Objective-C runtime 拾遺（四）—— 不常用的程式/執行緒通訊方法

canopus4u發表於2016-09-17

起

前段時間在寫Promise時，調研了iOS有哪些通訊的方法。delegate,notification,GCD是常見的方法，除此之外還有一些方法，在此記錄共享一下。

NSPipe

官方這樣解釋:

NSPipe objects provide an object-oriented interface for accessing pipes. An NSPipe object represents both ends of a pipe and enables communication through the pipe. A pipe is a one-way communications channel between related processes; one process writes data, while the other process reads that data. The data that passes through the pipe is buffered; the size of the buffer is determined by the underlying operating system. NSPipe is an abstract class, the public interface of a class cluster.

表示一個可以單向通訊的物件，只能一端讀一端寫。

NSPipe很簡單，就兩個屬性：

@property (readonly, retain) NSFileHandle *fileHandleForReading;
@property (readonly, retain) NSFileHandle *fileHandleForWriting;

跟上文表述一致。具體看這個例子吧,idea很贊。iOS IO 重定向（NSLog to UITextView）

NSPipe還可以用在socket中。NSPipe用作通訊時，只能傳遞流式的資料。NSPipe通過檔案是可以跨程式通訊的。

訊號量

dispatch_semaphore常用作生產消費者模型中，是GCD中用來做併發控制的。雖然不常見,但的確是可以通過dispatch_semaphore_create dispatch_semaphore_signal dispatch_semaphore_wait這幾個方法來進行通訊。

資料很多，隨便搜。
遺憾的是，引數傳遞是個問題，而且用作執行緒間的通訊也很牽強，會讓程式碼難於理解。

NSPort

NSPort是一個通訊的通道，通過NSPortMessage來傳送訊息

例子

- (void) foo {
  NSPort *port = [NSMachPort port];
  port.delegate = self;

  [[NSRunLoop currentRunLoop] addPort:port forMode:NSDefaultRunLoopMode];

  SomeOtherWorker *worker = [[SomeOtherWorker alloc] init];
  [NSThread detachNewThreadSelector:@selector(launchWithPort:)
                             toTarget:worker
                           withObject:port];
}

- (void)handlePortMessage:(NSMessagePort*)message{
    NSUInteger msgId = [[message valueForKeyPath:@"msgid"] integerValue]; //[message msgid]
    NSPort *localPort = [message valueForKeyPath:@"localPort"];//[message receivePort]
    NSPort *remotePort = [message valueForKeyPath:@"remotePort"]//[message sendPort];
    ......
}

Worker Class

@implementation SomeOtherWorker
{
    NSPort* _remotePort;
    NSPort* _myPort;
}

- (void)launchWithPort:(NSPort *)port {
    _remotePort = port;
    [[NSThread currentThread] setName:@"SomeOtherThread"];
    [[NSRunLoop currentRunLoop] run];

    _myPort = [NSMachPort port];
    _myPort.delegate = self;

    [[NSRunLoop currentRunLoop] addPort:_myPort forMode:NSDefaultRunLoopMode];
    [_remotePort sendBeforeDate:[NSDate date]
                         msgid:kMsg1
                    components:nil
                          from:_myPort
                      reserved:0];
}

#pragma mark - NSPortDelegate 如不接收父執行緒的訊息，則不用實現
- (void)handlePortMessage:(NSPortMessage *)message
{
}
@end

要注意的
NSPort能傳遞msgid和components。msgid是一個uint，而components是這樣說的：

The data to send in the message. components should contain only NSData and NSPort objects, and the contents of the NSData objects should be in network byte order.

執行時發現如果傳NSData的話，拿到是個OS_dispatch_data型別的例項。暫時不太懂。

CF的使用方法參考這裡

其他參考