面试题
1.你理解的多线程？
2.ios的多线程方案有哪几种？你更倾向于哪一种？
3.你在项目中用过GCD?
4.GCD的队列类型
5.说一下OperationQueue和GCD的区别、以及各自的优势
6.线程安全的处理手段有哪些？
7.OC你了解的锁有哪些？
- 自旋和互斥对比？
- 使用以上锁需要注意哪些？
- 用C/OC/C++，任选其一，实现自旋或互斥？
下面我们来看看几个例子
代码详见 gitHub_Demo
例1
#import "ViewController_1.h"
@interface ViewController_1 ()
@end
@implementation ViewController_1
- (void)viewDidLoad {
[super viewDidLoad];
//这句代码的本质是往Runloop中添加定时器 如果在主线程，runloop自动开启好了的
[self performSelector:@selector(test1) withObject:nil afterDelay:.0];//afterDelay-->异步执行的 主队列
//主队列异步执行时，会先执行完主线程上的代码，然后在主线程上顺序执行任务，不会有新的线程产生，所有任务都是在主线程上完成的
NSLog(@"%@",[NSThread currentThread]);
sleep(1);
dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
dispatch_async(queue, ^{
sleep(2);
NSLog(@"asyncThread--%@",[NSThread currentThread]);
NSLog(@"1");
//如果是子线程需要自己手动去启动runloop
[self performSelector:@selector(test) withObject:nil afterDelay:.0];
//手动去启动runloop
// [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
NSLog(@"3");
});
NSLog(@"4");
}
-(void)test{
NSLog(@"2");
}
-(void)test1{
NSLog(@"test1Thread---%@",[NSThread currentThread]);
NSLog(@"test1");
}
@end
打印：
没有手动去启动runloop
Multithreading[17114:917201] {number = 1, name = main}
Multithreading[17114:917201] 4
Multithreading[17114:917201] test1Thread---{number = 1, name = main}
Multithreading[17114:917201] test1
Multithreading[17114:917255] asyncThread--{number = 3, name = (null)}
Multithreading[17114:917255] 1
Multithreading[17114:917255] 3
=========================================
手动去启动runloop
Multithreading[17130:918365] {number = 1, name = main}
Multithreading[17130:918365] 4
Multithreading[17130:918365] test1Thread---{number = 1, name = main}
Multithreading[17130:918365] test1
Multithreading[17130:918422] asyncThread--{number = 3, name = (null)}
Multithreading[17130:918422] 1
Multithreading[17130:918422] 2
Multithreading[17130:918422] 3
例2
- (void)test{
NSLog(@"2");
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
NSThread *thread = [[NSThread alloc] initWithBlock:^{
NSLog(@"1"); //一完成任务之后，子线程就退出了
}];
[thread start];
[self performSelector:@selector(test) onThread:thread withObject:nil waitUntilDone:YES];
NSLog(@"===End====");
}
运行结果：NSLog(@"1") 之后 崩溃了
Multithreading_01.png
- (void)test{
NSLog(@"2");
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
NSThread *thread = [[NSThread alloc] initWithBlock:^{
NSLog(@"1");
//一完成任务之后，子线程就退出了
}];
[thread start];
[self performSelector:@selector(test) onThread:thread withObject:nil waitUntilDone:NO];
sleep(2);
NSLog(@"===End====");
}
打印：
Multithreading[19178:1044135] 1
Multithreading[19178:1043871] ===End====
Multithreading_02.png
修改崩溃：
- (void)test{
NSLog(@"2");
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
NSThread *thread = [[NSThread alloc] initWithBlock:^{
NSLog(@"1");
[[NSRunLoop currentRunLoop] addPort:[[NSPort alloc] init] forMode:NSDefaultRunLoopMode];
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
}];
[thread start];
[self performSelector:@selector(test) onThread:thread withObject:nil waitUntilDone:YES];
sleep(2);
NSLog(@"===End====");
}
打印：
Multithreading[19214:1046668] 1
Multithreading[19214:1046668] 2
Multithreading[19214:1046548] ===End====
【开启了runloop后，延长了子线程的生命】
【如果没有，则会执行完任务子线程就退出了】
iOS中的常见多线程方案
Multithreading_03.png
GCD的常用函数
Multithreading_04.png
GCD的队列
Multithreading_05.png
//异步开启子线程，执行任务
-(void)test1{
dispatch_queue_t queue = dispatch_get_global_queue(0, 0); //全局并发队列
dispatch_async(queue, ^{
NSLog(@"%@",[NSThread currentThread]);
// {number = 3, name = (null)}
});
}
//同步，在当前线程执行任务
-(void)test2{
dispatch_queue_t queue = dispatch_get_global_queue(0, 0); //全局并发队列
dispatch_sync(queue, ^{
NSLog(@"%@",[NSThread currentThread]);
// {number = 1, name = main}
});
}
//同步，在当前线程执行任务（并发无效 ）
-(void)test3{
dispatch_queue_t queue = dispatch_get_global_queue(0, 0); //全局并发队列
dispatch_sync(queue, ^{
for(int i=0;i<5;i++){
NSLog(@"执行任务1:%@",[NSThread currentThread]);
}
});
dispatch_sync(queue, ^{
for(int i=0;i<5;i++){
NSLog(@"执行任务2:%@",[NSThread currentThread]);
}
});
/*
执行任务1:{number = 1, name = main}
执行任务1:{number = 1, name = main}
执行任务1:{number = 1, name = main}
执行任务1:{number = 1, name = main}
执行任务1:{number = 1, name = main}
执行任务2:{number = 1, name = main}
执行任务2:{number = 1, name = main}
执行任务2:{number = 1, name = main}
执行任务2:{number = 1, name = main}
执行任务2:{number = 1, name = main}
*/
}
//异步，开启新线程执行任务（并发）
-(void)test4{
dispatch_queue_t queue = dispatch_get_global_queue(0, 0); //全局并发队列
dispatch_async(queue, ^{
for(int i=0;i<5;i++){
NSLog(@"执行任务1:%@",[NSThread currentThread]);
}
});
dispatch_async(queue, ^{
for(int i=0;i<5;i++){
NSLog(@"执行任务2:%@",[NSThread currentThread]);
}
});
/*
执行任务1:{number = 3, name = (null)}
执行任务2:{number = 4, name = (null)}
执行任务1:{number = 3, name = (null)}
执行任务2:{number = 4, name = (null)}
执行任务2:{number = 4, name = (null)}
执行任务1:{number = 3, name = (null)}
执行任务1:{number = 3, name = (null)}
执行任务2:{number = 4, name = (null)}
执行任务1:{number = 3, name = (null)}
执行任务2:{number = 4, name = (null)}
*/
}
//串行队列异步执行任务 （按顺序执行）
-(void)test5{
dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_SERIAL); //串行队列
dispatch_async(queue, ^{
for(int i=0;i<5;i++){
NSLog(@"执行任务1:%@",[NSThread currentThread]);
}
});
dispatch_async(queue, ^{
for(int i=0;i<5;i++){
NSLog(@"执行任务2:%@",[NSThread currentThread]);
}
});
/*
执行任务1:{number = 3, name = (null)}
执行任务1:{number = 3, name = (null)}
执行任务1:{number = 3, name = (null)}
执行任务1:{number = 3, name = (null)}
执行任务1:{number = 3, name = (null)}
执行任务2:{number = 3, name = (null)}
执行任务2:{number = 3, name = (null)}
执行任务2:{number = 3, name = (null)}
执行任务2:{number = 3, name = (null)}
执行任务2:{number = 3, name = (null)}
*/
}
//在当前线程（此时是主线程），串行执行任务
-(void)test6{
dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_SERIAL); //串行队列
dispatch_sync(queue, ^{
for(int i=0;i<5;i++){
NSLog(@"执行任务1:%@",[NSThread currentThread]);
}
});
dispatch_sync(queue, ^{
for(int i=0;i<5;i++){
NSLog(@"执行任务2:%@",[NSThread currentThread]);
}
});
/*
执行任务1:{number = 1, name = main}
执行任务1:{number = 1, name = main}
执行任务1:{number = 1, name = main}
执行任务1:{number = 1, name = main}
执行任务1:{number = 1, name = main}
执行任务2:{number = 1, name = main}
执行任务2:{number = 1, name = main}
执行任务2:{number = 1, name = main}
执行任务2:{number = 1, name = main}
执行任务2:{number = 1, name = main}
*/
}
//主队列里面异步执行（此时没有开启新的线程）
-(void)test7{
dispatch_queue_t queue = dispatch_get_main_queue();
dispatch_async(queue, ^{
for(int i=0;i<5;i++){
NSLog(@"执行任务1:%@",[NSThread currentThread]);
}
});
dispatch_async(queue, ^{
for(int i=0;i<5;i++){
NSLog(@"执行任务2:%@",[NSThread currentThread]);
}
});
/*
执行任务1:{number = 1, name = main}
执行任务1:{number = 1, name = main}
执行任务1:{number = 1, name = main}
执行任务1:{number = 1, name = main}
执行任务1:{number = 1, name = main}
执行任务2:{number = 1, name = main}
执行任务2:{number = 1, name = main}
执行任务2:{number = 1, name = main}
执行任务2:{number = 1, name = main}
执行任务2:{number = 1, name = main}
*/
}
容易混淆的术语
Multithreading_06.png
dispatch_sync和dispatch_async用来控制是否要开启新的线程
队列的类型，决定了任务的执行方式（并发、串行）
1.并发队列
2.串行队列
3.主队列（也是一个串行队列）
注意：异步的它不一定 要开启新的线程（只是具备开启新的线程的能力）
主队列里面异步执行任务
只要是sync（同步），或者是在主队列里，他就是在当前线程里面执行任务，那它一定是串行执行任务
没有开启新的线程，那它肯定是串行 执行任务的
各种队列的执行效果
Multithreading_07.png
总结：
Multithreading_08.png
友情链接：
gitHub_Demo
多线程（二）
多线程（三）
多线程（四）