This will break if
7f1ac34d41,
2f6e2c87ab,
a3a5420922
are reverted:
```
io.grpc.ContextTest > initContextWithCustomClassLoaderWithCustomLogger FAILED
java.lang.ExceptionInInitializerError
at io.grpc.ContextTest$LoadMeWithStaticTestingClassLoader.run(ContextTest.java:789)
at io.grpc.ContextTest.initContextWithCustomClassLoaderWithCustomLogger(ContextTest.java:760)
Caused by:
java.lang.RuntimeException: Storage override had failed to initialize
at io.grpc.Context.storage(Context.java:134)
at io.grpc.Context.current(Context.java:163)
at io.grpc.ContextTest$LoadMeWithStaticTestingClassLoader$1.publish(ContextTest.java:773)
at java.util.logging.Logger.log(Logger.java:738)
at java.util.logging.Logger.doLog(Logger.java:765)
at java.util.logging.Logger.log(Logger.java:875)
at io.grpc.Context.<clinit>(Context.java:122)
... 2 more
```
Using static initialization is possible, but quite complex to handle
logging and circular loading. Lazy loading prevents an entire class of
circular dependencies.
Turns out avoiding log() alone in the static initialization is not
enough. isLoggable() can also be overridden and call back to Context.
We take a another approach, save the exception and log it outside of
the initialization block.
Futures almost universally should be handled in some way when being
returned, either to receive the value or to cancel scheduled tasks to
prevent leaks.
Netty is a bit of a special case though, since it constantly returns
futures that you ignore (even adding a listener returns the "this"
future). So we want to suppress the warning for code using Netty instead
of trying to fix it. When we enable ErrorProne in the build, we should
start passing -Xep:FutureReturnValueIgnored:OFF in the compilerArgs.
Currently Context propagate in-thread by its own ThreadLocal, and
cross-thread propagation must be done with the mechanisms provied by
gRPC Context. However, there are frameworks (e.g. what we are using
inside Google) which have already established context-propagation
mechanisms. If gRPC Context may ride on top of them, it would be
propagated automatically without additional effort from the application.
The Storage API allows gRPC Context to be attached to anything. The
default implementation still uses its own ThreadLocal. If an override
implementation is present, gRPC Context will use it.
The Context API is not particularly gRPC-specific, and will be used by
Census as its context propagation mechanism.
Removed all dependencies to make it easy for other libraries to depend
on.
ZHANG Dapeng
Eric Anderson
Kun Zhang
Carl Mastrangelo
zpencer
Kun Zhang