Communication between process using NSPipe,NSTask

Question

I need to realize a communication between two threads using NSPipe channels, the problem is that I don't need to call terminal command by specifying this methods.

[task setCurrentDirectoryPath:@"....."];
[task setArguments:];

I just need to write some data

NSString * message = @"Hello World";
[stdinHandle writeData:[message dataUsingEncoding:NSUTF8StringEncoding]];

and on the other thread to receive this message

NSData *stdOutData = [reader availableData];
NSString * message = [NSString stringWithUTF8String:[stdOutData bytes]]; //My Hello World

For example such things in C# can be easy done with NamedPipeClientStream, NamedPipeServerStream classes where pipes are registered by id string.

How to achieve it in Objective-C?

Sliest

Is your question about two threads within the same process, or about separate processes that communicate via a pipe? – Bazaar

Its about two threads that communicate via a pipe – Sliest

How can achieve separate processes that communicate via a pipe? – Karakorum

Answer 1

If I understand your question correctly, you can just create a NSPipe and use one end for reading and one end for writing. Example:

// Thread function is called with reading end as argument:
- (void) threadFunc:(NSFileHandle *)reader
{
    NSData *data = [reader availableData];
    NSString *message = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"%@", message);
}

- (void) test
{
    // Create pipe:
    NSPipe *pipe = [[NSPipe alloc] init];
    NSFileHandle *reader = [pipe fileHandleForReading];
    NSFileHandle *writer = [pipe fileHandleForWriting];

    // Create and start thread:
    NSThread *myThread = [[NSThread alloc] initWithTarget:self
                                                 selector:@selector(threadFunc:)
                                                   object:reader];
    [myThread start];

    // Write to the writing end of pipe:
    NSString * message = @"Hello World";
    [writer writeData:[message dataUsingEncoding:NSUTF8StringEncoding]];

    // This is just for this test program, to avoid that the program exits
    // before the other thread has finished.
    [NSThread sleepForTimeInterval:2.0];
}

Bazaar

ok. Im confused. How does this work to allow two apps to talk to each other. And where does the pipe set some sort of identifier to share between apps ? Also how many apps could use one Pipe set ? – Krucik

How can i convert data to URL in the same way? Because i need continuous playback from a stream of data using AVPlayer – Lewendal