object-c 多線程 加鎖

object-c的多線程如java的多線程一樣方便可靠。

一、線程創建與啓動
線程創建主要有二種方式：
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- (id)init; // designated initializer
- (id)initWithTarget:(id)target selector:(SEL)selector object:(id)argument;

當然，還有一種比較特殊，就是使用所謂的convenient method，這個方法可以直接生成一個線程並啓動它，而且無需爲線程的清理負責。這個方法的接口是：
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+ (void)detachNewThreadSelector:(SEL)aSelector toTarget:(id)aTarget withObject：(id)anArgument

前兩種方法創建後，需要手機啓動，啓動的方法是：
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- (void)start;

二、線程的同步與鎖
要說明線程的同步與鎖，最好的例子可能就是多個窗口同時售票的售票系統了。我們知道在java中，使用synchronized來同步，而iphone雖 然沒有提供類似java下的synchronized關鍵字，但提供了NSCondition對象接口。查看NSCondition的接口說明可以看 出，NSCondition是iphone下的鎖對象，所以我們可以使用NSCondition實現iphone中的線程安全。這是來源於網上的一個例 子：

SellTicketsAppDelegate.h 文件
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// SellTicketsAppDelegate.h
import
@interface SellTicketsAppDelegate : NSObject {
int tickets;
int count;
NSThread* ticketsThreadone;
NSThread* ticketsThreadtwo;
NSCondition* ticketsCondition;
UIWindow *window;
}
@property (nonatomic, retain) IBOutlet UIWindow *window;
@end

SellTicketsAppDelegate.m 文件
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// SellTicketsAppDelegate.m
import “SellTicketsAppDelegate.h”
@implementation SellTicketsAppDelegate
@synthesize window;
- (void)applicationDidFinishLaunching:(UIApplication *)application {

tickets = 100;
count = 0;
// 鎖對象
ticketCondition = [[NSCondition alloc] init];
ticketsThreadone = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
[ticketsThreadone setName:@"Thread-1"];
[ticketsThreadone start];
ticketsThreadtwo = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
[ticketsThreadtwo setName:@"Thread-2"];
[ticketsThreadtwo start];
//[NSThread detachNewThreadSelector:@selector(run) toTarget:self withObject:nil];
// Override point for customization after application launch
[window makeKeyAndVisible];
}
- (void)run{
while (TRUE) {
// 上鎖
[ticketsCondition lock];
if(tickets > 0){
[NSThread sleepForTimeInterval:0.5];
count = 100 – tickets;
NSLog(@”當前票數是:%d,售出:%d,線程名:%@”,tickets,count,[[NSThread currentThread] name]);
tickets–;
}else{
break;
}
[ticketsCondition unlock];
}
}
- (void)dealloc {
[ticketsThreadone release];
[ticketsThreadtwo release];
[ticketsCondition release];
[window release];
[super dealloc];
}
@end

三、線程的交互
線程在運行過程中，可能需要與其它線程進行通信，如在主線程中修改界面等等，可以使用如下接口：
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- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait

由於在本過程中，可能需要釋放一些資源，則需要使用NSAutoreleasePool來進行管理,如：
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- (void)startTheBackgroundJob {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
// to do something in your thread job
…
[self performSelectorOnMainThread:@selector(makeMyProgressBarMoving) withObject:nil waitUntilDone:NO];
[pool release];
}

轉自iOS分享網  http://iosshare.cn