Android的 - SQLite的+共享preferences，2线程同时进行读/写？ [英] Android -- SQLite + SharedPreferences, 2 Threads Simultaneous Read/Write?

问题描述

我有一个程序（实际的应用程序和一个BroadcastReceiver）可能可能尝试连接到和修改SQLite数据库和共享preferences文件的两个部分。

1）我知道你可以建立多个连接到一个SQLite数据库。我也读了SQLite的可以锁定的数据库，当它试图修改或从数据库（UPDATE，INSERT，等等）读，让我怎么妥善处理，其中2个线程试图修改的情况下，在/读取单个SQLite数据库同一时间？

现在，我有这个code片段在我的数据库连接code /等级：

 私人SQLiteDatabase MyDatabase的;
公共布尔插入（ContentValues​​ columnValueMap）抛出异常
    {
        长期结果为0;
        INT企图= 0;
        做
        {
            如果（myDatabase.isDbLockedByOtherThreads（）及！＆安培;！myDa​​tabase.isDbLockedByCurrentThread（））
            {
                同步（MyDatabase的）
                {
                    结果= myDatabase.insertOrThrow（TABLE_NAME，TEXT，columnValueMap）;
                    如果（结果== 0 ||结果== -1）
                    {
                        返回false;
                    }
                    返回true;
                }
            }
            其他
            {
                视频下载（50）;
            }
            尝试++;
        }而（尝试＆LT; = 5）;

        抛出新的异常（数据库被锁定！）;
    }
 

2）我也担心同时访问一个共享preferences文件（不要紧，哪个线程被访问的第一，我只是担心被抛出的错误）？

感谢。

建议更改

 公共布尔插入（ContentValues​​ columnValueMap）抛出异常
    {
        长期结果为0;
        同步（MyDatabase的）
        {
            结果= myDatabase.insertOrThrow（TABLE_NAME，SMS_TEXT，columnValueMap）;

            如果（结果== 0 ||结果== -1）
            {
                返回false;
            }
            返回true;
        }
    }
 

解决方案

首先，数据库已经建成的锁定支持，并且它默认打开。如果你想成为安全，请拨打 SQLiteOpenDatabase.setLockingEnabled（真）。

至于访问共享preferences，我就封装了所有访问共享preferences（读，写），因为全部使用同步的小功能。 （确保它们的原子）。

I have two parts of a program (the actual app and a BroadcastReceiver) that could possibly try to connect to and modify a SQLite database and a SharedPreferences file.

1) I know you can make multiple connections to a single SQLite database. I also read that SQLite can "lock" the database when it attempts to modify or read from a database (UPDATE, INSERT, etc), so how do I properly handle the case where 2 threads try to modify/read a single SQLite database at the same time?

Right now, I have have this code snippet in my database connection code/class:

private SQLiteDatabase myDatabase;
public boolean insert(ContentValues columnValueMap) throws Exception
    {
        long result = 0;
        int attempt =0;
        do
        {
            if(!myDatabase.isDbLockedByOtherThreads() && !myDatabase.isDbLockedByCurrentThread())
            {
                synchronized (myDatabase)
                {
                    result=myDatabase.insertOrThrow(TABLE_NAME, TEXT, columnValueMap);
                    if(result ==0 || result == -1)
                    {
                        return false;
                    }
                    return true;
                }
            }
            else
            {
                Thread.sleep(50);
            }
            attempt++;
        }while(attempt<=5);

        throw new Exception("Database Locked!");
    }

2) Do I also have to worry about simultaneous access for a SharedPreferences file (It doesn't matter which thread gets access first, I'm just worried about errors being thrown)?

Thanks.

[EDIT] Proposed change

public boolean insert(ContentValues columnValueMap) throws Exception
    {
        long result = 0;
        synchronized (myDatabase)
        {
            result=myDatabase.insertOrThrow(TABLE_NAME, SMS_TEXT, columnValueMap);

            if(result ==0 || result == -1)
            {
                return false;
            }
            return true;
        }
    }

解决方案

First of all, databases have built in locking support, and it's turned on by default. If you want to be safe, call SQLiteOpenDatabase.setLockingEnabled(true).

As for access to the shared preferences, I would encapsulate all access to SharedPreferences (read and write) in small functions that all use synchronized. (Be sure that they are atomic).

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