dispatch_after()的奇怪行为

Question

我正在编写一个同时执行多项任务的应用程序.一个特殊的任务是每200毫秒做一次工作.为实现这一点,我使用了两种相互调用的方法.第一种方法只调用第二种方法,第二种方法使用dispatch_after()以延迟调用第一种方法.

经过几次迭代(300-400次)后,dispatch_after中的块在200 ms后不会执行.执行块需要大约5-10秒.请让我知道行为的原因(延迟).我也试过NSThread(sleepForTimeInterval :),我也遇到了同样的问题.我卡住了.请帮我.

代码如下.

Screen.h

#import <Foundation/Foundation.h>

@interface Screen : NSObject

-(void) firstMethod;
-(void) secondMethod;
@end

---

Screen.m

#import "Screen.h"

@implementation Screen

int i=0;
dispatch_queue_t another_queue;
dispatch_time_t pop_time;

-(Screen*) init {
    self = [super init];
    if (self) {
        another_queue = dispatch_queue_create("com.test.timer.2", NULL);
    }
    return self;
}

-(void) firstMethod {
    i++;
    NSLog(@"i value : %d",i);
    [self secondMethod];
}

-(void) secondMethod {
    pop_time = dispatch_time(DISPATCH_TIME_NOW, 200 * NSEC_PER_MSEC);
    dispatch_after(pop_time, another_queue, ^(void){
        [self firstMethod];
    });
}

@end

---

AppDelegate.h

#import <Cocoa/Cocoa.h>
#import "Screen.h"

@interface AppDelegate : NSObject <NSApplicationDelegate>

@property (assign) IBOutlet NSWindow *window;

@end

---

AppDelegate.m

#import "AppDelegate.h"

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    // Insert code here to initialize your application
    Screen* screen = [[Screen alloc] init];
    dispatch_queue_t first_queue = dispatch_queue_create("com.test.timer", NULL);
    dispatch_block_t blk =^(void) {
        [screen firstMethod];
    };
    dispatch_async(first_queue, blk);
}

@end

Answer 1

发生这种情况时,您的应用是否处于前台？如果没有,你可能只是看到App Nap开始.它所做的一件事是在后台应用程序中限制计时器.