iOS - Objective-C - 如何在等待时停止 NSThread？

Question

我有一个 nsthread，其中有一个 while 循环。它在 main 方法中从“线程安全”队列中获取对象。当我离开包含这个 nsthread 对象的 UIViewController 时，我调用 nsthread cancel 方法，但它并没有停止，因为它被“queueLock”NSCondition 锁定了。当我回到这个 UIViewController 时，将创建一个新的 nsthread 并从队列中获取对象，但是前一个线程仍然存在并且它们都尝试使用队列中的相同对象，这会导致内存管理问题。我的问题是当我离开 UIViewController 时，我应该如何停止这个线程。

NSThread主要方法:

NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
while ([self isCancelled] == NO) {
    RenderRequest *renderRequest = [queue get];
    [self doRender:renderRequest];
    [renderRequest release];    
}

[pool drain];

这是队列类的get方法:

- (id) get {
    id toRet = nil;
    [queueLock lock];
    @try {
       while ([queueContents count] == 0) {
            [queueLock wait];
        }

        toRet = [queueContents lastObject];
        [queueContents removeLastObject];
    }

    @finally {
         [queueLock unlock];
         return toRet;
    }
}

谢谢!

Answer 1

我写了一个简单的demo，希望对你有帮助:)

演示.h

#import <Foundation/Foundation.h>

@interface test : NSObject
{
    NSCondition *queueCondition;
    NSThread *queueThread;

    NSMutableArray *queueTask;

    NSTimer *timer;
}
- (id)init;
@end

演示.m

#import "demo.h"

@interface demo (PrivateMethods)
- (void)threadTest;
- (void)cancelThread;
- (void)addTask;
@end


@implementation demo

- (id)init
{
    self = [super init];
    if (self) {
        if (!queueThread) {
            if (!queueCondition) {
                queueCondition = [[NSCondition alloc] init];
            }

            if (!queueTask) {
                queueTask = [[NSMutableArray alloc] initWithCapacity:5];
            }

            queueThread = [[NSThread alloc] initWithTarget:self selector:@selector(threadTest) object:nil];
            [queueThread start];

            [self performSelector:@selector(cancelThread) withObject:nil afterDelay:10];

            if (!timer) {
                timer = [[NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(addTask) userInfo:nil repeats:YES] retain];
            }
        }
    }
    return self;
}

- (void)dealloc
{
    [queueThread release];
    [queueCondition release];
    [queueTask release];
    [timer invalidate];
    [timer release];
    [super dealloc];
}

- (void)threadTest
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    while (![[NSThread currentThread] isCancelled]) {
        [queueCondition lock];
        [queueCondition wait];

        if ([queueTask count] == 0) {
            [queueCondition unlock];
            continue;
        }

        NSString *str = nil;
        while ((str = [queueTask lastObject])) {
            NSLog(@"getTask: %@", [queueTask lastObject]);
            [queueTask removeLastObject];

        }

        [queueCondition unlock];
    }
    NSLog(@"threadTest end");
    [pool drain];
}

- (void)addTask
{
    [queueCondition lock];
    if (!queueTask) {
        queueTask = [[NSMutableArray alloc] initWithCapacity:5];
    }
    [queueTask addObject:@"new task"];
    [queueCondition signal];
    NSLog(@"add: new task");
    [queueCondition unlock];
}

- (void)cancelThread
{
    [timer invalidate];

    [queueThread cancel];

    [queueCondition lock];
    [queueCondition signal];
    [queueCondition unlock];
}
@end