IPC on macOS

Transcript

1. IPC on macOS
   

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2. Before we dive in
   The Berkeley Software Distribution (BSD) is an operating
   system based on early Unix.
   

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3. BSD became the basics for several open-source OS:
   FreeBSD, OpenBSD, NetBSD, DragonFly BSD, TrueOS and
   Darwin
   

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4. Darwin is an open-source Unix-like operating system
   first released by Apple in 2000
   

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5. Darwin forms the core set of components upon which
   macOS, iOS, watchOS, tvOS, iPadOS and audioOS are
   based
   

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7. BSD supports POSIX standard, so POSIX APIs are
   avaliable to us on macOS.
   

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8. POSIX == Portable Operating System Interface
   

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9. Available IPC techniques
   

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10. BSD
    1. BSD sockets
    2. BSD pipes
    3. BSD signals
    

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11. Other low level
    1. Shared Memory + Semaphores for large resources
    (like movie)
    

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12. Darwin low-level
    1. Mach Ports
    

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13. The Mach port object is the underlying primitive used for
    all interprocess communication in macOS
    

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14. High-level macOS-specific
    1. Apple Events
    2. High-performance counterpart of Apple Events —
    CFMessagePort and friends
    3. Distributed Notifications
    4. Distributed objects (NSConnection and friends)
    5. XPC (C API and Objective-C API)
    

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15. Even higher level
    no explicit setup for communication
    1. NSPasteboard
    2. Services API
    

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16. BSD Sockets
    You can implement inter-process communication using
    BSD sockets via:
    — POSIX API (socket() and friends)
    — Core Foundation API (CFSocket and friends; also used
    for networking)
    

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17. BSD Pipes
    One-way communication. 2 types:
    — Unnamed pipe (example: command line shell cat
    magic.txt | grep -e Gwendoyln sends the contents of
    magic.text to the grep command)
    — Named pipe is a special type of file without any
    content on filesystem
    

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18. BSD signals
    Usually a process terminates on receiving a signal. But it
    can implement a signal handler function to override this
    behaviour.
    Used by OS kernel to tell the process about an exception
    (like division by 0). Command line kill command is
    another example of using signals.
    The signal namespace is just one integer, so collisions
    are very possible.
    Not recommended to use signals for IPC.
    

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19. Shared Memory + Semaphores
    A process allocates a memory region, that can be read
    and written by other processes.
    Advantages:
    * data is never copied
    * any process with appropriate permission can read and
    write
    Disadvantage:
    * fragile—if it is corrupted, all processes are corrupted
    Access it from one process, use more conventional IPC.
    

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20. Mach Ports
    Available APIs:
    — Darwin C API
    — Core Foundation — CFMachPort and friends
    — Foundation — NSMachPort and friends
    

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21. Darwin C API: sending
    natural_t data;
    mach_port_t port;
    struct {
    mach_msg_header_t header;
    mach_msg_body_t body;
    mach_msg_type_descriptor_t type;
    } message;
    message.header = (mach_msg_header_t) {
    .msgh_remote_port = port,
    .msgh_local_port = MACH_PORT_NULL,
    .msgh_bits = MACH_MSGH_BITS(MACH_MSG_TYPE_COPY_SEND, 0),
    .msgh_size = sizeof(message)
    };
    

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22. message.body = (mach_msg_body_t) {
    .msgh_descriptor_count = 1
    };
    message.type = (mach_msg_type_descriptor_t) {
    .pad1 = data,
    .pad2 = sizeof(data)
    };
    mach_msg_return_t error = mach_msg_send(&message.header);
    if (error == MACH_MSG_SUCCESS) {
    // ...
    }
    

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23. Darwin C API
    Not recommended to use directly: interfaces will change
    with kernel updates.
    

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24. CFMachPort & NSMachPort
    

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25. Apple Events
    

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26. Apple Events
    NSAppleEventManager *appleEventManager = [NSAppleEventManager sharedAppleEventManager];
    [appleEventManager setEventHandler:self
    andSelector:@selector(handleAppleEvent:withReplyEvent:)
    forEventClass:kInternetEventClass
    andEventID:kAEGetURL];
    

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28. CFMessagePort
    

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29. CFMessagePort
    High-performance counterpart of Apple Events
    

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30. private struct RemoteServerPortName {
    static let client = "com.hideez.port.client"
    static let server = "com.hideez.port.server"
    }
    private var inPort: CFMessagePort?
    func startListening() {
    guard nil == inPort else {
    return
    }
    inPort = CFMessagePortCreateLocal(
    nil, RemoteServerPortName.client as CFString!, getInMessageCallback(), nil, nil)
    let runLoopSource = CFMessagePortCreateRunLoopSource(nil, inPort, 0);
    CFRunLoopAddSource(CFRunLoopGetCurrent(), runLoopSource, CFRunLoopMode.commonModes);
    }
    func getInMessageCallback() -> CFMessagePortCallBack {
    return {(port: CFMessagePort?, messageId:Int32, data: CFData?,
    _: UnsafeMutableRawPointer?) -> Unmanaged? in
    RemoteServer.shared.handleInMessage(port: port, messageId: messageId, data: data)
    }
    }
    

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31. func postMessage(message: RemoteMessageOut,
    waitForResponse wait: Bool = false) -> RemoteServerResponse? {
    guard let outPort = CFMessagePortCreateRemote(
    nil, RemoteServerPortName.server as CFString!) else {
    return nil
    }
    var respData: Unmanaged? = Unmanaged.passRetained(CFDataCreate(nil, nil, 0)!)
    CFMessagePortSendRequest(
    outPort,
    message.id.rawValue,
    (message.data ?? Data()) as CFData,
    30.0,
    wait ? 30.0 : 0.0,
    wait ? CFRunLoopMode.defaultMode.rawValue : nil,
    &respData)
    let data = respData!.takeUnretainedValue() as Data
    CFMessagePortInvalidate(outPort)
    return data.isEmpty ? nil : NSKeyedUnarchiver.unarchiveObject(with: data) as? [String : Any]
    }
    

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32. Distributed Notifications
    

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33. [NSDistributedNotificationCenter default addObserver:self
    selector:@selector(_openPreferences)
    name:notificationName
    object:nil];
    

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34. distributedNotificationCenter.postNotificationName(@"NotificationName",
    object: nil,
    userInfo: userInfo,
    deliverImmediately: true)
    

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35. Distributed objects
    Deprecated and has
    !!!
    

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36. Distributed objects
    NSConnection and friends
    are deprecated and have
    !!!
    

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37. XPC
    Available APIs:
    — C API (use from C, C++ code)
    — Objective-C API (use from Objective-C, Swift)
    

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38. Obj-C XPC — modern API
    — Protocol-oriented(!)
    — Available since 10.8 (year of 2012)
    — API of choice for IPC on macOS
    

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42. IPC workshop
    

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43. Thank you!
    

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