如何在 macOS 的非主线程上有一个事件循环？

Question

与this other question 相关：我需要收集有关macOS 上当前活动应用程序的信息。

链接的 QA 答案提供了一种机制，可在活动应用程序更改时收到警报（事件），但在单独的线程上运行时会崩溃：

FocusDetector::AppFocus focus;
focus.run();

//std::thread threadListener(&FocusDetector::AppFocus::run, &focus); //Does not works
//if (threadListener.joinable())
//{
//  threadListener.join();
//}

.

    *** Assertion failure in +[NSUndoManager _endTopLevelGroupings], /xxxxxxx/NSUndoManager.m:363
2020-11-24 08:54:41.758 focus_detection[81935:18248374] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '+[NSUndoManager(NSInternal) _endTopLevelGroupings] is only safe to invoke on the main thread.'
*** First throw call stack:
(
    0   CoreFoundation            0x00007fff3006cb57 __exceptionPreprocess + 250
    1   libobjc.A.dylib           0x00007fff68eb35bf objc_exception_throw + 48
    2   CoreFoundation            0x00007fff30095d08 +[NSException raise:format:arguments:] + 88
    3   Foundation                0x00007fff32787e9d -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 191
    4   Foundation                0x00007fff326c45ee +[NSUndoManager(NSPrivate) _endTopLevelGroupings] + 440
    5   AppKit                    0x00007fff2d25165c -[NSApplication run] + 864
    6   focus_detection           0x0000000104b1a010 _ZN13FocusDetector8AppFocus3runEv + 128
    7   focus_detection           0x0000000104b19547 _ZNSt3__1L8__invokeIMN13FocusDetector8AppFocusEFvvEPS2_JEvEEDTcldsdeclsr3std3__1E7forwardIT0_Efp0_Efp_spclsr3std3__1E7forwardIT1_Efp1_EEEOT_OS6_DpOS7_ + 119
    8   focus_detection           0x0000000104b1944e _ZNSt3__1L16__thread_executeINS_10unique_ptrINS_15__thread_structENS_14default_deleteIS2_EEEEMN13FocusDetector8AppFocusEFvvEJPS7_EJLm2EEEEvRNS_5tupleIJT_T0_DpT1_EEENS_15__tuple_indicesIJXspT2_EEEE + 62
    9   focus_detection           0x0000000104b18c66 _ZNSt3__114__thread_proxyINS_5tupleIJNS_10unique_ptrINS_15__thread_structENS_14default_deleteIS3_EEEEMN13FocusDetector8AppFocusEFvvEPS8_EEEEEPvSD_ + 118
    10  libsystem_pthread.dylib   0x00007fff6a260109 _pthread_start + 148
    11  libsystem_pthread.dylib   0x00007fff6a25bb8b thread_start + 15
)
libc++abi.dylib: terminating with uncaught exception of type NSException
Abort trap: 6

这显然与NSApplication有关，文档说明：

每个应用都使用一个 NSApplication 实例来控制主事件循环

因此，我正在寻找另一种监听事件的方法，它不限于主事件循环（或主线程。

直观地说，应该可以在单独的线程中获取有关当前应用程序焦点的信息。

我不知道如何解决这个问题，抱歉没有提供太多研究。我确实在互联网上研究了“NSNotification不在主线程中”和其他类似的句子，但没有成功。

问题：

如何在主线程外监听activeAppDidChangeNSNotification？

Answer 1

将观察者置于下面的以下通知中，并让他们调用您的方法。 NotificationCenter 是singleton 有充分的理由，而您当然可以创建自己的。我猜[NSWorkspace sharedWorkspace] 是一个单身人士，[[NSWorkspace sharedWorkspace] notificationCenter] 被命名为 - 要​​观察的通知中心。在您的情况下，期望的发送对象是 nil，因为您不知道要观察哪个对象更具体。

#import <AppKit/AppKit.h>

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    // Insert code here to initialize your application
    [[[NSWorkspace sharedWorkspace] notificationCenter]
        addObserver:self
        selector:@selector(activeAppDidChange:)
        name:NSWorkspaceDidActivateApplicationNotification
        object:nil
    ];
    [[[NSWorkspace sharedWorkspace] notificationCenter]
        addObserver:self
        selector:@selector(activeAppDidTerminate:)
        name:NSWorkspaceDidTerminateApplicationNotification
        object:nil
    ];
    // id<NSObject> myObserver;
    _myObserver = [[[NSWorkspace sharedWorkspace] notificationCenter] 
        addObserverForName:NSWorkspaceDidHideApplicationNotification
        object:nil 
        queue:[NSOperationQueue mainQueue] 
        usingBlock:^(NSNotification * _Nonnull note) {
            // do stuff in block
            NSRunningApplication *app = note.userInfo[NSWorkspaceApplicationKey];
            NSLog(@"%u %@ %ld", 
               app.processIdentifier, 
               app.bundleIdentifier, 
               (long)app.activationPolicy
            );
        }
    ];
}
-(void)activeAppDidChange:(NSNotification *)note {
    NSLog(@"%@",note.userInfo.debugDescription);
}
-(void)activeAppDidTerminate:(NSNotification *)note {
    NSLog(@"%@",note.userInfo.debugDescription);
}

Answer 2

只是证明您可以在非 mainThread 的线程上接收通知。

// ThreadManagerExample.h
#import <AppKit/AppKit.h>
#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface ThreadManagerExample : NSObject
@property (nonatomic, readonly) BOOL started;
@property (nonatomic, readonly) uint64_t looptime;
-(void)start;
-(void)stop;
@end

NS_ASSUME_NONNULL_END

// ThreadManagerExample.m
#import "ThreadManagerExample.h"

static const double kThreadPriority = 1.0;

@interface ReceivingThread : NSThread
@property (nonatomic, weak) ThreadManagerExample * threadManager;
@end

@interface ThreadManagerExample ()
@property (nonatomic, strong) ReceivingThread *thread;
@property (nonatomic, readwrite) BOOL started;
@property (nonatomic, readwrite) uint64_t looptime;
@end

@implementation ThreadManagerExample
-(void)dealloc {
    [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(startThread) object:nil];
    if ( _thread ) {
        [_thread cancel];
        while ( !_thread.isFinished ) {
            [NSThread sleepForTimeInterval:0.01];
        }
    }
}
-(instancetype)init {
    if ( !(self = [super init]) ) return nil;
    _looptime = 1000000000; // 1 sec
    return self;
}

-(void)startThread {
    if ( !_thread) {
        self.thread = [ReceivingThread new];
        _thread.threadManager = self;
        _thread.name=@"ReceivingThread";
        [_thread setThreadPriority:kThreadPriority];
        [_thread start];
    }
}

-(void)start {
    if ( !_thread ) {
        @synchronized ( self ) {
            self.started = YES;
        }
        [self performSelector:@selector(startThread) withObject:nil afterDelay:0.0];
    }
}

-(void)stop {
    @synchronized ( self ) {
        self.started = NO;
    }
    if ( _thread ) {
        [_thread cancel];
        self.thread = nil;
    }
}
@end

@implementation ReceivingThread {
    BOOL somethinghappend;
    NSString *oldBundleIdentifier;
    NSString *lastbundleIdentifier;
    pid_t oldPID;
    pid_t focusedPID;
}
-(instancetype)init {
    if (!(self=[super init])) return nil;
    [[[NSWorkspace sharedWorkspace] notificationCenter] addObserver:self selector:@selector(mimi:) name:NSWorkspaceDidActivateApplicationNotification object:nil];
    return self;
}
-(void)mimi:(NSNotification*)note {
    NSRunningApplication *app = note.userInfo[NSWorkspaceApplicationKey];
    lastbundleIdentifier = app.bundleIdentifier;
    focusedPID = app.processIdentifier;
    if (![oldBundleIdentifier isEqualToString:lastbundleIdentifier]) {
        somethinghappend = YES;
    }
    oldBundleIdentifier = lastbundleIdentifier;
    oldPID = focusedPID;
}
-(void)main {
    [NSThread setThreadPriority:kThreadPriority];
    while ( !self.isCancelled ) {
        uint64_t nextLoop = 0;
        @synchronized ( _threadManager ) {
            if (somethinghappend) {
                NSLog(@"%@ %u",lastbundleIdentifier, focusedPID);
                somethinghappend = NO;
            }
            uint64_t now = mach_absolute_time();
            nextLoop = now + _threadManager.looptime;
        }
        mach_wait_until(nextLoop);
    }
}
@end

实例和启动就像..

if (!_manager) _manager = [[ThreadManagerExample alloc] init];
[_manager start];

停止

[_manager stop];
_manager = nil; // if needed

因此，当循环时间设置为 1 秒时，它将每秒检查最后收到的 bundleIdentifier 是否已更改。您可以通过检查 bundleIdentifier 是否与 [[NSBundle mainBundle] bundleIdentifier] 不同来扩展 -(void)mimi: 方法，以了解您是否自己变得活跃并在需要时忽略它。

编辑来自Apple Docs

NSRunningApplication 是线程安全的，因为它的属性是原子返回的。但是，它仍然受制于上述主运行循环策略。如果您从后台线程访问 NSRunningApplication 的实例，请注意，当主运行循环运行（或不运行）时，它的随时间变化的属性可能会在您的下方发生变化。