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Intro to XPC inter-process communication

November 12, 2018

Intro to XPC inter-process communication

This presentation gives basic understanding how XPC works on macOS and how to establish it.


November 12, 2018

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  1. We are NOT talking about XPC Services here. We are

    talking XPC as API fo inter-process communication
  2. XPC benefits 1. Performance: lazy (on-demand) automatic launching XPC services

    2. Architecture: one executable can represent several services 3. Security: making services with minimum privileges 4. Stability: crashing one process doesn't affect another
  3. Adding an executable, that can be called via XPC 1.

    Copy configuration plist to appropriate system location* 2. Change plist owner to root 3. Add plist to lauchd (load or bootstrap) 4. Put service's executable to location, defined in configuration plist 5. Run client! *System locations — user agent for current user: ~/Library/LaunchAgents/ — user agent for all users: /Library/LaunchAgents/ — daemon: /Library/LaunchDaemons/
  4. Method signature restrictions for XPC calls Methods should return Void.

    Parameters could be: 1. Arithmetic types (int, char, float, double, uint64_t, NSUInteger, and so on) 2. BOOL 3. C strings 4. C structures and arrays containing only the types listed above 5. Objective-C classes, that implement the NSSecureCoding protocol (e.g. NSString or custom classes). 6. NSArray, NSDictionary and other collections with objects, conforming to NSSecureCoding. 7. Only one block (reply block), that returns Void and receives parameters of types, listed above.
  5. Passing objects by copy and by proxy Passing by copy

    is a recommended and performant way. Passing by proxy decreases performance and should be avoided.