SQLite的并发问题

news/2025/9/24 12:09:27/文章来源:https://www.cnblogs.com/Caisenberg/p/19108799

转载自：C# 下 SQLite 并发操作与锁库问题的 5 种解决方案_51CTO博客_sqlcipher c#

SQLite是轻量级的数据库，可用于嵌入式设备，仅需几百KB的内存即可工作，整个数据库存储在单一文件中，便于管理，迁移，备份。无需繁琐配置。

轻量高性能必然带来一定的局限，这次遇到的就是SQLite数据库的并发操作问题

关键点：在多线程或多进程并发访问的场景下，同一时刻仅允许单个线程进行写入操作。

现象：database is locked 错误

问题描述：在一个线程正在执行写入操作的过程中，另一个线程的写入请求只能被迫等待，等待时间过长超过系统预设的超时时间（通常5s可更改）就会触发此错误。

解决方案

1. 读写锁

2. 事务

3. WAL模式

4. 连接池

5. 多线程模式

详细说明

1. 读写锁

确保资源不被争抢导致崩溃

读写锁

using System.Threading;public class SqliteDataManager
{//ReaderWriterLockSlim类提供读写锁private static ReaderWriterLockSlim _rwLock = new ReaderWriterLockSlim;private static string _connString = "Data Source=mydb.db;Version=3;";// 读操作（允许多线程并发）public void ReadData{_rwLock.EnterReadLock;  // 获取读锁try{using (var conn = new SQLiteConnection(_connString)){conn.Open;var cmd = conn.CreateCommand;cmd.CommandText = "SELECT * FROM MyTable";using (var reader = cmd.ExecuteReader){while (reader.Read) { /* 读取数据 */ }}}}finally{_rwLock.ExitReadLock;  // 必须在finally中释放}}// 写操作（独占锁）public void WriteData(string value){_rwLock.EnterWriteLock;  // 获取写锁try{using (var conn = new SQLiteConnection(_connString)){conn.Open;var cmd = conn.CreateCommand;cmd.CommandText = "INSERT INTO MyTable VALUES (@Value)";cmd.Parameters.AddWithValue("@Value", value);cmd.ExecuteNonQuery;}}finally{_rwLock.ExitWriteLock;  // 必须释放}}
}

可升级为写锁的读锁，可减少锁竞争，避免重复加锁

可升级为写锁的读锁

public sealed class SqliteConnectionManager
{private static readonly ReaderWriterLockSlim _lock = new ReaderWriterLockSlim;private static SQLiteConnection _conn;public static SQLiteConnection GetConnection{_lock.EnterUpgradeableReadLock;  // 可升级为写锁的读锁try{if (_conn == null){_lock.EnterWriteLock;  // 升级为写锁try{if (_conn == null){_conn = new SQLiteConnection("Data Source=mydb.db");_conn.Open;}}finally { _lock.ExitWriteLock; }}return _conn;}finally { _lock.ExitUpgradeableReadLock; }}
}

具体使用

查看代码

using System;
using System.Data.SQLite;
using System.Threading;class DatabaseManager
{private static SQLiteConnection _connection;private static readonly ReaderWriterLockSlim _lock = new ReaderWriterLockSlim();public static SQLiteConnection GetConnection(){if(_connection==null){_lock.EnterWriteLock;try{if(_connection == null){_connection=new SQLiteConnection("Data Source=database.db");}}finally{_lock.ExitWriteLock();}return _connection;}public static void InsertUser(string name) { var connection = GetConnection();_lock.EnterWriteLock(); try { //写锁中使用了事务using (var transaction = connection.BeginTransaction()) { try { using (var command = new SQLiteCommand(connection)) { command.CommandText = "INSERT INTO Users (Name) VALUES (@name)";                        command.Parameters.AddWithValue("@name", name); command.ExecuteNonQuery(); } transaction.Commit(); } catch (Exception ex) { transaction.Rollback(); } } } finally { _lock.ExitWriteLock(); }}public static void SelectUsers() { var connection = GetConnection(); _lock.EnterReadLock(); try { using (var command = new SQLiteCommand("SELECT * FROM Users", connection)) { using (var reader = command.ExecuteReader()) { while (reader.Read()) { Console.WriteLine(reader["Name"]); } } } } finally { _lock.ExitReadLock(); }}}}
}

2.事务

保障数据完整性，事务具有原子性，内部的所有操作要么成功要么一起失败并回滚到插入之前的状态。一般只在读的时候使用事务。

在写入时使用事务

public static void InsertUser(string name) 
{ var connection = GetConnection(); using (var transaction = connection.BeginTransaction()) { try { using (var command = new SQLiteCommand(connection)) { command.CommandText = "INSERT INTO Users (Name) VALUES (@name)"; command.Parameters.AddWithValue("@name", name); command.ExecuteNonQuery(); } transaction.Commit(); } catch (Exception ex) { transaction.Rollback(); }} 
}