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Merge change I2c5380a6 into eclair-mr2

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* changes:
  Fix a bug in the Settings contract class (introduced in an ... iffy ... fix to a race condition) that breaks the caching of non-existent Settings/Secure/ Gservices values (causing lots of unnecessary database queries).
This commit is contained in:
Android (Google) Code Review
2009-11-24 17:25:37 -08:00
parent df7edf5d92 799f721fcb
commit ee6c7e491b
2 changed files with 48 additions and 47 deletions
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2
core/java/android/database/sqlite/SQLiteDatabase.java
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@@ -1897,7 +1897,7 @@ public class SQLiteDatabase extends SQLiteClosable {
samplePercent = 100;
} else {
samplePercent = (int) (100 * nanos / QUERY_LOG_TIME_IN_NANOS) + 1;
if (mRandom.nextInt(100) < samplePercent) return;
if (mRandom.nextInt(100) >= samplePercent) return;
}
if (sql.length() > QUERY_LOG_SQL_LENGTH) sql = sql.substring(0, QUERY_LOG_SQL_LENGTH);

93
core/java/android/provider/Settings.java
View File

@@ -38,6 +38,7 @@ import android.os.*;
import android.telephony.TelephonyManager;
import android.text.TextUtils;
import android.util.AndroidException;
import android.util.Config;
import android.util.Log;
import java.net.URISyntaxException;
@@ -442,6 +443,7 @@ public final class Settings {
public static final String AUTHORITY = "settings";
private static final String TAG = "Settings";
private static final boolean LOCAL_LOGV = Config.LOGV || false;
public static class SettingNotFoundException extends AndroidException {
public SettingNotFoundException(String msg) {
@@ -478,61 +480,60 @@ public final class Settings {
private static class NameValueCache {
private final String mVersionSystemProperty;
// the following needs synchronization because this structure is accessed from different
// threads and they could be performing clear(), get(), put() at the same time.
private final Map<String, String> mValues =
Collections.synchronizedMap(new HashMap<String, String>());
private long mValuesVersion = 0;
private final Uri mUri;
NameValueCache(String versionSystemProperty, Uri uri) {
// Must synchronize(mValues) to access mValues and mValuesVersion.
private final HashMap<String, String> mValues = new HashMap<String, String>();
private long mValuesVersion = 0;
public NameValueCache(String versionSystemProperty, Uri uri) {
mVersionSystemProperty = versionSystemProperty;
mUri = uri;
}
String getString(ContentResolver cr, String name) {
public String getString(ContentResolver cr, String name) {
long newValuesVersion = SystemProperties.getLong(mVersionSystemProperty, 0);
if (mValuesVersion != newValuesVersion) {
mValues.clear();
mValuesVersion = newValuesVersion;
}
/*
* don't look for the key using containsKey() method because (key, object) mapping
* could be removed from mValues before get() is done like so:
*
* say, mValues contains mapping for "foo"
* Thread# 1
* performs containsKey("foo")
* receives true
* Thread #2
* triggers mValues.clear()
* Thread#1
* since containsKey("foo") = true, performs get("foo")
* receives null
* thats incorrect!
*
* to avoid the above, thread#1 should do get("foo") instead of containsKey("foo")
* since mValues is synchronized, get() will get a consistent value.
*
* we don't want to make this method synchronized tho - because
* holding mutex is not desirable while a call could be made to database.
*/
String value = mValues.get(name);
if (value == null) {
Cursor c = null;
try {
c = cr.query(mUri, new String[] { Settings.NameValueTable.VALUE },
Settings.NameValueTable.NAME + "=?", new String[]{name}, null);
if (c != null && c.moveToNext()) value = c.getString(0);
mValues.put(name, value);
} catch (SQLException e) {
// SQL error: return null, but don't cache it.
Log.w(TAG, "Can't get key " + name + " from " + mUri, e);
} finally {
if (c != null) c.close();
synchronized (mValues) {
if (mValuesVersion != newValuesVersion) {
if (LOCAL_LOGV) {
Log.v(TAG, "invalidate [" + mUri.getLastPathSegment() + "]: current " +
newValuesVersion + " != cached " + mValuesVersion);
}
mValues.clear();
mValuesVersion = newValuesVersion;
}
if (mValues.containsKey(name)) {
return mValues.get(name); // Could be null, that's OK -- negative caching
}
}
return value;
Cursor c = null;
try {
c = cr.query(mUri, new String[] { Settings.NameValueTable.VALUE },
Settings.NameValueTable.NAME + "=?", new String[]{name}, null);
if (c == null) {
Log.w(TAG, "Can't get key " + name + " from " + mUri);
return null;
}
String value = c.moveToNext() ? c.getString(0) : null;
synchronized (mValues) {
mValues.put(name, value);
}
if (LOCAL_LOGV) {
Log.v(TAG, "cache miss [" + mUri.getLastPathSegment() + "]: " +
name + " = " + (value == null ? "(null)" : value));
}
return value;
} catch (SQLException e) {
Log.w(TAG, "Can't get key " + name + " from " + mUri, e);
return null; // Return null, but don't cache it.
} finally {
if (c != null) c.close();
}
}
}