NSCondition : 一個(gè)線程可能需要等待其它線程返回結(jié)果.
本例中,使用 condition 對(duì)"生產(chǎn)","購(gòu)買(mǎi)"兩個(gè)線程加鎖,實(shí)現(xiàn)
->生產(chǎn)一個(gè)商品
->發(fā)生一次購(gòu)買(mǎi)
->再生產(chǎn)一個(gè)商品
循環(huán).
[condition wait]之后當(dāng)前線程會(huì)被阻塞直到 [condition signal]
1.生產(chǎn)

@interface Producer : NSObject
@property (nonatomic, assign) BOOL shouldProduce;

@property (nonatomic, strong) NSString *itemName;

@property (nonatomic, strong) NSCondition *condition;

@property (nonatomic, strong) NSMutableArray *collector;

- (instancetype)initWithConditon:(NSCondition *)condition collector:(NSMutableArray *)collector;
- (void)produce;
@end

@implementation Producer

- (instancetype)initWithConditon:(NSCondition *)condition collector:(NSMutableArray *)collector{
    
    self = [super init];
    if (self) {
        self.condition = condition;
        self.collector = collector;
        self.shouldProduce = NO;
        self.itemName = nil;
    }
           return self;
}

-(void)produce{
    self.shouldProduce = YES;
    while (self.shouldProduce) {
        [self.condition lock];
        if (self.collector.count > 0 ) {
            [self.condition wait];
        }
        [self.collector addObject:@"iPhone"];
        NSLog(@"生產(chǎn):iPhone");
        [self.condition signal];
        [self.condition unlock];
    }
}

2.消費(fèi)者

#import <Foundation/Foundation.h>

@interface Consumer : NSObject
@property (nonatomic, assign) BOOL shouldConsumer;

@property (nonatomic, strong) NSString *itemName;

@property (nonatomic, strong) NSCondition *condition;

@property (nonatomic, strong) NSMutableArray *collector;
- (instancetype)initWithConditon:(NSCondition *)condition collector:(NSMutableArray *)collector;
- (void)consumer;
@end

#import "Consumer.h"

@implementation Consumer
- (instancetype)initWithConditon:(NSCondition  *)condition collector:(NSMutableArray *)collector{
    
    self = [super init];
    if (self) {
        self.condition = condition;
        self.collector = collector;
        self.shouldConsumer = NO;
        self.itemName = nil;
    }
    return self;
}

-(void)consumer{
    self.shouldConsumer = YES;
    while (self.shouldConsumer) {
        [self.condition lock];
        if (self.collector.count == 0 ) {
            [self.condition wait];
        }
        
        NSString *item = [self.collector objectAtIndex:0];
        NSLog(@"買(mǎi)入:%@",item);
        [self.collector removeObjectAtIndex:0];
        [self.condition signal];
        [self.condition unlock];
    }
}
@end

3.開(kāi)始搶購(gòu)

    NSMutableArray *pipeline = [NSMutableArray array];
    NSCondition *conditon = [NSCondition new];
    
    Producer *p = [[Producer alloc]initWithConditon:conditon collector:pipeline];
    Consumer *c = [[Consumer alloc]initWithConditon:conditon collector:pipeline];
    [[[NSThread alloc] initWithTarget:p selector:@selector(produce) object:p] start];
    [[[NSThread alloc] initWithTarget:c selector:@selector(consumer) object:c] start];

4.結(jié)束生產(chǎn),購(gòu)買(mǎi)

  p.shouldProduce = NO;
  c.shouldConsumer = NO;

5.結(jié)果

2017-06-04 20:55:18.051 Condition[63117:2614482] 生產(chǎn):iPhone
2017-06-04 20:55:18.051 Condition[63117:2614483] 買(mǎi)入:iPhone
2017-06-04 20:55:18.051 Condition[63117:2614482] 生產(chǎn):iPhone
2017-06-04 20:55:18.052 Condition[63117:2614483] 買(mǎi)入:iPhone
2017-06-04 20:55:18.052 Condition[63117:2614482] 生產(chǎn):iPhone
2017-06-04 20:55:18.052 Condition[63117:2614483] 買(mǎi)入:iPhone
2017-06-04 20:55:18.053 Condition[63117:2614482] 生產(chǎn):iPhone
2017-06-04 20:55:18.053 Condition[63117:2614483] 買(mǎi)入:iPhone
2017-06-04 20:55:18.054 Condition[63117:2614482] 生產(chǎn):iPhone
...
無(wú)限循環(huán)

form:<高性能iOS應(yīng)用開(kāi)發(fā)>
(原書(shū)中有些錯(cuò)誤,此處已修改.不知道是原版還是翻譯的鍋,這本書(shū)里錯(cuò)誤巨多)