+1 - Ok, I think I've come around to option (a). We can go head and add a new execute(timeout, TimeUnit) method to the java API that is blocking. We can leave the existing execute() method alone, except for documenting what it is doing.
I would like implement execute(timeout, TimeUnit) on the server side as well. Since this Execution class is shared between both client and server APIs, it would be unfortunate to have a method on Execution that simply doesn't work on the server side. -Dan On Thu, Sep 5, 2019 at 9:25 AM Alberto Gomez <alberto.go...@est.tech> wrote: > Hi all, > > First of all, thanks a lot Dan and Jacob for your feedback. > > As we are getting close to the deadline I am adding here some conclusions > and a refined proposal in order to get some more feedback and if possible > some voting on the two alternatives proposed (or any other in between if > you feel any of them is lacking something). > > I also add some draft code to try to clarify a bit the more complex of the > alternatives. > > > Proposal summary (needs a decision on which option to implement): > > ------------------------------------------------------------------------------------------- > > In order to make the API more coherent two alternatives are proposed: > > a) Remove the timeout from the ResultCollector::getResult() / document > that the timeout has no effect, taking into account that > Execution::execute() is always blocking. > Additionally we could add the timeout parameter to the > Execution::execute() method of the Java API in order to align it with the > native client APIs. This timeout would not be the read timeout on the > socket but a timeout for the execution of the operation. > > b) Change the implementation of the Execution::execute() method without > timeout to be non-blocking on both the Java and native APIs. This change > has backward compatibility implications, would probably bring some > performance decrease and could pose some difficulties in the implementation > on the C++ side (in the handling of timed out operations that hold > resources). > > > The first option (a) is less risky and does not have impacts regarding > backward compatibility and performance. > > The second one (b) is the preferred alternative in terms of the expected > behavior from the users of the API. This option is more complex to > implement and as mentioned above has performance and backward compatibility > issues not easy to be solved. > > Following is a draft version of the implementation of b) on the Java > client: > > https://github.com/Nordix/geode/commit/507a795e34c6083c129bda7e976b9223d1a893da > > Following is a draft version of the implementation of b) on the C++ native > client: > > https://github.com/apache/geode-native/commit/a03a56f229bb8d75ee71044cf6196df07f43150d > > Note that the above implementation of b) in the C++ client implies that > the Execution object returned by the FunctionService cannot be destroyed > until the thread executing the function asynchronously has finished. If the > function times out, the Execution object must be kept until the thread > finishes. > > > Other considerations > ------------------------- > > * Currently, in the function execution Java client there is not a > possibility to set a timeout for the execution of functions. The closest to > this is the read timeout that may be set globally for function executions > but this is not really a timeout for operations. > > * Even if the API for function execution is the same on clients and > servers, the implementation is different between them. On the clients, the > execute() methods are blocking while on the servers it is non-blocking and > the invoker of the function blocks on the getResult() method of the > ResultCollector returned by the execute() method. > Even if having both blocking and non-blocking implementation of execute() > in both clients and servers sounds desirable from the point of view of > orthogonality, this could bring complications in terms of backward > compatibility. Besides, a need for a blocking version of function execution > has not been found. > > -Alberto G. > > On 29/8/19 16:48, Alberto Gomez wrote: > > Sorry, some corrections on my comments after revisiting the native > client code. > > When I said that the timeout used in the execution() method (by means of > a system property) was to set a read timeout on the socket, I was only > talking about the Java client. In the case of the native clients, the > timeout set in the execute() method is not translated into a socket > timeout but it is the time to wait for the operation to complete, i.e., > to get all the results back. > > Things being so, I would change my proposal to: > > - Change the implementation of execute() on both Java and native clients > to be non-blocking (having the blocking/non-blocking behavior > configurable in the release this is introduced and leaving only the > non-blocking behavior in the next release). > > - Either remove the execute() with timeout methods in the native clients > (with a deprecation release) or implement the execute(timeout) method in > the Java client to be blocking (to work as the native client does > today). In case the method times out, the connection will not be closed. > If the operation times out due to the socket timeout (system property), > then the connection will be closed as it is now done in the Java client. > > - Do not implement the blocking execute(timeout) method on the server > and leave the current execute() implementation on the server as it is > (non-blocking) > > Does this make sense? > > -Alberto > > On 29/8/19 12:56, Alberto Gómez wrote: > > > Hi Dan, > > Discussing these matters by e-mail is getting tricky. > > Let's see if I understand you correctly and also if I am being clear > enough. > > Please, see my comments inline. > > On 29/8/19 0:49, Dan Smith wrote: > > > Sorry for the slow response, I've been trying to decide what I think > is the > right approach here. > > For (1) - conceptually, I don't have a problem with having both blocking > and non blocking methods on Execution. So adding blocking versions of > execute() with a timeout seems ok. But I do think if we add them we > need to > implement them on both the client and the server to behave the same way. > That shouldn't be too hard on the server since execute(timeout) can just > call getResult(timeout) internally. > > > > We have to take into account that, currently, the timeout in execute() > is not the same thing as the timeout in getResult(). > > On the one hand, the timeout set in execute() (via System property in > the Java client, and with a parameter in the native client) sets a > readtimeout on the socket which just means that if nothing is read > from the socket after sending the request to the server for the given > timeout, the corresponding exception will be thrown. It looks to me > more like a protection against possible communication failures rather > than a mechanism to decide if results took too long to be provided. So > I would not link the presence of the timeout parameter in the method > to the nature of the method (blocking or non-blocking). I think we > could have this read timeout set and at the same time keep that method > as non-blocking. > > On the other hand, the timeout set in getResult() is a timeout to wait > for all the results to be received from the moment the method is invoked. > > Therefore, I would not implement the blocking version of execute() on > the server by calling getResult() at the end. > > Apart from that, I doubt if it would make sense to set this > readTimeout in the execute() methods from servers given that the > communication is very different to the one done with clients. I also > doubt that anyone would be interested in the blocking version of > execute() on the server. > > My proposal was to add the readtimeout to the execute() methods in the > Java client in order to align the Java client and the native client. > This change would be independent to the decision we make regarding the > change of execute() to non-blocking. To achieve this alignment, > alternatively, we could remove the timeout parameter in execute() from > the native clients and have it as a global property for the client to > be set by whatever mechanism available as it is done in the Java > client today. > > Were you proposing that the execute() methods with timeout were > blocking and the ones without timeout non-blocking? Not sure if this > is something you meant. > > > > > For (2) - Although I think the original authors of this API probably did > intend for execute() to be non-blocking, the fact is that it does > block on > the client and most users are probably calling execute from a client. > So I > do agree we probably shouldn't change the behavior at this point. > Perhaps > we can just clearly document the current behavior of execute() as > part of > adding these new methods. Going forward we can add new methods to > Execution > that are clearly non-blocking (submit?, invoke?) and implement them > consistently on *both* the client in the server, but that doesn't > have to > be in the scope of this proposal. > > > > The problem I see with adding new non-blocking methods (new/submit...) > is that it would be a solution for the current users of the client > regarding backwards compatibility. But, on the server side, we would > have to move the current logic of execute() which is non-blocking to > the new methods and change the current execute() behavior to blocking. > We would not impact the users of the client but we would impact the > users of the server. > > Again, I would propose to aim at: > > a) either leave execute() on the client as blocking > > b) or change execute() on the client to be non-blocking but on the > Geode release this is introduced, have it configurable. The default > behavior would be blocking (deprecated behavior) but could be set to > non-blocking with a system property. On the next release, the blocking > behavior would be removed. > > - Alberto G. > > > > -Dan > > On Fri, Aug 23, 2019 at 4:28 AM Alberto Gomez <alberto.go...@est.tech > ><mailto:alberto.go...@est.tech> > wrote: > > > > Hi Jake, > > Please, see my answers below. > > On 22/8/19 21:16, Jacob Barrett wrote: > > > On Aug 21, 2019, at 8:49 AM, Alberto Gomez <alberto.go...@est.tech > ><mailto:alberto.go...@est.tech> > > > wrote: > > > 2. Timeout in ResultCollector::getResult() and Execution::execute() > > > blocking > > > Regarding the timeout in the ResultCollector::getResult() method > > > problem and the blocking/non-blocking confusion for > Execution::execute() > two alternatives are considered: > > > a) Remove the possibility of setting a timeout on the > > > ResultCollector::getResult() method on the client side as with the > current > client implementation it is useless. This could be done by removing the > method with the timeout parameter from the public API. > > > It would be advisable to make explicit in the documentation that the > > > getResult() method does not wait for results to arrive as that > should have > already been done in the Execution::execute() invocation. > > > This alternative is very simple and would keep things pretty much as > > > they are today. > > > To be honest I think approach would go against what a user “thinks” is > > > going on. Given that there hasn’t been a timeout on execute I > assumed it > was asynchronous and that the getResult blocked until timeout or > results > arrived. Typically these two calls were done back to back. > > You are right if you look at the Java client. But if you look at the > native clients, the timeout is there, both in the C++ and the C# cases > which would indicate that it is a blocking call. > > See > > > https://geode.apache.org/releases/latest/cppdocs/a00725.html#aa918a5e193745950e12ca4feb9c5d776 > > and > > > https://geode.apache.org/releases/latest/dotnetdocs/a00882.html#ae0a814049482ca424f89c13ab1099c3d > > > > b) Transform the Execution::execute() method on the client side > into a > > > non-blocking method. > > > This alternative is more complex and requires changes in all the > > > clients. Apart from that it has implications on the public client > API it > requires moving the exceptions offered currently by the > Execution::execute() method to the ResultCollector::getResult() and new > threads will have to be managed. > > > I think this is more in line with what users expect is going on > based on > > > the current API, I know I have. If were are going to make any change I > think this is the one. I don’t think the behavior change is a > problem since > it's what is expected to be happening anyway. > > > An outline of a possible implementation for option b) would be: > > * Instead of invoking the ServerRegionProxy::executeFunction() > > > directly as it is done today, create a Future that invokes this > method and > returns the resultCollector passed as parameter. > > > Do you really think we need to introduce Futures here into the API? I > > > feel like the ResultCollector acts as the Future. I don’t think any > change > needs to be made to the API in this regard. The ResultCollector > implementation would just simply block as implied by the api for the > timeout period. I would change the method to have units though and > deprecate the method without units. > > I did not mean to introduce Futures in the API. My idea was to use Java > Futures internally so that the ResultCollector returned by the > getResult() method would wrap the Java Future with the ResultCollector > that would actually hold the result. > > An alternative would be to leave the logic of blocking to each > implementation ResultCollector. In the case of the > DefaultResultCollector, we could use a CountDownLatch that would be > decremented when endResults() is called and that would make getResult() > block by using CountDown.await(...). > > The advantage of using Futures internally is that the blocking logic > would not have to be implemented on every ResultCollector > implementation. > > > > -Jake > > > > > - Alberto > > >
