In other words would work where MarshalInputStream is used.
Sent from my Samsung device. Include original message ---- Original message ---- From: Michał Kłeczek <michal@kleczekorg> Sent: 08/02/2017 06:51:55 am To: dev@river.apache.org Subject: Re: OSGi - deserialization remote invocation strategy I think you have misunderstood my question. I want my implementation of RemoteEventListener to be a smart proxy. How do u support that? On Tue, 7 Feb 2017 at 20:26, Peter <j...@zeus.net.au> wrote: > No, it's just an example, no such restriction. But it is restricted to > JERI. > > RemoteEvents have been extended also in JGDMS to use MarshalledInstance > and JErI instead of MarshalledObjects and JRMP. All methods that rely on > MarshalledObject have been deprecated and replacements provided with the > exception of Activation constructors. > > MarshalledInstance has also been made extensible to allow other > serialization formats to be supported by the api. > > But we're diverging... > > Cheers, > > Peter. > > Sent from my Samsung device. > > Include original message > ---- Original message ---- > From: Michał Kłeczek <mic...@kleczek.org> > Sent: 08/02/2017 06:07:19 am > To: dev@river.apache.org > Subject: Re: OSGi - deserialization remote invocation strategy > > Hmm.. I see. > > So your solution explicitly only handles cases of looking up a service > in the ServiceRegistrar. > > How about smart RemoteEventListeners? They are not published in any > lookup service. > > Thanks, > Michal > > Peter wrote: > > > In the JGDMS fork of River, in addition to Reggie's proxy returing >unmarshalled service proxy's from the ServiceRegistrar lookup method, >SafeServiceRegistrar provides a lookup method that returns instances of >java.lang.reflect.Proxy that implement interfaces to retrieve the service, >it's attributes and it's codebase uri and signer certs > > > > > The client can authenticate, filter and grant permissions (for >deserialization and codebase download) before retrieving the service proxy >using a method call. > > > > > In this case the service proxy is obtained by from the reflection proxy >instead of MarshalledIstance. > > > > Cheers, > > > > Peter. > > > > Sent from my Samsung device. > > > > Include original message > > ---- Original message ---- > > From: "Michał Kłeczek (XPro Sp z o. o.)"<michal.klec...@xpro.biz> > > Sent: 08/02/2017 05:51:07 am > > To: dev@river.apache.org > > Subject: Re: OSGi - deserialization remote invocation strategy > > > > > So I must have misunderstood the part about smart proxies being obtained >via "reflection proxies" or MarshalledInstances. > > > > What are these "reflection proxies"? > > > > Thanks, > > Michal > > > > Peter wrote: > > No, no bootstrap objects. > > > > Cheers, > > > > Peter. > > > > > > > > Sent from my Samsung device. > > > > Include original message > > ---- Original message ---- > > From: "Michał Kłeczek (XPro Sp. z o. o.)"<michal.klec...@xpro.biz> > > Sent: 08/02/2017 12:28:50 am > > To: dev@river.apache.org > > Subject: Re: OSGi - deserialization remote invocation strategy > > > > Are you proposing to provide a bootstrap object that will download some > > meta information prior to class resolution? > > > > How does it differ from simply changing annotations to be those > > "bootstrap objects" instead of Strings? > > > > Thanks, > > Michal > > > > Peter wrote: > > Proposed JERI OSGi class loading strategy during deserialization. > > > > Record caller context - this is the default bundle at the beginning of > > the stack. It is obtained by the InvocationHandler on the > > client side. The InvocationDispatcher on the server side has the > > calling context of the Remote > > implementation. The reflection dynamic proxy must be installed in the > > client's class loader, so the > > InvocationHandler knows exactly what it is, it will be passed to the > > MarshalInputStream. Any > > interfaces not found in the client's bundle can be safely shed. For a > > smart proxy the reflection proxy will > > be installed in the smart proxy loader. The smart proxy is obtained > > either via a reflection proxy or a MarshalledInstance. > > MarshalledInstance also passes in the callers loader to the > > MarshalInputStream. > > > > The smart proxy classloader is not a child loader of the clients > > loader, instead it's a bundle that imports > > service api packages, with a version range that overlaps those already > > imported by the client. > > > > Both Invocationhandler and InvocationDispatcher utilise > > MarshalInputStream and MarshalOutputStream, for marshalling parameters > > and return values. > > > > The codebase annotation bundle's manifest contains a list of package > > imports. > > > > Do we need to make a list of package imports for every new bundle that > > we load? > > Do we need to record the wiring and packages and their imports from > > the remote end? > > > > I don't think so, the bundles themselves contain this information, I > > think we just need to keep the view of available classes relevant to > > the current object being deserialized. > > > > Codebase Annotations are exact versions! They need to be to allow the > > service to ensure the correct proxy codebase is used. Other proxy > > codebases will be installed in the client, possibly different > > versions, but these won't be visible through the resolved > > dependencies, because the proxy codebases only import packages at the > > client and OSGi restricts visibility to the current bundle's own > > classes and any imported packages. > > Instead of appending dependencies to the codebase annotation they'll > > need be defined in the proxy's bundle manifest. Of course if an > > identical version of a proxy codebase bundle is already installed at > > the client, this will be used again. > > > > Because a bundle generally imports packages (importing entire bundles > > is discouraged in OSGi), there may be classes > > that aren't visible from those bundles, such as transient imports, but > > also including private packages that aren't exported, private > > implementations need to be deserialized, but is it possible to do so > > safely, without causing package > > conflicts? Private implementation classes can be used as fields > > within an exported public object, but cannot and should not > > escape their private scope, doing so risks them being resolved to a > > bundle with the version of the remote end, instead of the locally > > resolved / wired package, causing ClassClassExceptions. > > > > Initial (naive) first pass strategy of class resolution (for each > > branch in the serialized object graph)?: > > 1. Try current bundle on the stack (which will be the callers > > bundle if we haven't loaded any new bundles yet). > > 2. Then use the package name of a class to determine if the package > > is loaded by any of the bundles > > referenced by the callers bundle imports (to handle any private > > implementation packages > > that aren't in the current imports). Is this a good idea? Or should > > we go straight to step 3 > > and let the framework resolve common classes, what if we use a > > different version to the > > client's imported bundle? Should we first compare our bundle > > annotation to the currently > > imported bundles and select one of those if it's a compatible > > version? Yes, this could be an > > application bundle, otherwise goto 3. > > 3. Load bundle from annotation (if already loaded, it will be an > > exact version match). Place the > > new bundle on top of the bundle stack, remove this bundle from the > > stack once all fields of > > this object have been deserialized, returning to the previous bundle > > context. We are relying > > on the current bundle to wire itself up to the same package versions > > of the clients bundle > > imports, for shared classes. Classes that use different bundles will > > not be visible to the client, > > but will need to be visible to the current object's bundle. > > 4. Place a bundle reference on the stack when a new object is > > deserialized from the stream and > > remove it once all fields have been deserialized. (we might need to > > remember stack depth) > > 5. Don't place non bundle references on the stack. For example > > system class loader or any > > other class loader, we want resolution to occur via the OSGi > > resolution process. > > > > What about a simpler strategy (again naive), where we don't attempt to > > resolve private implementation classes? > > 1. The calling class' bundle, is given priority. > > 2 Load bundle from annotation (exact version), when not found in > > calling class. > > 3. No stack, what if an application bundle from server is loaded > > that conflicts with an existing > > bundle resolved by the client? > > 4. What about walking back through the stack? Probably > > unnecessary, as the containing object > > will reference the class by a common interface, the outer object may > > not need to reference > > it at all. But what if the outer object passed it in during > > construction? > > > > Revised strategy: > > 1. Attempt to load from current bundle on stack (the stack begins > > with the client's Bundle, each > > node in the graph has its bundle added to the stack and is also > > removed after that node is completely deserialized. > > 2. If unsuccessful, walk back through deserialized bundle reference > > stack and attempt to load class. > > Why not start at the beginning of the stack? We are expecting bundles > > to wire up to > > currently loaded versions, but bundles can import different package > > versions for > > implementation, safest to start with current bundle and consult parent > > if not found in the current bundle > > dependency graph, ie possibly passed in during object construction or > > an handback > > implemented in the client, from an earlier invocation or dependency > > injected. > > 3. The client is responsible for determining compatibility with the > > service api it's interested in > > > from the Import Package Entry's, prior to unmarshalling a service proxy. > > 4. If a bundle previously on the stack resolves a class, then this > > object's bundle reference is placed > > on the top of the stack, it is removed once the current object and all > > it's fields have been completely deserialized. > > 5. Load bundle from annotation (exact version). > > 6. No attempt will be made to directly load from wired bundles, > > always rely on wires, > > otherwise we may utilise an incompatible package / bundle. > > > > Do we need a graph of the wiring from the remote end? > > During serialization (from the remote end) do we need to determine if > > > a bundle has dependants and send some sort of version range information? > > When a class descriptor is read in from a stream, the class descriptor > > contains information > > about fields and it's serializable supertype class (if it exists) > > are also read in from the stream, before any field objects are read > > in, the declared field types > > are visible from the bundle of the current object being deserialized. > > The objects that will be > > assigned to those field types must also resolve to those types. Hence > > bundles being resolved as part > > of deserialization must favour already resolved packages for imports. > > What if a bundle requires a specific package version? This is why the > > bundle must be given first > > attempt to resolve an objects class and rely on the bundle dependency > > resolution process. > > OSGi must be allowed to wire up dependencies, we must avoid attempting > > to make decisions about > > compatibility and use the current bundle wires instead (our stack). > > > > The BundleReference stack is designed to follow the wires (dependency > > links between bundles), > > to allow private classes to be resolved, as they're not visible from > > other bundles. > > > > We can't rely on annotations to resolve private classes, because we > > can't predict the way bundle > > dependency's are resolved in remote JVM's. > > > > General recommendations for OSGi: > > * The service should use as wide a version range as possible for > > service api. > > * It is better to create new service api in a new bundle than to > > evolve in a backward compatible manner, as > > an incremental change may not be compatible if additional classes and > > methods are missing > > from the client, that the service proxy depends on. > > * Don't split packages. > > * Private implementation classes are ok, provided they remain > > within public exported classes and don't escape, otherwise > > they may not link up properly upon deserialization. > > * The proxy should minimise the package imports it uses. > > * There must be only one compatible service api version installed > > already in the client. > > * Duplicates of incompatible versions of service api are ok. > > > > The catch is, it may not be possible to build the bundle stack without > > some programming hooks in ObjectInputStream. > > > > Unfortunately we don't have any control over OIS, the necessary hooks > > could however be added to AtomicMarshalInputStream. > > > > Cheers, > > > > Peter. > > > > > > > > > > > > > > >
