SQLiteDatabase close() 函数在多线程时导致 NullPointerException [英] SQLiteDatabase close() function causing NullPointerException when multiple threads
问题描述
我在我的项目中发现,Android 上 SQLiteDatabase 实现中的 close() 函数在运行打开数据库、插入数据然后关闭数据库的多个线程时抛出 NullPointerException.除非我允许每个线程在插入数据库后关闭(),否则一切都运行顺利.
I discovered in my project that the close() function in the SQLiteDatabase implementation on Android throws a NullPointerException when running multiple threads that open the database, insert data, and then close the database. Everything runs smoothly unless I allow each thread to close() after inserting into the database.
这是其中一个写作线程的示例
Here is an example of what one of the writing threads might look like
ContentValues values = new ContentValues();
values.put(CallDetailsStorageConstants.COLUMN_NAME_REMOTE_NAME_IDX, (String) "");
values.put(CallDetailsStorageConstants.COLUMN_NAME_REMOTE_MEETINGID_IDX, (String) "");
CalculonDatabase callDetailsOpenHelper = CalculonDatabase.getInstance(mContext);
SQLiteDatabase dbw = callDetailsOpenHelper.getWritableDatabase();
long rowid = 0;
try {
rowid = dbw.insertWithOnConflict(CallDetailsTable.CALL_DETAILS_TABLE_NAME, null, values, SQLiteDatabase.CONFLICT_REPLACE);
} catch (SQLiteConstraintException e) {
e.printStackTrace();
} finally {
dbw.close();
}
你可以看到最后调用了 close() .运行多个线程时,我收到此异常.
You can see that at the end a call to close() is made. When running multiple threads I get this exception.
11-03 03:39:26.128: E/AndroidRuntime(977): FATAL EXCEPTION: Thread-17
11-03 03:39:26.128: E/AndroidRuntime(977): java.lang.NullPointerException
11-03 03:39:26.128: E/AndroidRuntime(977): at android.database.sqlite.SQLiteStatement.releaseAndUnlock(SQLiteStatement.java:283)
11-03 03:39:26.128: E/AndroidRuntime(977): at android.database.sqlite.SQLiteStatement.executeUpdateDelete(SQLiteStatement.java:96)
11-03 03:39:26.128: E/AndroidRuntime(977): at android.database.sqlite.SQLiteDatabase.executeSql(SQLiteDatabase.java:1933)
11-03 03:39:26.128: E/AndroidRuntime(977): at android.database.sqlite.SQLiteDatabase.execSQL(SQLiteDatabase.java:1864)
11-03 03:39:26.128: E/AndroidRuntime(977): at android.database.sqlite.SQLiteDatabase.beginTransaction(SQLiteDatabase.java:636)
11-03 03:39:26.128: E/AndroidRuntime(977): at android.database.sqlite.SQLiteDatabase.beginTransactionNonExclusive(SQLiteDatabase.java:551)
11-03 03:39:26.128: E/AndroidRuntime(977): at android.database.sqlite.SQLiteStatement.acquireAndLock(SQLiteStatement.java:240)
11-03 03:39:26.128: E/AndroidRuntime(977): at android.database.sqlite.SQLiteStatement.executeInsert(SQLiteStatement.java:111)
11-03 03:39:26.128: E/AndroidRuntime(977): at android.database.sqlite.SQLiteDatabase.insertWithOnConflict(SQLiteDatabase.java:1737)
11-03 03:39:26.128: E/AndroidRuntime(977): at com.smash.DBWritingThread.run(DBWritingThread.java:50)
我的问题是为什么只有在使用 close() 函数时才会发生此错误?另外,是否可以在更晚的时间使用 close() 或可能永远不会使用?
My question then is why does this error happen only when using the close() function? Also, is it ok to use close() at a much later time or possibly never?
非常感谢有关此问题的任何提示.
Any tips with this issue are very much appreciated.
推荐答案
我有你的答案!
永远不要关闭数据库.就是这么简单.
Never close the db. It is that simple.
确保每个应用程序只有一个,重复,*一个 Helper 实例.与所有线程共享.
Make sure you only have one, repeat, *one Helper instance per application. Share it with all threads.
http://www.touchlab.co/blog/single-sqlite-connection/
这里有一些关于 sqlite 和锁定内部结构的更多信息:
Here's some more info on the internals of sqlite and locking:
http://www.touchlab.co/blog/android-sqlite-locking/
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