appleevent versus notification

Question

I am looking for a high performance inter process communication system in macos X.

What is the best system? AppleEvents or NSNotifications?

Answer 1

Distributed notifications (i.e. notifications sent through NSDistributedNotificationCenter) are most likely not a good option if your goal is high performance and/or reliability. Here is Apple's own take on this subject:

Posting a distributed notification is an expensive operation. The notification gets sent to a system-wide server that distributes it to all the tasks that have objects registered for distributed notifications. The latency between posting the notification and the notification’s arrival in another task is unbounded. In fact, when too many notifications are posted and the server’s queue fills up, notifications may be dropped. http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Classes/NSDistributedNotificationCenter_Class/Reference/Reference.html

Depending on what you mean by "high performance", you might want to look into distributed objects, or plain old Unix IPC mechanisms (sockets, pipes, shared memory etc).

Answer 2

If you control both the sender and the recipient, you can open a socket between the two processes ( man socketpair ), which is quite high performance. You can also open a file in a shared location ( like /tmp ) and write to it from one process and read from the other, which is quite speedy. You can also open two TCP/IP ports on the local machine, one in each process, and then send from one to the other "over the network".

If your only two choices are NSNotifications or AppleEvents, well, AppleEvents will likely perform better.