DistributedSystems-Mertz&McCarthy
Source:h8p://www.itu.int/en/ITU-D/StaAsAcs/Documents/facts/ICTFactsFigures2015.pdf
DistributedSystems-Mertz&McCarthy
Source:h8p://www.itu.int/en/ITU-D/StaAsAcs/Documents/facts/ICTFactsFigures2015.pdf
DistributedSystems-Mertz&McCarthy
Source:h8p://www.comscoredatamine.com/2013/12/amazon-ebay-drive-heavy-app-usage-while-mulA-channel-retailers-rely-on-mobile-web/
DistributedSystems-Mertz&McCarthy
Source:h8p://www.comscoredatamine.com/2012/10/mobile-phones-and-tablets-now-account-for-1-in-8-u-s-internet-page-views/
DistributedSystems-Mertz&McCarthy
Source:h8p://www.comscore.com/Insights/Blog/Number-of-Mobile-Only-Internet-Users-Now-Exceeds-Desktop-Only-in-the-U.S
DistributedSystems-Mertz&McCarthy
•  Intheforeseeablefuture,mobiledeviceswillbethemost
prevalentwaythatpeopleaccesstheInternet,and
therefore,distributedsystems.
•  Learninggoalsfortoday’sclass:
1.  Tounderstandmobilephonesascomponentsinadistributed
system.
•  I.e.asadistributedsystemisanapplicaAonorservicebuiltfromasetof
heterogeneouscompuAngsystemsthatcommunicatebypassing
messages,amobilephoneisoVenoneofthosecompuAngsystems
2.  TocreateasimplenaAvemobileapplicaAonthat
communicateswithothersystemsinadistributedsystem.
(Indoingso,demysAfymobileapps:theyarejustjava
programslikeotherswe'vebuilt.)
DistributedSystems-Mertz&McCarthy
•  AnAndroidphoneisjust:
–  acomputerrunningLinux
–  withnetworkingcapability
–  somespecialized
hardware(phone,gps
camera)
–  andasoVware
stackto
support
wriAng
applicaAons
DistributedSystems-Mertz&McCarthy
Typeof
applica,on
Class?
Method(s)toimplement?
Configura,on
informa,onfile?
Plain
Java
ApplicaAon
Web
ApplicaAon
Android
ApplicaAon
DistributedSystems-Mertz&McCarthy
Typeof
applica,on
Class?
Method(s)toimplement?
Configura,on
informa,onfile?
Plain
Java
ApplicaAon
AnyPOJO
main()
None
Web
ApplicaAon
Android
ApplicaAon
DistributedSystems-Mertz&McCarthy
Typeof
applica,on
Class?
Method(s)toimplement?
Configura,on
informa,onfile?
Plain
Java
ApplicaAon
AnyPOJO
main()
Web
ApplicaAon
ExtendH8pServlet
doGet(),init(),doPost(),etc. web.xml
None
Android
ApplicaAon
DistributedSystems-Mertz&McCarthy
•  AnAndroidappwitha
userinterfaceiscalledan
AcAvity
•  Androidappsextend
AcAvityorasubclasssuch
asAppCompatAcAvity
•  AbasicAndroidapp
needstoonlyimplement
theonCreate()method
Source:h8ps://developer.android.com/reference/android/app/AcAvity.html
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="ds.cmu.edu.helloandroid”>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity
ds.cmu.edu.helloandroid.MainActivity
android:name=".MainActivity"
android:label="@string/app_name"
android:theme="@style/AppTheme.NoActionBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
ds.cmu.edu.helloandroid.
MainAcAvity.java
publicclassMainAcAvityextendsAppCompatAcAvity{
@Override
protectedvoidonCreate(BundlesavedInstanceState){
…
DistributedSystems-Mertz&McCarthy
Typeof
applica,on
Class?
Method(s)toimplement?
Configura,on
informa,onfile?
Plain
Java
ApplicaAon
AnyPOJO
main()
Web
ApplicaAon
ExtendH8pServlet
doGet(),init(),doPost(),etc. web.xml
Android
ApplicaAon
ExtendAcAvity
(oroneofits
subclassessuchas
AppCompatAcAvity)
onCreate(),onPause(),etc. AndroidManifest.xml
None
DistributedSystems-Mertz&McCarthy
•  AnAndroidapp’sUIisdefined
–  inxmlfiles
–  withintheresdirectory
•  TwoediAngmodes:
–  Design(WYSIWYG)
–  Text(xml)
•  Thecompleteresdirectoryiscompiledfromxml
intoJavaclassesthatdefinetheRobject
•  ThereforeR.referstoUIelementsdefinedinthe
resdirectory
–  IfRisundefined,itmeanstheresxmlhasanerror.
DistributedSystems-Mertz&McCarthy
•  SeeTable1at:
h8ps://developer.android.com/guide/topics/resources/providing-resources.html
•  Somekeyelements
–  layout
•  HowUIarearranged(linear,grid,etc.)
–  drawable
•  Picture(bitmap)files(jpg,png,etc.
–  menu
•  ApplicaAonmenus
–  values
•  ConstantvaluessuchasstaAcstrings,colors,etc.
DistributedSystems-Mertz&McCarthy
•  TheglobalvariableRreferstoallUIresources.
•  TosettheUIlayout:
–  setContentView(R.layout.ac)vity_main);
•  acAvity_main.xmlwouldbeintheres/layoutdirectory
•  TofindUIelements,usefindViewById:
–  Bu8onsubmitBu8on=(Bu8on)findViewById(R.id.submit);
•  ThiswouldrefertoaBu8onintheUIwiththeID==submit
DistributedSystems-Mertz&McCarthy
•  Roles
–  User(person1)
–  UI(person2)
•  Scenario
–  UsertossesUIballs,whichtheyprocessquicklyandpass
back.
–  IfoneoftheballsissomethingthattakesalongAme,then
subsequentballstossedfromUseraredroppedwhileUI
completesit.
•  Haveyouexperiencedthis?
•  Howcanyousolveit?
DistributedSystems-Mertz&McCarthy
•  Newrole
–  Helper(person3)
•  UIcanpassoffrequeststhatwilltakealongAme
toHelper
•  WhenHelperisfinished,itcanpasstheresults
backtoUI
–  Thescreenisadatastructure,youdon’twantmulAple
threadschangingit.
–  AllUIchangesshouldbedonebytheUIonly
DistributedSystems-Mertz&McCarthy
Examplecomparisonoflatency,scaledtoifaCPUcycletook1second
Event
Latency
Scaled
1CPUCycle
0.3nsec
1sec
MainMemory
120nsec
6min
SolidStateDisk
50–150µsec
2–6days
RotaAonalDisk
1–10ms
1–12months
InternetSFtoNYC
40ms
4years
Source:SystemsPerformance:EnterpriseandtheCloud1stEdiAonbyBrendanGregg,ISBN-13:978-0133390094
YoudoNOTwantyourUIwaiAngfor4yearsbeforeitcanrespond
toyourscrollgestureorbu8onclick!
DistributedSystems-Mertz&McCarthy
UI(Main)Thread
onPreExecute()
onPostExecute()
HelperThread
doInBackground()
DistributedSystems-Mertz&McCarthy
•  TheAndroiddevelopershaveasetofvideos.
•  OneishowtogetstartedwithAndroidStudio.
–  h8ps://www.youtube.com/watch?v=Z98hXV9GmzY
DistributedSystems-Mertz&McCarthy