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

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

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