Build failure on Ubuntu

[hkurokawa]

Description

I tried to build the project on Ubuntu (14.04.3 LTS, x86-64) and encountered the below compile error.

$ ./gradlew clean assembleRelease
Incremental java compilation is an incubating feature.
:agera:clean
:testapp:clean UP-TO-DATE
:extensions:content:clean UP-TO-DATE
:extensions:database:clean UP-TO-DATE
:extensions:net:clean UP-TO-DATE
:extensions:rvadapter:clean UP-TO-DATE
:agera:preBuild UP-TO-DATE
:agera:preReleaseBuild UP-TO-DATE
:agera:compileReleaseNdk UP-TO-DATE
:agera:compileLint
:agera:copyReleaseLint UP-TO-DATE
:agera:checkReleaseManifest
:agera:prepareReleaseDependencies
:agera:compileReleaseAidl
:agera:compileReleaseRenderscript
:agera:generateReleaseBuildConfig
:agera:mergeReleaseShaders
:agera:compileReleaseShaders
:agera:generateReleaseAssets
:agera:mergeReleaseAssets
:agera:generateReleaseResValues UP-TO-DATE
:agera:generateReleaseResources
:agera:packageReleaseResources
:agera:processReleaseManifest
:agera:processReleaseResources
:agera:generateReleaseSources
:agera:incrementalReleaseJavaCompilationSafeguard
:agera:compileReleaseJavaWithJavac
:agera:compileReleaseJavaWithJavac - is not incremental (e.g. outputs have changed, no previous execution, etc.).
/home/hiroshi/git/github.com/google/agera/agera/src/main/java/com/google/android/agera/Common.java:106: error: cannot find symbol
  static final class WorkerHandler extends Handler {
                                           ^
  symbol:   class Handler
  location: class Common
...

Environment

OS: Ubuntu 14.04.3 LTS, x86-64
Java: Oracle Java 64-bit 1.8.0_66-b17
Android Studio: 2.1

Solution

A bit strangely, when I changed the order of import statements in com.google.android.agera.Common as below, the compile error was gone:

diff --git a/agera/src/main/java/com/google/android/agera/Common.java b/agera/src/main/java/com/google/android/agera/Common.java
index 8bad1a8..47627bd 100644
--- a/agera/src/main/java/com/google/android/agera/Common.java
+++ b/agera/src/main/java/com/google/android/agera/Common.java
@@ -18,10 +18,10 @@ package com.google.android.agera;
 import static com.google.android.agera.Preconditions.checkNotNull;
 import static com.google.android.agera.Result.failure;

+import android.os.Handler;
 import com.google.android.agera.BaseObservable.Worker;
 import com.google.android.agera.Observables.LowPassFilterObservable;

-import android.os.Handler;
 import android.os.Message;
 import android.support.annotation.NonNull;

I'm afraid it might be related to com.google.android.agera.Common and com.google.android.agera.BaseObservable has a cyclic package dependency. Though I believe the Java specification allows that, it might cause a bug or an unexpected behaviour of Java compiler.

For your information, I tried Oracle Java 7 and OpendJDK 7 but the result was same.

Thanks.

[hkurokawa]

Just FYI, I could not reproduce the issue on Mac OS X (Oracle Java 1.8.0_65-b17). And also, I found a JEP which might be related to this issue, http://openjdk.java.net/jeps/216, which seems included in Java 9.

[Deleted user]

Looks like Travis CI has been running 1.7.0_76-b13, on Linux with no problems. I'm running 1.8.0_92 myself, but that's on OSX. Have you tried the latest version of 1.8 (I guess it's u92?), see if the problem is there too?
#30 from the other week reports the same issue on 1.7.0_79, 1.8.0_66 and 1.8.0_91

[hkurokawa]

I tried 1.8.0_92-b14 but had no luck. So was 1.7.0_80-b15. When I compiled the project on Mac, the error didn't occur so it seems the problem is specific to Linux Java. I tried 9-ea+114 and the javac command succeeded but it seems Gradle doesn't support Java 9 yet.

Also, I found if I pulled up com.google.android.agera.Common.WorkerHandler to, say, com.google.android.agera.WorkerHandler, the error was gone. So it seems to be related to nested class.

Besides, I found if I deleted the static import statements in com.google.android.agera.Common, the error r was gone as well:

diff --git a/agera/src/main/java/com/google/android/agera/BaseObservable.java b/agera/src/main/java/com/google/android/agera/BaseObservable.java
index 4938fd1..396cec0 100644
--- a/agera/src/main/java/com/google/android/agera/BaseObservable.java
+++ b/agera/src/main/java/com/google/android/agera/BaseObservable.java
@@ -15,9 +15,6 @@
  */
 package com.google.android.agera;

-import static com.google.android.agera.Common.WorkerHandler.MSG_LAST_REMOVED;
-import static com.google.android.agera.Common.WorkerHandler.MSG_UPDATE;
-import static com.google.android.agera.Common.workerHandler;
 import static com.google.android.agera.Preconditions.checkState;

 import com.google.android.agera.Common.WorkerHandler;
@@ -97,16 +94,16 @@ public abstract class BaseObservable implements Observable {

     Worker(@NonNull final BaseObservable baseObservable) {
       this.baseObservable = baseObservable;
-      this.handler = workerHandler();
+      this.handler = Common.workerHandler();
       this.updatablesAndHandlers = NO_UPDATABLES_OR_HANDLERS;
       this.size = 0;
     }

     synchronized void addUpdatable(@NonNull final Updatable updatable) {
-      add(updatable, workerHandler());
+      add(updatable, Common.workerHandler());
       if (size == 1) {
-        if (handler.hasMessages(MSG_LAST_REMOVED, this)) {
-          handler.removeMessages(MSG_LAST_REMOVED, this);
+        if (handler.hasMessages(Common.WorkerHandler.MSG_LAST_REMOVED, this)) {
+          handler.removeMessages(Common.WorkerHandler.MSG_LAST_REMOVED, this);
         } else {
           handler.obtainMessage(WorkerHandler.MSG_FIRST_ADDED, this).sendToTarget();
         }
@@ -116,13 +113,13 @@ public abstract class BaseObservable implements Observable {
     synchronized void removeUpdatable(@NonNull final Updatable updatable) {
       remove(updatable);
       if (size == 0) {
-        handler.obtainMessage(MSG_LAST_REMOVED, this).sendToTarget();
+        handler.obtainMessage(Common.WorkerHandler.MSG_LAST_REMOVED, this).sendToTarget();
       }
     }

     void dispatchUpdate() {
-      if (!handler.hasMessages(MSG_UPDATE, this)) {
-        handler.obtainMessage(MSG_UPDATE, this).sendToTarget();
+      if (!handler.hasMessages(Common.WorkerHandler.MSG_UPDATE, this)) {
+        handler.obtainMessage(Common.WorkerHandler.MSG_UPDATE, this).sendToTarget();
       }
     }

Anyway, I know this is not your code fault. But I think there are a few options for us:

1. Reorder the import statements
2. Pull up the nested static class
3. Delete the static import statements
4. Leave it (some Linux users might not be able to compile the code) until Java 9 comes to Gradle

Any idea?

[Deleted user]

I leaning towards 2 (and you're right, 4 is unreasonable). Have a fix coming up, let me know if it works out for you.

[Deleted user]

Still a seriously strange problem, some odd corner case of the java compiler I suppose :)

[hkurokawa]

I agree. And here is one thing I forgot to mention, a similar bug is reported to OpenJDK, which should be fixed with Java 9: https://bugs.openjdk.java.net/browse/JDK-7101822

And thank you for your fix. I tried with the latest source code and I could compile the code successfully. 👍