Description
Introduction
ThisassignmentisanextensionofProgrammingAssignment2,PartA.Youwillextendyour groupmessengertoaddorderingguarantees,implementingatotalorderingacrossmessengerinstancesthatpreservesFIFOordering. Messageswillbestoredinyourcontentprovider asimplementedinPartA.Asyouknowbynow,youmustfollowtheseinstructionsexactly. Failure to do so may result in no credit for this assignment. Please read this document in its entirety before you begin. It is long, but that is only because it is complicated and precise. Revisit the instructions regularly as you implement tobesureyou’reimplementingwhatisrequired. Therearenotesattheendthatmayassist you if you encounter common problems; make sure to review them as you go, as well. This assignment will require you to:
• Implement a FIFO total ordering algorithm.
• Detect and handle failure of a single messenger instance.
1 GettingStarted
We are providing a project template for you to get started. As in the previous assignments, the template configures a number of things on your behalf. It is important that you do not change settings that you do not have to change to complete your project.
2 TheGroupMessengerApp
The graded portion of this project is an implementation of the group messenger app with ordering guarantees and message storage in a content provider with the same interface as Part A (but a different URI; see below). You will need to download the project from GitHub Classroom and open it in Android Studio. You should have received the GitHub Classroom invitation for this project via Piazza. InstructionsforcloningtheprojectandopeningitinAndroidStudioarethesameasbefore,exceptthatthebaserepositorynameisGroupMessenger2. YoucanfindYouTubetutorials detailing the process here. For this portion of the project, you will need to run five emulators. We will be using the multi-portconfigurationasdescribedinproject1. Yourappwillopenoneserversocketthat
1Thisassignmentisbased,withpermission,onanassignmentdevelopedandusedbySteveKoinhisversion of CSE 486/586. Large portions of text are used verbatim from that assignment.
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listensonport10000,butitwillconnecttoadifferentportnumberontheIPaddress10.0.2.2 for each emulator, as follows: emulatorserial port emulator-5554 11108 emulator-5556 11112 emulator-5558 11116 emulator-5560 11120 emulator-5562 11124
2.1 TotalOrdering Implementingtheorderingfunctionalityisthebulkofthisassignment,andtogetfullcredit youwillhavetosuccessfullyprovideorderedmessagesinthefaceofthefailureofasingleapp instanceduringexecution. Yourappshouldprovideatotalorderingforincomingmessages among all app instances, and that total ordering should preserve FIFO ordering (hereafter, total-FIFO ordering). Total and FIFO ordering are as defined in class. The results of this ordering will be stored in your content provider, as described below.
2.1.1 Requirements 1. The URI of your content provider must be: content://edu.buffalo.cse.cse486586.groupmessenger2.provider NotethatthisisdifferentfromProject2,PartA! The other requirements for the content provider are as in Project 2, Part A.
2. Each app should multicast every user-entered message to all app instances, including the one that is sending the message. In the rest of this description, “multicast” always means sending a message to all app instances. It must be able to do this when all five emulators are running simultaneously.
3. Your app should use B-multicast. It should not implement R-multicast.
4. You will need to find or design and implement an algorithm that provides total-FIFO ordering underasingleprocessfailure.
5. There will be at most one failure of an app instance during execution. This failure will be emulatedbyforceclosinganapplicationinstance. Wewillemulateacrash-stopfailure: the failed app will not return during the execution run.
(a) Every message should be used in detection of node failure. (b) You should use a timeout on socket read to detect failure. Choose a reasonable timeout(e.g.,500ms),andconsideranodefailedifitdoesnotrespondwithinthe timeout. (c) This will require handling socket timeout exceptions explicitly (and differentiatingthemfromothersocketexceptions,suchasatcreation,connection,orendof file).
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(d) Do not rely only on socket creation or connection status to determine if a node has failed. It is not a safe or sufficient solution! Please also use read timeout exceptions. (e) You cannot assume which app instance will fail, and different app instances will be killed randomly on different testing runs. Therefore your algorithm should notrelyon,e.g.,asinglecentralizedsequencer,asitwillthenbeunabletohandle the failure of that sequencer. (f) You should implement a decentralized algorithm (e.g., something based on ISIS) forordering,sothatyourmessengercanordermessagesinthefaceofappfailure. (g) It is important to make sure that your app does not stall following failure. You should clean up any state related to the detected failure, then move on.
6. When there is a node failure, the grader will not check the ordering of messages sent bythefailednode. See Testing, below, for more details.
7. Everymessageshouldbestoredinthecontentprovideronthelocaldeviceindividually by each app instance. Each message should be stored as a key-value pair, with the key being the final delivery sequence number for the message (as a Java string) and the value being the actual message (as a Java string). The delivery sequence number for thispurposeshouldstartwith0andincreaseby1foreachmessage. Notethatthismay not,andneednot,bethesameastheprioritiesagreeduponbyyourtotalorderingalgorithm.
2.2 Testing We have testing programs to help you see how your code does with our grading criteria. If youfindroughedgesinthetestingprograms,pleasereportitsotheteachingstaffcanfixit. The instructions for using the testing programs are the following:
• Downloadatestingprogramforyourplatform. Ifyourplatformdoesnotrunit,please report it.
1. Windows: Tested on 64-bit Windows 8. 2. Linux: Testedon64-bitDebian9and64-bitUbuntu17.10(seebelowforimportant information about 64-bit systems). 3. Mac OS: Tested on 64-bit Mac OS 10.9 Mavericks.
• Before you run the program, please make sure that you are running all five AVDs. You can usepython run_avd.py 5to start them. • Remember to start the emulator network by runningset_redir.py 10000. • Unlike previous testing programs, this test will require you to provide your APK as a command line argument, and will take care of installing and uninstalling it on the emulators.
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• Runthetestingprogramfromthecommandline. Thetestingprogramtakesanumber of command-line arguments to control its execution, which you can view with the-h argument. You may find them helpful for debugging.
• It may issue some warnings or errors during execution. Some of them are normal, some may indicate errors in your program. Examine them to find out!
• The testing program will give you partial and final scores.
Thetestingwillproceedintwophases,wherethefirstphasetestsyourapplicationinthe absenceoffailures,andthesecondtestsitwithasingleappfailure. Asdescribedabove,you mustimplementadecentralizedfailuredetectionandhandlingalgorithmthatdeterministicallyidentifiesfailures. Ifyouuseacentralizedornondeterministic(e.g.,randomized)failure detection algorithm, or do not uniformly handle failures by cleaning up and moving on, the score you get for the second part is not guaranteed. The ordering of messages sent by the failed app, in the event of app failure, will not be considered by the grader. In particular, it is possible that some app instances will have successfully delivered messages from the failed app, while others will not, and that is OK. The grader will examine the total-FIFO ordering guarantees only for the messages sent by live nodes. Note that, in phase 2 of the testing, this means that the grader may indicate that a particular key is missing; this is the message sequence number that the grader is verifying. It may not be the exact key due to failure. Thegraderismulti-threaded,anderroranddiagnosticmessagesfromthevariousthreads are uncoordinated. This means that an error message may appear early in the execution, or in with other log messages, rather than cleanly at the end of execution. You will have to examine the output to determine where and when errors may have occurred. Remember during your own testing that you may see strange contents in your content provider if you do not uninstall your application between tests. In particular, updating the app from Android Studio does not uninstall the existing app first, so the content provider’s state will not be cleared. You can uninstall your app by hand with the following command: adb -s uninstall edu.buffalo.cse.cse486586.groupmessenger2
Notesfor64-bitLinux: Thetestingprogramiscompiled32-bit. Ifyougetanerrorlikethe following, or the shell reports command not found when you run the executable, install the 32-bitlibzfor your system: ./simplemessenger-grading.linux: error while loading shared libraries: libz.so.1: cannot open shared object file: No such file or directory OnDebian-baseddistributions,youcanaccomplishthiswiththecommandapt-get install zlib1g:i386 as root (you may need to use sudo or su). If apt-get reports an error about the architectureorsaysthepackageisnotfound,youmayneedtoenablemultiarch. Todothis, rundpkg –add-architecture i386as root, then update your APT repositories withapt-get updateas root. Once this is done, you should be able to install the 32-bitlibz. For other distributions you will need to consult your distribution documentation.
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3 Submission We use UB CSE autograder for submission. You can find autograder athttps://autograder. cse.buffalo.edu/, and log in with your UBITName and password. Once again, it is critical that you follow everything below exactly. Failure to do so willlead tonocreditforthisassignment. Zip up your entire Android Studio project source tree in a single zip file. Ensure that all of the following are true: 1. You didnot create your zip file from inside theGroupMessenger1directory. 2. Thetop-leveldirectoryinyourzipfileisGroupMessenger1orGroupMessenger1-, and it containsbuild.gradleand all of your sources. 3. Youusedaziputilityandnotanyothercompressionorarchivetool: thismeansno7-Zip, no RAR, no tar, etc.
4 Deadline
This project is due 2018-03-09 11:59:00 AM. This is one hour before our class. This is a firm deadline. If the timestamp on your submission is 11:59:01, it is a late submission. You are expected to attend class on this day!
5 Grading
This assignment is 10% of your final grade. Credit for this assignment will be apportioned as follows:
• 4%: Your group messenger provides total-FIFO ordering guarantees with messages stored in the content provider.
• 6%: Your group messenger provides total-FIFO ordering guarantees with message stored in the content provider for all correct app instances under a single app failure.
Thus, an application that provides correct total-FIFO ordering both with and without a single app failure will receive a total of 10%: 4% for correct operation without any failures, and 6% for correct operation in the face of a single app failure.
Notes
• Pleasedonotuseaseparatetimertohandlefailures,asthiswillmakedebuggingvery difficult and is likely to introduce race conditions. Use socket timeouts and handle all possible exceptions that may be thrown when there is a failure. They are: SocketTimeoutException,StreamCorruptedException,EOFException,andtheparentIOException.
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• PleasereuseyourTCPconnectionswithasingleremotehost,insteadofcreatinganew socket every time you send a message. You can use the same socket for both sending to and receiving from a remote AVD. Think about how you will coordinate this. • Please do not use Java object serialization (i.e., implementing Serializable). This will cause very large messages to be sent and received, with unnecessarily large message overhead.
• Please do not assume that a fixed number of messages will be sent in your system. Your implementation should be able to handle an arbitrary number of messages, and you should not hardcode such a value in any way.
• Remember that there is a cap on the number of AsyncTasks that you can execute simultaneously. Plan accordingly, to keep the total number of threads that you require under this limit (which is about five).