Create Mac memory pressure observer

发表于 |

Mac的资料真心少，先来看看iOS是怎么做的。

memory pressure observer on iOS

how to observe

  • 可以监听 UIApplicationDidReceiveMemoryWarningNotification 通知。
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[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(XXX)
name:UIApplicationDidReceiveMemoryWarningNotification 
object:nil];
  • 实现 UIViewController 自身的方法didReceiveMemoryWarning，该方法在 App 接收到 memory warning 会被调用，可以在方法中释放当前不再使用的资源。
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- (void)didReceiveMemoryWarning;

how to mock

  • 模拟器菜单
    hardware -> simulate memory warning

  • 模拟发通知 UISimulatedMemoryWarningNotification

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CFNotificationCenterPostNotification(CFNotificationCenterGetDarwinNotifyCenter(), (CFStringRef)@"UISimulatedMemoryWarningNotification", NULL, NULL, true);
  • 私有 API
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[[UIApplication sharedApplication] performSelector:@selector(_performMemoryWarning)];

memory pressure observer on Mac

终于要切入正题，按照iOS调研的节奏开始查资料～

how to observe

以下来自 Github

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static dispatch_source_t source = nil;
source = dispatch_source_create(DISPATCH_SOURCE_TYPE_MEMORYPRESSURE, 0,  DISPATCH_MEMORYPRESSURE_WARN | DISPATCH_MEMORYPRESSURE_CRITICAL, dispatch_get_main_queue());
dispatch_source_set_event_handler(source, ^{
dispatch_source_memorypressure_flags_t pressureLevel = dispatch_source_get_data(source);
[NSNotificationCenter.defaultCenter postNotificationName:DidReceiveMemoryWarningNotification
object:nil
userInfo:@{ @"pressure": @(pressureLevel) }];
});
dispatch_resume(source);

其中 dispatch_source_create 的解释：

Creates a new dispatch source to monitor low-level system objects and automatically submit a handler block to a dispatch queue in response to events.

可以监控的 system objects 很多，包括 Timer，Signal， MemoryPressure 等。

其中 memoryPressure level 的定义如下： 

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#define DISPATCH_MEMORYPRESSURE_NORMAL		0x01
#define DISPATCH_MEMORYPRESSURE_WARN		0x02
#define DISPATCH_MEMORYPRESSURE_CRITICAL	0x04

how to mock

目前找到的方法,
在 terminal 输入：

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sudo memory_pressure -S -l critical -s 15

-S causes the system to simulate the specified memory pressure (warn | critical), and -s tells how many seconds to hold that simulated pressure.