一、什么ContentProvider
二、如何使用ContentProvider
三、沙场练兵-实例操练
四、深入理解ContentProvider原理
为什么使用ContentProvider可以实现跨进程的通讯，第一反应肯定是这货和binder有关，因为android中只有稍微跟跨进程搭上边的，必定想到binder。
下面就来分析ContentProvider是怎么一步一步利用binder实现跨进程通信的：
1、首先你得创建一个ContentProvider运行在进程A,如上篇博客
AndroidManifest.xml中定义provider：
<provider
android:name=".MyContentProvider"
android:authorities="telefk"//这个很重要，Uri中的主机名，查询数据就靠它
android:enabled="true"
android:exported="true">
</provider>
2、进程B中通过如下接口来访问进程A的数据：
getContentResolver().query(uri,columns,null,null,null);
getContentResolver（）实际调用的ContextImpl.java的方法返回mContentResolver对象
此对象在ContextImpl的构造方法中实例化
mContentResolver = new ApplicationContentResolver(this, mainThread, user);
现在来看query方法，其在ContentResolver.java中定义：
public final @Nullable Cursor query(final @NonNull Uri uri, @Nullable String[] projection,
@Nullable String selection, @Nullable String[] selectionArgs,
@Nullable String sortOrder, @Nullable CancellationSignal cancellationSignal) {
Preconditions.checkNotNull(uri, "uri");
IContentProvider unstableProvider = acquireUnstableProvider(uri);//这个函数很关键，通过指定的Uri找到我们刚刚定义的provider
if (unstableProvider == null) {
return null;
}
IContentProvider stableProvider = null;
......
接下来看acquireUnstableProvider()函数：
百转千回，最终走到了刚刚返回的ApplicationContentResolver.java中
@Override
protected IContentProvider acquireUnstableProvider(Context c, String auth) {
return mMainThread.acquireProvider(c,
ContentProvider.getAuthorityWithoutUserId(auth),
resolveUserIdFromAuthority(auth), false);
}
这里又调用了ActivityThread.java 的acquireProvider()方法，我们继续往下跟：
public final IContentProvider acquireProvider(
Context c, String auth, int userId, boolean stable) {
final IContentProvider provider = acquireExistingProvider(c, auth, userId, stable);//刚开始这里很定为空
if (provider != null) {
return provider;
}
// There is a possible race here. Another thread may try to acquire
// the same provider at the same time. When this happens, we want to ensure
// that the first one wins.
// Note that we cannot hold the lock while acquiring and installing the
// provider since it might take a long time to run and it could also potentially
// be re-entrant in the case where the provider is in the same process.
IActivityManager.ContentProviderHolder holder = null;
try {
holder = ActivityManagerNative.getDefault().getContentProvider(
getApplicationThread(), auth, userId, stable);//很关键，请注意这里跨进程调到ActivityManagerService.java的方法
} catch (RemoteException ex) {
}
if (holder == null) {
Slog.e(TAG, "Failed to find provider info for " + auth);
return null;
}
// Install provider will increment the reference count for us, and break
// any ties in the race.
holder = installProvider(c, holder, holder.info,
true /*noisy*/, holder.noReleaseNeeded, stable);
return holder.provider;
}
我们继续来看ActivityManagerService.java 的getContentProvider()方法:
@Override
public final ContentProviderHolder getContentProvider(
IApplicationThread caller, String name, int userId, boolean stable) {
enforceNotIsolatedCaller("getContentProvider");
if (caller == null) {
String msg = "null IApplicationThread when getting content provider "
+ name;
Slog.w(TAG, msg);
throw new SecurityException(msg);
}
// The incoming user check is now handled in checkContentProviderPermissionLocked() to deal
// with cross-user grant.
return getContentProviderImpl(caller, name, null, stable, userId);
}
肾呐～还没到头！又继续往下走，大家继续坚持：
//这个方法很长，我们挑选重点的分析，方法第二个参数name就是我们刚刚query传进来的uir的authorityprivate final ContentProviderHolder getContentProviderImpl(IApplicationThread caller,
String name, IBinder token, boolean stable, int userId) {
ContentProviderRecord cpr;//AMS中用来记录provider的，还有其他三大组件AcitityRecord、ServiceRecord、BroadcastRecord
ContentProviderConnection conn = null;
ProviderInfo cpi = null;//这个应该是PMS解析应用的AndroidManifest得来的信息 ......
// First check if this content provider has been published...
cpr = mProviderMap.getProviderByName(name, userId);
......
如果发现对应的provider 已经运行，这个我们之后再分析，先分析没有运行的情况：
boolean providerRunning = cpr != null;
if (providerRunning) {
cpi = cpr.info;
String msg;
checkTime(startTime, "getContentProviderImpl: before checkContentProviderPermission");
if ((msg = checkContentProviderPermissionLocked(cpi, r, userId, checkCrossUser))
!= null) {
throw new SecurityException(msg);
}
checkTime(startTime, "getContentProviderImpl: after checkContentProviderPermission");
if (r != null && cpr.canRunHere(r)) {
// This provider has been published or is in the process
// of being published... but it is also allowed to run
// in the caller‘s process, so don‘t make a connection
// and just let the caller instantiate its own instance.
ContentProviderHolder holder = cpr.newHolder(null);
// don‘t give caller the provider object, it needs
// to make its own.
holder.provider = null;
return holder;
}
final long origId = Binder.clearCallingIdentity();
checkTime(startTime, "getContentProviderImpl: incProviderCountLocked");
// In this case the provider instance already exists, so we can
// return it right away.
conn = incProviderCountLocked(r, cpr, token, stable);
if (conn != null && (conn.stableCount+conn.unstableCount) == 1) {
if (cpr.proc != null && r.setAdj <= ProcessList.PERCEPTIBLE_APP_ADJ) {
// If this is a perceptible app accessing the provider,
// make sure to count it as being accessed and thus
// back up on the LRU list. This is good because
// content providers are often expensive to start.
checkTime(startTime, "getContentProviderImpl: before updateLruProcess");
updateLruProcessLocked(cpr.proc, false, null);
checkTime(startTime, "getContentProviderImpl: after updateLruProcess");
}
}
if (cpr.proc != null) {
if (false) {
if (cpr.name.flattenToShortString().equals(
"com.android.providers.calendar/.CalendarProvider2")) {
Slog.v(TAG, "****************** KILLING "
+ cpr.name.flattenToShortString());
Process.killProcess(cpr.proc.pid);
}
}
checkTime(startTime, "getContentProviderImpl: before updateOomAdj");
boolean success = updateOomAdjLocked(cpr.proc);
maybeUpdateProviderUsageStatsLocked(r, cpr.info.packageName, name);
checkTime(startTime, "getContentProviderImpl: after updateOomAdj");
if (DEBUG_PROVIDER) Slog.i(TAG_PROVIDER, "Adjust success: " + success);
// NOTE: there is still a race here where a signal could be
// pending on the process even though we managed to update its
// adj level. Not sure what to do about this, but at least
// the race is now smaller.
if (!success) {
// Uh oh... it looks like the provider‘s process
// has been killed on us. We need to wait for a new
// process to be started, and make sure its death
// doesn‘t kill our process.
Slog.i(TAG, "Existing provider " + cpr.name.flattenToShortString()
+ " is crashing; detaching " + r);
boolean lastRef = decProviderCountLocked(conn, cpr, token, stable);
checkTime(startTime, "getContentProviderImpl: before appDied");
appDiedLocked(cpr.proc);
checkTime(startTime, "getContentProviderImpl: after appDied");
if (!lastRef) {
// This wasn‘t the last ref our process had on
// the provider... we have now been killed, bail.
return null;
}
providerRunning = false;
conn = null;
}
}
Binder.restoreCallingIdentity(origId);
}
if (!providerRunning) {
try {
checkTime(startTime, "getContentProviderImpl: before resolveContentProvider");
cpi = AppGlobals.getPackageManager().
resolveContentProvider(name,
STOCK_PM_FLAGS | PackageManager.GET_URI_PERMISSION_PATTERNS, userId);
checkTime(startTime, "getContentProviderImpl: after resolveContentProvider");
} catch (RemoteException ex) {
}
if (cpi == null) {
return null;
}
// If the provider is a singleton AND
// (it‘s a call within the same user || the provider is a
// privileged app)
// Then allow connecting to the singleton provider
singleton = isSingleton(cpi.processName, cpi.applicationInfo,
cpi.name, cpi.flags)
&& isValidSingletonCall(r.uid, cpi.applicationInfo.uid);
if (singleton) {
userId = UserHandle.USER_OWNER;
}
cpi.applicationInfo = getAppInfoForUser(cpi.applicationInfo, userId);
checkTime(startTime, "getContentProviderImpl: got app info for user");
String msg;
checkTime(startTime, "getContentProviderImpl: before checkContentProviderPermission");
if ((msg = checkContentProviderPermissionLocked(cpi, r, userId, !singleton))
!= null) {
throw new SecurityException(msg);
}
checkTime(startTime, "getContentProviderImpl: after checkContentProviderPermission");
if (!mProcessesReady && !mDidUpdate && !mWaitingUpdate
&& !cpi.processName.equals("system")) {
// If this content provider does not run in the system
// process, and the system is not yet ready to run other
// processes, then fail fast instead of hanging.
throw new IllegalArgumentException(
"Attempt to launch content provider before system ready");
}
// Make sure that the user who owns this provider is running. If not,
// we don‘t want to allow it to run.
if (!isUserRunningLocked(userId, false)) {
Slog.w(TAG, "Unable to launch app "
+ cpi.applicationInfo.packageName + "/"
+ cpi.applicationInfo.uid + " for provider "
+ name + ": user " + userId + " is stopped");
return null;
}
ComponentName comp = new ComponentName(cpi.packageName, cpi.name);
checkTime(startTime, "getContentProviderImpl: before getProviderByClass");
cpr = mProviderMap.getProviderByClass(comp, userId);
checkTime(startTime, "getContentProviderImpl: after getProviderByClass");
final boolean firstClass = cpr == null;
if (firstClass) {
final long ident = Binder.clearCallingIdentity();
try {
checkTime(startTime, "getContentProviderImpl: before getApplicationInfo");
ApplicationInfo ai =
AppGlobals.getPackageManager().
getApplicationInfo(
cpi.applicationInfo.packageName,
STOCK_PM_FLAGS, userId);
checkTime(startTime, "getContentProviderImpl: after getApplicationInfo");
if (ai == null) {
Slog.w(TAG, "No package info for content provider "
+ cpi.name);
return null;
}
ai = getAppInfoForUser(ai, userId);
cpr = new ContentProviderRecord(this, cpi, ai, comp, singleton);//很关键的，首先创建cpr,然后再启动目标进程
时间： 2024-08-06 11:56:18