Question

我尝试让一个函数等待另一个函数，我想使用NSCondionLock来实现这一目标。我不是在寻求帮助，但我真的希望有人能给我一个体面的教程或示例来解释NSConditionLock，或者可能建议一个更好的方法。

Answer 1

编辑：正如@Bonshington所评论的那样，这个答案是指NSCondition（而不是NSConditionLock）：

- (void) method1 {

    [myCondition lock];
    while (!someCheckIsTrue)
        [myCondition wait];


    // Do something.


    [myCondition unlock];
}

- (void) method2 {

    [myCondition lock];


    // Do something.


    someCheckIsTrue = YES;
    [myCondition signal];
    [myCondition unlock];
}

someCheckIsTrue可以是任何东西，它可以是一个简单的BOOL变量，甚至可以是[myArray count] == 0 && color == kColorRed之类的东西，也没关系。只有在一种方法中，你在锁定时检查条件并且在另一种方法中进行更改才能使条件成为真正同时具有锁定 。神奇的是wait和signal部分：wait实际上解锁了锁，并在其他一个名为signal的线程后重新获取锁。

Answer 2

对于那些想要在这里进行样本测试课程的人，我发布了我要做的事情，并了解NSCondition的工作原理。

// --- MyTestClass.h File --- //
@interface MyTestClass

- (void)startTest;

@end

// --- MyTestClass.m File --- //
@implementation MyTestClass
{
    NSCondition *_myCondition;
    BOOL _someCheckIsTrue;
}

- (id)init
{
    self = [super init];
    if (self) 
    {
        _someCheckIsTrue = NO;
        _myCondition = [[NSCondition alloc] init];
    }
    return self;
}

#pragma mark Public Methods

- (void)startTest
{
    [self performSelectorInBackground:@selector(_method1) withObject:nil];

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        sleep(5);
        [self performSelectorInBackground:@selector(_method2) withObject:nil];
    });
}

#pragma mark Private Methods

- (void)_method1
{
    NSLog(@"STARTING METHOD 1");

    NSLog(@"WILL LOCK METHOD 1");
    [_myCondition lock];
    NSLog(@"DID LOCK METHOD 1");

    while (!_someCheckIsTrue)
    {
        NSLog(@"WILL WAIT METHOD 1");
        [_myCondition wait];
        NSLog(@"DID WAIT METHOD 1");
    }

    NSLog(@"WILL UNLOCK METHOD 1");
    [_myCondition unlock];
    NSLog(@"DID UNLOCK METHOD 1");

    NSLog(@"ENDING METHOD 1");
}

- (void)_method2
{
    NSLog(@"STARTING METHOD 2");

    NSLog(@"WILL LOCK METHOD 2");
    [_myCondition lock];
    NSLog(@"DID LOCK METHOD 2");

    _someCheckIsTrue = YES;

    NSLog(@"WILL SIGNAL METHOD 2");
    [_myCondition signal];
    NSLog(@"DID SIGNAL METHOD 2");

    NSLog(@"WILL UNLOCK METHOD 2");
    [_myCondition unlock];
    NSLog(@"DID UNLOCK METHOD 2");
}

@end


// --- Output --- //
/*
2012-11-14 11:01:21.416 MyApp[8375:3907] STARTING METHOD 1
2012-11-14 11:01:21.418 MyApp[8375:3907] WILL LOCK METHOD 1
2012-11-14 11:01:21.419 MyApp[8375:3907] DID LOCK METHOD 1
2012-11-14 11:01:21.421 MyApp[8375:3907] WILL WAIT METHOD 1
2012-11-14 11:01:26.418 MyApp[8375:4807] STARTING METHOD 2
2012-11-14 11:01:26.419 MyApp[8375:4807] WILL LOCK METHOD 2
2012-11-14 11:01:26.419 MyApp[8375:4807] DID LOCK METHOD 2
2012-11-14 11:01:26.420 MyApp[8375:4807] WILL SIGNAL METHOD 2
2012-11-14 11:01:26.420 MyApp[8375:4807] DID SIGNAL METHOD 2
2012-11-14 11:01:26.421 MyApp[8375:4807] WILL UNLOCK METHOD 2
2012-11-14 11:01:26.421 MyApp[8375:3907] DID WAIT METHOD 1
2012-11-14 11:01:26.421 MyApp[8375:4807] DID UNLOCK METHOD 2
2012-11-14 11:01:26.422 MyApp[8375:3907] WILL UNLOCK METHOD 1
2012-11-14 11:01:26.423 MyApp[8375:3907] DID UNLOCK METHOD 1
2012-11-14 11:01:26.423 MyApp[8375:3907] ENDING METHOD 1
*/

Answer 3

NSConditionLock示例程序。

#import <Foundation/Foundation.h>

#define IDLE 0
#define START 1
#define TASK_1_FINISHED 2
#define TASK_2_FINISHED 3
#define CLEANUP_FINISHED 4

#define SHARED_DATA_LENGTH 1024 * 1024 * 1024

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSConditionLock *lock = [[NSConditionLock alloc] initWithCondition:IDLE];
        char *shared_data = calloc(SHARED_DATA_LENGTH, sizeof(char));

        [NSThread detachNewThreadWithBlock:^{
            [lock lockWhenCondition:START];

            NSLog(@"[Thread-1]: Task 1 started...");
            for (size_t i = 0; i < SHARED_DATA_LENGTH; i++) {
                shared_data[i] = 0x00;
            }
            [lock unlockWithCondition:TASK_1_FINISHED];
        }];

        [NSThread detachNewThreadWithBlock:^{
            [lock lockWhenCondition:TASK_1_FINISHED];
            NSLog(@"[Thread-2]: Task 2 started...");
            for (size_t i = 0; i < SHARED_DATA_LENGTH; i++) {
                char c = shared_data[i];
                shared_data[i] = ~c;
            }
            [lock unlockWithCondition:TASK_2_FINISHED];
        }];

        [NSThread detachNewThreadWithBlock:^{
            [lock lockWhenCondition:TASK_2_FINISHED];

            NSLog(@"[Thread-3]: Cleaning up...");
            free(shared_data);
            [lock unlockWithCondition:CLEANUP_FINISHED];
        }];

        NSLog(@"[Thread-main]: Threads set up. Waiting for 2 task to finish");
        [lock unlockWithCondition:START];
        [lock lockWhenCondition:CLEANUP_FINISHED];
        NSLog(@"[Thread-main]: Completed");
    }
    return 0;
}

Answer 4

Playground的@ GRiMe2D答案的

Swift 5 版本：

let myCondition = NSCondition()

var someCheckIsTrue = false

func method1() {
    print("STARTING METHOD 1")

    print("WILL LOCK METHOD 1")
    myCondition.lock()
    print("DID LOCK METHOD 1")

    while (!someCheckIsTrue) {
        print("WILL WAIT METHOD 1")
        myCondition.wait()
        print("DID WAIT METHOD 1")
    }

    print("WILL UNLOCK METHOD 1")
    myCondition.unlock()
    print("DID UNLOCK METHOD 1")

    print("ENDING METHOD 1")
}

func method2() {
    print("STARTING METHOD 2")

    print("WILL LOCK METHOD 2")
    myCondition.lock()
    print("DID LOCK METHOD 2")

    someCheckIsTrue = true

    print("WILL SIGNAL METHOD 2")
    myCondition.signal()
    print("DID SIGNAL METHOD 2")

    print("WILL UNLOCK METHOD 2")
    myCondition.unlock()
    print("DID UNLOCK METHOD 2")

    print("ENDING METHOD 2")
}

DispatchQueue.global().async {
    method1()
}

DispatchQueue.global().asyncAfter(deadline: DispatchTime.now() + 0.5) {
    method2()
}

我如何使用NSConditionLock？或NSCondition

4 个答案: