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Posted to notifications@fluo.apache.org by keith-turner <gi...@git.apache.org> on 2017/05/04 23:24:23 UTC
[GitHub] incubator-fluo issue #829: Observers implemented as lambdas showing up multi...
GitHub user keith-turner opened an issue:
https://github.com/apache/incubator-fluo/issues/829
Observers implemented as lambdas showing up multiple times in metrics
With the changes for #816 observers implemented as lambdas end with different names on different nodes in metrics.
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[GitHub] incubator-fluo issue #829: Observers implemented as lambdas showing up multi...
Posted by keith-turner <gi...@git.apache.org>.
Github user keith-turner commented on the issue:
https://github.com/apache/incubator-fluo/issues/829
I did some research to see if these numbers generated for lambdas are stable w.r.t to a compiled class files. From what I read online, it seems they are not. The first number (before the slash) seems to be runtime encounter order and I have not been able to find out what the second number represents.
I ran simple test to prove to myself that the first number is encounter order.
```java
public class Test {
public static Runnable getL1(){
return () -> System.out.println("foo");
}
public static Runnable getL2(){
return () -> System.out.println("bar");
}
public static void main(String[] args) {
System.out.println(getL1().getClass().getSimpleName());
System.out.println(getL2().getClass().getSimpleName());
System.out.println(getL1().getClass().getSimpleName());
System.out.println(getL2().getClass().getSimpleName());
}
}
```
The program above prints
```
Test$$Lambda$1/834600351
Test$$Lambda$2/1418481495
Test$$Lambda$1/834600351
Test$$Lambda$2/1418481495
```
In the program below I change the order of the first two prints so that the class name returned by `getL2()` is printed first.
```java
public class Test {
public static Runnable getL1(){
return () -> System.out.println("foo");
}
public static Runnable getL2(){
return () -> System.out.println("bar");
}
public static void main(String[] args) {
System.out.println(getL2().getClass().getSimpleName());
System.out.println(getL1().getClass().getSimpleName());
System.out.println(getL1().getClass().getSimpleName());
System.out.println(getL2().getClass().getSimpleName());
}
}
```
The program above prints
```
Test$$Lambda$1/834600351
Test$$Lambda$2/1418481495
Test$$Lambda$2/1418481495
Test$$Lambda$1/834600351
```
This shows that a lambda at the same position in source code can end up with different classnames on different processes depending on the encounter order.
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[GitHub] incubator-fluo issue #829: Observers implemented as lambdas showing up multi...
Posted by keith-turner <gi...@git.apache.org>.
Github user keith-turner commented on the issue:
https://github.com/apache/incubator-fluo/issues/829
One option for solving this is to use the column name in metrics instead of the classname. I discussed this offline with @ctubbsii and he suggested letting the user specify a name. This made me thing that the new ObserverRegistry should have a Fluent interface (it currently has two methods that take a bunch of arguments). @ctubbsii suggested the following method names for the fluent interface.
```java
ObserverRegistry or;
or.observer(...).named(...).forColumn(...).withWeakNotifications().register();
or.observer(...).forColumn(...).withWeakNotifications().register();
```
We discussed that the `named(...)` method could be optional and it would fall back to the column name if that was not used. The advantage of allowing the user to optionally specify a name is that the column name may not always be something that is human readable.
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[GitHub] incubator-fluo issue #829: Observers implemented as lambdas showing up multi...
Posted by asfgit <gi...@git.apache.org>.
Github user asfgit closed the issue at:
https://github.com/apache/incubator-fluo/issues/829
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[GitHub] incubator-fluo issue #829: Observers implemented as lambdas showing up multi...
Posted by keith-turner <gi...@git.apache.org>.
Github user keith-turner commented on the issue:
https://github.com/apache/incubator-fluo/issues/829
Things are much better after this change
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[GitHub] incubator-fluo issue #829: Observers implemented as lambdas showing up multi...
Posted by keith-turner <gi...@git.apache.org>.
Github user keith-turner commented on the issue:
https://github.com/apache/incubator-fluo/issues/829
I have been playing around with the idea of making the observer registry fluent. I realized its nice to have the observer come last for the case when the observer is a multi-line lambda. To make the observer come last, I am thinking of using the following method names.
```java
ObserverRegistry obsRegistry;
obsRegistry.forColumn(col1, NotificationType.STRONG).useObserver((tx,row,col) -> {
//multi-line observer
});
//register an observer with an alias used for metrics and possibly logging
ObserverRegistry obsRegistry;
obsRegistry.forColumn(col2, NotificationType.WEAK).aliasedAs("foo42").useObserver((tx,row,col) -> {
//multi-line observer
});
```
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