ios FMDB多线程"is currently in use", "database is locked"问题的解决

骑猪看日落 2022-06-08 07:44 232阅读 0赞

is currently in use” 出现的场景是这样的，多线程操作数据库，每个线程都使用了FMDatabase实例

FMDatabase是不具备线程安全的，如果两个线程中同时操作数据库，就会”is currently in use” ；FMDatabasequeue其实是一个调度队列（G-C-D），数据库的操作必须是顺序执行，不能两个数据库的操作同时执行，如果是两个线程各自创建了FMDatabaseQueue的实例，线程同时执行时，就会出现相同的数据库操作同时触发，导致”database is locked“，所以必须是一个FMDatabaseQueue实例下，多个线程下同时操作，其实是在排在同一个队列中逐一操作的，没有同时操作。

解决办法：

自定义一个 DatabaseHelper类

DatabaseHelper.h

#import <Foundation/Foundation.h>
    #import "FMDB.h"
    
    @interface DatabaseHelper : NSObject
    @property(nonatomic,strong)NSString *dbName;
    +(DatabaseHelper*) sharedInstance;
    -(void)inDatabase:(void(^)(FMDatabase*))block;
    - (void)inTransaction:(void (^)(FMDatabase *db, BOOL *rollback))block;
    - (void)close;
    
    @end

DatabaseHelper.m

#import "DatabaseHelper.h"
    
    @interface DatabaseHelper()
    
    @property(nonatomic,strong)NSString *dbPath;
    
    @end
    @implementation DatabaseHelper
    {
        FMDatabaseQueue* queue;
    }
    
    -(NSString *)dbPath {
        if (!_dbPath) {
            _dbPath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject] stringByAppendingPathComponent:@"datas.db"];
            NSLog(@"%@",_dbPath);
        }
        return _dbPath;
    }
    
    -(id) init
    {
        self = [super init];
        if(self){
            //NSString *dbFilePath = [PathResolver databaseFilePath];
            queue = [FMDatabaseQueue databaseQueueWithPath:self.dbPath];
        }
        return self;
    }
    
    +(DatabaseHelper*)sharedInstance
    {
        static dispatch_once_t pred = 0;
        __strong static id _sharedObject = nil;
        dispatch_once(&pred, ^{
            _sharedObject = [[self alloc] init];
        });
        return _sharedObject;
    }
    
    -(void)inDatabase:(void(^)(FMDatabase*))block
    {
        [queue inDatabase:^(FMDatabase *db){
            block(db);
        }];
    }
    
    - (void)inTransaction:(void (^)(FMDatabase *db, BOOL *rollback))block {
        [queue inTransaction:^(FMDatabase *db, BOOL *rollback) {
            block(db,rollback);
        }];
    }
    
    - (void)close {
        [queue close];
    }
    @end

案例：

#import "ViewController.h"
    #import "DatabaseHelper.h"
    @interface ViewController ()
    @property(nonatomic,strong)DatabaseHelper *dbQueue;
    @end
    
    @implementation ViewController
    -(DatabaseHelper *)dbQueue {
        if (!_dbQueue) {
            _dbQueue = [DatabaseHelper sharedInstance];//单例
        }
        return _dbQueue;
    }
    
    - (void)viewDidLoad {
        [super viewDidLoad];
        dispatch_queue_t q1 = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
        for (int i=0; i<1000; i++) {
            dispatch_async(q1, ^{
                [self.dbQueue inTransaction:^(FMDatabase *db, BOOL *rollback) {
                    BOOL isSucess = [db executeUpdate:@"create table  if not exists test(id INTEGER  PRIMARY KEY AUTOINCREMENT, name TEXT, nameTwo TEXT)"];
                    BOOL isSucess2 = [db executeUpdate:@"insert into test(name) values('YKJ')"];
                    BOOL isSucess3 = [db executeUpdate:@"insert into test(nameTwo) values('ZJT')"];
                    BOOL isSucess4 = [db executeUpdate:@"UPDATE test SET name = 'ting'"];
                    BOOL isSucess5 = [db executeUpdate:@"UPDATE test SET nameTwo = 'tingJin'"];
                    if (!isSucess || isSucess2 || isSucess3 || isSucess4 || isSucess5) {
                        *rollback = YES;//回滚
                        return;
                    }
                }];
            });
        }
        
    }
    @end

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