多线程之NSInvocationOperation
多线程编程是防止主线程堵塞，增加运行效率等等的最佳方法。而原始的多线程方法存在很多的毛病，包括线程锁死等。在Cocoa中，Apple提供了NSOperation这个类，提供了一个优秀的多线程编程方法。
本次介绍NSOperation的子集，简易方法的NSInvocationOperation：
@implementation MyCustomClass
- (void)launchTaskWithData:(id)data
{
//创建一个NSInvocationOperation对象，并初始化到方法
//在这里，selector参数后的值是你想在另外一个线程中运行的方法（函数，Method）
//在这里，object后的值是想传递给前面方法的数据
NSInvocationOperation* theOp = [[NSInvocationOperation alloc] initWithTarget:self
selector:@selector(myTaskMethod:) object:data];
// 下面将我们建立的操作“Operation”加入到本地程序的共享队列中（加入后方法就会立刻被执行）
// 更多的时候是由我们自己建立“操作”队列
[[MyAppDelegate sharedOperationQueue] addOperation:theOp];
}
// 这个是真正运行在另外一个线程的“方法”
- (void)myTaskMethod:(id)data
{
// Perform the task.
}
@end一个NSOperationQueue 操作队列，就相当于一个线程管理器，而非一个线程。因为你可以设置这个线程管理器内可以并行运行的的线程数量等等。下面是建立并初始化一个操作队列：
@interface MyViewController : UIViewController {
NSOperationQueue *operationQueue;
//在头文件中声明该队列
}
@end
@implementation MyViewController
- (id)init
{
self = [super init];
if (self) {
operationQueue = [[NSOperationQueue alloc] init]; //初始化操作队列
[operationQueue setMaxConcurrentOperationCount:1];
//在这里限定了该队列只同时运行一个线程
//这个队列已经可以使用了
}
return self;
}
- (void)dealloc
{
[operationQueue release];
//正如Alan经常说的，我们是程序的好公民，需要释放内存！
[super dealloc];
}
@end简单介绍之后，其实可以发现这种方法是非常简单的。很多的时候我们使用多线程仅仅是为了防止主线程堵塞，而NSInvocationOperation就是最简单的多线程编程，在iPhone编程中是经常被用到的。
///////////////////////////////////////////////////////////////////////////////////////////////////
1 在主线程里加入一个loading画面……
2 {
3 [window addSubview:view_loading];
4 [NSThread detachNewThreadSelector:@selector(init_backup:) toTarget:self withObject:nil];
5 }
可以通过performSelectorOhMainThread更新UI元素，比如设置进度条等等。最后消除loading画面，载入主View。
7 - (void)init_backup:(id)sender
8 {
9 NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
10
11 // ...
12 int i = status;
13 [self performSelectorOnMainThread:@selector(show_loading:) withObject:[NSNumber numberWithInt:i] waitUntil Done:NO];
14
15 [view_loading removeFromSuperview];
16 [window addSubview:tabcontroller_main.view];
17 [pool release];
18 }
///////////////////////////////////////////////////////
利用iphone的多线程实现和线程同步
从接口的定义中可以知道，NSThread和大多数iphone的接口对象一样，有两种方式可以初始化：
一种使用initWithTarget :(id)target selector:(SEL)selector object:(id)argument，但需要负责在对象的retain count为0时调用对象的release方法清理对象。
另一种则使用所谓的convenient method,这个方便接口就是detachNewThreadSelector，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。
#import <UIKit/UIKit.h>
@interface SellTicketsAppDelegate : NSObject <UIApplicationDelegate> {
int tickets;
int count;
NSThread* ticketsThreadone;
NSThread* ticketsThreadtwo;
NSCondition* ticketsCondition;
UIWindow *window;
}
@property (nonatomic, retain) IBOutlet UIWindow *window;
@end
然后在实现中添加如下代码：
// SellTicketsAppDelegate.m
// SellTickets
//
// Created by sun dfsun2009 on 09-11-10.
// Copyright __MyCompanyName__ 2009. All rights reserved.
//
#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];
}
@end
-------------------------------------------------------------------------------------
// 定义
#import <UIKit/UIKit.h>
@interface ThreadSyncSampleViewController : UIViewController {
int _threadCount;
NSCondition *_myCondition;
}
@end
//实现文件如下:
#import "ThreadSyncSampleViewController.h"
@implementation ThreadSyncSampleViewController
/*
// The designated initializer. Override to perform setup that is required before the view is loaded.
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
if (self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]) {
// Custom initialization
}
return self;
}
*/
/*
// Implement loadView to create a view hierarchy programmatically, without using a nib.
- (void)loadView {
}
*/
// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
[super viewDidLoad];
//
//_myCondition = nil;
//
_myCondition = [[NSCondition alloc] init];
//
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:30
target:self
selector:@selector(threadTester)
userInfo:nil
repeats:YES];
[timer fire];
}
- (void)threadTester{
[_myCondition lock];
_threadCount = -2;
//如果有n个要等待的thread，这里置成 -n
[_myCondition unlock];
//
NSLog(@"");
NSLog(@"------------------------------------------------------------------------------");
[NSThread detachNewThreadSelector:@selector(threadOne) toTarget:self withObject:nil];
[NSThread detachNewThreadSelector:@selector(threadTwo) toTarget:self withObject:nil];
[NSThread detachNewThreadSelector:@selector(threadThree) toTarget:self withObject:nil];
return;
}
- (void)threadOne{
NSLog(@"@@@ In thread 111111 start.");
[_myCondition lock];
int n = rand()%5 + 1;
NSLog(@"@@@ Thread 111111 Will sleep %d seconds ,now _threadCount is : %d",n,_threadCount);
sleep(n);
//[NSThread sleepForTimeInterval:n];
_threadCount ++ ;
NSLog(@"@@@ Thread 111111 has sleep %d seconds ,now _threadCount is : %d",n,_threadCount);
[_myCondition signal];
NSLog(@"@@@ Thread 1111111 has signaled ,now _threadCount is : %d",_threadCount);
[_myCondition unlock];
NSLog(@"@@@ In thread one complete.");
[NSThread exit];
return;
}
- (void)threadTwo{
NSLog(@"### In thread 2222222 start.");
[_myCondition lock];
int n = rand()%5 + 1;
NSLog(@"### Thread 2222222 Will sleep %d seconds ,now _threadCount is : %d",n,_threadCount);
sleep(n);
// [NSThread sleepForTimeInterval:n];
_threadCount ++ ;
NSLog(@"### Thread 2222222 has sleep %d seconds ,now _threadCount is : %d",n,_threadCount);
[_myCondition signal];
NSLog(@"### Thread 2222222 has signaled ,now _threadCount is : %d",_threadCount);
[_myCondition unlock];
//_threadCount ++ ;
NSLog(@"### In thread 2222222 complete.");
[NSThread exit];
return;
}
- (void)threadThree{
NSLog(@"<<< In thread 333333 start.");
[_myCondition lock];
while (_threadCount < 0) {
[_myCondition wait];
}
NSLog(@"<<< In thread 333333 ,_threadCount now is %d ,will start work.",_threadCount);
[_myCondition unlock];
NSLog(@"<<< In thread 333333 complete.");
[NSThread exit];
return;
}
/*
// Override to allow orientations other than the default portrait orientation.
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
// Return YES for supported orientations
return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
*/
- (void)didReceiveMemoryWarning {
// Releases the view if it doesn't have a superview.
[super didReceiveMemoryWarning];
// Release any cached data, images, etc that aren't in use.
}
- (void)viewDidUnload {
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}
- (void)dealloc {
[_myCondition release];
[super dealloc];
}
@end