In Mac OS X, a program has a number of ways to communicate with other programs.
These mechanisms for interprocess communication often exists in different layers of the system. Each often has its own specific purposes, limitations, and intended scenarios. Some are more suitable than others for code written at a certain level of the system; for example, a kernel extension would not make use of Apple events. An Apple event is a high-level semantic event that an application can send to itself, to other applications on the same computer, or to applications on a remote computer.
Apple events are the primary method for interapplication communication on Mac OS X. Apple event objects have a well-defined data structure with support for extensible, hierarchical data types. Applications typically use Apple events to request services and information from other applications, or to provide services and information in response to such requests. A well-defined Apple event suite can also support a rich scripting interface through AppleScript. Apple event objects can take a significant amount of time to create, so you will not usually want to use Apple events in performance-critical situations.
A distributed notification is a message posted by any process to a per-machine notification center, which in turn broadcasts the message to any processes interested in receiving it. Included with the notification is an identifier of the sender, and, optionally, a dictionary containing additional information. Distributed notifications are ideal for simple notification-type events. For example, a notification might communicate the status of a certain piece of critical hardware, such as the network interface, or a typesetting machine. There is no way to restrict the set of processes that are allowed to receive a distributed notification.
Any process which registers for a given notification may receive it. Because distributed notifications use a string for the unique registration key, there exists potential for namespace conflicts.
Mac OS X Internals: A Systems Approach by Amit Singh
Distributed notifications are true notifications because there is no opportunity for the receiver to reply to a notification. Starting with Mac OS X version Applications including the notify. To view the man pages for the routines defined in notify. The Core Foundation CFMessagePort object implements a fast, efficient mechanism for transferring raw data from one process to another process on the same machine.
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Sockets support two-way communication between any number of processes. A socket is an object which associates an address with a file descriptor. Sockets should be used for all network communication in Mac OS X. There are two primary variants of sockets, file and network. File sockets are addressed as filenames and for various reasons do not support communication between processes on different machines. Network sockets are addressed using the network host name combined with the port number for example, www. Using CFSocket instead of raw sockets calls allows Core Foundation to abstract any potential differences between operating systems, as well as providing a more object-oriented interface which you may find easier to program.
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This allows you to keep the number of threads in your application to an absolute minimum, which is good for performance. A pipe is a communication portal with one sending and one receiving end. Data written to a pipe is read in first-in, first-out FIFO order.
In order to read or write data from a pipe, both the reading and the writing end of the pipe must be open. Unnamed pipes must be created by a common ancestor process which then hands the pipe descriptor number to both child processes. A named pipe is represented by a file in the file system called a FIFO special file. A named pipe must be created with a unique name known to both the sending and receiving processes.
Actually, the version available in Fink compiles fine, but does not support Real codecs. The latest source files fail out of the box with a compilation error since they tries to use a "-rdynamic" option with GCC. Removing that option by hacking the config files gets past compiling, but just causes mplayer to crash later when trying to load Real files. I sent a private email to the original hint author fracai , and he admitted that he based his hint on something he does in Linux.
So, the named pipes is a legitimate concept, but the mplayer conversion of RealAudio files is a bit of a "tease". If anyone else can get mplayer to properly read Real files, I'd love to know! Lost your password?
Mac OS X Manual Page For pipe(2)
Powered by the Parse. Like inline pipes , named pipes allow output from one application to be sent to another. Named pipes, however, allow not just stdout redirection, but also redirection of any data output that would be written to disk. I was introduced to named pipes when I was converting a Real media file to MP3, and didn't want to save the uncompressed PCM audio in between conversion while using mplayer and lame.
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Named pipes take it a step further by abstracting the concept of the pipe within the command line to a file representation. The mplayer - lame combination doesn't support the inline pipe, but you can output PCM audio in real time by playing the Real media with mplayer , and lame will accept streaming PCM audio. The process goes something like this: Create the pipe: mkfifo aNamedPipe Start lame with the pipe as input: lame -q 2 -b aNamedPipe output.
Named pipes are treated like regular files and can be removed with the rm command. The above example streams what would have been a very large file directly to the input of lame ; While this example uses audio, named pipes are useful for many other tasks. I'll end with the interesting exercise of what happens when multiple processes attempt to read the same pipe. Using named pipes via mkfifo 10 comments Create New Account. The following comments are owned by whoever posted them. This site is not responsible for what they say. Using named pipes via mkfifo Authored by: fracai on Oct 27, '04 AM.
I should note that the last example really needs 3 sessions. Using named pipes via mkfifo Authored by: mzs on Oct 27, '04 PM. Named pipes are still pipes and not regular files.
Authored by: dantheox on Oct 27, '04 PM. For whatever reason, the shorten command line program doesn't accept "-" as a valid output file stdout. To get around the problem, I've been using named pipes. Here's my shn2mp3 script:!
Nice hint - could be really useful, but I can't seem to get shorten to work. My mistake! Using named pipes via mkfifo Authored by: nvdingo on Nov 01, '04 PM.