Objective-C runtime 拾遗（四）—— 不常用的进程/线程通信方法

起

前段时间在写Promise时，调研了iOS有哪些通信的方法。delegate,notification,GCD是常见的方法，除此之外还有一些方法，在此记录共享一下。

NSPipe

官方这样解释:

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.

表示一个可以单向通信的对象，只能一端读一端写。

NSPipe很简单，就两个属性：

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

跟上文表述一致。具体看这个例子吧,idea很赞。iOS IO 重定向（NSLog to UITextView）

NSPipe还可以用在socket中。NSPipe用作通信时，只能传递流式的数据。NSPipe通过文件是可以跨进程通信的。

信号量

dispatch_semaphore常用作生产消费者模型中，是GCD中用来做并发控制的。虽然不常见,但的确是可以通过dispatch_semaphore_create dispatch_semaphore_signal dispatch_semaphore_wait这几个方法来进行通信。

资料很多，随便搜。
遗憾的是，参数传递是个问题，而且用作线程间的通信也很牵强，会让代码难于理解。

NSPort

NSPort是一个通信的通道，通过NSPortMessage来传送消息

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 如不接收父线程的消息，则不用实现
- (void)handlePortMessage:(NSPortMessage *)message
{
}
@end

要注意的
NSPort能传递msgid和components。msgid是一个uint，而components是这样说的：

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.

运行时发现如果传NSData的话，拿到是个OS_dispatch_data类型的实例。暂时不太懂。

CF的使用方法参考这里

其他参考