CppPromise

CppPromise is a concurrent computing library I built at Verily with Limu Xiao, as part of the Verily Retinal Camera project.

Introduction

NOTE! We just got approval from Verily to Open Source CppPromise. Check it out at github.com/cpppromise/cpppromise.

The library allows programmers to build their C++ programs as a series of independent event loops, each with its own independent state, passing messages consisting of (logically) immutable data. A programmer can write an API for an event loop that manages a camera sensor in a system, for example, as follows:

class CameraSensorProcess : public cpppromise::Process {
 public:
  cpppromise::Promise<Image> GetNextImageFromCamera();
}

Another event loop could then use this as:

{
  myCameraProcess_->GetNextImageFromCamera().Then([](Image result) {
    // Do something with the result
    // This closure runs in the thread of the calling event loop
  });
}

Programmers can do idiomatic Then() chaining as they would in JavaScript, and avoid concurrent state modification hazards. A proper use of the system is one where application programmers do not use std::thread or std::mutex directly.

The system also includes a pub/sub mechanism that operates similarly.

This work allowed Verily people of all experience – including mechanical engineers – to contribute to the core C++ software without the usual hazards. This in turn allowed engineers with experience in machine learning, image processing, and the application domain, to work directly with us, and was both a morale and technical force multiplier.