xref: /frameworks/base/docs/html-intl/intl/vi/guide/components/processes-and-threads.jd

page.title=Tin trnh v Lung
page.tags=vng i, nn

@jd:body

<div id="qv-wrapper">
<div id="qv">

<h2>Trong ti liu ny</h2>
<ol>
<li><a href="#Processes">Tin trnh</a>
  <ol>
    <li><a href="#Lifecycle">Vng i tin trnh</a></li>
  </ol>
</li>
<li><a href="#Threads">Lung</a>
  <ol>
    <li><a href="#WorkerThreads">Lung trnh thc hin</a></li>
    <li><a href="#ThreadSafe">Phng php an ton vi lung</a></li>
  </ol>
</li>
<li><a href="#IPC">Truyn thng Lin Tin trnh</a></li>
</ol>

</div>
</div>

<p>Khi mt thnh phn ng dng bt u v ng dng khng c bt k thnh phn no khc
ang chy, h thng Android s khi ng mt tin trnh Linux mi cho ng dng bng mt lung
thc thi n l. Theo mc nh, tt c thnh phn ca cng ng dng s chy trong cng tin trnh v lung
(c gi l lung "chnh"). Nu mt thnh phn ng dng bt u v  tn ti mt tin trnh
cho ng dng  (bi mt thnh phn khc t ng dng  tn ti), khi  thnh phn c
bt u bn trong tin trnh  v s dng cng lung thc thi. Tuy nhin, bn c th sp xp cho
cc thnh phn khc nhau trong ng dng ca mnh  chy trong cc tin trnh ring bit, v bn c th to thm
lung cho bt k tin trnh no.</p>

<p>Ti liu ny trnh by v cch cc tin trnh v lung vn hnh trong mt ng dng Android.</p>


<h2 id="Processes">Tin trnh</h2>

<p>Theo mc nh, tt c thnh phn ca cng ng dng s chy trong cng tin trnh v hu ht cc ng dng
s khng thay i iu ny. Tuy nhin, nu bn thy rng mnh cn kim sot mt thnh phn
c th thuc v mt tin trnh no , bn c th lm vy trong tp bn k khai.</p>

<p>Mc nhp bn k khai i vi mi loi phn t thnh phn&mdash;<a href="{@docRoot}guide/topics/manifest/activity-element.html">{@code
&lt;activity&gt;}</a>, <a href="{@docRoot}guide/topics/manifest/service-element.html">{@code
&lt;service&gt;}</a>, <a href="{@docRoot}guide/topics/manifest/receiver-element.html">{@code
&lt;receiver&gt;}</a>, v <a href="{@docRoot}guide/topics/manifest/provider-element.html">{@code
&lt;provider&gt;}</a>&mdash;s h tr mt thuc tnh {@code android:process} m c th quy nh mt
tin trnh m thnh phn  s chy trong . Bn c th t thuc tnh ny sao cho tng thnh phn chy
trong chnh tin trnh ca n hoc sao cho mt s thnh phn chia s mt tin trnh trong khi cc thnh phn khc th khng.  Bn cng c th t
{@code android:process} sao cho cc thnh phn ca nhng ng dng khc nhau chy trong cng
tin trnh&mdash;vi iu kin rng ng dng chia s cng ID ngi dng Linux v c k bng cng cc
chng ch.</p>

<p>Phn t <a href="{@docRoot}guide/topics/manifest/application-element.html">{@code
&lt;application&gt;}</a> cng h tr mt thuc tnh {@code android:process},  t mt
gi tr mc nh p dng cho tt c thnh phn.</p>

<p>Android c th quyt nh tt mt tin trnh ti mt thi im no , khi b nh thp v theo yu cu ca cc
tin trnh khc ang phc v ngi dng tc th hn. Cc thnh phn
ng dng ang chy trong tin trnh b tt b th sau  s b hy.  Tin trnh c
khi ng li cho nhng thnh phn  khi li c vic cho chng thc hin.</p>

<p>Khi quyt nh b nhng tin trnh no, h thng Android s cn nhc tm quan trng tng i so vi
ngi dng.  V d, h thng sn sng hn khi tt mt tin trnh lu tr cc hot ng khng cn
hin th trn mn hnh, so vi mt tin trnh lu tr cc hot ng ang hin th. V th, quyt nh v vic c
chm dt mt tin trnh hay khng ph thuc vo trng thi ca cc thnh phn ang chy trong tin trnh . Cc quy tc
c s dng  quyt nh s chm dt tin trnh no c trnh by  bn di. </p>


<h3 id="Lifecycle">Vng i tin trnh</h3>

<p>H thng Android c gng duy tr mt tin trnh ng dng lu nht c th, nhng
cui cng th n cng cn loi b cc tin trnh c  ly li b nh cho cc tin trnh mi hoc quan trng hn.  
xc nh gi li nhng tin trnh no
v loi b nhng tin trnh no, h thng s t tng tin trnh vo mt "phn cp tm quan trng" da trn
nhng thnh phn ang chy trong tin trnh v trng thi ca nhng thnh phn .  Nhng tin trnh c tm quan trng
thp nht b loi b trc, ri n nhng tin trnh c tm quan trng thp th hai, v c th tip tc, min l cn cn thit
 khi phc ti nguyn ca h thng.</p>

<p>C nm cp trong phn cp tm quan trng. Danh sch sau trnh by cc loi
tin trnh khc nhau theo th t tm quan trng (tin trnh th nht l <em>quan trng nht</em> v c
<em>tt b sau cng</em>):</p>

<ol>
  <li><b>Tin trnh tin cnh</b>
    <p>Mt tin trnh c yu cu cho vic m ngi dng ang thc hin.  Mt
      tin trnh c coi l ang trong tin cnh nu bt k iu no sau y l ng:</p>

      <ul>
        <li>N lu tr mt {@link android.app.Activity} m ngi dng ang tng tc vi (phng php ca {@link
android.app.Activity}, {@link android.app.Activity#onResume onResume()},  c
gi).</li>

        <li>N lu tr mt {@link android.app.Service} gn kt vi hot ng m ngi dng ang
tng tc vi.</li>

        <li>N lu tr mt {@link android.app.Service} ang chy "trong tin cnh"&mdash;m
dch v  gi {@link android.app.Service#startForeground startForeground()}.

        <li>N lu tr mt {@link android.app.Service} m ang thc thi mt trong cc lnh
gi li ca vng i ca n ({@link android.app.Service#onCreate onCreate()}, {@link android.app.Service#onStart
onStart()}, hoc {@link android.app.Service#onDestroy onDestroy()}).</li>

        <li>N lu tr mt {@link android.content.BroadcastReceiver} m ang thc thi phng php {@link
        android.content.BroadcastReceiver#onReceive onReceive()} ca n.</li>
    </ul>

    <p>Nhn chung, ti bt k thi im xc nh no cng ch tn ti mt vi tin trnh tin cnh.  Chng ch b tt b
nh mt gii php cui cng&mdash;nu b nh qu thp ti mc chng u khng th tip tc chy c.  Nhn chung, ti thi im
, thit b  t ti trng thi phn trang b nh, v th vic tt b mt s tin trnh tin cnh l
bt buc  m bo giao din ngi dng c phn hi.</p></li>

  <li><b>Tin trnh hin th</b>
    <p>Mt tin trnh m khng c bt k thnh phn tin cnh no, nhng vn c th
      nh hng ti ni dung m ngi dng nhn thy trn mn hnh. Mt tin trnh c coi l hin th nu mt trong hai
      iu kin sau l ng:</p>

      <ul>
        <li>N lu tr mt {@link android.app.Activity} m khng nm trong tin cnh, nhng vn
hin th vi ngi dng (phng php {@link android.app.Activity#onPause onPause()} ca n  c gi). 
iu ny c th xy ra, v d, nu hot ng tin cnh  bt u mt hp thoi, n cho php
hot ng trc c nhn thy pha sau n.</li>

        <li>N lu tr mt {@link android.app.Service} c gn kt vi mt hot ng
hin th (hoc tin cnh).</li>
      </ul>

      <p>Mt tin trnh tin cnh c coi l cc k quan trng v s khng b tt b tr khi lm vy
l bt buc  gi cho tt c tin trnh tin cnh chy. </p>
    </li>

  <li><b>Tin trnh dch v</b>
    <p>Mt tin trnh m ang chy mt dch v  c bt u bng phng php {@link
android.content.Context#startService startService()} v khng ri vo mt trong hai
th loi cao hn. Mc d tin trnh dch v khng trc tip gn vi bt k th g m ngi dng thy, chng
thng ang lm nhng vic m ngi dng quan tm n (chng hn nh pht nhc chy ngm hoc
ti xung d liu trn mng), v th h thng vn gi chng chy tr khi khng c  b nh 
duy tr chng cng vi tt c tin trnh tin cnh v hin th. </p>
  </li>

  <li><b>Tin trnh nn</b>
    <p>Mt tin trnh lu tr mt hot ng m hin ti khng hin th vi ngi dng (phng php
{@link android.app.Activity#onStop onStop()} ca hot ng  c gi). Nhng tin trnh ny khng c tc ng
trc tip ti tri nghim ngi dng, v h thng c th b chng i vo bt c lc no  ly li b nh cho mt
tin trnh tin cnh,
hin th hoc dch v. Thng th c nhiu tin trnh ngm ang chy, v th chng c gi
trong mt danh sch LRU (t s dng gn y nht)  m bo rng tin trnh vi hot ng
m ngi dng nhn thy gn y nht l tin trnh cui cng s b tt b. Nu mt hot ng trin khai cc phng php vng i ca n
ng cch, v lu trng thi hin ti ca n, vic tt b tin trnh ca hot ng  s khng c nh hng c th thy c ti
tri nghim ngi dng, v khi ngi dng iu hng li hot ng , hot ng s khi phc
tt c trng thi hin th ca n. Xem ti liu <a href="{@docRoot}guide/components/activities.html#SavingActivityState">Hot ng</a>
 bit thng tin v vic lu v khi phc trng thi.</p>
  </li>

  <li><b>Tin trnh trng</b>
    <p>Mt tin trnh m khng gi bt k thnh phn ng dng hin hot no.  L do duy nht  gi cho
kiu tin trnh ny hot ng  l nhm mc ch lu b nh n,  ci thin thi gian khi ng vo ln ti khi thnh phn
cn chy trong n.  H thng thng tt b nhng tin trnh ny  cn bng ti nguyn tng th
ca h thng gia cc b m n tin trnh v b m n nhn lin quan.</p>
  </li>
</ol>


  <p>Android xp hng mt tin trnh  mc cao nht m n c th, da vo tm quan trng ca
cc thnh phn ang hot ng trong tin trnh .  V d, nu mt tin trnh lu gi mt dch v v hot ng
hin th, tin trnh  s c xp hng l tin trnh hin th ch khng phi tin trnh dch v.</p>

  <p>Ngoi ra, xp hng ca mt tin trnh c th tng bi cc tin trnh khc ph thuc vo
n&mdash;mt tin trnh m ang phc v mt tin trnh khc khng th b xp thp hn tin trnh m n
ang phc v. V d, nu mt trnh cung cp ni dung trong tin trnh A ang phc v mt my khch trong tin trnh B, hoc nu mt
dch v trong tin trnh A c gn kt vi mt thnh phn trong tin trnh B, t nht tin trnh A s lun c coi
l quan trng nh tin trnh B.</p>

  <p>Do mt tin trnh ang chy mt dch v c xp hng cao hn mt tin trnh c cc hot ng nn,
mt hot ng m khi ng mt thao tc nhp gi c th lm tt vic khi ng mt <a href="{@docRoot}guide/components/services.html">dch v</a> cho thao tc , thay v
ch to mt lung trnh thc hin&mdash;nht l khi thao tc  s c th din ra lu hn hot ng.
V d, mt hot ng m ang ti mt nh ln mt trang web nn bt u mt dch v  thc hin
vic ti ln sao cho vic ti ln c th tip tc chy ngm ngay c khi ngi dng ri khi hot ng.
Vic s dng mt dch v s bo m rng thao tc t nht s c mc u tin nh "tin trnh dch v",
khng ph thuc vo iu xy ra vi hot ng. y cng chnh l l do hm nhn qung b nn
s dng dch v thay v ch a cc thao tc tn thi gian vo mt lung.</p>




<h2 id="Threads">Lung</h2>

<p>Khi mt ng dng c khi chy, h thng s to mt lung thc thi cho ng dng,
gi l lung "chnh." Lung ny rt quan trng bi n ph trch phn phi cc s kin ti
nhng widget giao din ngi dng ph hp, bao gm cc s kin v. N cng l lung m
trong  ng dng ca bn tng tc vi cc thnh phn t b cng c UI ca Android (cc thnh phn t cc gi {@link
android.widget} v {@link android.view}). Nh vy, lung chnh i khi cng c gi l
lung UI.</p>

<p>H thng <em>khng</em> to mt lung ring cho tng thc th ca thnh phn. Tt c
thnh phn chy trong cng tin trnh u c khi to trong lung UI, v cc lnh gi ca h thng ti
tng thnh phn c phn phi t lung . H qu l cc phng php hi p li lnh
gi li ca h thng (chng hn nh {@link android.view.View#onKeyDown onKeyDown()}  bo co hnh ng ca ngi dng
hoc mt phng php gi li vng i) s lun chy trong lung UI ca tin trnh.</p>

<p>V d, khi ngi dng chm vo mt nt trn mn hnh, lung UI ca ng dng ca bn s phn phi
s kin chm ti widget, n lt mnh, widget s t trng thi c nhn v ng mt yu cu v hiu ha ti 
hng i s kin. Lung UI loi yu cu khi hng i v thng bo vi widget rng n nn t v li
.</p>

<p>Khi ng dng ca bn thc hin cng vic nng  hi p tng tc ca ngi dng, m hnh lung n nht
ny c th dn n hiu nng km tr khi bn trin khai ng dng ca mnh mt cch ph hp. C th, nu
mi th ang xy ra trong lung UI, vic thc hin nhng thao tc ko di nh truy cp mng hay
truy vn c s d liu s chn ton b UI. Khi lung b chn, khng s kin no c th c phn phi,
bao gm c s kin v. T phng din ca ngi dng, ng dng
c v nh ang b treo. Thm ch t hn, nu lung UI b chn trong lu hn vi giy
(hin ti l khong 5 giy), ngi dng s c hin th hp thoi khng ph bin "<a href="http://developer.android.com/guide/practices/responsiveness.html">ng dng
khng phn hi</a>" (ANR). Khi , ngi dng c th quyt nh thot ng dng ca mnh v g ci t n
nu h khng thoi mi.</p>

<p>Ngoi ra, b cng c UI ca Android <em>khng</em> an ton vi lung. V vy, bn khng c thao tc
UI ca mnh t mt lung trnh thc hin&mdash;bn phi thc hin tt c thao tc i vi giao din ngi dng ca mnh t lung
UI. V vy, c hai quy tc n gin i vi m hnh lung n l ca Android:</p>

<ol>
<li>Khng c chn lung UI
<li>Khng c truy cp b cng c UI ca Android t bn ngoi lung UI
</ol>

<h3 id="WorkerThreads">Lung trnh thc hin</h3>

<p>V m hnh lung n l nu trn, iu thit yu i vi tnh phn hi ca UI
ng dng ca bn  l bn khng c chn lung UI. Nu bn c thao tc cn thc hin
khng mang tnh cht tc thi, bn nn m bo thc hin chng trong cc lung ring (lung chy ngm" hoc
"trnh thc hin").</p>

<p>V d, bn di l mt s m cho mt i tng theo di nhp c chc nng ti xung mt hnh nh t mt lung
ring v hin th n trong mt {@link android.widget.ImageView}:</p>

<pre>
public void onClick(View v) {
    new Thread(new Runnable() {
        public void run() {
            Bitmap b = loadImageFromNetwork("http://example.com/image.png");
            mImageView.setImageBitmap(b);
        }
    }).start();
}
</pre>

<p>Thot u, iu ny c v nh din ra n tha, v n to mt lung mi  x l thao tc
mng. Tuy nhin, n vi phm quy tc th hai ca m hnh lung n nht: <em>khng c truy cp
b cng c UI ca Android t bn ngoi lung UI</em>&mdash;mu ny sa i {@link
android.widget.ImageView} t lung trnh thc hin thay v t lung UI. iu ny c th dn n
hnh vi bt ng, khng c nh ngha m c th gy kh khn v tn thi gian theo di.</p>

<p> sa vn  ny, Android gii thiu mt vi cch  truy cp lung UI t cc lung
khc. Sau y l mt danh sch cc phng php c th tr gip:</p>

<ul>
<li>{@link android.app.Activity#runOnUiThread(java.lang.Runnable)
Activity.runOnUiThread(Runnable)}</li>
<li>{@link android.view.View#post(java.lang.Runnable) View.post(Runnable)}</li>
<li>{@link android.view.View#postDelayed(java.lang.Runnable, long) View.postDelayed(Runnable,
long)}</li>
</ul>

<p>V d, bn c th sa m trn bng cch s dng phng php {@link
android.view.View#post(java.lang.Runnable) View.post(Runnable)}:</p>

<pre>
public void onClick(View v) {
    new Thread(new Runnable() {
        public void run() {
            final Bitmap bitmap = loadImageFromNetwork("http://example.com/image.png");
            mImageView.post(new Runnable() {
                public void run() {
                    mImageView.setImageBitmap(bitmap);
                }
            });
        }
    }).start();
}
</pre>

<p>Gi th trin khai ny  an ton vi lung: thao tc mng c thc hin t mt lung ring
trong khi {@link android.widget.ImageView} c thao tc t lung UI.</p>

<p>Tuy nhin, khi m s phc tp ca thao tc tng ln, kiu m ny c th b phc tp ha v
kh duy tr.  x l nhng tng tc phc tp hn bng mt lung trnh thc hin, bn c th cn nhc
s dng mt {@link android.os.Handler} trong lung trnh thc hin ca mnh,  x l cc th c chuyn t lung
UI. Mc d vy, gii php tt nht l m rng lp {@link android.os.AsyncTask},
iu ny s n gin ha vic thc thi cc tc v ca lung trnh thc hin cn tng tc vi UI.</p>


<h4 id="AsyncTask">S dng AsyncTask</h4>

<p>{@link android.os.AsyncTask} cho php bn thc hin cng vic khng ng b trn giao din
ngi dng ca mnh. N thc hin cc thao tc chn trong mt lung trnh thc hin ri pht hnh kt qu trn
lung UI m khng yu cu bn t x l cc lung v/hoc trnh x l.</p>

<p> s dng n, bn phi to lp con {@link android.os.AsyncTask} v trin khai phng php gi li {@link
android.os.AsyncTask#doInBackground doInBackground()}, phng php ny chy trong mt tp hp
cc lung chy ngm.  cp nht UI ca mnh, bn nn trin khai {@link
android.os.AsyncTask#onPostExecute onPostExecute()}, n s mang li kt qu t {@link
android.os.AsyncTask#doInBackground doInBackground()} v chy trong lung UI, v th bn c th nng cp
UI ca mnh mt cch an ton. Sau , bn c th chy tc v bng cch gi {@link android.os.AsyncTask#execute execute()}
t lung UI.</p>

<p>V d, bn c th trin khai v d trc bng cch s dng {@link android.os.AsyncTask} theo
cch ny:</p>

<pre>
public void onClick(View v) {
    new DownloadImageTask().execute("http://example.com/image.png");
}

private class DownloadImageTask extends AsyncTask&lt;String, Void, Bitmap&gt; {
    /** The system calls this to perform work in a worker thread and
      * delivers it the parameters given to AsyncTask.execute() */
    protected Bitmap doInBackground(String... urls) {
        return loadImageFromNetwork(urls[0]);
    }
    
    /** The system calls this to perform work in the UI thread and delivers
      * the result from doInBackground() */
    protected void onPostExecute(Bitmap result) {
        mImageView.setImageBitmap(result);
    }
}
</pre>

<p>Lc ny, UI an ton v m n gin hn, v n tch ring cng vic thnh
phn s c thc hin trn mt lung trnh thc hin v phn s c thc hin trn lung UI.</p>

<p>Bn nn c ti liu tham kho {@link android.os.AsyncTask} hiu y  v
cch s dng lp ny, nhng sau y l phn trnh by tng quan nhanh v hot ng ca n:</p>

<ul>
<li>Bn c th quy nh loi tham s, cc gi tr tin , v gi tr
cui cng ca tc v, bng cch s dng cc kiu chung</li>
<li>Phng php {@link android.os.AsyncTask#doInBackground doInBackground()} s t ng thc thi
trn mt lung trnh thc hin</li>
<li>{@link android.os.AsyncTask#onPreExecute onPreExecute()}, {@link
android.os.AsyncTask#onPostExecute onPostExecute()}, v {@link
android.os.AsyncTask#onProgressUpdate onProgressUpdate()} u c gi ra trn lung UI</li>
<li>Gi tr c tr v bi {@link android.os.AsyncTask#doInBackground doInBackground()} c gi ti
{@link android.os.AsyncTask#onPostExecute onPostExecute()}</li>
<li>Bn c th gi {@link android.os.AsyncTask#publishProgress publishProgress()} vo bt c lc no trong {@link
android.os.AsyncTask#doInBackground doInBackground()}  thc thi {@link
android.os.AsyncTask#onProgressUpdate onProgressUpdate()} trn lung UI</li>
<li>Bn c th hy b tc v vo bt c lc no t bt k lung no</li>
</ul>

<p class="caution"><strong>Ch :</strong> Mt vn  khc m bn c th gp phi khi s dng mt lung
trnh thc hin  l nhng ln khi ng li bt ng trong hot ng ca bn do mt <a href="{@docRoot}guide/topics/resources/runtime-changes.html">thay i trong cu hnh thi gian chy</a>
(chng hn nh khi ngi dng thay i hng mn hnh), iu ny c th lm hng lung trnh thc hin ca bn. 
xem cch bn c th duy tr tc v ca mnh khi din ra mt trong nhng ln khi ng li ny v cch hy b tc v cho ph hp
khi hot ng b hy, hy xem m ngun cho ng dng mu <a href="http://code.google.com/p/shelves/">Shelves</a>.</p>


<h3 id="ThreadSafe">Phng php an ton vi lung</h3>

<p> Trong mt s tnh hung, cc phng php bn trin khai c th c gi ra t nhiu hn mt lung, v v th
phi c ghi sao cho an ton vi lung. </p>

<p>iu ny ch yu ng vi cc phng php m c th c gi t xa&mdash;chng hn nh cc phng php trong mt <a href="{@docRoot}guide/components/bound-services.html">dch v gn kt</a>. Khi mt lnh gi trn mt
phng php c trin khai trong mt {@link android.os.IBinder} khi u trong cng tin trnh m
{@link android.os.IBinder IBinder} ang chy, phng php  s c thc thi trong lung ca hm gi.
Tuy nhin, khi lnh gi khi u trong mt tin trnh khc, phng php s c thc thi trong mt lung c chn t
mt tp hp cc lung m h thng duy tr trong cng tin trnh nh {@link android.os.IBinder
IBinder} (n khng c thc thi trong lung UI ca tin trnh).  V d, trong khi phng php
{@link android.app.Service#onBind onBind()} ca dch v s c gi t lung UI ca tin trnh
ca dch v, cc phng php c trin khai trong i tng m {@link android.app.Service#onBind
onBind()} tr v (v d, mt lp con trin khai cc phng php RPC) s c gi t cc lung
trong tp hp. V mt dch v c th c nhiu hn mt my khch, nhiu hn mt lung tp hp c th s dng
cng mt phng php {@link android.os.IBinder IBinder} ti cng mt thi im.  V th, cc phng php {@link android.os.IBinder
IBinder} phi c trin khai sao cho an ton vi lung.</p>

<p> Tng t, mt trnh cung cp ni dung c th nhn cc yu cu d liu khi ngun trong cc tin trnh khc.
Mc d cc lp {@link android.content.ContentResolver} v {@link android.content.ContentProvider}
n i chi tit v cch truyn thng lin tin trnh c qun l, cc phng php {@link
android.content.ContentProvider} hi p nhng yu cu &mdash;cc phng php {@link
android.content.ContentProvider#query query()}, {@link android.content.ContentProvider#insert
insert()}, {@link android.content.ContentProvider#delete delete()}, {@link
android.content.ContentProvider#update update()}, v {@link android.content.ContentProvider#getType
getType()}&mdash;c gi t mt tp hp lung trong tin trnh ca trnh cung cp ni dung, ch khng phi lung
UI cho tin trnh .  V nhng phng php ny c th c gi t bt k s lng lung no ti
cng thi im, chng cng phi c trin khai sao cho an ton vi lung. </p>


<h2 id="IPC">Truyn thng Lin Tin trnh</h2>

<p>Android cung cp mt c ch cho truyn thng lin tin trnh (IPC) bng cch s dng cc lnh gi th tc t xa
(RPC), trong  mt phng php c gi bi mt hot ng hoc thnh phn ng dng khc, nhng c thc thi
t xa (trong mt tin trnh khc), vi bt k kt qu no c tr v
hm gi. iu ny i hi vic phn tch mt lnh gi phng php v d liu ca n v cp  m h iu hnh
c th hiu c, truyn pht n t tin trnh v khong trng a ch cc b n tin trnh v
khong trng a ch t xa, sau  t hp li v pht hnh li lnh gi  .  Sau , cc gi tr tr v c
pht theo hng ngc li.  Android cung cp tt c m  thc hin nhng giao tc
IPC ny, v th bn c th tp trung vo vic nh ngha v trin khai giao din lp trnh RPC. </p>

<p> thc hin IPC, ng dng ca bn phi lin kt vi mt dch v, bng cch s dng {@link
android.content.Context#bindService bindService()}.  bit thm thng tin, hy xem hng dn cho nh pht trin <a href="{@docRoot}guide/components/services.html">Dch v</a>.</p>


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<h2>Beginner's Path</h2>

<p>For information about how to perform work in the background for an indefinite period of time
(without a user interface), continue with the <b><a
href="{@docRoot}guide/components/services.html">Services</a></b> document.</p>
-->