【发布时间】：2011-07-15 07:51:37
【问题描述】：
我试图让一个函数等待另一个函数，我想使用 NSCondionLock 来完成此操作。我不是在寻求帮助，而是真的希望有人可以向我展示一个体面的教程或示例来解释 NSConditionLock，或者可能提出更好的方法。
【问题讨论】：
标签： iphone ios locking conditional-statements
【发布时间】：2011-07-15 07:51:37
【问题描述】：
编辑：正如@Bonshington 评论的那样，这个答案指的是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，没关系。重要的是，在一种方法中在您拥有锁时检查条件，而在另一种方法中，您进行更改以使条件变为真在拥有锁时也 .神奇的是wait 和signal 部分：wait 实际上解锁了锁并在其他一些名为signal 的线程之后重新获取它。
【讨论】：
-
如何申报？它只是 NSConditionLock *lock = [[NSConditionLock alloc] init] 吗？我应该在调用需要同步的两个函数的任何方法中声明它吗？抱歉，如果我没有正确格式化我的评论，这是我第一次真正发布。
-
您应该在您的类中将其声明为实例变量
NSConditionLock *lock;。然后你用lock = [[NSConditionLock alloc] init];在你的init中初始化它，就是这样。此外，在dealloc中，您只需释放它：[lock release];。或者如果方法在不同的类中，那么你需要在两个方法都可以访问的地方定义锁。 -
@gurooj：首先，方法必须在不同的线程上运行。所以他们可能不会互相打电话，否则你会陷入僵局。现在，首先
method1需要运行并点击wait，然后method2将使用signal唤醒它。 -
NSConditionLock 没有等待，信号。它的 NSCondition
-
@MobileMon: No. 引用documentation of
signal: 你使用这个方法唤醒一个正在等待条件的线程。 （强调我的）
对于那些想要在这里上一个示例测试类的人，我发布了我所做的事情，以了解 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
*/
【讨论】：
-
谢谢，但您的示例并未说明为什么使用
while (!_someCheckIsTrue)而不是if (!_someCheckIsTrue)。
Swift 5 版本的 @vilanovi 来自 Playground 的回答：
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()
}
【讨论】：
-
为什么method2()会锁定和解锁？需要吗？
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;
}
【讨论】：