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Posted to user@geode.apache.org by Paul Perez <pa...@pymma.com> on 2017/01/22 11:45:58 UTC
Access to Cache reference from Listener code deployed in a server
Hello All,
I hope you have a good weekend.
I have some questions regarding the code to write in a Listener such as an
AsyncEventListener to get a reference to a cache when the listener is
deployed in a server.
I tried to deployed a simple AsyncEventlistener on a server. So I Create a
event queue from gfsh
Create an Asynchronous Event Queue: create async-event-queue --id=myAEQ
--listener=pymma.testgeode01.MyFirstAsynchronousEventListener
--parallel=true
Create a region :create region --name=customerRegion --type=PARTITION
--group=groupA --async-event-queue-id=myAEQ
In the example given in the Java doc
http://geode.apache.org/releases/latest/javadoc/index.html the access to
the cache is provided by a CacheHelper:
final Region duplicateRegion =
CacheHelper.getCache().getRegion(originalRegionName + "_DUP");
Since I did not find any reference to what a Cache Helper is and from where
it comes from, at the first glance, in my current POC, I created my own
cache helper with the static method getCache.
public static Cache getCache () {
Properties properties = new Properties();
properties.setProperty("locators","localhost[10334]");
Cache cache = new CacheFactory(properties).create();
return cache;
}
It could be also a Clientcache.
In my example I duplicated the entries from customerRegion to another region
and it works well.
Nevertheless, since the Listener is deployed in a server itself, I though
that a reference to the cache could be given to the event by a more direct
way. The interface AsyncEventListener is outside the scope of this topic. I
tried to search if there was not a special class CacheHelper and I found one
similar named CacheRegionHelper. But without documentation in the Java API I
did not want to use it.
So if Geode community has few minutes to reply, I would like to ask these
questions:
In the example provided in the API, what is The CacheHelper? Is it a class
provided in Geode Libraries or do we need to develop by ourself.
In that case, Do we consider the CacheHelper as a regular client and use the
cache factory to create it?.
Or does it exist a direct way to access to a cache reference through the
Server the listener is deploy in?
Or may be there is another solution I completely missed?
Thank you for your help.
Best regards
Paul
RE: Access to Cache reference from Listener code deployed in a server
Posted by Paul Perez <pa...@pymma.com>.
Hello John,
It is more than helpful, it is clear complete and documented with lot of reference.
I knew that the Cache was a singleton but I did not make the link you presented in your response.
Thank you very much for your time and your attention. I really appreciate it
Best regards
Paul
From: John Blum [mailto:jblum@pivotal.io]
Sent: 23 January 2017 00:12
To: user@geode.apache.org; paul.perez@pymma.com
Subject: Re: Access to Cache reference from Listener code deployed in a server
Hi Paul-
Yes, the later...
> Or may be there is another solution I completely missed?
A Geode cache instance is a "Singleton" in the Geode JVM process (technically, by ClassLoader, however, you only ever create 1 instance per JVM). So...
You can use the <http://data-docs-samples.cfapps.io/docs-gemfire/latest/javadocs/japi/com/gemstone/gemfire/cache/CacheFactory.html#getAnyInstance()> CacheFactory.getAnyInstance() [1] to return the "single" instance of a Geode "peer" cache (server-side) and the <http://data-docs-samples.cfapps.io/docs-gemfire/latest/javadocs/japi/com/gemstone/gemfire/cache/client/ClientCacheFactory.html#getAnyInstance()> ClientCacheFactory.getAnyInstance() [2] to get the "single" instance of a Geode "client" cache.
Typically, you always create Geode cache applications that are 1 or the other... i.e. either a peer (embedded) cache application (i.e. as in an actual peer member in the cluster (distributed system)) or more typically, as a cache client application.
However, if you really don't know, then you can inspect your cache instance using logic similar to <https://github.com/spring-projects/spring-data-gemfire/blob/1.9.0.RC1/src/main/java/org/springframework/data/gemfire/util/CacheUtils.java#L54-L62> this [3] (for a client), and <https://github.com/spring-projects/spring-data-gemfire/blob/1.9.0.RC1/src/main/java/org/springframework/data/gemfire/util/CacheUtils.java#L77-L85> this [4] (for a peer), and/or even combine this logic in some way, as needed, since both <http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/Cache.html> Cache [5] (peer) and <http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/client/ClientCache.html> ClientCache [6] (client) extends <http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/GemFireCache.html> GemFireCache [7]. The reason why the logic in [3] & [4] is more elaborate then just the instanceof check is because there is only 1 implementation of all these interfaces, <https://github.com/apache/geode/blob/rel/v1.0.0-incubating/geode-core/src/main/java/org/apache/geode/internal/cache/GemFireCacheImpl.java#L241> GemFireCacheImpl [8].
In some Geode callback APIs, they give you a reference to the Region. From that, you can get the cache instance. For example..
<http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/asyncqueue/AsyncEventListener.html> AsyncEventListener [9], processEvents(:List< <http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/asyncqueue/AsyncEvent.html> AsyncEvent>) [10], which extends <http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/wan/GatewayQueueEvent.html> GatewayQueueEvent [11], which as the method <http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/wan/GatewayQueueEvent.html#getRegion--> getRegion():Region<K, V> [12], and the Region interface has the method, <http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/Region.html#getRegionService--> getRegionService() [13], which is exactly what the cache instance is ( <http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/GemFireCache.html> GemFireCache [7] implements the <http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/RegionService.html> RegionService interface [14], and therefore can be cast accordingly.
Anyway, there are typically multiple ways to get a reference to the cache instance.
In Spring, it is much more elegant since I can inject/auto-wire a reference to the cache instance in my AsyncEventListener implementation (defined as a bean in the Spring context). However, you must be very careful what Geode objects you inject into a Geode callback, like AsyncEventListener, since you could create a circular reference (Region A -> AEQ -> Listener -> Region (?), which is decidedly bad, particularly if ? == A.
Anyway, hope this helps.
Cheers,
John
[1] http://data-docs-samples.cfapps.io/docs-gemfire/latest/javadocs/japi/com/gemstone/gemfire/cache/CacheFactory.html#getAnyInstance()
[2] http://data-docs-samples.cfapps.io/docs-gemfire/latest/javadocs/japi/com/gemstone/gemfire/cache/client/ClientCacheFactory.html#getAnyInstance()
[3] https://github.com/spring-projects/spring-data-gemfire/blob/1.9.0.RC1/src/main/java/org/springframework/data/gemfire/util/CacheUtils.java#L54-L62
[4] https://github.com/spring-projects/spring-data-gemfire/blob/1.9.0.RC1/src/main/java/org/springframework/data/gemfire/util/CacheUtils.java#L77-L85
[5] http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/Cache.html
[6] http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/client/ClientCache.html
[7] http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/GemFireCache.html
[8] https://github.com/apache/geode/blob/rel/v1.0.0-incubating/geode-core/src/main/java/org/apache/geode/internal/cache/GemFireCacheImpl.java#L241
[9] http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/asyncqueue/AsyncEventListener.html
[10] http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/asyncqueue/AsyncEvent.html
[11] http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/wan/GatewayQueueEvent.html
[12] http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/wan/GatewayQueueEvent.html#getRegion--
[13] http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/Region.html#getRegionService--
[14] http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/RegionService.html
On Sun, Jan 22, 2017 at 3:45 AM, Paul Perez <paul.perez@pymma.com <ma...@pymma.com> > wrote:
Hello All,
I hope you have a good weekend.
I have some questions regarding the code to write in a Listener such as an AsyncEventListener to get a reference to a cache when the listener is deployed in a server.
I tried to deployed a simple AsyncEventlistener on a server. So I Create a event queue from gfsh
Create an Asynchronous Event Queue: create async-event-queue --id=myAEQ --listener=pymma.testgeode01.MyFirstAsynchronousEventListener --parallel=true
Create a region :create region --name=customerRegion --type=PARTITION --group=groupA --async-event-queue-id=myAEQ
In the example given in the Java doc http://geode.apache.org/releases/latest/javadoc/index.html the access to the cache is provided by a CacheHelper:
final Region duplicateRegion = CacheHelper.getCache().getRegion(originalRegionName + "_DUP");
Since I did not find any reference to what a Cache Helper is and from where it comes from, at the first glance, in my current POC, I created my own cache helper with the static method getCache.
public static Cache getCache () {
Properties properties = new Properties();
properties.setProperty("locators","localhost[10334]");
Cache cache = new CacheFactory(properties).create();
return cache;
}
It could be also a Clientcache.
In my example I duplicated the entries from customerRegion to another region and it works well.
Nevertheless, since the Listener is deployed in a server itself, I though that a reference to the cache could be given to the event by a more direct way. The interface AsyncEventListener is outside the scope of this topic. I tried to search if there was not a special class CacheHelper and I found one similar named CacheRegionHelper. But without documentation in the Java API I did not want to use it.
So if Geode community has few minutes to reply, I would like to ask these questions:
In the example provided in the API, what is The CacheHelper? Is it a class provided in Geode Libraries or do we need to develop by ourself.
In that case, Do we consider the CacheHelper as a regular client and use the cache factory to create it?.
Or does it exist a direct way to access to a cache reference through the Server the listener is deploy in?
Or may be there is another solution I completely missed?
Thank you for your help.
Best regards
Paul
--
-John
john.blum10101 (skype)
Re: Access to Cache reference from Listener code deployed in a server
Posted by John Blum <jb...@pivotal.io>.
Hi Paul-
Yes, the later...
> Or may be there is another solution I completely missed?
A Geode cache instance is a "Singleton" in the Geode JVM process
(technically, by ClassLoader, however, you only ever create 1 instance per
JVM). So...
You can use the CacheFactory.getAnyInstance()
<http://data-docs-samples.cfapps.io/docs-gemfire/latest/javadocs/japi/com/gemstone/gemfire/cache/CacheFactory.html#getAnyInstance()>
[1]
to return the "single" instance of a Geode "peer" cache (server-side) and
the ClientCacheFactory.getAnyInstance()
<http://data-docs-samples.cfapps.io/docs-gemfire/latest/javadocs/japi/com/gemstone/gemfire/cache/client/ClientCacheFactory.html#getAnyInstance()>
[2]
to get the "single" instance of a Geode "client" cache.
Typically, you always create Geode cache applications that are 1 or the
other... i.e. either a peer (embedded) cache application (i.e. as in an
actual peer member in the cluster (distributed system)) or more typically,
as a cache client application.
However, if you really don't know, then you can inspect your cache instance
using logic similar to this
<https://github.com/spring-projects/spring-data-gemfire/blob/1.9.0.RC1/src/main/java/org/springframework/data/gemfire/util/CacheUtils.java#L54-L62>
[3]
(for a client), and this
<https://github.com/spring-projects/spring-data-gemfire/blob/1.9.0.RC1/src/main/java/org/springframework/data/gemfire/util/CacheUtils.java#L77-L85>
[4]
(for a peer), and/or even combine this logic in some way, as needed, since
both *Cache
<http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/Cache.html>*
[5]
(peer) and *ClientCache
<http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/client/ClientCache.html>*
[6]
(client) extends *GemFireCache
<http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/GemFireCache.html>*
[7].
The reason why the logic in [3] & [4] is more elaborate then just the
instanceof check is because there is only 1 implementation of all these
interfaces, GemFireCacheImpl
<https://github.com/apache/geode/blob/rel/v1.0.0-incubating/geode-core/src/main/java/org/apache/geode/internal/cache/GemFireCacheImpl.java#L241>
[8].
In some Geode callback APIs, they give you a reference to the *Region*.
From that, you can get the cache instance. For example..
AsyncEventListener
<http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/asyncqueue/AsyncEventListener.html>
[9],
processEvents(:List<AsyncEvent
<http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/asyncqueue/AsyncEvent.html>
>) [10], which extends GatewayQueueEvent
<http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/wan/GatewayQueueEvent.html>
[11], which as the method getRegion():Region<K, V>
<http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/wan/GatewayQueueEvent.html#getRegion-->
[12], and the *Region* interface has the method, getRegionService()
<http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/Region.html#getRegionService-->
[13],
which is exactly what the cache instance is (GemFireCache
<http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/GemFireCache.html>
[7]
implements the RegionService
<http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/RegionService.html>
interface [14], and therefore can be cast accordingly.
Anyway, there are typically multiple ways to get a reference to the cache
instance.
In *Spring*, it is much more elegant since I can inject/auto-wire a
reference to the cache instance in my AsyncEventListener implementation
(defined as a bean in the *Spring* context). However, you must be very
careful what Geode objects you inject into a Geode callback, like
AsyncEventListener, since you could create a circular reference (*Region* A
-> AEQ -> Listener -> *Region* (?), which is decidedly bad, particularly if
? == A.
Anyway, hope this helps.
Cheers,
John
[1]
http://data-docs-samples.cfapps.io/docs-gemfire/latest/javadocs/japi/com/gemstone/gemfire/cache/CacheFactory.html#getAnyInstance()
[2]
http://data-docs-samples.cfapps.io/docs-gemfire/latest/javadocs/japi/com/gemstone/gemfire/cache/client/ClientCacheFactory.html#getAnyInstance()
[3]
https://github.com/spring-projects/spring-data-gemfire/blob/1.9.0.RC1/src/main/java/org/springframework/data/gemfire/util/CacheUtils.java#L54-L62
[4]
https://github.com/spring-projects/spring-data-gemfire/blob/1.9.0.RC1/src/main/java/org/springframework/data/gemfire/util/CacheUtils.java#L77-L85
[5]
http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/Cache.html
[6]
http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/client/ClientCache.html
[7]
http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/GemFireCache.html
[8]
https://github.com/apache/geode/blob/rel/v1.0.0-incubating/geode-core/src/main/java/org/apache/geode/internal/cache/GemFireCacheImpl.java#L241
[9]
http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/asyncqueue/AsyncEventListener.html
[10]
http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/asyncqueue/AsyncEvent.html
[11]
http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/wan/GatewayQueueEvent.html
[12]
http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/wan/GatewayQueueEvent.html#getRegion--
[13]
http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/Region.html#getRegionService--
[14]
http://geode.apache.org/releases/latest/javadoc/org/apache/geode/cache/RegionService.html
On Sun, Jan 22, 2017 at 3:45 AM, Paul Perez <pa...@pymma.com> wrote:
> Hello All,
>
>
>
> I hope you have a good weekend.
>
> I have some questions regarding the code to write in a Listener such as an
> AsyncEventListener to get a reference to a cache when the listener is
> deployed in a server.
>
>
>
> I tried to deployed a simple AsyncEventlistener on a server. So I Create a
> event queue from gfsh
>
>
>
> *Create an Asynchronous Event Queue: *create async-event-queue --id=myAEQ
> --listener=pymma.testgeode01.MyFirstAsynchronousEventListener
> --parallel=true
>
> *Create a region* :create region --name=customerRegion
> --type=PARTITION --group=groupA --async-event-queue-id=myAEQ
>
>
>
> In the example given in the Java doc http://geode.apache.org/
> releases/latest/javadoc/index.html the access to the cache is provided
> by a CacheHelper:
>
> final Region duplicateRegion = CacheHelper.getCache().getRegion(originalRegionName
> + "_DUP");
>
>
>
> Since I did not find any reference to what a Cache Helper is and from
> where it comes from, at the first glance, in my current POC, I created
> my own cache helper with the static method getCache.
>
> public static Cache getCache () {
>
> Properties properties = new Properties();
>
> properties.setProperty("locators","localhost[10334]");
>
> Cache cache = new CacheFactory(properties).create();
>
> return cache;
>
> }
>
> It could be also a Clientcache.
>
> In my example I duplicated the entries from customerRegion to another
> region and it works well.
>
>
>
> Nevertheless, since the Listener is deployed in a server itself, I though
> that a reference to the cache could be given to the event by a more direct
> way. The interface AsyncEventListener is outside the scope of this topic. I
> tried to search if there was not a special class CacheHelper and I found
> one similar named CacheRegionHelper. But without documentation in the Java
> API I did not want to use it.
>
>
>
> So if Geode community has few minutes to reply, I would like to ask these
> questions:
>
>
>
> In the example provided in the API, what is The CacheHelper? Is it a class
> provided in Geode Libraries or do we need to develop by ourself.
>
> In that case, Do we consider the CacheHelper as a regular client and use
> the cache factory to create it?.
>
> Or does it exist a direct way to access to a cache reference through the
> Server the listener is deploy in?
>
>
>
> Or may be there is another solution I completely missed?
>
>
>
> Thank you for your help.
>
>
>
> Best regards
>
>
>
> Paul
>
>
>
--
-John
john.blum10101 (skype)