Hi Tsz-Wo,

True, there is only one version of opencensus in Ratis. Since we do shading of 
io.grpc we end up with new shaded class of ContextUtils (same fully qualified 
class name, but the reference of io.grpc inside the class is 
modified/relocated), we also have non shaded ContextUtils. Both are referred 
through Ratis dependency.

The below is dependency tree of Ratis:

[INFO] +- org.apache.ratis:ratis-proto-shaded:jar:0.1.1-alpha-SNAPSHOT:compile  
          =========> Modified opencensus packed with proto-shaded
[INFO] |  +- com.google.auto.value:auto-value-annotations:jar:1.6:compile
[INFO] |  +- com.google.guava:guava:jar:24.1-jre:compile
[INFO] |  |  +- com.google.code.findbugs:jsr305:jar:1.3.9:compile
[INFO] |  |  +- org.checkerframework:checker-compat-qual:jar:2.0.0:compile
[INFO] |  |  +- com.google.errorprone:error_prone_annotations:jar:2.1.3:compile
[INFO] |  |  +- com.google.j2objc:j2objc-annotations:jar:1.1:compile
[INFO] |  |  \- org.codehaus.mojo:animal-sniffer-annotations:jar:1.14:compile
[INFO] |  \- com.squareup:javapoet:jar:1.10.0:compile
[INFO] +- org.apache.ratis:ratis-common:jar:0.1.1-alpha-SNAPSHOT:compile
[INFO] |  +- org.slf4j:slf4j-api:jar:1.7.10:compile
[INFO] |  +- org.slf4j:slf4j-log4j12:jar:1.7.10:compile
[INFO] |  |  \- log4j:log4j:jar:1.2.17:compile
[INFO] |  \- io.dropwizard.metrics:metrics-core:jar:3.2.5:compile
[INFO] +- org.apache.ratis:ratis-client:jar:0.1.1-alpha-SNAPSHOT:compile
[INFO] +- org.apache.ratis:ratis-server:jar:0.1.1-alpha-SNAPSHOT:compile
[INFO] +- org.apache.ratis:ratis-netty:jar:0.1.1-alpha-SNAPSHOT:compile
[INFO] |  \- org.jctools:jctools-core:jar:2.1.2:compile
[INFO] \- org.apache.ratis:ratis-grpc:jar:0.1.1-alpha-SNAPSHOT:compile
[INFO]    +- io.opencensus:opencensus-api:jar:0.12.2:compile                    
        =========> Original jar
[INFO]    |  \- io.grpc:grpc-context:jar:1.9.0:compile
[INFO]    \- io.opencensus:opencensus-contrib-grpc-metrics:jar:0.12.2:compile


nvadivelu@HW12726 ~/w/t/p/o/t/dependency> javap -classpath 
".:./opencensus-api-0.12.2.jar" io.opencensus.trace.unsafe.ContextUtils         
                                                             
Compiled from "ContextUtils.java"
public final class io.opencensus.trace.unsafe.ContextUtils {
  public static final io.grpc.Context$Key<io.opencensus.trace.Span> 
CONTEXT_SPAN_KEY;
  static {};
}

nvadivelu@HW12726 ~/w/t/p/o/t/dependency> javap -classpath 
".:./ratis-proto-shaded-0.1.1-alpha-SNAPSHOT.jar" 
io.opencensus.trace.unsafe.ContextUtils
Compiled from "ContextUtils.java"
public final class io.opencensus.trace.unsafe.ContextUtils {
  public static final 
org.apache.ratis.shaded.io.grpc.Context$Key<io.opencensus.trace.Span> 
CONTEXT_SPAN_KEY;
  static {};
}


-Nanda

On 5/8/18, 4:16 AM, "Tsz Wo Sze" <szets...@gmail.com> wrote:

    > The problem is because of two different definition of 
io.opencensus.trace.unsafe.ContextUtils class present in the classpath. The 
reason for having two different definition of ContextUtils in classpath is due 
to the fact that we are shading/relocating io.grpc and not io.opencensus.
    
    Nanda, in Ratis, there is only one version (0.12.2) of opencensus.  It
    seems that another version of opencensus is pulled outside Ratis.
    
    Tsz-Wo
    
    
    On Mon, May 7, 2018 at 11:58 AM, Nandakumar Vadivelu
    <nvadiv...@hortonworks.com> wrote:
    > I'm not sure why the file is missing, I can see the attachment in my 
"sent items".
    >
    > Patch content for reference
    >
    > diff --git a/ratis-grpc/pom.xml b/ratis-grpc/pom.xml
    > index a3c3cc1..ebb73cc 100644
    > --- a/ratis-grpc/pom.xml
    > +++ b/ratis-grpc/pom.xml
    > @@ -85,15 +85,5 @@
    >        <artifactId>jctools-core</artifactId>
    >      </dependency>
    >
    > -    <dependency>
    > -      <groupId>io.opencensus</groupId>
    > -      <artifactId>opencensus-api</artifactId>
    > -      <version>${io.opencensus.version}</version>
    > -    </dependency>
    > -    <dependency>
    > -      <groupId>io.opencensus</groupId>
    > -      <artifactId>opencensus-contrib-grpc-metrics</artifactId>
    > -      <version>${io.opencensus.version}</version>
    > -    </dependency>
    >    </dependencies>
    >  </project>
    >
    > I will also create a jira under RATIS
    >
    > -Nanda
    >
    > On 5/8/18, 12:23 AM, "Ted Yu" <yuzhih...@gmail.com> wrote:
    >
    >     I don't see patch attached.
    >
    >     Please create RATIS JIRA and attach there.
    >
    >     Thanks
    >
    >     On Mon, May 7, 2018 at 10:24 AM, Nandakumar Vadivelu <
    >     nvadiv...@hortonworks.com> wrote:
    >
    >     > Hi All,
    >     >
    >     > Below is the exception which we get with Ratis 0.2.0
    >     >
    >     > java.lang.NoSuchFieldError: CONTEXT_SPAN_KEY
    >     >   at org.apache.ratis.shaded.io.grpc.internal.CensusTracingModule$
    >     > ServerTracer.filterContext(CensusTracingModule.java:340)
    >     >   at org.apache.ratis.shaded.io.grpc.internal.StatsTraceContext.
    >     > serverFilterContext(StatsTraceContext.java:121)
    >     >   at org.apache.ratis.shaded.io.grpc.internal.ServerImpl$
    >     > ServerTransportListenerImpl.createContext(ServerImpl.java:482)
    >     >   at org.apache.ratis.shaded.io.grpc.internal.ServerImpl$
    >     > ServerTransportListenerImpl.streamCreated(ServerImpl.java:416)
    >     > <stack trace truncated>
    >     >
    >     >
    >     > The problem is because of two different definition of
    >     > io.opencensus.trace.unsafe.ContextUtils class present in the 
classpath.
    >     > The reason for having two different definition of ContextUtils in 
classpath
    >     > is due to the fact that we are shading/relocating io.grpc and not
    >     > io.opencensus.
    >     >
    >     >
    >     > With shading we are generating the below definition which ends up in
    >     > ratis-proto-shaded jar
    >     >
    >     > package io.opencensus.trace.unsafe;
    >     >
    >     > import org.apache.ratis.shaded.io.grpc.Context;
    >     > import io.opencensus.trace.Span;
    >     >
    >     > /**
    >     >  * Util methods/functionality to interact with the {@link
    >     > org.apache.ratis.shaded.io.grpc.Context}.
    >     >  *
    >     >  * <p>Users must interact with the current Context via the public 
APIs in
    >     > {@link
    >     >  * io.opencensus.trace.Tracer} and avoid usages of the {@link
    >     > #CONTEXT_SPAN_KEY} directly.
    >     >  *
    >     >  * @since 0.5
    >     >  */
    >     > public final class ContextUtils {
    >     >   // No instance of this class.
    >     >   private ContextUtils() {}
    >     >
    >     >   /**
    >     >    * The {@link org.apache.ratis.shaded.io.grpc.Context.Key} used to
    >     > interact with {@link org.apache.ratis.shaded.io.grpc.Context}.
    >     >    *
    >     >    * @since 0.5
    >     >    */
    >     >   public static final Context.Key<Span> CONTEXT_SPAN_KEY =
    >     > Context.key("opencensus-trace-span-key");
    >     > }
    >     >
    >     >
    >     > Since we have added io.opencensus as direct dependency in 
ratis-grpc we
    >     > get the below definition in io.opencensus:opencensus-api:jar
    >     >
    >     > package io.opencensus.trace.unsafe;
    >     >
    >     > import io.grpc.Context;
    >     > import io.opencensus.trace.Span;
    >     >
    >     > /**
    >     >  * Util methods/functionality to interact with the {@link 
io.grpc.Context}.
    >     >  *
    >     >  * <p>Users must interact with the current Context via the public 
APIs in
    >     > {@link
    >     >  * io.opencensus.trace.Tracer} and avoid usages of the {@link
    >     > #CONTEXT_SPAN_KEY} directly.
    >     >  *
    >     >  * @since 0.5
    >     >  */
    >     > public final class ContextUtils {
    >     >   // No instance of this class.
    >     >   private ContextUtils() {}
    >     >
    >     >   /**
    >     >    * The {@link io.grpc.Context.Key} used to interact with {@link
    >     > io.grpc.Context}.
    >     >    *
    >     >    * @since 0.5
    >     >    */
    >     >   public static final Context.Key<Span> CONTEXT_SPAN_KEY =
    >     > Context.key("opencensus-trace-span-key");
    >     > }
    >     >
    >     > Both of the jars end up in classpath and ContextUtils is getting 
loaded
    >     > from io.opencensus:opencensus-api:jar which is causing the problem.
    >     >
    >     > The simple fix would be to remove the dependency of io.opencensus 
from
    >     > ratis-grpc/pom.xml (patch for the same is attached in this mail). 
This is
    >     > not a permanent fix, as any application might bring in
    >     > io.opencensus:opencensus-api:jar of its own.
    >     >
    >     > We have to find a way to shade io.opencensus:opencensus-api:jar.
    >     >
    >     > Note: from the comment in ratis-proto-shaded/pom.xml: Cannot 
relocate
    >     > io.opencensus due to AutoValue code generation
    >     >
    >     >
    >     > -Nanda
    >     >
    >     > On 5/7/18, 3:28 PM, "Lokesh Jain" <lj...@hortonworks.com> wrote:
    >     >
    >     >     We found an issue while updating ozone to Ratis snapshot build
    >     > 0.1.1-alpha-4309324-SNAPSHOT (https://issues.apache.org/
    >     > jira/browse/HDDS-19). I feel we should hold the release till this is
    >     > fixed. Please let us know of your opinion as well.
    >     >
    >     >     Thanks
    >     >     Lokesh
    >     >
    >     >
    >     >
    >     >
    >
    >
    
    

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