[jira] [Commented] (ARIES-1383) Provide option to disable the provisioning of dependencies at install time.

["ASF subversion and git services (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARIES-1383?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15122154#comment-15122154 ] 

ASF subversion and git services commented on ARIES-1383:
--------------------------------------------------------

Commit 1727424 from [~jwross@us.ibm.com] in branch 'aries/trunk'
[ https://svn.apache.org/r1727424 ]

[ARIES-1383] Provide option to disable the provisioning of dependencies at install time.

As part of the implemented locking strategy, three locks are used. The Global Read/Write Lock (GRWL) is used to ensure thread safety among all operations: install, install
dependencies, resolve, start, stop, and uninstall. The write lock is acquired for install, install dependencies, and uninstall. The read lock is acquired for resolve, start, and stop.
The Global Mutual Exlusion Lock (GMEL) is used to prevent cycle deadlocks when acquiring the state change locks of individual subsystems. Every subsystem has a Local State Change Lock
(LSCL). These locks are used to prevent more than one state change operation at a time to occur for the same subsystem.

A condition exists for the GMEL. The condition is used in order to notify waiting threads that the LSCL of at least one subsystem was released and that at least one thread may now be
able to proceed. Threads that fail to acquire the LSCL of a subsystem while holding the GMEL will release all currently held locks and wait for the condition to apply. This is
necessary because, when starting, the target subsystem must be locked before any other affected subsystems since the latter may only be computed after dependencies, which may include
other subsystems, are installed.

The consequences of this strategy is that installs and uninstalls are synchronous while resolutions, starts, and stops are asynchronous as long as the same subsystem is not affected.
It may be possible to create an even more granular locking mechanism in the future if dictated by performance requirements.

> Provide option to disable the provisioning of dependencies at install time.
> ---------------------------------------------------------------------------
>
>                 Key: ARIES-1383
>                 URL: https://issues.apache.org/jira/browse/ARIES-1383
>             Project: Aries
>          Issue Type: Improvement
>          Components: Subsystem
>    Affects Versions: subsystem-2.0.6, subsystem-2.0.8
>            Reporter: John Ross
>            Assignee: John Ross
>
> PROBLEM
> -------------
> The Subsystems specification states that all dependencies of a subsystem must have been installed in order to attain the INSTALLED state. If required dependencies are not found, the installation must fail.
> This functionality was described in order to achieve fail-fast functionality. If an environment cannot support the dependencies of a subsystem, it is rejected right away.
> However, there are deployment situations where it is valuable to delay the installation of dependencies. For example, you may wish to independently and simultaneously install a suite of subsystems whose contents have interleaving dependencies. This is currently not possible because the local repository of one subsystem is not available to others. The resources will not be available to others until they become part of the System Repository (assuming a compatible sharing policy) once the INSTALLED state is acquired. In the meantime, the other subsystems fail installation.
> There are three potential workarounds to this issue, none of which may be acceptable to a particular Subsystems consumer.
> (1) Provide all content as part of a remote repository. Note that this would require the Subsystem-Content header to be computed by the subsystem provider and not by the implementation.
> (2) Package all subsystems into a single ESA and make use of parent-child relationships.
> (3) Manage the install order manually. Note that this would not handle the case of circular dependencies.
> A solution that will allow for the independent and simultaneous installation of multiple subsystems with interleaving content dependencies, thus giving a deployer more flexibility, is desirable.
> PROPOSED SOLUTION
> -----------------------------
> A custom directive is introduced: apache-aries-provision-dependencies. The possible values are "install" and "resolve", which indicate the time at which dependency provisioning should occur. The default value is "install" which results in the current behavior. This directive may be specified as part of the Subsystem-Type header. A value of "resolve" indicates that dependencies should not be provisioned at installation time. Rather, this step will occur when the subsystem is resolved which typically happens as part of the start process.
> A subsystem with apache-aries-provision-dependencies:=resolve will remain in the INSTALLING state until it is started. This is an indication to administration programs monitoring subsystems via the service registry that the subsystem has not yet had its dependencies provisioned. When the subsystem is started, the transition from INSTALLING to INSTALLED will then occur as it does today. Assuming the provisioning of dependencies succeeds, the subsystem will then immediately transition into the RESOLVING state and proceed as normal.
> State transitions when apache-aries-provision-dependencies:=start:
> 	install() : <void> -> INSTALLING
>                        <void> -> INSTALLING -> INSTALL_FAILED -> UNINSTALLING -> UNINSTALLED (if installation fails for some reason other than dependency provisioning)
> 	start() : INSTALLING -> INSTALLED -> RESOLVING -> RESOLVED -> STARTING -> ACTIVE
> 		     INSTALLING -> INSTALLING (if provisioning of dependencies fails)
>                      INSTALLING -> INSTALLED -> RESOLVING -> INSTALLED (if runtime resolution fails)
> 		
> 		     INSTALLING -> INSTALLED -> RESOLVING -> RESOLVED -> STARTING -> RESOLVED (if starting fails)
> Child scoped subsystems inherit the apache-aries-provision-dependencies value of the first scoped ancestor unless explicitly overridden.  Unscoped subsystems always inherit the apache-aries-provision-dependencies value of the first scoped ancestor and may not override the value. The root subsystem always has a value of apache-aries-provision-dependencies:=install.
> ALTERNATIVE SOLUTIONS
> ---------------------------------
> (1) Make the local repositories of installing subsystems available to other installing subsystems. The specification does not allow local repositories to be registered as a Repository service, although it does not explicitly address the possibility of a particular implementation sharing them internally. Nevertheless, the intent of the spec seems clear in that it should not be assumed that a subsystem provider desires their content to be shared with others.
> POTENTIAL ISSUES
> -------------------------
> (1) The proposed solution will break the contract of the install methods specified on the Subsystem and AriesSubsystem interfaces, which require that either the returned subsystem is in the INSTALLED state or that the installation fails with an exception. However, it is assumed that the explicit declaration of the apache-aries-provision-dependencies directive with a value of "resolve" grants the implementation permission to do so. An alternative would be to return the Subsystem in the INSTALLED state even though none of the dependencies have been installed. However, this would also violate the specification and may confuse third party applications monitoring subsystem services via the registry.
> (2) A subsystem may have more than one parent but at most one scoped parent. This means that additional parents will always be features (or other unscoped subsystems). The question is how should apache-aries-provision-dependencies inheritance work when there are multiple parents with conflicting values. A simplifying assumption would be that features may not override the value of the scoped parent. This implies that features should fail installation if they contain a value of apache-aries-provision-dependencies that conflicts with the scoped subsystem within the same region.
> TEST CASES
> ------------------
> (1) A set of subsystems with interleaving content dependencies are able to be independently, simultaneously, and successfully installed and started.
> (2) Subsystem with apache-aries-provision-dependencies:=resolve is in the INSTALLING state after a successful installation.
> (3) Subsystem with apache-aries-provision-dependencies:=resolve is available as a service after a successful installation.
> (4) Subsystem with apache-aries-provision-dependencies:=resolve does not have its dependencies installed after a successful installation.
> (5) Subsystem with apache-aries-provision-dependencies:=resolve undergoes the following state transitions when starting: INSTALLING -> INSTALLED -> RESOLVING -> RESOLVED -> STARTING -> ACTIVE.
> (6) Subsystem with apach-earies-provision-dependencies:=resolve has its dependencies installed after a successful start.
> (7) Subsystem with apache-aries-provision-dependencies:=resolve is in the INSTALL_FAILED state after an unsuccessful installation.
> (8) Subsystem with apache-aries-provision-dependencies:=resolve is not available as a service after an unsuccessful installation.
> (9) Subsystem with apache-aries-provision-dependencies:=resolve is in the INSTALLING state when dependencies cannot be provisioned after invoking the start method.
> (10) Subsystem fails installation if the apache-aries-provision-dependencies directive has a value other than "install" or "resolve".
> (11) Subsystem with apache-aries-provision-dependencies:=resolve undergoes the following state transitions when starting fails due to a runtime resolution failure: INSTALLING -> INSTALLED -> RESOLVING -> INSTALLED.
> (12) Subsystem with apache-aries-provision-dependencies:=resolve undergoes the following state transitions when starting fails due to a start failure: INSTALLING -> INSTALLED -> RESOLVING -> RESOLVED -> STARTING -> RESOLVED.
> (13) The root subsystem has apache-aries-provision-dependencies:=install.
> (14) Subsystem with explicit apache-aries-provision-dependencies:=install works as before.
> (15) Unscoped subsystem with a value of apache-aries-provision-dependencies that is different than the scoped parent fails installation.
> (16) Unscoped subsystem with a value of apache-aries-provision-dependencies that is the same as the scoped parent installs successfully.
> (17) Scoped subsystem with a value of apache-aries-provision-dependencies that is the same as the scoped parent behaves accordingly.
> (18) Scoped subsystem with a value of apache-aries-provision-dependencies that overrides the scoped parent behaves accordingly.
> (19) Scoped subsystem with only features as parents is able to override the value of apache-aries-provision-dependencies.
> (20) Install a scoped subsystem, S1, with apache-aries-provision-dependencies:=resolve. Install two features, F1 and F2, independently as children of S1. F1 has bundle B1 as content. F2 has bundle B2 as content. B2 has B1 as a dependency. B1 should be a constituent of F1 but not of the root subsystem.
> (21) Install a scoped subsystem, S1, with apache-aries-provision-dependencies:=resolve. Install two features, F1 and F2, independently as children of S1. F1 has bundle B1 and B2 as content. F2 has bundle B2 and B3 as content. B2 is shared content. B1 has a dependency on bundle B4, B2 has a dependency on bundle B5. B3 has a dependency on bundle B6. Start F1. Dependency bundles B4 and B5 should be provisioned but not B6.



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