commit	ca7ba4d0ac3ab452c5db60befc8be37fd6e2339b	[log] [tgz]
author	Nathaniel Manista <nathaniel@google.com>	Fri Apr 20 02:49:34 2018 +0000
committer	Nathaniel Manista <nathaniel@google.com>	Wed May 02 18:24:47 2018 +0000
tree	813d64334b810569555737be39f3d81bc9f4dc7c
parent	d3eaf64687416c19177ba6a078f9f11599c063b9 [diff]

Keep Core memory inside cygrpc.Channel objects

This removes invocation-side completion queues from the _cygrpc API.
Invocation-side calls are changed to no longer share the same lifetime
as Core calls.

Illegal metadata is now detected on invocation rather than at the start
of a batch (so passing illegal metadata to a response-streaming method
will now raise an exception immediately rather than later on when
attempting to read the first response message).

It is no longer possible to create a call without immediately starting
at least one batch of operations on it. Only tests are affected by this
change; there are no real use cases in which one wants to start a call
but wait a little while before learning that the server has rejected
it.

It is now required that code above cygrpc.Channel spend threads on
next_event whenever events are pending. A cygrpc.Channel.close method
is introduced, but it merely blocks until the cygrpc.Channel's
completion queues are drained; it does not itself drain them.

Noteworthy here is that we drop the cygrpc.Channel.__dealloc__ method.
It is not the same as __del__ (which is not something that can be added
to cygrpc.Channel) and there is no guarantee that __dealloc__ will be
called at all or that it will be called while the cygrpc.Channel
instance's Python attributes are intact (in testing, I saw both in
different environments). This commit does not knowingly break any
garbage-collection-based memory management working (or "happening to
appear to work in some circumstances"), though if it does, the proper
remedy is to call grpc.Channel.close... which is the objective towards
which this commit builds.

13 files changed

tree: 813d64334b810569555737be39f3d81bc9f4dc7c

README.md

gRPC - An RPC library and framework

Documentation

You can find more detailed documentation and examples in the doc and examples directories respectively.

Installation & Testing

See INSTALL for installation instructions for various platforms.

See tools/run_tests for more guidance on how to run various test suites (e.g. unit tests, interop tests, benchmarks)

See Performance dashboard for the performance numbers for the latest released version.

Repository Structure & Status

This repository contains source code for gRPC libraries for multiple languages written on top of shared C core library src/core.

Libraries in different languages may be in different states of development. We are seeking contributions for all of these libraries.

Language	Source
Shared C [core library]	src/core
C++	src/cpp
Ruby	src/ruby
Python	src/python
PHP	src/php
C#	src/csharp
Objective-C	src/objective-c

Language	Source repo
Java	grpc-java
Go	grpc-go
NodeJS	grpc-node
Dart	grpc-dart

See MANIFEST.md for a listing of top-level items in the repository.

Overview

Remote Procedure Calls (RPCs) provide a useful abstraction for building distributed applications and services. The libraries in this repository provide a concrete implementation of the gRPC protocol, layered over HTTP/2. These libraries enable communication between clients and servers using any combination of the supported languages.

Interface

Developers using gRPC typically start with the description of an RPC service (a collection of methods), and generate client and server side interfaces which they use on the client-side and implement on the server side.

By default, gRPC uses Protocol Buffers as the Interface Definition Language (IDL) for describing both the service interface and the structure of the payload messages. It is possible to use other alternatives if desired.

Surface API

Starting from an interface definition in a .proto file, gRPC provides Protocol Compiler plugins that generate Client- and Server-side APIs. gRPC users typically call into these APIs on the Client side and implement the corresponding API on the server side.

Synchronous vs. asynchronous

Synchronous RPC calls, that block until a response arrives from the server, are the closest approximation to the abstraction of a procedure call that RPC aspires to.

On the other hand, networks are inherently asynchronous and in many scenarios, it is desirable to have the ability to start RPCs without blocking the current thread.

The gRPC programming surface in most languages comes in both synchronous and asynchronous flavors.

Streaming

gRPC supports streaming semantics, where either the client or the server (or both) send a stream of messages on a single RPC call. The most general case is Bidirectional Streaming where a single gRPC call establishes a stream where both the client and the server can send a stream of messages to each other. The streamed messages are delivered in the order they were sent.

Protocol

The gRPC protocol specifies the abstract requirements for communication between clients and servers. A concrete embedding over HTTP/2 completes the picture by fleshing out the details of each of the required operations.

Abstract gRPC protocol

A gRPC RPC comprises of a bidirectional stream of messages, initiated by the client. In the client-to-server direction, this stream begins with a mandatory Call Header, followed by optional Initial-Metadata, followed by zero or more Payload Messages. The server-to-client direction contains an optional Initial-Metadata, followed by zero or more Payload Messages terminated with a mandatory Status and optional Status-Metadata (a.k.a.,Trailing-Metadata).

Implementation over HTTP/2

The abstract protocol defined above is implemented over HTTP/2. gRPC bidirectional streams are mapped to HTTP/2 streams. The contents of Call Header and Initial Metadata are sent as HTTP/2 headers and subject to HPACK compression. Payload Messages are serialized into a byte stream of length prefixed gRPC frames which are then fragmented into HTTP/2 frames at the sender and reassembled at the receiver. Status and Trailing-Metadata are sent as HTTP/2 trailing headers (a.k.a., trailers).

Flow Control

gRPC inherits the flow control mechanisms in HTTP/2 and uses them to enable fine-grained control of the amount of memory used for buffering in-flight messages.