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object-c 多线程 加锁

object-c的多线程如java的多线程一样方便可靠。

一、线程创建与启动

线程创建主要有二种方式:

[cpp] view plaincopy

- (id)init; // designated initializer

- (id)initwithtarget:(id)target selector:(sel)selector object:(id)argument;

当然,还有一种比较特殊,就是使用所谓的convenient method,这个方法可以直接生成一个线程并启动它,而且无需为线程的清理负责。这个方法的接口是:

[cpp]  view plain copy

+ (void)detachnewthreadselector:(sel)aselector totarget:(id)atarget withobject:(id)anargument

前两种方法创建后,需要手机启动,启动的方法是:

- (void)start;

二、线程的同步与锁

要说明线程的同步与锁,最好的例子可能就是多个窗口同时售票的售票系统了。我们知道在java中,使用synchronized来同步,而iphone虽然没有提供类似java下的synchronized关键字,但提供了nscondition对象接口。查看nscondition的接口说明可以看出,nscondition是iphone下的锁对象,所以我们可以使用nscondition实现iphone中的线程安全。这是来源于网上的一个例子:

sellticketsappdelegate.h 文件

// 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

[cpp]   view plain copy

// sellticketsappdelegate.m

import “sellticketsappdelegate.h”

@implementation sellticketsappdelegate

@synthesize window;

- (void)applicationdidfinishlaunching:(uiapplication *)application {

tickets = 100;

count = 0;

// 锁对象

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) {

// 上锁

[ticketscondition lock];

if(tickets > 0){

[nsthread sleepfortimeinterval:0.5];

count = 100 – tickets;

nslog(@”当前票数是:%d,售出:%d,线程名:%@”,tickets,count,[[nsthread currentthread] name]);

tickets–;

}else{

break;

[ticketscondition unlock];

- (void)dealloc {

[ticketsthreadone release];

[ticketsthreadtwo release];

[ticketscondition release];

[window release];

[super dealloc];

三、线程的交互

线程在运行过程中,可能需要与其它线程进行通信,如在主线程中修改界面等等,可以使用如下接口:

- (void)performselectoronmainthread:(sel)aselector withobject:(id)arg waituntildone:(bool)wait

由于在本过程中,可能需要释放一些资源,则需要使用nsautoreleasepool来进行管理,如:

- (void)startthebackgroundjob {

nsautoreleasepool *pool = [[nsautoreleasepool alloc] init];

// to do something in your thread job

[self performselectoronmainthread:@selector(makemyprogressbarmoving) withobject:nil waituntildone:no];

[pool release];