问题描述
||
Apple的Grand Central dispatch（GCD）很棒，但仅适用于iOS 4.0或更高版本。 Apple的文档说，“ [[A]序列化操作队列的行为与Grand Central dispatch中的串行调度队列不完全相同”（因为该队列不是FIFO，但是顺序由依赖项和优先级确定）。
在发布GCD之前支持OS版本的同时，实现与GCD的串行调度队列相同效果的正确方法是什么？或换一种说法，在想要支持低于4.0版本的iOS应用中，推荐的处理简单后台处理（进行Web服务请求等）的方法是什么？
解决方法
似乎人们将花很多精力来重写NSRunloop。根据NSRunloop文档：
您的应用程序无法创建
或显式管理NSRunLoop
对象。每个NSThread对象，
包括应用程序的主
线程，具有一个NSRunLoop对象
自动为其创建
需要。
因此，肯定的答案是创建一个可用的队列：
- (void)startRunLoop:(id)someObject
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
[[NSRunLoop currentRunLoop] run];
[pool release];
}
...
NSThread *serialDispatchThread = [[NSThread alloc]
initWithTarget:self
selector:@selector(startRunLoop:)
object:nil];
[serialDispatchThread start];
[object
performSelector:@selector(whatever:)
onThread:serialDispatchThread
withObject:someArgument
waitUntilDone:NO];
#import <Foundation/Foundation.h>
@interface PseudoTask : NSObject
{
id target_;
SEL selector_;
id queue_;
}
@property (nonatomic,readonly) id target;
- (id)initWithTarget:(id)target selector:(SEL)selector queue:(id)queue;
- (void)exec;
@end
@implementation PseudoTask
@synthesize target=target_;
- (id)initWithTarget:(id)target selector:(SEL)selector queue:(id)queue;
{
self = [super init];
if (self) {
target_ = [target retain];
selector_ = selector;
queue_ = [queue retain];
}
return self;
}
- (void)exec
{
[target_ performSelector:selector_];
}
- (void)dealloc
{
[target_ release];
[queue_ release];
}
@end
@interface PseudoSerialQueue : NSObject
{
NSCondition *condition_;
NSMutableArray *array_;
NSThread *thread_;
}
- (void)addTask:(id)target selector:(SEL)selector;
@end
@implementation PseudoSerialQueue
- (id)init
{
self = [super init];
if (self) {
array_ = [[NSMutableArray alloc] init];
condition_ = [[NSCondition alloc] init];
thread_ = [[NSThread alloc]
initWithTarget:self selector:@selector(execQueue) object:nil];
[thread_ start];
}
return self;
}
- (void)addTask:(id)target selector:(SEL)selector
{
[condition_ lock];
PseudoTask *task = [[PseudoTask alloc]
initWithTarget:target selector:selector queue:self];
[array_ addObject:task];
[condition_ signal];
[condition_ unlock];
}
- (void)quit
{
[self addTask:nil selector:nil];
}
- (void)execQueue
{
for (;;) {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
[condition_ lock];
while (array_.count == 0)
[condition_ wait];
PseudoTask *task = [array_ objectAtIndex:0];
[array_ removeObjectAtIndex:0];
[condition_ unlock];
if (!task.target) {
[pool drain];
break;
}
[task exec];
[task release];
[pool drain];
}
}
- (void)dealloc
{
[array_ release];
[condition_ release];
}
@end
PseudoSerialQueue *q = [[[PseudoSerialQueue alloc] init] autorelease];
[q addTask:self selector:@selector(test0)];
[q addTask:self selector:@selector(test1)];
[q addTask:self selector:@selector(test2)];
[q quit];
NSOperationQueue
main
- (void)startOperations
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
[[AppDelegate condition] lock];
while (![[[AppDelegate queue] operations] count] <= 0)
{
[[AppDelegate condition] wait];
}
NSOperation *newOperation = [alloc,init]....;
[[AppDelegate queue] addOperation:newOperation];
[[AppDelegate queue] waitUntilAllOperationsAreFinished]; // Don\'t forget this!
NSOperation *newOperation1 = [alloc,init]....;
[[AppDelegate queue] addOperation:newOperation1];
[[AppDelegate queue] waitUntilAllOperationsAreFinished]; // Don\'t forget this!
NSOperation *newOperation2 = [alloc,init]....;
[[AppDelegate queue] addOperation:newOperation2];
[[AppDelegate queue] waitUntilAllOperationsAreFinished]; // Don\'t forget this!
// Add whatever number operations you need for this single job
[[AppDelegate queue] signal];
[[AppDelegate queue] unlock];
[NotifyDelegate orWhatever]
[pool drain];
}