文集
iOS开发之多线程（1）—— 概述
iOS开发之多线程（2）—— Thread
iOS开发之多线程（3）—— GCD
iOS开发之多线程（4）—— Operation
iOS开发之多线程（5）—— Pthreads
iOS开发之多线程（6）—— 线程安全与各种锁
目录
版本
简介
- 操作
- 同步 & 异步
- 队列
- 串行 & 并行
基本用法
- 不使用队列
- 使用队列
2.1 四种添加操作(任务)方法
2.2 其他属性方法
2.3 线程间通信
版本
Xcode 11.5
Swift 5.2.2
简介
我们先来讨论相关理论知识点, 代码部分统一放到后文.
Operation基于GCD封装, 完全面向对象. 对应于GCD, Operation也有任务和队列的概念, 只不过在Operation中任务(block)被称为操作(operation).
Operation支持以下关键功能:
- 操作之间添加依赖
- 使用KVO监听操作的执行状态
- 对操作进行优先级排序
- 取消操作
操作
- 在GCD中, 任务代码只能写在block中, 并且需要放到队列(dispatch queue)中去执行.
- 而在Operation中, 操作对象可以单独执行, 也可以添加到队列 (operation queue)去执行.
Operation是一个抽象类, 代表一个任务. 通常我们使用它的子类NSInvocationOperation或NSBlockOperation来编写任务代码. 当然也可以直接使用Operation, 不过需要重写main方法, 在main里面编写任务代码.
3种创建方式:
- NSInvocationOperation (swift不支持): 此类调用选择器方法(selector), 在方法里面编写任务代码.
- NSBlockOperation (swift对应BlockOperation): 此类采用block方式, 在block中编写任务代码.
- NSOperation (swift对应Operation): 需要重写main方法, 在main里面编写任务代码.
2种执行方式:
- 不添加到队列, 手动调用operation的start方法.
- 添加到队列, 系统自动调用start方法.
具体如何使用请看下小节.
同步 & 异步
在GCD中, 同步和异步分别对应dispatch_sync和dispatch_async方法.
在Operation中, 没有这种方法.
苹果文档
如果计划手动执行操作对象，而不是将其添加到队列中，则可以将操作设计为以同步或异步方式执行。默认情况下，操作对象是同步的。当start()直接从代码中调用同步操作的方法时，该操作将在当前线程中立即执行。
默认情况下，操作对象以同步方式执行-也就是说，它们在调用其start方法的线程中执行其任务。
为了获得最佳性能，您应该将操作设计为尽可能异步，使应用程序在执行操作时可以自由地做其他工作。
- 如果不使用队列, operation默认以同步方式执行. 但我们有办法使之异步执行: 新建一个新线程, 然后在新线程里面调用start方法.
- 如果使用队列, 系统默认以异步方式执行. 但我们可以使用waitUntilAllOperationsAreFinished (operation queue方法)进行等待, 以确保操作完成后才继续往下执行.
注意: 与GCD的同步执行不同, 这里虽然设置了等待, 但是一般不在当前线程执行, 而是新开一个线程来执行, 但会保证队列里的所有任务完成后才继续往下执行.
队列
队列 (Operation Queue)有两种: 主队列和非主队列 (自定义队列).
- 主队列通过mainQueue获得, 主队列里的任务都是放到主线程执行 (不包括使用addExecutionBlock:添加的额外操作, 因其可能在其他线程执行).
- 非主队列 (自定义队列) 即一般 alloc init 出来的队列, 默认在子线程中异步执行. 通多设置最大并发数(maxConcurrentOperationCount)来控制队列是串行还是并发.
添加操作(任务)到队列有四种方式:
- addOperation:
添加一个现有的Operation (或者其子类). - addOperations:waitUntilFinished:
可添加多个现有的Operation (或者其子类), 可设置等待所有操作完成后方可继续往下执行. - addOperationWithBlock:
直接添加一个block - addBarrierBlock:
添加栅栏, 顺带一个任务. 等栅栏前的所有任务都执行完, 再执行本栅栏的任务, 起到隔离同步等待的目的.
串行 & 并行
主队列是串行队列. 自定义队列默认是并发队列, 但可通多设置最大并发数(maxConcurrentOperationCount)来控制队列是串行还是并发.
maxConcurrentOperationCount
-1, 默认值, 并发队列;
=0, 不执行任何操作;
=1, 串行队列;
<0, 除-1默认值外, 其他负值均报错;
>1, 并发队列, 如果数值过大, 最终并发数由系统决定.
基本用法
1. 不使用队列
OC
#pragma mark - NSInvocationOperation (调用selector方法)
// 使用 NSInvocationOperation
- (void)useInvocationOperation {
NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(doInvocationOperation) object:nil];
[operation start];
}
// 任务
- (void)doInvocationOperation {
NSLog(@"%s, thread:%@", __func__, [NSThread currentThread]);
}
//---------------------------------------------------------------------------------------------------
//log:
//-[ViewController doInvocationOperation], thread:<NSThread: 0x6000017ec2c0>{number = 1, name = main}
#pragma mark - NSBlockOperation (使用block)
// 使用 NSBlockOperation
- (void)useBlockOperation {
NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"%s, thread:%@", __func__, [NSThread currentThread]);
}];
[operation start];
}
//---------------------------------------------------------------------------------------------------
//log:
//-[ViewController useBlockOperation]_block_invoke, thread:<NSThread: 0x600000760100>{number = 1, name = main}
#pragma mark - 自定义Operation (重写main)
- (void)useCustomOperation {
MyOperation *operation = [[MyOperation alloc] init];
[operation start];
}
//---------------------------------------------------------------------------------------------------
//log:
//-[MyOperation main], thread:<NSThread: 0x600000618280>{number = 1, name = main}
MyOperation.m
@implementation MyOperation
- (void)main {
NSLog(@"%s, thread:%@", __func__, [NSThread currentThread]);
}
@end
在自定义Operation中, 调用start方法后, 系统会执行多项安全检查, 最终会调用main方法.
Swift
//MARK: - 使用 BlockOperation (block)
@objc func useBlockOperation() {
let operation = BlockOperation.init {
print("\(#function), thread:\(Thread.current)")
}
operation.start()
}
//---------------------------------------------------------------------------------------------------
//log:
//useBlockOperation(), thread:<NSThread: 0x600003f78000>{number = 1, name = main}
//MARK: - 使用 自定义Operation (重写main)
@objc func useCustomOperation() {
let operation = CustomOperation.init()
operation.start()
}
//---------------------------------------------------------------------------------------------------
//log:
//main(), thread:<NSThread: 0x600003ec8cc0>{number = 1, name = main}
class CustomOperation: Operation {
override func main() {
print("\(#function), thread:\(Thread.current)")
}
}
2. 使用队列
2.1 四种添加操作(任务)方法
OC
NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
// 1 addOperation:
NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op1 thread:%@", [NSThread currentThread]);
}] ;
[operationQueue addOperation:op1];
// 2 addOperations:waitUntilFinished:
NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op2 thread:%@", [NSThread currentThread]);
}] ;
NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op3 thread:%@", [NSThread currentThread]);
}] ;
NSBlockOperation *op4 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op4 thread:%@", [NSThread currentThread]);
}] ;
[operationQueue addOperations:@[op2, op3, op4] waitUntilFinished:YES];
NSLog(@"queue finished");
// 3 addOperationWithBlock:
[operationQueue addOperationWithBlock:^{
NSLog(@"block thread:%@", [NSThread currentThread]);
}];
// 4 addBarrierBlock:
[operationQueue addBarrierBlock:^{
NSLog(@"barrier thread:%@", [NSThread currentThread]);
}];
//---------------------------------------------------------------------------------------------------
//log:
//op2 thread:<NSThread: 0x600002ec7c80>{number = 6, name = (null)}
//op4 thread:<NSThread: 0x600002eaf180>{number = 4, name = (null)}
//op1 thread:<NSThread: 0x600002ed77c0>{number = 5, name = (null)}
//op3 thread:<NSThread: 0x600002eaf140>{number = 3, name = (null)}
//queue finished
//block thread:<NSThread: 0x600002ec7c80>{number = 6, name = (null)}
Swift
let operationQueue = OperationQueue.init()
// 1 addOperation(_ op: Operation)
let op1 = BlockOperation.init {
print("op1, thread:\(Thread.current)")
}
operationQueue.addOperation(op1)
// 2 addOperations(_ ops: [Operation], waitUntilFinished wait: Bool)
let op2 = BlockOperation.init {
print("op2, thread:\(Thread.current)")
}
let op3 = BlockOperation.init {
print("op3, thread:\(Thread.current)")
}
let op4 = BlockOperation.init {
print("op4, thread:\(Thread.current)")
}
operationQueue.addOperations([op2, op3, op4], waitUntilFinished: true)
// 3 addOperation(_ block: @escaping () -> Void)
operationQueue.addOperation {
print("block, thread:\(Thread.current)")
}
// 4 addBarrierBlock(_ barrier: @escaping () -> Void)
operationQueue.addBarrierBlock {
print("barrier, thread:\(Thread.current)")
}
//---------------------------------------------------------------------------------------------------
log:
op3, thread:<NSThread: 0x600002399200>{number = 4, name = (null)}
op1, thread:<NSThread: 0x6000023c34c0>{number = 5, name = (null)}
op2, thread:<NSThread: 0x600002398f80>{number = 6, name = (null)}
op4, thread:<NSThread: 0x6000023d42c0>{number = 7, name = (null)}
block, thread:<NSThread: 0x600002398f80>{number = 6, name = (null)}
barrier, thread:<NSThread: 0x600002398f80>{number = 6, name = (null)}
2.2 其他属性方法
maxConcurrentOperationCount
- (void)setOperationCount {
NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
NSLog(@"start");
NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op1 thread:%@", [NSThread currentThread]);
}] ;
NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op2 thread:%@", [NSThread currentThread]);
}] ;
NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op3 thread:%@", [NSThread currentThread]);
}] ;
NSBlockOperation *op4 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op4 thread:%@", [NSThread currentThread]);
}] ;
/**
-1, 默认值, 并发队列;
=0, 不执行任何操作;
=1, 串行队列;
<0, 除-1默认值外, 其他负值均报错;
>1, 并发队列, 如果数值过大, 最终并发数由系统决定.
*/
operationQueue.maxConcurrentOperationCount = 1;
[operationQueue addOperations:@[op1, op2, op3, op4] waitUntilFinished:YES];
NSLog(@"end");
}
//---------------------------------------------------------------------------------------------------
log:
start
op1 thread:<NSThread: 0x600000b181c0>{number = 5, name = (null)}
op2 thread:<NSThread: 0x600000b75f80>{number = 6, name = (null)}
op3 thread:<NSThread: 0x600000b75f80>{number = 6, name = (null)}
op4 thread:<NSThread: 0x600000b75f80>{number = 6, name = (null)}
end
我们看到:
由于是串行队列, 没有添加依赖和设置优先级, 所以会按照1~4顺序执行;
又因为设置了等待(waitUntilFinished:YES), 所以end最后才打印;
开不开新线程, 由系统决定.
添加依赖
addDependency:
设置优先级
typedef NS_ENUM(NSInteger, NSOperationQueuePriority) {
NSOperationQueuePriorityVeryLow = -8L,
NSOperationQueuePriorityLow = -4L,
NSOperationQueuePriorityNormal = 0,
NSOperationQueuePriorityHigh = 4,
NSOperationQueuePriorityVeryHigh = 8
};
取消队列里所有任务
- (void)cancelAllOperations;
2.3 线程间通信
- (void)callMainQueue {
NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
[operationQueue addOperationWithBlock:^{
NSLog(@"block, thread:%@", [NSThread currentThread]);
// call main queue
[NSOperationQueue.mainQueue addOperationWithBlock:^{
NSLog(@"main, thread:%@", [NSThread currentThread]);
}];
}];
}
//---------------------------------------------------------------------------------------------------
log:
block, thread:<NSThread: 0x600003ee0580>{number = 6, name = (null)}
main, thread:<NSThread: 0x600003ea0240>{number = 1, name = main}
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