Android core java source

* Licensed under the Apache License, Version 2.0 (the «License»);

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

* http://www.apache.org/licenses/LICENSE-2.0

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an «AS IS» BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

package android . os ;

import android . annotation . NonNull ;

import android . annotation . Nullable ;

import android . annotation . SystemApi ;

import android . compat . annotation . UnsupportedAppUsage ;

import android . util . Log ;

import android . util . MutableInt ;

import com . android . internal . annotations . GuardedBy ;

import dalvik . annotation . optimization . CriticalNative ;

import dalvik . annotation . optimization . FastNative ;

import libcore . util . HexEncoding ;

import java . nio . charset . StandardCharsets ;

import java . security . MessageDigest ;

import java . security . NoSuchAlgorithmException ;

import java . util . ArrayList ;

import java . util . Arrays ;

import java . util . HashMap ;

/**

* Gives access to the system properties store. The system properties

* store contains a list of string key-value pairs.

Use this class only for the system properties that are local. e.g., within

* an app, a partition, or a module. For system properties used across the

* boundaries, formally define them in *.sysprop files and use the

* auto-generated methods. For more information, see

* «https://source.android.com/devices/architecture/sysprops-apis»>Implementing

* System Properties as APIs.

@SystemApi

public class SystemProperties

private static final String TAG = «SystemProperties» ;

private static final boolean TRACK_KEY_ACCESS = false ;

/**

* Android O removed the property name length limit, but com.amazon.kindle 7.8.1.5

* uses reflection to read this whenever text is selected (http://b/36095274).

* @hide

@UnsupportedAppUsage ( trackingBug = 172649311 )

public static final int PROP_NAME_MAX = Integer . MAX_VALUE ;

/** @hide */

public static final int PROP_VALUE_MAX = 91 ;

@UnsupportedAppUsage

@GuardedBy ( «sChangeCallbacks» )

private static final ArrayList < Runnable >sChangeCallbacks = new ArrayList < Runnable >();

@GuardedBy ( «sRoReads» )

private static final HashMap < String , MutableInt >sRoReads =

TRACK_KEY_ACCESS ? new HashMap <>() : null ;

private static void onKeyAccess ( String key )

if (! TRACK_KEY_ACCESS ) return ;

if ( key != null && key . startsWith ( «ro.» ))

synchronized ( sRoReads )

MutableInt numReads = sRoReads . getOrDefault ( key , null );

if ( numReads == null )

numReads = new MutableInt ( 0 );

sRoReads . put ( key , numReads );

numReads . value ++;

if ( numReads . value > 3 )

Log . d ( TAG , «Repeated read (count=» + numReads . value

+ «) of a read-only system property ‘» + key + «‘» ,

new Exception ());

// The one-argument version of native_get used to be a regular native function. Nowadays,

// we use the two-argument form of native_get all the time, but we can’t just delete the

// one-argument overload: apps use it via reflection, as the UnsupportedAppUsage annotation

// indicates. Let’s just live with having a Java function with a very unusual name.

@UnsupportedAppUsage

private static String native_get ( String key )

return native_get ( key , «» );

@FastNative

@UnsupportedAppUsage ( maxTargetSdk = Build . VERSION_CODES . P )

private static native String native_get ( String key , String def );

@FastNative

@UnsupportedAppUsage ( maxTargetSdk = Build . VERSION_CODES . P )

private static native int native_get_int ( String key , int def );

@FastNative

@UnsupportedAppUsage

private static native long native_get_long ( String key , long def );

@FastNative

@UnsupportedAppUsage ( maxTargetSdk = Build . VERSION_CODES . P )

private static native boolean native_get_boolean ( String key , boolean def );

@FastNative

private static native long native_find ( String name );

@FastNative

private static native String native_get ( long handle );

@CriticalNative

private static native int native_get_int ( long handle , int def );

@CriticalNative

private static native long native_get_long ( long handle , long def );

@CriticalNative

private static native boolean native_get_boolean ( long handle , boolean def );

// _NOT_ FastNative: native_set performs IPC and can block

@UnsupportedAppUsage ( maxTargetSdk = Build . VERSION_CODES . P )

private static native void native_set ( String key , String def );

@UnsupportedAppUsage ( maxTargetSdk = Build . VERSION_CODES . P )

private static native void native_add_change_callback ();

private static native void native_report_sysprop_change ();

/**

* Get the String value for the given .

* @param key the key to lookup

* @return an empty string if the isn’t found

* @hide

@NonNull

@SystemApi

public static String get ( @NonNull String key )

if ( TRACK_KEY_ACCESS ) onKeyAccess ( key );

return native_get ( key );

/**

* Get the String value for the given .

* @param key the key to lookup

* @param def the default value in case the property is not set or empty

* @return if the isn’t found, return if it isn’t null, or an empty

* string otherwise

* @hide

@NonNull

@SystemApi

public static String get ( @NonNull String key , @Nullable String def )

if ( TRACK_KEY_ACCESS ) onKeyAccess ( key );

return native_get ( key , def );

/**

* Get the value for the given , and return as an integer.

* @param key the key to lookup

* @param def a default value to return

* @return the key parsed as an integer, or def if the key isn’t found or

* cannot be parsed

* @hide

@SystemApi

public static int getInt ( @NonNull String key , int def )

if ( TRACK_KEY_ACCESS ) onKeyAccess ( key );

return native_get_int ( key , def );

/**

* Get the value for the given , and return as a long.

* @param key the key to lookup

* @param def a default value to return

* @return the key parsed as a long, or def if the key isn’t found or

* cannot be parsed

* @hide

@SystemApi

public static long getLong ( @NonNull String key , long def )

if ( TRACK_KEY_ACCESS ) onKeyAccess ( key );

return native_get_long ( key , def );

/**

* Get the value for the given , returned as a boolean.

* Values ‘n’, ‘no’, ‘0’, ‘false’ or ‘off’ are considered false.

* Values ‘y’, ‘yes’, ‘1’, ‘true’ or ‘on’ are considered true.

* (case sensitive).

* If the key does not exist, or has any other value, then the default

* result is returned.

* @param key the key to lookup

* @param def a default value to return

* @return the key parsed as a boolean, or def if the key isn’t found or is

* not able to be parsed as a boolean.

* @hide

@SystemApi

public static boolean getBoolean ( @NonNull String key , boolean def )

if ( TRACK_KEY_ACCESS ) onKeyAccess ( key );

return native_get_boolean ( key , def );

/**

* Set the value for the given to .

* @throws IllegalArgumentException for non read-only properties if the exceeds

* 91 characters

* @throws RuntimeException if the property cannot be set, for example, if it was blocked by

* SELinux. libc will log the underlying reason.

* @hide

@UnsupportedAppUsage

public static void set ( @NonNull String key , @Nullable String val )

if ( val != null && ! key . startsWith ( «ro.» ) && val . getBytes ( StandardCharsets . UTF_8 ). length

> PROP_VALUE_MAX )

throw new IllegalArgumentException ( «value of system property ‘» + key

+ «‘ is longer than » + PROP_VALUE_MAX + » bytes: » + val );

if ( TRACK_KEY_ACCESS ) onKeyAccess ( key );

native_set ( key , val );

/**

* Add a callback that will be run whenever any system property changes.

* @param callback The that should be executed when a system property

* changes.

* @hide

@UnsupportedAppUsage

public static void addChangeCallback ( @NonNull Runnable callback )

synchronized ( sChangeCallbacks )

if ( sChangeCallbacks . size () == 0 )

native_add_change_callback ();

sChangeCallbacks . add ( callback );

/**

* Remove the target callback.

* @param callback The that should be removed.

* @hide

@UnsupportedAppUsage ( maxTargetSdk = Build . VERSION_CODES . R , trackingBug = 170729553 )

public static void removeChangeCallback ( @NonNull Runnable callback )

synchronized ( sChangeCallbacks )

if ( sChangeCallbacks . contains ( callback ))

sChangeCallbacks . remove ( callback );

@SuppressWarnings ( «unused» ) // Called from native code.

private static void callChangeCallbacks ()

ArrayList < Runnable >callbacks = null ;

synchronized ( sChangeCallbacks )

//Log.i(«foo», «Calling » + sChangeCallbacks.size() + » change callbacks!»);

if ( sChangeCallbacks . size () == 0 )

return ;

callbacks = new ArrayList < Runnable >( sChangeCallbacks );

final long token = Binder . clearCallingIdentity ();

try

for ( int i = 0 ; i < callbacks . size (); i ++)

try

callbacks . get ( i ). run ();

> catch ( Throwable t )

// Ignore and try to go on. Don’t use wtf here: that

// will cause the process to exit on some builds and break tests.

Log . e ( TAG , «Exception in SystemProperties change callback» , t );

> finally

Binder . restoreCallingIdentity ( token );

/**

* Notifies listeners that a system property has changed

* @hide

@UnsupportedAppUsage

public static void reportSyspropChanged ()

native_report_sysprop_change ();

/**

* Return a digest of the given keys and their values as a

* hex-encoded string. The ordering of the incoming keys doesn’t change the

* digest result.

* @hide

public static @NonNull String digestOf ( @NonNull String . keys )

Arrays . sort ( keys );

try

final MessageDigest digest = MessageDigest . getInstance ( «SHA-1» );

for ( String key : keys )

final String item = key + «=» + get ( key ) + «\n» ;

digest . update ( item . getBytes ( StandardCharsets . UTF_8 ));

return HexEncoding . encodeToString ( digest . digest ()). toLowerCase ();

> catch ( NoSuchAlgorithmException e )

throw new RuntimeException ( e );

@UnsupportedAppUsage

private SystemProperties ()

/**

* Look up a property location by name.

* @name name of the property

* @return property handle or if property isn’t set

* @hide

@Nullable public static Handle find ( @NonNull String name )

long nativeHandle = native_find ( name );

if ( nativeHandle == 0 )

return null ;

return new Handle ( nativeHandle );

/**

* Handle to a pre-located property. Looking up a property handle in advance allows

* for optimal repeated lookup of a single property.

* @hide

public static final class Handle

private final long mNativeHandle ;

/**

* @return Value of the property

@NonNull public String get ()

return native_get ( mNativeHandle );

/**

* @param def default value

* @return value or on parse error

public int getInt ( int def )

return native_get_int ( mNativeHandle , def );

/**

* @param def default value

* @return value or on parse error

public long getLong ( long def )

return native_get_long ( mNativeHandle , def );

/**

* @param def default value

* @return value or on parse error

public boolean getBoolean ( boolean def )

return native_get_boolean ( mNativeHandle , def );

private Handle ( long nativeHandle )

mNativeHandle = nativeHandle ;

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