufficient, but to support any actual multiprocess communication (e.g. sending or accepting Mojo invitations), a second IPC initialization step is required.

IPC Initialization

Internal Mojo IPC implementation requires background TaskRunner on which it can watch for inbound I/O from other processes. This is configured using a ScopedIPCSupport object, which keeps IPC support alive through the extent of its lifetime.

Typically an application will create a dedicated background thread and give its TaskRunner to Mojo. Note that in Chromium, we use the existing “IO thread” in the browser process and content child processes.

#include "base/threading/thread.h"
#include "mojo/edk/embedder/embedder.h"
#include "mojo/edk/embedder/scoped_ipc_support.h"

int main(int argc, char** argv) {

  base::Thread ipc_thread("ipc!");
      base::Thread::Options(base::MessageLoop::TYPE_IO, 0));

  // As long as this object is alive, all Mojo API surface relevant to IPC
  // connections is usable, and message pipes which span a process boundary will
  // continue to function.
  mojo::edk::ScopedIPCSupport ipc_support(

  return 0;

This process is now fully prepared to use Mojo IPC!

Note that all existing process types in Chromium already perform this setup very early during startup.

Connecting Two Processes

Once IPC is initialized, you can bootstrap connections to other processes by using the public Invitations API.