任何语言都不能避而不谈线程这个东东，虽然他是和平台相关的鸟，虽说unix哲学比较讨厌线程的说...线程不是万能灵药,但有些场合还是需要的.谈到线程就不得不考虑同步和死锁问题,见如下代码:

#import <Foundation/Foundation.h>

#define msg(...) NSLog(__VA_ARGS__)

@interface Foo:NSObject{
	int i;
	//NSLock *lock;
	NSRecursiveLock *lock;
}

@property(atomic) int i;

@end

@implementation Foo
	@synthesize i;

	-(id)init{
		self = [super init];
		if(self){
			i = 0;
			//lock = [[NSLock alloc] init];
			lock = [[NSRecursiveLock alloc] init];
		}
		return self;
	}

	-(void)loop{
		int org_i = 0;
		for(int x = 0;x < 5000;++x){
			org_i = i;
			[self inc];
			//self.i++;
			msg(@"%@:i has %d to %d",[[NSThread currentThread] name],\
				org_i,i);
		}
	}

	-(void)inc{
		//@synchronized(self){
			[lock lock];
			i++;
			[lock unlock];
		//}
	}

	-(int)val{
		return i;
	}

@end

#define msg(...) NSLog(__VA_ARGS__)

int main(int argc,char *argv[])
{
	@autoreleasepool{
		id t = nil;
		Foo *foo = [[Foo alloc] init];
		NSMutableArray *ary = [[NSMutableArray alloc]init];
		for(int i = 0;i<10;++i){
			t = [[NSThread alloc] initWithTarget:foo selector:@selector(loop) \
				object:nil];
			[t setName:[NSString stringWithFormat:@"thread_%d",i]];
			[ary addObject:t];
		}

		for(NSThread *t in ary){
			[t start];
		}

		BOOL quit = NO;
		while(true){
			for(NSThread *t in ary){
				quit = [t isFinished];
				if(!quit) break;
			}
			if(quit) break;
			[NSThread sleepForTimeInterval:1.0];
		}

		msg(@"at last val is %d",[foo val]);
	}
	return 0;
}

以上代码涉及到线程的创建和同步代码.除了通过线程实例方法initWithTarget:...方法创建以外还可以通过线程类方法+detachNewThreadSelector:...来创建,后一种方法创建后线程立即执行,而前一种方法需要使用-start方法启动线程.线程的同步可以通过NSLock类的lock和unlock方法,或者可以使用obj-c的关键字:@synchronize来实现快速快速同步语义.对于类属性来说,可以通过关键字atomic来声明该属性的原子性,不过实际执行好像不能确保同步,本猫哪里没考虑到呢?

我在使用NSURLConnection类获取网络数据的时候发现协议回调方法无法被回调,开始我以为可能回调需要时间执行,所以我在主线程中使用了循环+sleep函数等待其isFinished回调的完成.但是这个循环永远也不会结束.后来发现NSURLConnection类的工作需要在主线程的"剩余时间片"中完成,所以你sleep还是不行,等于主线程直接睡眠了不会分到时间片啊.这时你可以使用F库中提供的NSRunLoop类的功能来完成:

[[NSRunLoop currentRunLoop] runUntilDate ...]

Cocoa GUI框架不是线程安全的,这意味着其他线程如果需要更新GUI组件必须通过主线程来实现,这可以通过NSObject实例方法-performSelectorOnMainThread:withObject:waitUntilDone:来实现;同样的除了指定让主线程做事之外,还可以指定让其他后台线程上执行选择器:-performSelector:onThread:waitIntilDone: .

线程是一种比较底层的OS提供的接口,obj-c提供了包装线程的更高级的逻辑接口,这就是NSOperation和NSOperationQueue类,这种新型线程模型核心称为GCD.你只需把需要完成的任务放入NSOperationQueue队列中,该队列会根据系统cpu情况自动生成和销毁一定数目的线程来完成工作,你就不用操心啦.你可以派生NSOperation类并覆写其main方法来添加任务单元;你也可以使用F库自带的更方便的更专注于任务的NSInvocationOperation和NSBlockOperation类来描述任务单元.最后你可以使用-waitUntilAllOperationsAreFinished方法等待队列中所有任务都完成.下面我写了一个简单的利用队列多线程完成任务的代码,每一项任务单元就是给文件改名(但不改文件夹的名字),所有都在代码里喽:

#import <Foundation/Foundation.h>

#define msg(...) printf("[%d]\n",__LINE__);NSLog(__VA_ARGS__)

@interface RenameConcur:NSObject{
	NSString *path;
	NSString *prefix;
}
	@property NSString *path;
	@property NSString *prefix;

	-(id)initWithPath:(NSString*)path andPrefix:(NSString*)prefix;
	-(void)renameWithPrefix;
@end

@implementation RenameConcur
	@synthesize path,prefix;

	-(id)initWithPath:(NSString*)path_v andPrefix:(NSString*)prefix_v{
		self = [super init];
		if(self){
			path = [path_v stringByExpandingTildeInPath];
			prefix = prefix_v;
		}
		return self;
	}

	-(id)init{
		return [self initWithPath:nil andPrefix:nil];
	}

	-(void)renameWithPrefix{
		if(!prefix || !path){
			msg(@"obj's prefix or path is nil!");
		}
		else{
			NSFileManager *fm = [NSFileManager defaultManager];

			BOOL is_dir = NO;
			if([fm fileExistsAtPath:path isDirectory:&is_dir] == NO){
				msg(@"file %@ is not exist!",path);
				return;
			}else if(is_dir){
				msg(@"path %@ is directory,do nothing!",path);
				return;
			}

			NSString *just_name = [path lastPathComponent];
			NSString *just_path = [path stringByDeletingLastPathComponent];
			NSString *new_path = [NSString stringWithFormat:@"%@/%@%@",just_path,prefix,just_name];

			if([fm moveItemAtPath:path toPath:new_path error:NULL] == NO){
				msg(@"rename %@ to %@ failed!",path,new_path);
				return;
			}
		}
	}
@end

int main(int argc,char *argv[])
{
	@autoreleasepool{
		/*
		NSString *path = @"~/src/objc_src/ddd.m";
		NSString *prefix = @"love_";
		RenameConcur *rnc = [[RenameConcur alloc] initWithPath:path andPrefix:prefix];
		[rnc renameWithPrefix];

		NSString *dir_path = [@"~/src/dir_love" stringByExpandingTildeInPath];
		NSFileManager *fm = [NSFileManager defaultManager];
		NSArray *files = [fm contentsOfDirectoryAtPath:dir_path error:NULL];
		msg(@"files : %@",files);

		for(NSString *file in files){
			[rnc setPath:[NSString stringWithFormat:@"%@/%@",dir_path,file]];
			[rnc renameWithPrefix];
		}
		*/
		NSProcessInfo *process = [NSProcessInfo processInfo];
		NSArray *args = [process arguments];
		if([args count] != 3){
			printf("usage : %s path prefix (notice : path's end don't with /)\n",\
				[[[args objectAtIndex:0] lastPathComponent] \
					cStringUsingEncoding:NSASCIIStringEncoding]);
			return 1;
		}
		NSString *dir_path = [[args objectAtIndex:1] stringByExpandingTildeInPath];
		NSString *prefix = [args objectAtIndex:2];
		NSFileManager *fm = [NSFileManager defaultManager];
		NSArray *files = [fm contentsOfDirectoryAtPath:dir_path error:NULL];
		if(!files){
			msg(@"get dir [%@] files's name failed!",dir_path);
			return 2;
		}

		NSOperationQueue *queue = [[NSOperationQueue alloc] init];
		for(NSString *file in files){
			RenameConcur *rnc_n = [[RenameConcur alloc] initWithPath:\
				[NSString stringWithFormat:@"%@/%@",dir_path,file] andPrefix:prefix];
			NSOperation *op = [[NSInvocationOperation alloc] initWithTarget:rnc_n \
				selector:@selector(renameWithPrefix) object:nil];
			[queue addOperation:op];
		}

		[queue waitUntilAllOperationsAreFinished];
	}
	return 0;
}