[中文版入口](README_cn.md)

## Sogou C++ Workflow

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As **Sogou\`s C++ server engine**, Sogou C++ Workflow supports almost all **back-end C++ online services** of Sogou, including all search services, cloud input method, online advertisements, etc., handling more than **10 billion** requests every day. This is an **enterprise-level programming engine** in light and elegant design which can satisfy most C++ back-end development requirements.

#### You can use it:

* To quickly build an **HTTP server**:

~~~cpp
#include <stdio.h>
#include "workflow/WFHttpServer.h"

int main()
{
    WFHttpServer server([](WFHttpTask *task) {
        task->get_resp()->append_output_body("<html>Hello World!</html>");
    });

    if (server.start(8888) == 0) { // start server on port 8888
        getchar(); // press "Enter" to end.
        server.stop();
    }

    return 0;
}
~~~

* As a **multifunctional asynchronous client**, it currently supports `HTTP`, `Redis`, `MySQL` and `Kafka` protocols.
* To implement **client/server on user-defined protocol** and build your own **RPC system**.
  * [srpc](https://github.com/sogou/srpc) is based on it and it is an independent open source project, which supports srpc, brpc, trpc and thrift protocols.
* To build **asynchronous workflow**; support common **series** and **parallel** structures, and also support any **DAG** structures.
* As a **parallel computing tool**. In addition to **networking tasks**, Sogou C++ Workflow also includes **the scheduling of computing tasks**. All types of tasks can be put into **the same** flow.
* As an **asynchronous file IO tool** in `Linux` system, with high performance exceeding any system call. Disk file IO is also a task.
* To realize any **high-performance** and **high-concurrency** back-end service with a very complex relationship between computing and networking.
* To build a **micro service** system.
  * This project has built-in **service governance** and **load balancing** features.
  * The [workflow-k8s](https://github.com/sogou/workflow-k8s) plugin enables using name service with Kubernetes automated deployment.
* Wiki link : [PaaS Architecture](https://github.com/sogou/workflow/wiki)

#### Compiling and running environment

* This project supports `Linux`, `macOS`, `Windows`, `Android` and other operating systems.
  * `Windows` version is currently released as an independent [branch](https://github.com/sogou/workflow/tree/windows), using `iocp` to implement asynchronous networking. All user interfaces are consistent with the `Linux` version.
* Supports all CPU platforms, including 32 or 64-bit `x86` processors, big-endian or little-endian `arm` processors, `loongson` processors.
* Relies on `OpenSSL`; `OpenSSL 1.1` and above is recommended. If you don't like SSL, you may checkout the [nossl](https://github.com/sogou/workflow/tree/nossl) branch. But still need to link `crypto` for `md5` and `sha1`.
* Uses the `C++11` standard and therefore, it should be compiled with a compiler which supports `C++11`. Does not rely on `boost` or `asio`.
* No other dependencies. However, if you need `Kafka` protocol, some compression libraries should be installed, including `lz4`, `zstd` and `snappy`.

### Get started (Linux, macOS):
~~~sh
git clone https://github.com/sogou/workflow
make
cd tutorial
make
~~~~

### Get started (Debian Linux):
Sogou C++ Workflow has been packaged for Debian. It is currently in Debian sid (unstable) but will eventually be placed into the stable repository.

In order to access the unstable repository, you will need to edit your /etc/apt/sources.list file.

Simply add the 'unstable' sub branch to your repo:
~~~~sh
deb http://deb.debian.org/ main contrib non-free 
--> 
deb http://deb.debian.org/ unstable main contrib non-free
~~~~

Once that is added, update your repo list and then you should be able to install it:
~~~~sh
sudo apt-get update
~~~~

To install the Workflow library for development purposes:
~~~~sh
sudo apt-get install libworkflow-dev
~~~~

To install the Workflow library for deployment:
~~~~sh
sudo apt-get install libworkflow1
~~~~

# Tutorials

* Client
  * [Creating your first task：wget](docs/en/tutorial-01-wget.md)
  * [Implementing Redis set and get：redis\_cli](docs/en/tutorial-02-redis_cli.md)
  * [More features about series：wget\_to\_redis](docs/en/tutorial-03-wget_to_redis.md)
* Server
  * [First server：http\_echo\_server](docs/en/tutorial-04-http_echo_server.md)
  * [Asynchronous server：http\_proxy](docs/en/tutorial-05-http_proxy.md)
* Parallel tasks and Series　
  * [A simple parallel wget：parallel\_wget](docs/en/tutorial-06-parallel_wget.md)
* Important topics
  * [About error](docs/en/about-error.md)
  * [About timeout](docs/en/about-timeout.md)
  * [About global configuration](docs/en/about-config.md)
  * [About DNS](docs/en/about-dns.md)
  * [About exit](docs/en/about-exit.md)
* Computing tasks
  * [Using the build-in algorithm factory：sort\_task](docs/en/tutorial-07-sort_task.md)
  * [User-defined computing task：matrix\_multiply](docs/en/tutorial-08-matrix_multiply.md)
  * [Use computing task in a simple way: go task](docs/en/about-go-task.md)
* Asynchronous File IO tasks
  * [Http server with file IO：http\_file\_server](docs/en/tutorial-09-http_file_server.md)
* User-defined protocol
  * [A simple user-defined protocol: client/server](docs/en/tutorial-10-user_defined_protocol.md)
* Timing tasks and counting tasks
  * [About timer](docs/en/about-timer.md)
  * [About counter](docs/en/about-counter.md)
  * [Conditional and resource pool](docs/en/about-conditional.md)
* Service governance
  * [About service governance](docs/en/about-service-governance.md)
  * [More documents about upstream](docs/en/about-upstream.md)
* Connection context
  * [About connection context](docs/en/about-connection-context.md)
* Built-in clients
  * [Asynchronous MySQL client：mysql\_cli](docs/en/tutorial-12-mysql_cli.md)
  * [Asynchronous Kafka client: kafka\_cli](docs/en/tutorial-13-kafka_cli.md)

#### System design features

We believe that a typical back-end program=protocol+algorithm+workflow and should be developed completely independently.

* Protocol
  * In most cases, users use built-in common network protocols, such as HTTP, Redis or various rpc.
  * Users can also easily customize user-defined network protocol. In the customization, they only need to provide serialization and deserialization functions to define their own client/server.
* Algorithm
  * In our design, the algorithm is a concept symmetrical to the protocol.
    * If protocol call is rpc, then algorithm call is an apc (Async Procedure Call).
  * We have provided some general algorithms, such as sort, merge, psort, reduce, which can be used directly.
  * Compared with a user-defined protocol, a user-defined algorithm is much more common. Any complicated computation with clear boundaries should be packaged into an algorithm.
* Workflow
  * Workflow is the actual business logic, which is to put the protocols and algorithms into the flow graph for use.
  * The typical workflow is a closed series-parallel graph. Complex business logic may be a non-closed DAG.
  * The workflow graph can be constructed directly or dynamically generated based on the results of each step. All tasks are executed asynchronously.

Basic task, task factory and complex task

* Our system contains six basic tasks: networking, file IO, CPU, GPU, timer, and counter.
* All tasks are generated by the task factory and automatically recycled after callback.
  * Server task is one kind of special networking task, generated by the framework which calls the task factory, and handed over to the user through the process function.
* In most cases, the task generated by the user through the task factory is a complex task, which is transparent to the user.
  * For example, an HTTP request may include many asynchronous processes (DNS, redirection), but for user, it is just a networking task.
  * File sorting seems to be an algorithm, but it actually includes many complex interaction processes between file IO and CPU computation.
  * If you think of business logic as building circuits with well-designed electronic components, then each electronic component may be a complex circuit.

Asynchrony and encapsulation based on `C++11 std::function`

* Not based on user mode coroutines. Users need to know that they are writing asynchronous programs.
* All calls are executed asynchronously, and there is almost no operation that occupies a thread.
  * Although we also provide some facilities with semi-synchronous interfaces, they are not core features.
* We try to avoid user's derivations, and encapsulate user behavior with `std::function` instead, including:
  * The callback of any task.
  * Any server's process. This conforms to the `FaaS` (Function as a Service) idea.
  * The realization of an algorithm is simply a `std::function`. But the algorithm can also be implemented by derivation.

Memory reclamation mechanism

* Every task will be automatically reclaimed after the callback. If a task is created but a user does not want to run it, the user needs to release it through the dismiss method.
* Any data in the task, such as the response of the network request, will also be recycled with the task. At this time, the user can use `std::move()` to move the required data.
* SeriesWork and ParallelWork are two kinds of framework objects, which are also recycled after their callback.
  * When a series is a branch of a parallel, it will be recycled after the callback of the parallel that it belongs to.
* This project doesn’t use `std::shared_ptr` to manage memory.

#### Any other questions?

You may check the [FAQ](https://github.com/sogou/workflow/issues/406) and [issues](https://github.com/sogou/workflow/issues) list first to see if you can find the answer.

You are very welcome to send the problems you encounter in use to [issues](https://github.com/sogou/workflow/issues), and we will answer them as soon as possible. At the same time, more issues will also help new users.

