commit	527fd67cc89a562cbdccd0f141ca6d186b653289	[log] [tgz]
author	Kun Zhang <zhangkun@google.com>	Fri Jun 17 09:47:41 2016 -0700
committer	Kun Zhang <zhangkun@google.com>	Fri Jul 08 11:36:16 2016 -0700
tree	4b6d4613c05c3dd3058d49b78635976586be4162
parent	e80b136495cf6511d61a17300fa1c43e8e7c2898 [diff]

core: Channel Idleness

Resolves #1276

Idle mode is where the channel does not keep live connections, and does
not have running NameResolver and LoadBalancer.

TransportSet aggregates the in-use state of transports, including the
delayed transport and real transports. Channel aggregates the in-use
state of TransportSets and delayed tranports.

Channel starts in idle mode. It exits idle mode if one of the following
occurs:
 1. A new Call requests for a transport.
 2. The channel's in-use state turns to true.
 3. Someone calls exitIdleMode().

Channel enters the idle mode if its in-use state has been false for the
configured timeout (disabled by default). It shuts down all
TransportSets, NameResolver and LoadBalancer. Interim transports and OOB
transports are LoadBalancer's responsibility.

There is a race that could cause annoyance if IDLE_TIMEOUT was too
small (e.g., 0). A TransportSet's delayed transport is holding streams,
which keeps its in-use state in true. When a real transport is ready,
all streams are transferred to the real transport, immediately after
which the delayed transport's in-use state turns to false, while the
real transport's in-use state may have not turned to true, because some
transport (e.g. netty) may have a brief delay between newStream() being
called and the stream being created internally. This could cause the
channel's aggregated in-use state be in false for a brief time, if which
is longer than IDLE_TIMEOUT, could make channel go to idle mode. Even
though the channel would go back to non-idle again, idle mode would
shutdown all transports and NameResolver and LoadBalancer which leads to
spurious error in the application.

We minimize the chance of such race by setting the minimum timeout to 1
second.

Related chanes:
- ManagedChannelImplTest now switched to use fake executors.
- Turn a few anonymous runnables into named classes. This is more useful for debugging.

16 files changed

tree: 4b6d4613c05c3dd3058d49b78635976586be4162

README.md

gRPC-Java - An RPC library and framework

gRPC-Java works with JDK 6. TLS usage typically requires using Java 8, or Play Services Dynamic Security Provider on Android. Please see the Security Readme.

Download

Download the JARs. Or for Maven with non-Android, add to your pom.xml:

<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-netty</artifactId>
  <version>0.14.0</version>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-protobuf</artifactId>
  <version>0.14.0</version>
</dependency>
<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-stub</artifactId>
  <version>0.14.0</version>
</dependency>

Or for Gradle with non-Android, add to your dependencies:

compile 'io.grpc:grpc-netty:0.14.0'
compile 'io.grpc:grpc-protobuf:0.14.0'
compile 'io.grpc:grpc-stub:0.14.0'

For Android client, use grpc-okhttp instead of grpc-netty and grpc-protobuf-nano or grpc-protobuf-lite instead of grpc-protobuf:

compile 'io.grpc:grpc-okhttp:0.14.0'
compile 'io.grpc:grpc-protobuf-nano:0.14.0'
compile 'io.grpc:grpc-stub:0.14.0'

Development snapshots are available in Sonatypes's snapshot repository.

For protobuf-based codegen, you can put your proto files in the src/main/proto and src/test/proto directories along with an appropriate plugin.

For protobuf-based codegen integrated with the Maven build system, you can use protobuf-maven-plugin:

<build>
  <extensions>
    <extension>
      <groupId>kr.motd.maven</groupId>
      <artifactId>os-maven-plugin</artifactId>
      <version>1.4.1.Final</version>
    </extension>
  </extensions>
  <plugins>
    <plugin>
      <groupId>org.xolstice.maven.plugins</groupId>
      <artifactId>protobuf-maven-plugin</artifactId>
      <version>0.5.0</version>
      <configuration>
        <!--
          The version of protoc must match protobuf-java. If you don't depend on
          protobuf-java directly, you will be transitively depending on the
          protobuf-java version that grpc depends on.
        -->
        <protocArtifact>com.google.protobuf:protoc:3.0.0-beta-2:exe:${os.detected.classifier}</protocArtifact>
        <pluginId>grpc-java</pluginId>
        <pluginArtifact>io.grpc:protoc-gen-grpc-java:0.14.0:exe:${os.detected.classifier}</pluginArtifact>
      </configuration>
      <executions>
        <execution>
          <goals>
            <goal>compile</goal>
            <goal>compile-custom</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

For protobuf-based codegen integrated with the Gradle build system, you can use protobuf-gradle-plugin:

apply plugin: 'java'
apply plugin: 'com.google.protobuf'

buildscript {
  repositories {
    mavenCentral()
  }
  dependencies {
    // ASSUMES GRADLE 2.12 OR HIGHER. Use plugin version 0.7.5 with earlier
    // gradle versions
    classpath 'com.google.protobuf:protobuf-gradle-plugin:0.7.7'
  }
}

protobuf {
  protoc {
    // The version of protoc must match protobuf-java. If you don't depend on
    // protobuf-java directly, you will be transitively depending on the
    // protobuf-java version that grpc depends on.
    artifact = "com.google.protobuf:protoc:3.0.0-beta-2"
  }
  plugins {
    grpc {
      artifact = 'io.grpc:protoc-gen-grpc-java:0.14.0'
    }
  }
  generateProtoTasks {
    all()*.plugins {
      grpc {}
    }
  }
}

How to Build

If you are making changes to gRPC-Java, see the compiling instructions.

Navigating Around the Source

Here's a quick readers' guide to the code to help folks get started. At a high level there are three distinct layers to the library: Stub, Channel & Transport.

Stub

The Stub layer is what is exposed to most developers and provides type-safe bindings to whatever datamodel/IDL/interface you are adapting. gRPC comes with a plugin to the protocol-buffers compiler that generates Stub interfaces out of .proto files, but bindings to other datamodel/IDL should be trivial to add and are welcome.

Key Interfaces

Stream Observer

Channel

The Channel layer is an abstraction over Transport handling that is suitable for interception/decoration and exposes more behavior to the application than the Stub layer. It is intended to be easy for application frameworks to use this layer to address cross-cutting concerns such as logging, monitoring, auth etc. Flow-control is also exposed at this layer to allow more sophisticated applications to interact with it directly.

Common

Client

Server

Transport

The Transport layer does the heavy lifting of putting and taking bytes off the wire. The interfaces to it are abstract just enough to allow plugging in of different implementations. Transports are modeled as Stream factories. The variation in interface between a server Stream and a client Stream exists to codify their differing semantics for cancellation and error reporting.

Note the transport layer API is considered internal to gRPC and has weaker API guarantees than the core API under package io.grpc.

gRPC comes with three Transport implementations:

The Netty-based transport is the main transport implementation based on Netty. It is for both the client and the server.
The OkHttp-based transport is a lightweight transport based on OkHttp. It is mainly for use on Android and is for client only.
The inProcess transport is for when a server is in the same process as the client. It is useful for testing.

Common

Client

Server

Examples

Tests showing how these layers are composed to execute calls using protobuf messages can be found here https://github.com/google/grpc-java/tree/master/interop-testing/src/main/java/io/grpc/testing/integration