NSOperationQueue队列中操作依赖相关思考

  • 添加依赖后,队列中网络请求任务有依赖关系时,任务结束判定以数据返回为准还是以发起请求为准?
  • waitUntilFinished方法容易误解。

依赖关系

//
//  ViewController.m
//  OperationTest0108
//
//  Created by LongMa on 2020/1/8.
//

#import "ViewController.h"
#import <AFNetworking/AFNetworking.h>

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self testQueue];
}

- (void)testQueue{
    NSOperationQueue *lQ = [[NSOperationQueue alloc] init];
    
    //任务最大并发数,与是否开启子线程无关。
//    lQ.maxConcurrentOperationCount = 1;
    
    NSBlockOperation *lOp0 = [NSBlockOperation blockOperationWithBlock:^{
        AFHTTPSessionManager *lMng = [AFHTTPSessionManager manager];
        [lMng POST:@"https://www.baidu.com" parameters:@{
            @"mapId" : @"1"
        } progress:^(NSProgress * _Nonnull uploadProgress) {
            
        } success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
            NSLog(@"0 suc");
        } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
            NSLog(@"0 error");
        }];
        
        NSLog(@"0 %@", [NSThread currentThread]);
    }];
    
    NSBlockOperation *lOp1 = [NSBlockOperation blockOperationWithBlock:^{
        AFHTTPSessionManager *lMng = [AFHTTPSessionManager manager];
               [lMng POST:@"https://www.baidu.com" parameters:@{
                   @"mapId" : @"1"
               } progress:^(NSProgress * _Nonnull uploadProgress) {
                   
               } success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
                   NSLog(@"1 suc");
               } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
                   NSLog(@"1 error");
           }];
        
        NSLog(@"1 %@", [NSThread currentThread]);
    }];
    
    NSBlockOperation *lOp2 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"2 %@", [NSThread currentThread]);
    }];
    
    [lOp0 addDependency:lOp1];
    
    NSLog(@"before add op");
    
    [lQ addOperations:@[lOp0] waitUntilFinished:NO];
    [lQ addOperations:@[lOp1] waitUntilFinished:NO];
    [lQ addOperations:@[lOp2] waitUntilFinished:NO];
}

@end

执行结果

2020-01-08 18:02:31.378260+0800 OperationTest0108[1583:527022] before add op
2020-01-08 18:02:31.378635+0800 OperationTest0108[1583:527045] 2 <NSThread: 0x283db43c0>{number = 4, name = (null)}
2020-01-08 18:02:31.379722+0800 OperationTest0108[1583:527047] 1 <NSThread: 0x283db4240>{number = 5, name = (null)}
2020-01-08 18:02:31.380265+0800 OperationTest0108[1583:527047] 0 <NSThread: 0x283db4240>{number = 5, name = (null)}
2020-01-08 18:02:31.915236+0800 OperationTest0108[1583:527022] 0 error
2020-01-08 18:02:31.921841+0800 OperationTest0108[1583:527022] 1 error

由上面log可知:任务结束判定以发起请求为准!数据返回是异步的,不受依赖关系影响!

waitUntilFinished方法

当把上面代码

[lQ addOperations:@[lOp0] waitUntilFinished:NO];

改为

[lQ addOperations:@[lOp0] waitUntilFinished:YES];

时,
log如下,没有正常执行操作:

2020-01-08 18:03:55.308276+0800 OperationTest0108[1587:527738] before add op

分析:
waitUntilFinished方法定义为:
If YES, the current thread is blocked until all of the specified operations finish executing. If NO, the operations are added to the queue and control returns immediately to the caller.
当为YES时,当前线程被阻塞,直到被添加的操作执行完毕。上面代码使线程依赖于lOp0执行完毕,而lOp0的执行依赖于lOp1执行完毕。由于lOp1比lOp0加入队列更晚。当上面代码被执行时,线程在等lOp0执行完毕,而此时lOp1还没被加入队列中,即lOp1还没开始执行,所以线程一直处于阻塞状态!当然,合理利用waitUntilFinished方法,也能实现想要的特殊效果。

posted @ 2020-01-08 18:13  Dast1  阅读(263)  评论(0编辑  收藏